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-   -   Retrofitting an '88 Legend FE display. (https://www.fuelly.com/forums/f10/retrofitting-an-88-legend-fe-display-5327.html)

GasSavers_bobski 07-09-2007 04:51 AM
Retrofitting an '88 Legend FE display.
 
Hey folks... I'm starting a new thread rather than further hijacking someone else's. I guess I'll start off with quoting the relevant posts:

Quote:
Originally Posted by bobski (Post 62478)
Quote:
Originally Posted by brucepick (Post 62451)
We already have all the technology
We've had the technology for decades. I've been working on retrofitting a display into my CRX:
https://www.fuelly.com/attachments/fo...5377e07196.jpg
It's the driver information display from an '88 Acura Legend... $30 from salvage. The only down side is that it's meant for a V6... The injector signal pulsewidth needs to be scaled 2/3 to work properly with my inline 4. It will still show changes in FE, just not an accurate measure in MPG or l/100km.
Quote:
Originally Posted by skewbe (Post 62506)
bobski, that's really cool to be reusing that component. I've been considering similiar 2/3 type circuits for other applications too.

Do you know the pinout on that thing or if the mpg/trip function will work with just volts and a vss/injector signal? Or is it integrated into the honda ecu?
Quote:
Originally Posted by bobski (Post 62531)
No, everything is thankfully external. I traced the single wire that runs to the ECU a few days ago... Inside the case, it runs to the no.1 injector pin via a 10k resistor. That's it.
The device actually has a whole bunch of functions: Clock (the unit takes the place of the clock in the legend), distance to empty indicator, trip odo, current fuel economy, average fuel economy, engine oil level, coolant level, washer fluid level, service and oil/filter inverval odos. It isn't installed yet, so there may be other functions lurking in the software that I haven't come across with simple power and ground.
https://www.fuelly.com/attachments/fo...64a8cf2a74.jpg
Lets see... The wire from the lighting switch is 12v+ to dim the display, the pink wire from the ECU is the switched ground injector signal via 10k resistor I was talking about above.
The fuel level sending unit needs to output 2-5 ohms when full, 25.5-39.5 ohms at half tank and 105-110 at empty. Conveniently the same values as the CRX sender. I haven't looked at the low fuel sensor... Judging from the circuit diagram, it's the same design as found in other Hondas and Acuras. I can look up specs if you want.
The coolant temp sender needs to output 158 ohms at 54?C/129?F and 32-49 ohms at 85?-110?C/185?-212?F. Also stock CRX values.
The fuel filler door switch is part of the door release lever, so I assume it's triggered momentarily when you pull the release... I haven't investigated further.
The engine oil level switch is in the oil pan... Too much work as far as I'm concerned. The only odd thing I noticed is that the corresponding wire in my donor car showed about 50 ohms of resistance. Not no connection or good continuity, but 50 ohms. The dipstick showed way over full, so I assume water got in the crank case... The switch may have been damaged.
The coolant level switch is built into the lid of the radiator overflow bottle... Simple on/off operation via a reed switch and float with internal magnet. The washer fluid switch is installed in the bottom of the bottle, similar design to the coolant switch.
The speedo and pulser are cable driven, so I assume that's also typical Honda spec... Four 12v pulses per cable revolution or whatever it is.

If you're going junkyarding, the display is on the top of the dash above the radio, HVAC controls and such. Make sure you've got an info display equipped car before you start disassembling things... The standard issue clock looks very similar to the info display when unpowered.
The control unit is above the glove box. Once disconnected from the box, the wiring harness between the display and control box can be pulled back towards the display intact. That way you don't have to deal with resoldering the wad of wires between the two.


So do you have a diagram for a good 2/3 pulsewidth scaler? It strikes me as a problem that might necessitate a processor, but I don't really know. Simply dropping every 3rd pulse might work as well, but it's hard to say how the info center would react to that.
Quote:
Originally Posted by skewbe (Post 62543)
I don't have a solid schematic yet, but for an application that can be off a few pulses I'm thinking an analog frequency->voltage->voltage Controlled Oscillator circuit will git 'r done (with appropriate input and output voltage tweaking).

https://www.uoguelph.ca/~antoon/gadgets/pll/pllfig3.gif
from:
https://www.uoguelph.ca/~antoon/gadgets/pll/pll.html

Here is a frequency to voltage chip that looks like it is built for a magnetic pickup, fyi:
https://www.national.com/pf/LM/LM2917.html

so basically we have
vss->LM2917->trim pot voltage divider to adjust ratio->VCO->voltage divider for instrument input.

