Interpret my O2 readings,, 95 VX - Fuelly Forums

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Old 05-22-2008, 09:04 PM   #1
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Interpret my O2 readings,, 95 VX

OKOK,,,

here we go...

I read the thread,, VX Lean burn monitor.... and had to have it.... Note I am new to all of this, but I am good both electrical and mechanical... so dont hesisitate to shoot me some crazy ideas to try...

Well, wanting to know if my newly acquired VX was going into lean burn mode, and after reading that thread, I headed to harbor freight and picked up 2 digital meters for a grand total of $6.52... and went home armed with my new knowledge.... oh and on the way home my CE light came on,, code 48... another reason for wanting the meters.....

Now, I get home and rip out the ecu,, solder on some wires to pins d22/d14 and also d14/d16, figured monitoring both is better than just one.... and its dark outside, soldering with a flash light... haha,,, ok,, remounted the ecu,,, slipped the meters into the cup holders, hooked them up,, set them for DC volts in the lowest range,, 20v.. that sucks about these,, would be nice if they had like a 5v range so it would be a bit more accurate... OH and before anyone asks,, I verified the readings with these meters to that of my Fluke, and all were within .02 volts of each other....

OK,,,,, So the ecu is free of codes now that it has been disconnected while I soldered.... I fire it up, point my flashlight at the meters and head down the road.....

now on to my readings.......

meter 1 is connected between ground and d14
meter 2 is connected between d14 and d16

all readings at operating temp....

At Idle,,,

2.95-3.08v meter 1
.38 - .42v meter 2(pump cell) ( yes positive voltage )

So it would seem to me that at idle I am in lean burn mode right there, or at least at the very edge of it... Is this wierd or normal?

Ok,,, crusing down the road... and I believe in lean burn mode for sure...

3.89v - 4.08v meter 1
1.29 - 1.40v meter 2 ( and yes again, positive volts... )

Do these numbers seem high to you,,,, chime in here TomO!!! I would thing for sure that it is in lean burn mode...

Ok,,, meter 1 drops down to 1.0++ when I hit the gas, and meter 2 goes negative voltage when I hit the gas..... Same thing if I try to maintain speed up a steep hill.... so hey, these numbers seem ok to me .....

But are they too high,, take the Idle numbers,, seem too high,, and even at that If I go to back of the car I swear it smells rich to me....


Now,, I put these in also to see what the numbers do when the CE light comes on,,, it did not come on in my test drive tonight, but tomorrow if it comes on I will record the voltages and post them... something is causing the code 48,,,,,, I want to see if when the ce light comes on if the car goes out of lean burn mode...... hym..........

OK.. thats about it for now,,,,, hope to hear from some of you guys on these readings....

thanks,,

john
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Old 05-23-2008, 04:28 AM   #2
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Wow, you found a VX, you found this forum, you got your hands on a service manual, and you know about Harbor Freight. And you're willing to solder with a flashlight. My prediction is that you're going to be fine.

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Originally Posted by pinbrew View Post
I am good both electrical and mechanical
It sure seems that way.

Quote:
I headed to harbor freight and picked up 2 digital meters for a grand total of $6.52
Nice. I thought they were $3.99 each.

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code 48
Maybe you already looked this up, but that code points at the LAF (O2 sensor). There's a troubleshooting procedure on p. 11-38. Probably you should run through that procedure. You've sort of done some of the steps already.

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solder on some wires to pins d22/d14 and also d14/d16
Since you might be tapping some more ECU wires down the road, you might want to consider something like this:

http://www.mouser.com/search/Product...538-19216-0018
http://www.vanco-online.com/index.ph...ucts_id=101458
http://www.magnadyne.com/index.cfm?M...&Web_CatID=193
http://www.radioshack.com/sm-quick-s...i-2998435.html

These are called Quick Splice Connectors or T-Tap Connectors.

I used the Shack product and it worked well.

For a more temporary connection, you could use some kind of a back probe:

http://www.backprobe.com/
http://www.smartchargers.com/products/22
http://www.amazon.com/Automotive-Bac.../dp/B000I16DKM

Or you just might want to keep soldering. Each approach has its own advantages.

You could also find a junk ECU and rip out the jacks (you would need to scrounge the plugs, too, obviously), and build your own complete test harness. But that seems like a lot of work, unless you had a bunch of different Hondas you needed to work on.

Quote:
would be nice if they had like a 5v range
HF has a fancier DMM for $33. I bought it cause I wanted the tach feature. The dwell feature is also handy, for monitoring injectors. And it has a 2v scale, which works perfectly for monitoring D14/D16. But it's too big to fit in the cupholders! I turn it sideways and wedge it into the dash, just to the right of the speedo. It's just the right size to sit securely in there.

