Lean Exhaust Code-Mechanic Can't Resolve-Please Help!

[JESSICAR]

1995 Buick Park Ave Base

We just had a re-manufactured engine from Jasper engines installed 3 weeks ago. When we brought it home we only had driven it 30 minutes before the check engine light came on. Code scanner detector pointed in direction of O2 sensor lean circuit. We replaced O2 Sensor, light stayed off for about 3 days, then came back.

We have brought it to a mechanic who has had it now for going on three weeks, and can't find the problem.

We have replaced: Computer, Mass Air Flow Sensor (3x), O2 sensor(3x). He has checked fuel filter, fuel pump, injectors, gasoline to check for excessive moisture, checked for vacuum leaks, and grounding wires. All these items came out fine.

Does anybody have any clue maybe what else we can look for? The car now has been in the shop for 3 weeks total, and we are very disappointed .. after spending money to have a re-manufactured engine dropped in to replaced a high mileage engine that had a blown oil seal and burned oil in plumes and now can't fix the problem? The code keeps coming back and the car runs like crap...... The mechanic is an 18 year veteran, and is stumped as well.. please.. any suggestions are helpful.

Thanks
-J

[maxwedge]

It is impossible to diagnose this from this desk, your mechanic is unable or is unwilling to fix/find this? Also exactly what is the code. Was this a complete engine or a long block that required using your intake and accessories? How does it run?, all these issues are omitted in your post.

[JESSICAR]

Originally Posted by maxwedge

It is impossible to diagnose this from this desk, your mechanic is unable or is unwilling to fix/find this? Also exactly what is the code. Was this a complete engine or a long block that required using your intake and accessories? How does it run?, all these issues are omitted in your post.

Thank You for responding.

1. The mechanic is willing and has replaced several items as a result, but has not been able to pin point the problem, and I am only trying to do my own research.

2. The code was 0131.

3. I actually am not sure how the car runs now, as I have not had it for three weeks. I do believe before we brought it to the mechanic due to the code that is was running a little rough, but nothing dramatic.

4. This was a complete re-manufactured engine from Jasper, and our mechanic is an authorized installer.

[maxwedge]

Make sure he knows about the 2 seals under the map sensor. It is possible they may have been left out when swapping the intake and or map sensor.

[RahX]

P0131 is a heated oxygen sensor circuit low signal.


DIAGNOSTIC AIDS
Using the Tech 1 scan tool, observe the long term fuel trim values at different RPM and air flow conditions. The scan tool also displays the fuel trim cells, so the long term fuel trim values can be checked in each of the cells to determine when DTC P0131 may have been set. If the conditions for DTC P0131 exist, the long term fuel trim values will be around 158 or greater.

* Heated oxygen sensor wire - Sensor pigtail may be mispositioned and contacting the exhaust manifold.
* Check for intermittent ground in wire between connector and sensor.
* Poor PCM to engine block ground.
* MAF sensor - A Mass Air Flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause the system to go lean. Disconnect the MAF sensor. If the lean condition is gone, replace the MAF sensor.
* Lean injector(s) - Perform Injector Coil/Balance test. Refer to System Diagnosis/Diagnostic Charts/C Charts/Chart C-2A Injector Coil/Balance Test. See: Symptom Related Diagnostic Procedures\A - E Charts & Related Test Procedures\C Charts\Chart C-2A Injector Coil/Balance Test Procedure
* Fuel contamination - Water, even in small amounts. near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can set a DTC P0131.
* Fuel pressure - System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the vehicle at various road speeds and/or loads to confirm. Refer to System Diagnosis/Diagnostic Charts/A Charts/Chart A-7 Fuel System Diagnosis. See: Symptom Related Diagnostic Procedures\A - E Charts & Related Test Procedures\A Charts\Chart A-7 Fuel System Diagnosis
* Exhaust leaks - If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor.
* Vacuum or crankcase leaks can cause a lean condition and/or possibly a high idle.
* If the above are OK, it is a faulty heated oxygen sensor.