Edit: oops, you are trying to divide the injector pulse, not the vss, you need to detect the duty cycle (read inductor) and make a new signal with the appropriate duty cycle...

edit: oops, looks like we are hikjacking a thread...

jwxr7 07-09-2007 08:26 AM
that is a great idea :thumbup: , Why haven't I thought of trying that? Saves alote of the hard stuff of DIY. Would it be better to stick with ones out of any pre obd2 car if it is going to go in an obd1 car? Seems like it would be simpler.
I'll have to do a walk around the junkyard and see what they have. What other cars would have a factory mpg read out? My buddy has a 95 newyorker with one. Most of the others I can think of are obd2.

I am geeked about trying this:D .

CO ZX2 07-09-2007 08:32 AM
Quote:
Originally Posted by jwxr7 (Post 62658)
that is a great idea :thumbup: , Why haven't I thought of trying that? Saves alote of the hard stuff of DIY. Would it be better to stick with ones out of any pre obd2 car if it is going to go in an obd1 car? Seems like it would be simpler.
I'll have to do a walk around the junkyard and see what they have. What other cars would have a factory mpg read out? My buddy has a 95 newyorker with one. Most of the others I can think of are obd2.

I am geeked about trying this:D .
Won't you need a unit compatible with you throttle body injector? And if you could only find a V6 unit, halve the readings?

mrmad 07-09-2007 08:36 AM
I don't see the circuit skewbe showed would work for what you need. The LN2917 is a frequency to voltage IC, meaning it will take a certain frequency and convert it to 0-5V. The input frequency is adjustable by changing different capacitor and resistance values on its inputs.

The next circuit then takes voltage measurements and converts them back to frequency. The problem here is you need to be meaursing pulse widths, and the output would have the same pulse width. Plus, the Legend display would be assuming the Legend's injector size.

I would think the easiest thing to do would be to connect it up and see if you can get it to read mpg and use it as a relative measure of mpg.

jwxr7 07-09-2007 08:42 AM
Quote:
Originally Posted by CO ZX2 (Post 62660)
Won't you need a unit compatible with you throttle body injector? And if you could only find a V6 unit, halve the readings?
It would probably be easier, but a multiport would work too. I would just have to come up with a multiplier that I can go by. It would be a useful instrument even if it is way off. I could see instant feedback which would lead to improved FE driving.
like mrmad said
Quote:
I would think the easiest thing to do would be to connect it up and see if you can get it to read mpg and use it as a relative measure of mpg.

I remembered my ex-girlfriend's 89 pontiac grandprix had a trip computer, and a friends 1990 olds cutlass supreme had that as an option too.

skewbe 07-09-2007 09:33 AM
Quote:
Originally Posted by mrmad (Post 62661)
I don't see the circuit skewbe showed would work for what you need.
Nope, it won't. It might be useful for calibrating the vss signal (i.e. if you had different sized tires than the computer expects) though.

I think the "put it on the passenger seat and wire it up and see how it does" approach is a reasonable suggestion.

I would be tempted to do the hiway mile marker thing compared with the trip and see if there is a factor you need to multiply the miles by, then compare actual fillups to the mpg readings and see if there is a fuel consumption multiplier (divisor).

Once you know the correction factors, you should be able to calculate a displayed MPG to use as a target for your honda and know how to convert it to an accurate MPG number. So basically you drive around with a not-so-arbitrary figure in your head of what the display should say if you are trying to maintain, say, 50mpg. Throw a calculator in the glovebox if necessary along with the conversion factors :) but it would be good to see that it does work on it's own without investing in extra circuitry, heck it'll probably be "good enough" to be very helpful as-is.

GasSavers_bobski 07-09-2007 09:34 AM
Quote:
Originally Posted by mrmad (Post 62661)
Plus, the Legend display would be assuming the Legend's injector size.
The Legend and the Civic injectors in my CRX are the same flow rate - 240cc/min. It's just that the Legend has 6 injectors where my CRX has 4. The display only measures the pulsewidth from one fuel injector, so it must be effectively multiplying that by 6 internally to get the total fuel flow.
I'm gonna to pick up some alligator clip jumpers and such to make temporarily rigging this thing in place easier. With any luck, I'll have it spitting out a reading this evening.