Maybe you can convince yourself that you really need to own (at least) 4 DMMs!

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meter 1 is connected between ground and d14
meter 2 is connected between d14 and d16
I haven't bothered with 1. I've done a lot of miles with 2, so my comments will be about 2.

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At Idle,,,

2.95-3.08v meter 1
.38 - .42v meter 2(pump cell) ( yes positive voltage )
The normal idle reading is about +0.2v. So something's wrong, right there. What's your idle rpm?

Quote:
Ok,,, crusing down the road... and I believe in lean burn mode for sure...

3.89v - 4.08v meter 1
1.29 - 1.40v meter 2 ( and yes again, positive volts... )

Do these numbers seem high to you,,,, chime in here TomO!!! I would thing for sure that it is in lean burn mode...

Ok,,, meter 1 drops down to 1.0++ when I hit the gas, and meter 2 goes negative voltage when I hit the gas..... Same thing if I try to maintain speed up a steep hill.... so hey, these numbers seem ok to me .....
I think you've moved the decimal point (for 2). And I think something weird is happening, because when 2 goes down, 1 should also go down, not up.

I see readings from roughly -0.8v to +0.8v. When I ask for moderate acceleration, it swings to roughly -0.3v. It will move smoothly to even more richness, as I open the throttle further (about -0.8v, at WOT). If I back off to a light setting and let it cruise, it swings the other way, to +0.3, or higher (as high as +0.8v), if the throttle is very light.

Quote:
But are they too high,, take the Idle numbers,, seem too high,, and even at that If I go to back of the car I swear it smells rich to me....
Maybe so. But a reading of +0.4v is definitely lean.

Have you verified that this is not a CA car, and you do have a 5-wire sensor?

Might as well verify that you have the right ECU. The number on it should say 37820-P07-A00 or 37820-P07-A01. The latter, actually, since it's a '95. Either should work fine, but A00 would indicate that it's not original. Not that this would really matter much, one way or another. But it should be one of those two.

I don't remember if you said in the other thread: how many miles on the car?
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Old 05-23-2008, 06:10 AM   #3
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The odometer says 114500 miles, I dont really believe it,,,, but maybe... The car has led a hard life,,, getting slammed to the ground, good little fender bender in the front,, carpet ripped out... you know, typical teenager reading a magazine,, working at waterburger, looking at those cars in the magazine,, wanting his car to look like those,,,, buying a $20 spring kit,,, managing to get it installed, not correctly I might add.... slapping some bigger rims,, oh and when I got it, every tire was a different brand..... hahah..

I have done alot to it in just a week... replaced the radiator support, bumber cover, shocks, springs, new master cyl, wheels, tires,,... found some original vx aluminum rims,, 13"... anyway!!!!

Ok, so I took some more readings this morning,,

seem about the same,

crusing down the highway,,

3.80v - 3.95v... meter 1, fairly constant unless I hit the gas
1.15v - 1.31v meter 3.. again fairly constant..

And no shift in the decimal point,, it reads 1.15 v!!!!!!!!!!!! peaks at about 1.65v at times.. goes as low as -1.4v under power,


Idle, no a/c looks about 6-700 rpm, but that is looking at the gauge in the car..

3.04v -3.15v meter 1
.24v-.48v meter 2

ECU # 37820-p07-a01

no check engine light yet,, maybe on the trip home.

I did do the checks on the LAF sensor in the manual, all voltages within range, basically the manual told me to try a good known ECU!!! I dont have another to try.. I really dont think it is the ECU,, but I guess anything is possible...

john
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Old 05-23-2008, 07:57 AM   #4
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I know that you mentioned that the car has been in the hands of a Ricer....did said Ricer ever mess with the exhaust system? I'm asking because I'm wondering if there isn't air leaking in from the exhaust flange from the manifold to the head, or even from the Cat Converter. Is there any signs of soot on the head near the header flange or at the flange of the header to the Cat Converter?
The LAF only reads the Oxygen content in the vicinity that it is in, so if air is leaking into the system, it will read it, and then the ECU will add a touch more fuel. So that means that an air leak can contribute to the slightly high readings and lower FE.

There has been a case of a bad sensor reading high and a bit sluggish. When the owner replaced the sensor with a new one his FE went back to where it was supposed to.

Now mind you, I'm just trying to eliminate problems here. And with your background you've provided, it seems that you will be able to get your VX running like it should with a little help from us and you'll be set.
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Old 05-23-2008, 08:05 AM   #5
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Quote:
Originally Posted by pinbrew View Post
The odometer says 114500 miles
It's possible that number is real, and that the kid didn't do any serious damage. It sounds like mostly what he did is superficial. It's also possible that your car is a real find, especially if there's no big rust problem. Low miles like that is unusual. Anyway, it's nice to know that you're giving the car the TLC it deserves. I think if you get the car into good shape it will hold its value, and be a worthwhile investment.

