89 GM3800 VIN "C" Service Engine Soon light

[Guest crazytrain2]

I forgot to ask, do you think a faulty Intake Air Temperature sensor could be contributing to my problems? (Engine related, not the psychological one's...lol)

Thanks

MW

[padgett]

Unlikely but what is it reading ? (Diagnostics will display in Centigrade). When cold OAT and IAT should be the same.

[Larry Schramm]

This might be a guess, but have you checked the grounds. Especially the one under/by the coil? Put a wrench on it and see if you can tighten it up some.

[jonlabree]

Yes, Your faulty air intake sensor can trigger the "Check Engine light". I have a modified air intake and when I start the engine a lot of times the "Check Engine light" comes on. When it starts to warm up it goes off. It has done this since I installed the air intake. Also, check the connections to it.

[2seater]

Ignition timing looks low. Probably caused by the high IAT, which will cause the ECM to pull timing due to high intake temperature. I do not believe it would cause the open loop or dead O2 reading, which is also not correct. If connections and sensors are okay, bad ECM?

[Guest crazytrain2]

I think I have found what I hope is the final culprit to my ongoing engine problems. A quick recap for those who haven't nor want to read this thread in it's entirety:

NOTE: This vehicle is a 1989 Buick Electra Park Ave Ultra not a Reatta (same engine & brake sys though)

1) SES light, "blinky" codes 13 (O2 sensor), 21 (TPS high voltage), 39 (TCC Circuit) and 41 (Caam Position Sensor)

2) Replaced O2 sensor, Cam Position Sensor and Cam Position Sensor Interrupter Magnet - No more SES light but engine was still running poorly.

3) Replaced plugs and wires, engine was still misfiring, SES light came back on "blinky" code 44 (Lean fuel Mixture)

Here's me - WTF??

4) Scan's were leading me in about 6 different direction's - Info from OBD1 is limited at best, plus I'm an idiot for never gained experience with using a multi meter. This is a train wreck waiting to happen isn't it! lol

Something in my little pea brain kept telling me that misfire sounded like the result of a MAF sensor going bad. (Always became worse at low speed, high torque situations ie. like when you shift into overdrive going up a slope) Granted it could be a coil pack but going against my therapists insistance I decided to listen to that voice and replaced the MAF sensor. I didn't blank out the coputer so it was backfiring a little for a short while but I took that as a good sign since ECM and or PCM were maxing out fuel mixture adjustments trying to compensate for the code 44 (Lean Fuel Mixture)

After a few days of use it has settled in and seems to be running ...let's just say "much better now"

Guess it goes to show that even a blind squirrel finds a nut every now and then. The End

Thanks ev1

MW

[TexasJohn55]

ct2, since my inductive timing light is broken, I had to go to H.F. and get one of those inline spark testers to use on a friends car. Was running ratty and 2 spark plugs weren't as clean. As suspected, it showed irregular spark, plugged in a new coil (had it with me) car was fixed and done in 15 minutes including short test drive. It may be worth checking. John

Edited June 5, 2013 by TexasJohn55 (see edit history)

[Guest crazytrain2]

John,

The Coil pack and module issue potential had crossed my mind as well. I still have the Magnavox coil pack set up and if I were going to replace was gonna switch to Delco style. Likely that down the road I will. There were so many potential causes of misfire issue (ie. fuel pump / regulator / filter, EGR, ECM, etc.) I was seriously debating if it was worth the cost. Truth be told I "modified" a MAF from a newer 3.8 by grinding down the plastic around the 2 probes so it would fit into my throttle valve! LOL .. Can you tell I worked on a farm as a kid?

Edited June 5, 2013 by crazytrain2 (see edit history)

[DAVES89]

That modification could be part of your problem. 2seater would probably know, hopefully he will chime in...

[2seater]

I don't know if the modified MAF is an issue or not. I do know, that in un-modified form, the frequency response is compatible with our ECM. As a matter of fact, I am using a vin L (TPI) MAF/throttle body assembly on my car right now, however, the MAF housing has a larger passage and the small formed tunnel on the sensor body becomes part of the smooth passageway. The sensor is sensitive to the quality of the airflow across it. It is possible the airflow across it is upset at some points? The screen, particularly in front of the sensor is needed to assure laminar flow for best operation. Some have removed the screen, and it will run, but many report unstable idle or other performance anomalies, depending on how smooth the airstream is ahead of the MAF. You could observe the MAF signal while driving to see what the ECM is seeing. If it jumps around at steady throttle, or is out of normal range, it should be replaced.

[Guest crazytrain2]

Don't get me wrong I definately DO NOT advocate this modified MAF approach. I just happened to have one of the sensors with the plastic "tunnel" design (AFH50M-03A) and other than the plastic surrounding the probes it appeareared to be identical to the existing MAF (AFH50M-02A) By reducing the diameter of the plastic surrounding the probes, it also removed the "tunnel" which in turn exposed the ends of the probes just like the original MAF design. I was and still am a bit concerned about signals being a bit off, but it worked.

Don't sweat it guys, I don't blame you a bit for cringing and shaking your head at this one. Crazytrain's Auto Repair !!!!

A warning to those of you reading this at home, DO NOT by any means attempt to do this yourself, leave this to the untrained, non professional mechanics such as myself......LOL:p

[padgett]

AFAIR the "L" MAF is designed to handle a higher airflow than the "C". Part is the larger venturi but I would not recommend putting an "L" MAF in a "C".

[2seater]

I sort of admire the bodging you did. I tinker in unapproved ways many times. Padgett does have a good point though. I do not know which L27 MAF you used. The early model TPI manifold I have (aluminum) flows very similar to the LN3 and the signal should be about the correct range, but no way to know for sure unless you watch it so it can be compared with more "conventional" installations. Later model L27's certainly do have a larger flow capacity and who knows where the calibration may be? The best example of what I mean is slightly different than the L27 above: I have a 3" diameter inline MAF for divorced mount, and it has exactly the same frequency range as the stock LN3, however it flows approximately 50% more at the same frequency. and the big 3.5" LS1 Chevy MAF has the same range also, but flow is way higher. They could be made to work because the ECM can read the signal just fine, but would require reprogramming to be accurate. At the least, monitor the MAF for oddities. Sometimes bad info. from a sensor is worse than no info.

[2seater]

I went out and looked at the two different MAF sensors and I am not sure how the L27 could be made to fit? The height of the sensor wires looks to be correct but the way the two different sensors seal in the housing is completely different. The stock one has an o-ring seal for a small recess around the smallest diameter passage where it inserts. The L27 has an o-ring around a large diameter plastic housing that inserts into a large diameter recess which isn't present on the LN3, so it won't insert fully unless almost all of the plastic is removed, and then a seal would need to be fabricated.

[Guest crazytrain2]

2Seater - you preetty much nailed it as to what I did. I removed the oring, then ground and sanded away all that "extra" plastic (used emery cloth sandpaper to keep it round) leaving only that quarter sized lip about 1/16" high and the 3/8" or so diameter plastic post with the nicon wire probes protruding (just like the LN3 MAF, cept more like chainsaw carpenter style...lol) I then used the oring as a seal by laying it on throttle body before inserting MAF. Finally, I had my wife start the car so that if something went wrong I could blame her

[2seater]

Ha, ha, haa. I use the wife test occassionally too. If it survives, I'm good to go. It sounds like a lot of work, but well thought out. I would still check for stable operation though.