GasSavers_bobski 07-09-2007 02:39 PM
https://www.fuelly.com/attachments/fo...2bfc3e5d73.jpg
It works!
The speed signal appears to be spot on. The stock mechanical trip odometer went from 172.4 to 191.1 miles over the course of the test drive, the info display trip odo read 18.7 miles.
The FE reading seems to average over the course of a few seconds. Coasting to a stop results in the MPG number gradually dropping to 0 a few seconds after you actually stop.
https://www.fuelly.com/attachments/fo...cbb1a6c596.jpgCruising at around 50 mph.
https://www.fuelly.com/attachments/fo...111d428ddd.jpgIt maxes out at 99 MPG. Too bad... The numerical display reads up to 199,999.
I'm not sure about the accuracy of the FE reading yet. It's definately displaying on the fly, but the average reading isn't right. I pulled into the garage, shut the engine off, fiddled with the cooling fans for a minute and then started trying to take pics of the trip milage reading.
When I gave up on the trip milage picture, I flipped to the average FE reading. It read 11.3 MPG... Seemed more than a little low, even with correction. As I stared at it, it ticked down to 10.8 MPG, then 10.4... This is with the engine off, mind you. Like a hypermiler's nightmare or something. :D
I think I know what's happening. The injectors are a switched ground system. When the ignition is on, one side of each injector is constantly powered. That means the wire between the ECU and injector has 12v+ until the ECU decides to fire the injector, at which point the injector's internal resistance limits current flow, the ECU sinks what current does make it through and the wire appears more or less grounded. So, the info unit takes 12v+ on the injector wire to mean the injector is closed, and ground to mean the injector is firing.
I was running the info display off a cigarette lighter outlet, which is switched on and off indirectly by the ACC contact of the ignition switch. With the ignition off and ACC power on, the injectors weren't getting any power, so the injector wire had 0 volts and maybe even a connection to ground. The info unit read this as the injector firing at 100% duty cycle while the car was standing still. The average FE plummeted.
So, I'll have to wire it up to ignition switched power, reset the average MPG meter and give it another try.

skewbe 07-09-2007 05:30 PM
cool beans, let us know if the mpg reading starts making sense (note my saturn reads .1gph with the engine off too ?!?)

GasSavers_TomO 07-09-2007 07:10 PM
Awesome! I'm going to my old junkyard and pick one of these up tomorrow. I'll get cracking on a How-to for the OBD1 guys.

GasSavers_bobski 07-09-2007 07:42 PM
Alright, I did another test run around half 55 mph, half at 70 mph and a dash of urban miles for flavor.
I reset the trip and average MPG meters first, and got a much more reasonable number as a result. I noticed that it takes a few hours for the info unit to lose it's settings when completely disconnected from power. I opened up the control unit and confirmed it has a CR-123 size battery soldered to one of the boards. I powered it up with a bench supply for a good hour this morning. If it was recording that time as 100% duty cycle on the injectors, that would explain the first test run's FE results.

Anyway, the test run results:
29.7 miles, averaging 31.2 MPG according to the unit.
I want to just apply +50% to that, but I figure I should actually go through the math to make sure that's a proper shortcut. Someone let me know if I screw up. :)
29.7 miles / 31.2 MPG reading = 0.952 imaginary gallons burned.
0.952 gallons / 6 imaginary injectors = 0.159 gallons actually metered.
0.159 * 4 actual injectors = 0.636 gallons actually burned.
29.7 miles / 0.636 gallons = 46.7 actual MPG.

And the alternative method...
31.2 measured MPG * 1.5 = 46.8 actual MPG.
Looks like rounding got the better of 0.1 MPG.

That's actually a new record for me, but I haven't done a full tank of highway driving since installing grille blocks. My previous record was about 42 MPG.

GasSavers_TomO 07-10-2007 07:44 PM
I found a Legend today that had the FE computer in it. It seems to be part of a Bose Package from the dealer/factory. Hopefully I can start on my How-to this weekend for the OBD1 guys. I'm planning on hooking up the coolant temp and fuel sender as well to utilize those aspects of the FE display. Hopefully it will tell how many gallons and what temp the coolant is in addition to the stock cluster's needles.