Quote:
new master cyl
I think that shouldn't fail this early, so maybe that's a clue that the true miles are higher.

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crusing down the highway,,

3.80v - 3.95v... meter 1, fairly constant unless I hit the gas
1.15v - 1.31v meter 3.. again fairly constant..
I know you mean meter 3.

Quote:
And no shift in the decimal point,, it reads 1.15 v!!!!!!!!!!!! peaks at about 1.65v at times.. goes as low as -1.4v under power,
OK, that seems very good, actually. You're getting a nice wide range from your O2 sensor. If I understand correctly, you're getting a maximum richness of -1.4v when you apply heavy throttle. And you're getting maximum leanness of +1.65v when you have very light throttle. That range of 3v is higher than I would expect. My car yields 1.6v, and from what TomO wrote, my range seems typical. So I'm surprised your range is so high, but I think bigger is actually better, in this instance.

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Idle, no a/c looks about 6-700 rpm, but that is looking at the gauge in the car..
That sounds just right. The spec is 650. I have found that the dash tach is reasonably accurate.

Quote:
3.04v -3.15v meter 1
.24v-.48v meter 2
That doesn't look exactly right. I think you should get a fairly steady +0.2v at idle. The way you're jumping up to +0.48v strikes me as an indication that something isn't right somewhere.

Quote:
ECU # 37820-p07-a01
Good.

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no check engine light yet,, maybe on the trip home.
Maybe you'll just never see that CEL again, and the origin of the code 48 will be a mystery. But maybe you have something intermittent going on, and the code will reappear. I wonder if there's a loose connection somewhere, from the kid messing with wiring.

Quote:
I did do the checks on the LAF sensor in the manual, all voltages within range
Good.

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basically the manual told me to try a good known ECU!!! I dont have another to try.. I really dont think it is the ECU,, but I guess anything is possible...
What I've heard is that it's very, very rare for an ECU to fail. So I bet that's not the issue.

Maybe if/when the code reappears, you might notice something interesting happen on the meters, right at that moment.

In the meantime, do the plugs/rotor etc, and drive it easy (shift early), and tell us what your next fill shows for mpg.

And that's a good idea Tom mentioned about looking at the exhaust manifold.
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Old 05-23-2008, 09:18 AM   #6
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I hope to catch something when the CEL comes back on... we will see what happens... I'll check all the connectors under the hood tonight when I get home.. as well I will look for any signs of the exhaust leaking... I wouldnt think it would be a problem with the positive pressure in the exhaust manafold,,,, well while driving down the road anyway...

the only thing that I can tell for sure right now about the exhaust is that the muffler has been changed to one of those round high flow loud ones.... you think I am loosing some needed back pressure, and should put me an original muffler back on?? Also I need to get under the car, it was so low that the downpipe could possible have a hole in it due to scraping on the pavement or something... I'll check it all out... and let you know

and thanks for the replys guys..
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Old 05-23-2008, 10:34 AM   #7
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Quote:
Originally Posted by pinbrew View Post
as well I will look for any signs of the exhaust leaking... I wouldn't think it would be a problem with the positive pressure in the exhaust manifold,,,, well while driving down the road anyway...
Just an FYI....Exhaust comes out as "pulses" from the head, and behind each pulse there is a chance for air to be drawn into the system via an opening. That is how the air can get into the system and skew the O2 reading.

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the only thing that I can tell for sure right now about the exhaust is that the muffler has been changed to one of those round high flow loud ones.... you think I am loosing some needed back pressure, and should put me an original muffler back on??
An OEM muffler would help, but is not absolutely necessary at this moment.

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Originally Posted by pinbrew View Post
Also I need to get under the car, it was so low that the downpipe could possible have a hole in it due to scraping on the pavement or something... I'll check it all out... and let you know

and thanks for the replys guys..
Let us know how it goes, and you're welcome. Glad to help out.
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Old 05-23-2008, 11:02 AM   #8
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To check the exhaust for leak, have someone hold a rag over the tailpipe, not enough restriction to kill the motor but slow it down a little. Listen for hissing around the suspect areas. You could use a piece of vac hose as a kind of stethoscope to isolate one if you find it.

regards
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Old 05-23-2008, 03:54 PM   #9
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OK, check this out.... dont flame me!! haha...

So did some tests today..... topped off my tank, at 3.5 gallons,, and when I top it off, its full to the brim... 107 miles,, thats driving like a granny and monitoring lean burn like a mother... wow that is pretty crappy mileage,, something is definatly wrong..... 30.57mpg...

