Extremely rich idle

[weba]

My daily 92 3.1 MPFI (stock) just bumped the emission test second time.

Just installed brand new cat converter on it, plugs and wires are 2 years old and in good shape.

It runs extremely rich at idle, everything else on the emission test passes with glory and with really good values, it just runs rich until gas pedal is touched. I can actually smell the fuel if standing still.


ALDL reader shows that o2 voltage jumps around crazy from 50 to 800mV all the time. BLM is 118 and INT 125. This is at 850-900rpm idle speed (it's COLD outside)


Are we looking at O2 sensor issue here or what? I have quite a hurry to get this fixed before it turns expensive because off the laws here.

Ideas appreciated.

[3400-95-Modified]

Coolant temp sensor? Make sure its sending the right signal to the ECM, if the dash is right that doesn't mean the sensor next too the cooling neck is right.

[weba]

ALDL reads 198-203 F

dash says 60C~ (140F?)

[3400-95-Modified]

O2 sensor should bounce...

Whats your fuel pressure at idle? also possible to have a leaking injector?

[weba]

Don't know about fuel pressure, i don't have anything to use measuring it.

Is there any way to test the injectors without taking the upper intake away?


MAP seems to behave normal, shows around 35KPA at idle.

So looks like it's not a MAP, o2, or a coolant sensor... more guesses?

[IsaacHayes]

Injector, or check the FPR make sure it's not leaking and dumping fuel back through the vacuum hose...
IAT would make it run richer some too, what's it show for intake temps...

[robertisaar]

a BLM of 118 is only 8.5% rich... meaning without O2 correction you're actually at 13.6:1 AFR instead of 14.7:1.

not sure why, but before tuning, wifey's GP ran at like 104BLM at idle... that's 11.95:1 without O2 correction.

what kind of fuel are you running?

the dash guage is about as accurate as one from a 1940 russian tank, so you can disregard it since the one the ECM reads is obviously working correctly.

[weba]

IAT shows 94F after started engine and slowly going down.

This time BLM was 128 and INT was 131, they seem to vary a bit.

Anyhow the idle HC readings (unburned fuel) was 5 times off the limits of what is legally allowed here.

So your guesses are stuck injector or faulty FPR? Great, nothing that i could find a replacement fast here...

[robertisaar]

IAT shows 94F after started engine and slowly going down.

This time BLM was 128 and INT was 131, they seem to vary a bit.

Anyhow the idle HC readings (unburned fuel) was 5 times off the limits of what is legally allowed here.

So your guesses are stuck injector or faulty FPR? Great, nothing that i could find a replacement fast here...

well, a 128 BLM is perfect fueling(or at least the O2 thinks so), so fueling may not be your issue(unless the O2 is junked)...

as for IAT: i'm not sure what kind of weather finland has.

[weba]

It's about 19F where my car is, i guess the warm~ engine bay radiates the heat to the sensor? (touching the intake pipe tells it's hot)

I need to check the vacuum hose on the FPR.. damn i wish there would be more room.

The hose going from T\B to the FPR seems to be ok, but it has a T-piece on it and i cannot see the condition of that extra hose leaving from it.. where does it go?

[robertisaar]

It's about 19F where my car is, i guess the warm~ engine bay radiates the heat to the sensor?

yes it will. anytime you're standing still, with the engine on or off, once the motor has started to warm up, it heat soaks the IAT.

[3400-95-Modified]

The hose going from T\B to the FPR seems to be ok, but it has a T-piece on it and i cannot see the condition of that extra hose leaving from it.. where does it go?

Its more or less just check to make sure that there is vac at the line going to the FPR, and that the line is not full of gas... that would show a bad diaphragm on the modulator which is leaking back into the vac system.

[weba]

Didn't see or smell any traces of fuel on it. Visual check is OK.

So what's left basically is stuck injector? I'm going to pull the intake off tomorrow and try my multimeter on them. I hope that does not cause intake leaks since getting new gasket sooner than 2 weeks is pretty hard.

[3400-95-Modified]

Upper plenum gasket should survive pretty well... Just be careful when removing it.

Basically whats left is a faulty reading O2 or stuck injector... You could try to just throw an O2 at it but I don't know how much that is over there.

[weba]

Maybe one from a Quad fits, worth a try..