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.
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.
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.
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.
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.
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.
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...
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.
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.