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Ok first problem to be posted on these G1 forums... and in my usual fashion its basically a mini-novel. here goes hehe

If you're not aware, I went through a lot of crap to get my Legend working well. I got it worked well enough to pass smog in September, but I knew it still has some demons running around in it...

I drive home from college every few weekends and the PGM-FI light almost always comes on.
It's always rear or front o2. Now I've switched these bastards twice, redid the wiring for the rear one (it was intermittently working). I've driven around with a multimeter attached and the o2 sensors aren't doing anything unusual when the light comes on. I believe that there is nothing wrong with the sensors. I'd blame the wiring closer to the ECU if it wasn't that i get front and rear codes (the wires aren't next to each other, why would these stop working and only these at the same time?). I'd think some other sensor is giving incorrect readings and the ECU is 'blaming' the o2 sensors but, I didn't think that ECUs this old (86) do consistency checking, only check for shorts or open connections (and through testing it doesn't seem the Legend's ECU 'notices' open ones, it just ****s itself without telling you).

I don't know if it matters but the light comes on at almost the same locations one way, and usually only in the morning or at night (in the past 2 months time of day doesn't seem to matter; before then it never came on in the afternoon).

From Redwood City to Davis:
1 A minute after I merge onto 101N, just as I'm passing this one exit

2 Just as I get in sight of the San Mateo Bridge (92E)

3 Right before uh.. this bridge whose name I can't remember (north of Oakland) on 80

From Davis to Redwood City:
Just about anywhere between Davis and Berkeley

It never comes on when I'm accelerating more than lightly (makes sense, open loop, it disregards the o2 sensors anyway) . With one exception, it has never come on below freeway speed (65mph).

Here's an email I wrote about watching the o2 sensor voltage:

I got the PGM-FI light to go on 4 times during my trip and 2 more times later in the day (I pulled over the first 3 times the light came on and turned the engine off then on). Although I didn't log anything useful, it doesn't matter because absolutely nothing interesting was going on. When I was barely on the gas, I could see the o2 sensor goin up and down around .5v. Anything more than light throttle and it would sit around .7v. To keep the car going at 70mph I had to press the gas enough to get it to stay at .7v. I'd expect it to fluctuate around this value but it didn't. And it stayed that way unless I abruptly let off the gas (then there'd be a delay, then it would drop down to .1v as the
engine slowed down, then it would go back up to about .5v until i pressed on the gas again and it went to .7v). The PGM-FI
light would come on at random times it seems. Then the o2 sensor voltage would still sit at .7v, but when I pressed on the gas I could watch it drop almost to 0v, like its giving the engine a fixed amount of gas no matter how much I jam the throttle. Awfully lean isn't it... One day I will club the people who wrote the software for this ECU to death with my Fluke.


:confused:

So now the question is, what next? Take out the ECU and check the connectors and harnesses... if that gives me nothing... dunno
 

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I dunno, but....

Try adjusting the TPS (Throttle Position Sensor)... It may be telling the computer that the throttle is in the wrong position, but the sensor is still working, therefore the computer doesn't throw you that code.

It's just a guess, but it won't cost anything to try it... The TPS is supposed to tell the computer how much gas is needed, end the O2 sensors tell the computer how much gas is in the exhaust (mixture to rich or too lean), so my guess is that the computer just thinks that the O2 sensors are toast...
 

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If your engine is not running right the 02 sensors may have become fould making them inoperative. Pull them out and see if they're carbon fould.
 

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i am not sure if it is my pgmfi but my exhaust is smelly not like burning oil but gassy. what could be causing this
 

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O2 sensors

Have you considered that maybe your catalytic converter is fud up? Or maybe a backup in your exhaust? Just grabbing at straws because if you let bad O2s go your cat will plug up.
 

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damn it must be the highway 80, mine turned on on the way to Sacramento and on teh way back. Grrrr................ so i had to keep resetting my ecu, i pull the ECU fuse and teh alternator fuse. i dunno, its not comin on anymore, knock on wood
 

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One other thing

When I bought my Civic in 96 it did the same thing. Same place driving home from work. Took it back to the dealer who couldn't figure it out. They gave me a new one and later said that the problem was caused by wires connected wrong (didn't get into it) but may be a connection needs to be switched.
 

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cdndvl said:
Try adjusting the TPS (Throttle Position Sensor)... It may be telling the computer that the throttle is in the wrong position, but the sensor is still working, therefore the computer doesn't throw you that code.

How do you adjust the TPS?
 

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My light comes on every time I drive my car, and has now for over a year. My car doesn't run any worse when it's on, so I have just learned to ignore it. Of coarse, I don't have to worry about safety inspections, let alone emmissions. Oh, I have no cat., so I know that's not the problem. Supposedly it's the rear O2 sensor, but I probably won't replace it. I still get 350 mile to a tank of gas even with 160,000 miles.
 

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tps not adjustable
lazy oxygen sensors may be culprit, even though ecu doesn't pick it up. only way to tell is to hang an analyzer or oscilloscope on the sensor.
even if you still get good mileage, you might be running too lean. -loss in power and smoothness, risk burning valves out from running too hot.

the ecu on the g1 is not very sensitive to o2sensor behavior like newer cars and will allow an out of spec sensor to pass. 15 years ago these o2 sensors cost a mint. today they are a fraction of what they cost before.... like 1/10-1/5 if you really shop around.
 
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