Thanks Bobski for sharing the info.

skewbe 07-10-2007 08:11 PM
Excellent bobski,

are you thinking about filtering out every third injector pulse? If these came on 4 cylinders, there may be a jumper or resistor inside the unit you could change, or there might possibly a pot to calibrate it.

GasSavers_TomO 07-10-2007 09:08 PM
I opened up the unit I got today...there is no jumper, per say, that can be set for a four cylinder motor. It looks like they made a component circuit for multiplying the injector pulse reading.

This is one complex unit for being made in the 80's! All that circuitry to decipher the various inputs it looks at takes up quite a bit of space. The unit has two boards. One is a Discrete component board (all resistors and transistors) while the other board is controller ICs and drivers for the display unit.

I would need to see a schematic breakdown of the two boards to change the multiplier for the FE reading.

PS- sorry for answering this for you Bobski, I'm not trying to step on your toes or steal your fire...just helping out.

GasSavers_bobski 07-10-2007 10:18 PM
Haha... no problem. I'm honestly more interested in just getting the unit working with my car than figuring out it's innards, but I'll be perfectly happy to read what others have to say about it. I can generally figure out basic circuits, look up component pinouts and such. I've read a textbook on logic gates and microprocessors, but since I've never taken any formal EE courses, I have various holes in my knowledge surrounding some pretty basic stuff, like proper usage of transistors... Switching versus amplification, how to avoid releasing their magic smoke, ect.
I can reliably put things together from diagrams, but designing new devices is generally beyond me.

Skewbe: Yes, I mentioned that in one of my quoted posts. Without knowledge of exactly how the system interprets the injector pulses, it's hard to say how it will react to a galloping signal, but I'm willing to try it.

Here's a pic of the control unit's two boards... If someone wants pics of both sides to trace or whatever, speak up and I'll take em.
https://www.fuelly.com/attachments/fo...2682c78c7d.jpg
The yellow connector goes to the display unit (which actually has some more circuitry in it, but not nearly as much), the white connector goes to the rest of the car.

skewbe 07-11-2007 04:58 AM
Yeesh :) I don't see anything to adjust.

Does the thing display RPM? Just thinking out loud here but you will have to tweak the pulse width if you want to keep that working too.

I dug up a dwell circuit on the diy mpg thread, that can take the injector duty cycle and turn it into a voltage. If there is a PWM circuit that can take a voltage and an rpm trigger signal and turn it into a signal of the same frequency but with a proportional pulse width...

GasSavers_bobski 07-11-2007 05:48 AM
Quote:
Originally Posted by skewbe (Post 63008)
Does the thing display RPM?
Not that I'm aware of. I'm not even sure why it watches the coolant gauge sender. An overheat warning maybe?

GasSavers_TomO 07-11-2007 05:46 PM
I'm guessing that the unit can display the temp as well as a low coolant warning for the coolant. Although I am just guessing here. It will be a week or two before I can start on installing my unit as I'm in the middle of renovating two decks at a friend's house (getting some great numbers for FE since it's all highway). I'll make a how-to and a report on the unit then.

GasSavers_bobski 07-12-2007 01:22 PM
While looking for a '94+ Integra gauge cluster (the yard sells whole clusters cheaper than a replacement lens - what I actually need - from Acura), I came across a '90 Legend today that had the owner's manual sitting on the front seat.
It's got 5 pages on the info system... I'll post them shortly. Gotta take pics and clean them up a little.
Taking a hint from the manual pages, I also found the odometer set function. Switch to the next service odometer page, and hold down the hour/-> button for 3 secs. The min/0-9 button changes the number, hour/-> switches to the next digit, and reset/set finishes.

Pages:
https://www.fuelly.com/attachments/fo...dec3eb949a.jpg
https://www.fuelly.com/attachments/fo...9d6f75de37.jpg
https://www.fuelly.com/attachments/fo...fb3b2f3345.jpg
https://www.fuelly.com/attachments/fo...293e234162.jpg
https://www.fuelly.com/attachments/fo...e88dea8151.jpg

GasSavers_TomO 07-12-2007 06:36 PM
Nice score Bobski!

skewbe 07-12-2007 07:07 PM
FYI, I find that I only use the average reading for my commute one way or errand. So that I have a MPG goal in mind and make adjustments to make that goal by the end of the trip.

