My car is running very rich

stang-geoff · May 22, 2010

Like the title says, it's running rich. The car also misfires at idle and cruising. I hooked up a scope to look at my 02 sensors and both banks read the same. The sensors weren't switching at all. Both of them had the same readings. They're 3 wire sensors and I'm not sure which one is the signal. One wire was reading .8 volts constant and the other wire was reading .2 volts constant.

I was surprised I didn't see a switching signal. I took the readings with the car warmed up at idle.

I also pulled codes, I have a DTC for my egr. signal voltage was to high in the closed position. I'm assuming that's just because of carbon buildup affecting the valves seated position.

I also have a DTC for my neutral position on my transmission. The wire is frayed so the circuit is open. I have trouble seeing that causing my car to run so rich though.

any suggestion guys?

Kdubslugga · May 23, 2010

Does it run rough all the time or just warmed up?

stang-geoff · May 23, 2010

It seems to run rough all the time at idle and light loads or cruising. Cold or hot.

HISSIN50 · May 23, 2010

What is the EGR reading? Make sure the solenoid didn't go sideways (and is now letting vacuum pass at all times, which would cause a crappy idle). Spec on the sensor is < ~0.60V IIRC, but generally one wants it below 0.40V baseline to allow transient wandering.

Have you double checked your O2 outputs with a DMM? I would. If your readings were as bad as reporeted, a code should have been generated. Make sure the car has been run for several minutes before testing.

Good luck.

stang-geoff · May 23, 2010

the car ran for an hour, no codes for the 02s. I'm wondering if something is causing the car to run in open loop??? I was surprised to see there was no switching. I disconnected them while the car was running also. It had zero effect on how the engine was running.

HISSIN50 · May 23, 2010

You should have had a CEL with them disconnected. Did you?

Was the measuring device functioning properly? If using something that does not have enough internal resistance, it can affect the reading.

Again, I'd just manually test them with a DMM.

stang-geoff · May 25, 2010

I did check the signal with a dmm, same voltage. The mustang is an 86, and as far as I know this car doesn't produce check engine lights. Sorry, I should have mentioned the year earlier.

The other day I looked at the ect sensor, and that looks like it's operating fine. One thing I did notice though is that unplugging it actually made the car run better when it was idling, but I think that unplugging it made the PCM think it's running really hot and it leaned out the mixture.

I just ordered a breakout box today so I can do some road tests and view the sensors. I also bought it because it's going to be about 10 times easier to look at sensor inputs.

I also looked at my pressure regulator. I think it's functioning fine. It was 35 psi at closed throttle and 42 psi with the vacuum hose removed.

I'm wondering what checks the pcm has to go through to go into closed loop. I know tp voltage, map values and ect voltage is important, what else should I look at?

HISSIN50 · May 25, 2010

Was the wiring to the O2's ok? If they have no power or ground, they can freeze at some arbitrary value.

If you confirmed those O2 readings, you know something is wrong since the O2's have no amplitude or frequency. I'd change them from side to side to see how the reading changes.

O2 temperature is what allows their feedback to be used (closed loop). They need to light off.
Your 86 should have HEGOs and you are correct, it does not have a functional CEL.

I would keep pursuing the O2 and EGR aspects, as you have codes for both and both can cause issues at idle and part throttle.

Good luck.

stang-geoff · May 25, 2010

No, there are no codes for the 02 sensors, just for my egr valve. I have thought of swapping the 02s around but they're both giving me the same signal, so I assumed they were working. I can check my circuits for the 02s and see if there are any shorts or resistance next.

HISSIN50 · May 25, 2010

If your O2's are frozen, there is an issue and should be a code for both banks. Wasn't one giving you 0.8V and one giving you 0.2V? Wait, re-read it again. Those values were not the output for each sensor - it was a value on the other two wires on a given O2 sensor. Gotcha. Apologies for my misunderstanding what you'd said.

So each O2 signal was fluctuating from 0.1 to 0.9V or so? That's what you should see on the signal for each one. If so, they should be fine.

How was the EGR baseline? Around 0.40V or under?

stang-geoff · May 26, 2010

No, they were not fluctuating. One wire was a constant .8 volts and the other wire was a constant .2 volts on the same sensor. I was getting this reading on both banks

HISSIN50 · May 26, 2010

The O2 signals need to fluctuate, and the CEL should be on if one or both is not.

stang-geoff · May 26, 2010

Again the car is an 86 so there isn't a check engine light and there are no dtcs for this, just for the evp sensor.

That's why I've been looking at sensors that could cause the engine to run in open loop and and/or cause the engine to run rich. I will also test the circuits for the 02 sensors and see if there's any faults.

I'm not sure what I should check though. I think my map sensor is functioning right. I ran it on a friend's f150 and it seemed to run just fine with it.

bagel77 · May 26, 2010

this may be long shot but when I had a problem with my car running rich it was a bad ground in my computer block. I guess it wasn't make good contact in the block so I pulled it out and grounded it right to the body. hope this is a little helpfull

this worked because the injectors fire on a negative pulse. the bad ground caused my injectors to basically dump fuel.....which if my thinking is correct..your O2's would not move because the mixture is not changing. just my 2cents

HISSIN50 · May 26, 2010

And again, if the O2's are frozen, there should be a code(s). Be sure the testing was done correctly. If your meter does not have enough internal resistance, it can remove all of the switching from the signal.

Since the only code you're throwing is for the EGR, the EGR code can shut off the EGR (obviously) and can affect deceleration fuel.

You'd likely need an oscilloscope to test your MAP. If it was way off and causing extreme richness, there should be fuel codes.

Unplugging the ECT removes fuel adaptation and affects AIR and EGR function.

stang-geoff · May 27, 2010

Well I found charts for eec-iv on fordfuelinjection.com. I look more into it when I get my breakout box

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