OK,, So I think to myself, crap I got better mileage when I drove it harder... so,,, little devil in my head,,, drive it even harder, just to see....
54 miles,,, 1.07 gallons of gas. 50.46mpg... now I know its more accurate to use more gas,, but I just had to see... and when I topped it off, it was more than full this time... soosoosoooo..

I was dogging it up to speed,, trying to get the vtec to engage,, not playing around,,, doing 75-80 the whole time.....

readings,,

while crusing at 75-80

2.98v meter1
.92v meter2

go figure,, something is amiss for sure,, noticed a little hesisatation here and there as well, .... now fix it and drive like a granny, or not and drive it like hell... hahah,,, well we know I want to fix it...

OK. got the CEL light to come on..... heres how... and I am positive its the same reason It came on before.....

you know when you first start the car,, the meters read .75v each.. for 20 seconds or so, maybe less..... Well I got into 1st gear pretty heavy before the sensors started reading,, boom CEL.. It then proceded to stay at .75v... waited,, waited..... no readings from the sensor.... ok,, so try this,,, while crusing, turned it off, clutched it back on,, CEL went off,,, about 10 seconds later the O2 sensor came alive and started reading...... back to normal....

HYM....... Man I love this crap..... SO... I know I have a little miss somewhere,, vtec does engage sometimes, not all the time, but sometimes... I was just wondering if it was always engaged thats why I was trying to see if I could feel it kick in..... I'll dig in tomorrow morning,, check the plugs and such,, and look for vacuum leaks / exh leaks...

Ok,, theory time,,,,,, I have a vacuum leak or exh leak making my 02 sensor read too lean,,, the computer sends more gas to compensate.. I am running rich all the time,, driving like a granny is using a ton of fuel,, it just keeps compensating,,,,, I drive like a mainiac 75-80 mpg,,, allowing the engine to actually use that extra fuel the computer is dishing out... viola,, better gas mileage..... hym....


so,, any opinions on this .???


thanks
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Old 05-23-2008, 05:14 PM   #10
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Originally Posted by pinbrew View Post
driving like a granny and monitoring lean burn like a mother
I think using light throttle and trying to maximize lean burn is not the best strategy. I ran a test on this which I described here: http://www.gassavers.org/showpost.ph...93&postcount=7

Quote:
when I topped it off, it was more than full this time
Try to use the same pump, and try to fill it the same way every time.

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I was dogging it up to speed,, trying to get the vtec to engage,, not playing around
You might be confused about VTEC. It engages at 2500 rpm, regardless of throttle setting. Don't worry about it. You should be trying to stay under 2500 rpm all the time, anyway.

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doing 75-80 the whole time
Do you mean 75 mph? That's too fast. I mean just from the perspective of FE, not as a moral judgment. I love speeding myself, whenever possible.

Quote:
while crusing at 75-80

2.98v meter1
.92v meter2
+0.92v (on meter 2) is very lean. A reading like that is usually associated with a very moderate throttle setting. But if you were really doing 75 mph, you weren't using a moderate throttle setting. So I'm surprised to see it so lean at that speed. But maybe it's true, and it's a good thing. I'm not sure.

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noticed a little hesisatation here and there as well
When it's very lean, I notice a little of that. So that fits with the very lean reading you reported.

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you know when you first start the car,, the meters read .75v each.. for 20 seconds or so, maybe less
That sounds sort of right for meter 1, but not meter 2. On meter 2, when cold, I see maximum richness for about 20 seconds. That means -0.8v. Did you flip the sign?

Quote:
..... Well I got into 1st gear pretty heavy before the sensors started reading,, boom CEL.. It then proceded to stay at .75v... waited,, waited..... no readings from the sensor
I don't know what you mean by "no readings." Did the meters indicate zero? That's the only thing I would call "no readings."

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I know I have a little miss somewhere
When very lean, a little roughness or hesitation is normal, I think. Just a little, when adding throttle.

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vtec does engage sometimes, not all the time, but sometimes
I think it probably engages 100% of the time, when you cross 2500 rpm. Whatever you're observing and calling vtec is probably something else.

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... I was just wondering if it was always engaged thats why I was trying to see if I could feel it kick in
I can feel some extra power over 2500 rpm, but it's smooth and subtle, not abrupt.

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I'll dig in tomorrow morning,, check the plugs and such,, and look for vacuum leaks / exh leaks...
Just looking at the plugs might tell you something. Make sure you have exactly the right plugs. And check the timing.

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I drive like a mainiac 75-80 mpg
You mean 75-80 mph, right? You can definitely improve FE if you slow down.

Shift early. Keep the revs low, but use large throttle settings. And then coast, if you have too much speed. Learn about P&G. My normal P&G routine is to use WOT alternately with coasting.

It's an interesting mystery. Keep us posted.
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