GasSavers_bobski 07-12-2007 07:14 PM
Quote:
Originally Posted by TomO (Post 63224)
Nice score Bobski!
Isn't it? There was an '89 owners manual there too, but it had been rained on, so I stuck with the '90. I actually found an '87 service manual at a different yard... They just gave it to me since I was buying a few other items. No info unit pages in that one, but I'm not one to turn down a free source of info. :)
Quote:
Originally Posted by skewbe (Post 63228)
FYI, I find that I only use the average reading for my commute one way or errand. So that I have a MPG goal in mind and make adjustments to make that goal by the end of the trip.
Yeah, the current MPG reading seems to jump around too much to be preticularly useful. Oh well.
Oh, I should have mentioned this earlier, but I did my first fillup since installing this thing today. The displayed average FE reading was 25.9, that corrects to 38.85 MPG. Pump/odometer calculated FE was 39.16 MPG.
That amounts a 0.07 gallon difference in fuel metered. Sounds to me like it could be a simple matter of where the pump cutoff activated.

GasSavers_TomO 07-13-2007 01:00 PM
That is good news to hear, Bobski. The conversion unit that you figured seems very viable. As soon as I can find a schematic of the unit I'll be able to find the circuit that tells the unit how many injectors are to be counted as well as the flow rate of said injectors. I'll be sure to share info and make a how-to so we can all enjoy, lol.

GasSavers_bobski 07-13-2007 02:18 PM
Well, if you look at the green circuit board, it has a very large IC on it that just screams processor. If it is, there's no reason to try to multiply, or really do much of anything to the injector pulse signal before sending it to a processor input pin. It would be much easier to multiply the signal once it's been converted to a numerical value, which will be done anyway to calculate miles/gallon. So, the circuit you're looking for may be a line of code.
While I don't want to discourage anyone from trying, I doubt anyone here is going to be interested enough to extract the program from the procesor (assuming it has an internal ROM), decompile and interpret it as has been done with many Honda ECUs. It would probably be less time consuming to write a program from scratch to run on the superMID architecture.

UfoTofU 07-13-2007 02:40 PM
This is an awesome thread!

Keep up the good work.

McPatrick 07-13-2007 03:20 PM
Before you know it salvage yards will experience a great influx of people asking for 'those Legend trip computers'. :)

jwxr7 07-16-2007 05:53 AM
Too bad my local junkyards don't seem to have any. They just crushed all of them at my favorite yard :( . Did any of the hondas from that era have the same trip computer? Otherwise I am going to look into using a trip computer out of some other car, too bad because you guys provided all the info to make this one work. It would be hard to know if you got all the guts needed to make a diff one work and then you have to figure out the wiring.

jwxr7 07-31-2007 10:22 AM
Did any of the hondas from that era have the same trip computer?

GasSavers_bobski 07-31-2007 02:00 PM
Not that I've seen. Maybe something in foreign markets.

skewbe 07-31-2007 02:59 PM
Hey Bobski, your mpg is climbing nicely, is that display mounted and helping?

GasSavers_bobski 07-31-2007 03:57 PM
I'm not sure just how much it's helping, but it's definately a reminder. Once I'm satisfied with it installation-wise, I plan to do some experimentation - effects of vehicle speed on FE, aero mods, windows down vs. up vs. A/C on... The usual fare.
Currently, the info system is mounted in it's final position and about 90% wired in, though I haven't put together the brackets to hold down the display yet - it's just sitting on the dash. Now that the coolant temp gauge is connected, it's started telling me to check the oil level when I switch the ignition on. I guess that input is supposed to be grounded when the level is where it's supposed to be.
I'm going to pull my car's engine and transmission in the next couple days - the transmission has been acting kinda weird when cold... I think it's the torque converter lockup control components sticking. It also seems to have more drive line slack than I would like. I have a spare transmission sitting on a shelf (actually the original transmission for this car), so I'm going to swap that in and store my current one as backup.
My plan is to replace all the seals in the bell housing while I'm in there... Replacing the engine's rear main seal requires dropping the oil pan, so I thought I would go ahead and pull the oil level switch from my donor Legend and install that as well.
So, I spent most of today under a 18.5 year old Acura, trying to get the oil pan off. It's a transverse V6, so the downpipe for the front bank of cylinders runs under the oil pan and joins the one from the rear bank. That means both front and rear exhaust manifolds have to be unbolted from the downpipe in order to remove it. Lucky me, some mechanic replaced the 14mm downpipe nuts on the rear manifold with 1/2" fasteners. Not realizing what was going on (every fastener on the car is supposed to be metric), I tried a 13mm socket (1/2" is about 12.7mm) on the nut and proceeded to round off the points. I went home and got a 1/2" socket, but the deed was done. Downpipe nuts see alot of heat, which burns off any oil film that might protect them from rust or lubricate the threads, so they take alot of force to remove... That nut is on there until someone cuts it off.
I worked around the down pipe as best I could, then tried bending it once the pan was unbolted, but there isn't enough room under the car to pry effectively.
So, my plan for tomorrow is to take a jumpstart pack (12v source), a 400 watt power inverter, an angle grinder and a recip saw to the junkyard. I'm gonna show that downpipe hell.

