1991 4.0 check engine light runs rich and stalls

cade.dopp2 · #1 11-17-2012, 09:13 AM

1991 4.0 v6. When I bought it it would stall every time I started to accelerate at low rpms. Injector cleaner helped alot. I also replaced air filter, fuel filter, pcv, engine coolant temp sensor. It fails emissions because the values are way too high in every category measured, I was told that means it is running too rich. Just pulled the codes and got koeo 16, 16, memory 41, 41 koer 42, 42. I think these codes have to do with the idm and o2 sensor, but it sounds more like a timing problem possibly?

It is running better than when I got it but it still shudders slightly when I'm accelrating.

Does anyone know where to start?

78_pinto · #2 11-17-2012, 10:24 AM

hi, take a full read through this and see if any of it rings a bell, it might help you to pinpoint where to start testing for the problem(s).

http://www.aa1car.com/library/trouble_code.htm

pooleo · #3 11-17-2012, 10:27 AM

run rich condition is a default reading from the 02 sensors. If you pulled an o2 sensor code thats probably the problem. Check to make sure any wires are not hanging on the exhaust and burned, rubbed against the firewall and cut and check to make sure they are plugged in.

78_pinto · #4 11-17-2012, 10:42 AM

Quote:

Originally Posted by pooleo

Check to make sure any wires are not hanging on the exhaust and burned, rubbed against the firewall and cut and check to make sure they are plugged in.

LOL ya do this first..... I always think that these things have been done and I take it for granted that if someone asks a question in here they have already done the most basic of the look over and wiggle tests....

you are 100% correct thou... seek out the obvious first... good call !!

FireRanger · #5 11-18-2012, 06:22 AM

Quote:

Originally Posted by cade.dopp2

Just pulled the codes and got koeo 16, 16, memory 41, 41 koer 42, 42. I think these codes have to do with the idm and o2 sensor, but it sounds more like a timing problem possibly?

The codes you pull won't do you much good. 16 indicates an idle problem. It doesn't tell you what the problem is or what is causing it. 41 and 42 are O2 sensor codes that completely contradict each other. 41 too lean, meaning not enough fuel or too much air. It can also mean the sensor's heater isn't working which would give a false lean condition. 42 means too rich, meaning too much fuel or not enough air.

It is hard to make heads of tails when the codes conflict. A bad IAC could cause your idle problem AND the lean condition. You could pull the IAC and clean or replace it. If this problem occurs even on cold start, this is very likely the problem. Oxygen sensors and computer settings are ignored during cold warmup, a condition called open-loop. Once the engine warms up, it starts using it's sensors and learned programming.

If that doesn't help, the sensor could be bad or the wiring leading to it could be bad.

You should also check your fuel pressure on the fuel rail. It should be >28psi at idle. Less would indicate a bade fuel pressure regulator or pump. Hesitating on acceleration is almost always a lack of fuel for one reason or another. Oh, also pull the vacuum line off the fuel pressure regulator to see what happens with that. If the diaphragm in the regulator is leaking, it will suck fuel into the intake manifold.

Quote:

Originally Posted by 78_pinto

hi, take a full read through this and see if any of it rings a bell, it might help you to pinpoint where to start testing for the problem(s).

http://www.aa1car.com/library/trouble_code.htm

None of that will help. He doesn't have OBD2.

cade.dopp2 · #6 11-18-2012, 08:48 AM

Thanks for the ideas so far, I'm going to get started tomorrow morning. I forget to mention that it usually runs better when it's cold than when it gets warmed up. If I take it straight to the highway I won't get a check engin light for about 50 miles when I slow down to take the off ramp, but if I drive it around town I get a light within 4 minutes. I know it is actually running rich despite the lean codes because I failed emissions with very high levels of CO and and HC.

FireRanger · #7 11-18-2012, 08:53 AM

That makes me think you're even more likely to find a bad IAC. In both cases, you're not getting codes until you let the engine warm up and idle. That's happening quickly around town, obviously. And it happens when you get off the highway and slow down/stop.

cade.dopp2 · #8 11-19-2012, 10:17 PM

I put my ohm meter on the iac and it was within range. Took it apart and it was dirty so I cleaned it. Didn't make a difference in how it runs or getting rid of codes. I decided to change spark plugs. Most of them were very black. After changing plugs it's running rougher. I checked to make sure I have all the wires connected tight. Now I also get a koeo 14 and 63.

Just realized that I tried unhooking the throttle position sensor to see if it would run better when hot if taken out of the closed loop, I think that's the code 63, but I'm not sure about the 14.

78_pinto · #9 11-19-2012, 11:16 PM

None of that will help. He doesn't have OBD2.

obd1 or 2 makes no difference, these are still the same sensors and they work in the same ways needing the same tests and the same codes are thrown no matter obd1 or 2

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black plugs, you are getting too much unburnt gas, search the lines of spark. there is a test for the coil, you can test that to make sure you are getting enough power there.

RangerGR · #10 11-19-2012, 11:36 PM

Does the 91 4.0 have a kcv-190(Positive crankcase ventiilation valve hose)off of the pcv? Google it for pic...I know if it goes bad from heat and wear(hole in 90* elbow off of the pcv), it will throw a bunch of codes..common problem for my 03...but its only if you have a vacuum leak & the part on the motor..good luck!

FireRanger · #11 11-20-2012, 03:51 AM

14 is an ignition system fault. Do you have a distributor or coil pack? If that's failing, it would clearly cause a rich condition with unburnt fuel. 63 is from the TPS being unplugged, so I wouldn't worry about that if it went away.

Quote:

Originally Posted by 78_pinto

obd1 or 2 makes no difference, these are still the same sensors and they work in the same ways needing the same tests and the same codes are thrown no matter obd1 or 2

None of that is true either. OBD1 and OBD2 are not the same codes and are nothing alike. The link you posted contains nothing at all about OBD1 or the codes he's getting.

cade.dopp2 · #12 11-20-2012, 09:10 AM

I replaced all the hose with the pcv when I switched it out. I have a coil pack.

FireRanger · #13 11-20-2012, 09:42 AM

Oh, ya you have the same truck I had, a '91 4L.

It's going to be tough when you have two conflicting indicators... a lean condition and a rich condition. I guess I would start with the O2 sensors and the try the coil pack. Also, make sure you check the wiring for the O2 sensors, not just the sensor itself.