Well... I'm going to try to remove it in one piece by grinding off the rounded nut, then I'll show it hell if it doesn't cooperate... Assuming the inverter can drive the recip saw. ^_^;

GasSavers_TomO 11-06-2007 05:52 AM
Any updates for us to drool over?

Danronian 11-06-2007 07:07 AM
I was thinking...I've seen these units on 4 cylinder fuel-injected chrysler cars (the optioned out "K" cars). I wonder how hard it would be to retrofit one of those to a Honda...

But yes, this legend one would be easy to find too, since I've seen a lot of these in the junkyard lately.

GasSavers_bobski 11-06-2007 06:13 PM
Quote:
Originally Posted by TomO (Post 80342)
Any updates for us to drool over?
Heh... Someone on the Legend forums asked the same thing not long ago. :)
Quote:
Originally Posted by bobski
Quote:
Originally Posted by highcrest
I would love to find out if you successfully got this computer up and running in your car.
Yep.
https://www.fuelly.com/attachments/fo...bb84bc3e07.jpg
It goes nicely with my car's frankenstein of the junkyard theme.
https://www.fuelly.com/attachments/fo...318ff02dd8.jpg
I still haven't hooked up the coolant reservoir, fuel door or fuel low switches. I gave up on the oil level switch when I realized there's almost no room in the oil pan for it and I would have to drill a hole in the engine block for it's bulkhead connector.
I started a thread about it on gassavers.org a while back... It's got a bunch more info.
That thread can be found here.

Rower4VT 07-11-2008 10:51 AM
What's the latest with the Legend computer? Get it finally installed and working consistantly? Any pictures of it installed?

occupant 07-19-2008 08:51 PM
I wonder if a later 80s Prelude would have something like this, maybe the 89-91 Si with 4-wheel steering, they got loaded down with gobs of gadgets.

GasSavers_bobski 07-21-2008 07:29 AM
Quote:
Originally Posted by Rower4VT (Post 110648)
Any pictures of it installed?
Scroll up a post.

Quote:
Originally Posted by occupant (Post 111771)
I wonder if a later 80s Prelude would have something like this, maybe the 89-91 Si with 4-wheel steering, they got loaded down with gobs of gadgets.
Possibly. I'll keep an eye out in the junkyards. Also, didn't the '92-96 generation have an optional digital dash? Maybe it has a MPG display built in.

Well, I think I have an ongoing accuracy problem figured out. My last tank of gas came out to 44.2 mpg, but the trip computer read 46.2 (once you add 50% as I described above someplace). The Legend and Civic injectors are supposed to have the same flow rates, so the meter should be accurate, right? Turns out the Legend and '92-95 Civic have different fuel pressure specs. The Legend manual says 36-41 psi is normal with the regulator vacuum line disconnected, while the Civic manual says 40-47 psi is normal. The Civic's higher pressure is forcing a little more fuel through the injector nozzles than would pass with the Legend spec. Since the computer judges MPG based on how long the fuel injectors are open, you get some inaccuracy. I guess I could try swapping in a Legend FPR, but then I would end up running a little lean in open-loop operation (hard acceleration).

GasSavers_bobski 08-25-2008 05:54 PM
Well, kinda bringing this thread back again. I've been PMing user nowhhs about his install over the past couple days... I thought it would be good to move the conversation here so others could benefit as well.

Quote:
Originally Posted by nowhhs
I want to first thank you for the effort you made in figuring out that installation. :thumbup: Thanks to you, I've more or less also successfully done the same thing in my 90 hatch. I just have one problem I was wondering if you might be able to help me with. I didn't bother hooking up any of the diagnostic stuff, since I didn't want to bother with all of the missing sensors, but I'm having a problem getting the "distance to empty" display to work. When I followed the diagram you printed on that thread and hooked up the yellow/white wire to A8, I still get N/A for a "distance to empty" and my average mileage display stops working correctly. Do I have to maybe do something to A14? Since you've obviously dug into this installation more than I have, I was wondering if you had any suggestions? Does yours work correctly, or is this just something I have to live with? Thanks again, Norm
Quote:
Originally Posted by bobski
Quote:
Originally Posted by nowhhs
[...] I'm having a problem getting the "distance to empty" display to work. When I followed the diagram you printed on that thread and hooked up the yellow/white wire to A8, I still get N/A for a "distance to empty" and my average mileage display stops working correctly. Do I have to maybe do something to A14?
What exactly do you mean by "stops working correctly"?
I have the same N/A reading for distance to empty. The Legend and Civic/CRX fuel level senders have the exact same resistance specifications, so I think you must need a sender assembly with a low fuel sensor on it. The info display probably uses the low fuel warning to calibrate or something. The fuel filler door switch could have something to do with it as well. The Legend owners manual says the display is supposed to estimate the distance to empty at all times based on average fuel consumption, then when the low fuel light comes on, show the fuel remaining.
On the bright side, the Legend fuel tank is about 50% larger than a Civic hatch/CRXs, so together with the 50%-lower-than-actual FE reading, it should come out fairly accurate (assuming we can get it working).
The low fuel sensor itself is kind of an odd device. The ones I've looked at in junkyard Accords are just a grounded can with one wire coming out. The low fuel warning light in my Integra gauge cluster comes on full-bright when I ground the signal wire, but when properly connected to a sensor, the light supposedly comes on slowly when the fuel gets low. As such, I don't know if you could easily wire something up that looks (from the info display's point of view) exactly like the sensor.
I think some european and japanese market Civics and CRXs may have come with the sensor and warning light. If you find a source for the sender assembly, let me know... The CRX and Civic hatch use the same gas tank so the senders should be the same as well.
Quote:
Originally Posted by nowhhs
By not working correctly, I meant I was getting really low readings, like 2.8 or 3.1 for average mpg over 150 miles or so. I reconnected it this morning and it seems to be working ok now????? The reason I PMed you was I thought you had gotten everything but the oil level sensor working, I didn't realize you were still struggling with this as well. Maybe we can figure this out together. It seems to me that if you want to make your low fuel light work, all you really need to do is pull out a unit from an accord and take the sensor off and add it to your gas gauge assembly. It might take a little welding or soldering, but I don't think it should be too hard. I don't have a light, so I don't really care. What I would like to have is the distance to empty work correctly, excluding the obvious inaccuracy of 50% (actually worse for me, I'm using 190cc injectors, so its more like 90% off). But the display should get more and more accurate as it approaches 0 if its using the fuel level input. This is what I figured out so far. This morning I grounded A4 and got a miles remaining display. It seems that A4 must be connected to a switch attached to the fuel door. When you open the door to fill the tank, the switch closes and grounds it. That seems to be what triggers the display. It seems to need to be closed for a while though, not just a brief signal, more like a minute or so. Problem one: it doesn't seem to base the readout off the fuel gauge, but rather from calculating 18 gallons divided by the average mpg. It was showing 463 miles remaining, with an average mpg of about 25, even though the tank was only 2/3 full. I've also attached A14 to 12vdc through a 100ohm resistor (just guessed a value). When I grounded A14 in addition to having it connected to 12vdc, the display switched to 2.5 gallons remaining, in other words tripping the low fuel function. I went to a junk yard and scavenged one of the low fuel sensors from an accord. It seems to have about 5000 ohms in air and 3000 ohms in water, I didn't check with gas. So I'm thinking just put a 3000 ohm resister in place would work for me, not you though. Problem two: When the display switches to gallons remaining. I was hoping it would stay there until the tank was actually that low, but it also appears to be based on calculating 2.5 divided by average mpg. Even though my tank was 2/3 full, the gallons left kept dropping. (I wonder what happens when it gets below 0?) Under no circumstances does the processor seem to use the fuel gauge input. Question for you: any idea what the value of the resistor in parallel with the low fuel light is? Knowing that would help me fine tune my A14 input. I'm out of ideas for the time being. Your turn?:confused:
Norm
Quote:
Originally Posted by bobski
Wow... Nice work.

Where are you tapping into power to drive the unit? I found that if you power it from an accessory circuit (stereo, cigarette lighter), it sees the injectors as running at 100% duty cycle until the fuel system power is switched on. This is simply a result of how the fuel injector circuit is set up and where the info display samples the state of the injectors.

My best guess regarding the resistor is that it allows some stray current to bypass the indicator light, delaying when it starts to light up.

The fuel door switch that I looked at was still installed on the car... I simply clipped my multimeter probe onto the ground and fuel door switch wires where I had cut the display and control units off the dash harness. The continuity function showed that the switch wire momentarily grounded when you pulled up on the fuel door release lever. It flipped back to an open circuit as soon as I let go of the release. It showed no change in response to re-closing the fuel door.

Do you have any objection to moving this discussion to my old install thread? It could be useful for anyone that decides to go the same route in the future.
Quote:
Originally Posted by nowhhs
I think it would be a great idea to move it to the original thread once we get something definitive figured out. If we dead end on this, there isn't really any point. On the other hand, someone else may have something valuable to contribute (TomO seems very knowledgeable), so go ahead (typing while thinking).

So you're saying that the reset from the fuel door was momentary? I'll have to look closer at that. The reason I would like the actual value of the resistor parallel to the low fuel light bulb, is that it works as a voltage divider along with the low fuel sensor. That means that A14 doesn't see a full 12 volts, the actual voltage depends on the values of the resistors on either side of A14. Any chance you can access that resistor and check the resistance? I think in the thread you mentioned you had 2 of these clusters? I would like to duplicate that circuit with light bulb, resistor, and low fuel sensor to see exactly what A14 wants to see. Thanks again.

GasSavers_bobski 08-25-2008 06:03 PM
Quote:
Originally Posted by nowhhs
So you're saying that the reset from the fuel door was momentary? I'll have to look closer at that.
Right, it's only triggered when the user is actually pulling on the lever.

Quote:
Originally Posted by nowhhs
The reason I would like the actual value of the resistor parallel to the low fuel light bulb, is that it works as a voltage divider along with the low fuel sensor. That means that A14 doesn't see a full 12 volts, the actual voltage depends on the values of the resistors on either side of A14.
Yeah, ok... You have the parallel combination of the bulb and resistor on one side, and the sensor pickup on the other. The voltage would divide between the two, making the signal at A14 either battery voltage - the bulb/resistor voltage drop, or ground (zero) + the sensor voltage drop... They should be the same thing.

Quote:
Originally Posted by nowhhs
Any chance you can access that resistor and check the resistance? I think in the thread you mentioned you had 2 of these clusters?
I have two '94-01 Integra clusters and an '88-91 CRX cluster. The CRX cluster doesn't have a low fuel lamp, and the Integra clusters don't have resistors as far as I can tell (I looked a few hours ago). I guess it's possible the resistor is built into the lamp or lamp socket... I'll go check that now.

nowhhs 08-25-2008 11:41 PM
bobski asked: "Where are you tapping into power to drive the unit? I found that if you power it from an accessory circuit (stereo, cigarette lighter), it sees the injectors as running at 100% duty cycle until the fuel system power is switched on. This is simply a result of how the fuel injector circuit is set up and where the info display samples the state of the injectors."

I tapped the VSS and injector signal directly from the ECU. The switched 12vdc, the constant 12vdc, the ground and the lighting dimmer I tapped from the factory clock plug and haven't had any problems. I had been using a DMM to monitor the duty cycle of the injectors before installing this also using the same tap point without a problem. I never saw 100% duty. It may be a problem if you are tapping the injector under the hood and get the wrong side. I'm just guessing though.

I also wanted to address TomO's comment as to where to find these units. They seem to be standard on the Legend LS models, irrespective of the Bose stereos. When I was searching for mine, I had to go through several yards and several times got excited when I found Bose stereos based on what he had said, but didn't find a mileage computer until I found the LS. Thats not positive, but I'm reasonably sure.


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