[JESSICAR]

Originally Posted by maxwedge

Make sure he knows about the 2 seals under the map sensor. It is possible they may have been left out when swapping the intake and or map sensor.

Thank You-but according to my husband no MAP sensor on this car.

[JESSICAR]

Originally Posted by RahX

P0131 is a heated oxygen sensor circuit low signal.


DIAGNOSTIC AIDS
Using the Tech 1 scan tool, observe the long term fuel trim values at different RPM and air flow conditions. The scan tool also displays the fuel trim cells, so the long term fuel trim values can be checked in each of the cells to determine when DTC P0131 may have been set. If the conditions for DTC P0131 exist, the long term fuel trim values will be around 158 or greater.

* Heated oxygen sensor wire - Sensor pigtail may be mispositioned and contacting the exhaust manifold.
* Check for intermittent ground in wire between connector and sensor.
* Poor PCM to engine block ground.
* MAF sensor - A Mass Air Flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause the system to go lean. Disconnect the MAF sensor. If the lean condition is gone, replace the MAF sensor.
* Lean injector(s) - Perform Injector Coil/Balance test. Refer to System Diagnosis/Diagnostic Charts/C Charts/Chart C-2A Injector Coil/Balance Test. See: Symptom Related Diagnostic Procedures\A - E Charts & Related Test Procedures\C Charts\Chart C-2A Injector Coil/Balance Test Procedure
* Fuel contamination - Water, even in small amounts. near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can set a DTC P0131.
* Fuel pressure - System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the vehicle at various road speeds and/or loads to confirm. Refer to System Diagnosis/Diagnostic Charts/A Charts/Chart A-7 Fuel System Diagnosis. See: Symptom Related Diagnostic Procedures\A - E Charts & Related Test Procedures\A Charts\Chart A-7 Fuel System Diagnosis
* Exhaust leaks - If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor.
* Vacuum or crankcase leaks can cause a lean condition and/or possibly a high idle.
* If the above are OK, it is a faulty heated oxygen sensor.

Thank You
All the steps you mentioned above were performed by the mechanic, and the O2 Sensor has been replaced 3 times now, and has still not been resolved. Now the mechanic is trying to talk to the engine place we purchased the engine.
This has been the most frustrating, I appreciate the responses!

[maxwedge]

Originally Posted by JESSICAR

Thank You-but according to my husband no MAP sensor on this car.

Correct, 96 was the first year for the map on this engine.

[JESSICAR]

Well after almost 3 weeks in the shop, the mechanic called and said we can pick the car up. BUT.. that it still seems to rum like shit when it idles. But "Drive it for a few days and see how it goes".

So we pick up the car, pay our hefty fee and drive home. Not more than 5 minutes, sitting waiting for a train, the check engine light goes on.

Fuming mad, I wrote down everything that I replaced, and what the mechanic said he checked and this morning, brought it to a different mechanic.

Within 2 hours the mechanic called said the diagnosis was a Warped Intake Manifold. The car will be ready today.

I find it very hard to believe that this 18 year mechanic couldn't find this problem. But I believe that my husband and I are victims of a scam. The reason I say this is that my husband has become "pals" with this mechanic over the past couple of years while being a delivery driver that stops at the shop. We have brought several of our issues to this mechanic to be fixed, most of which were "under the table" cash type repairs, not on shop time. He is the one that suggested the whole engine replacement since the previous engine blew an oil ring, and repairing seemed ridiculous when the cost of a whole re-manufactured engine was not that much more. Of course he did some of the work on his own time so of course we got a discount. So maybe this was his backwards way of getting more money. Who knows.. but how crappy. And I am sure that we will never see our money again, but on the bright side, I sort of have a new car huh?

Thanks for all your help guys!!! I always come to AF when I questions, and the answers are always here! It's great to find a good community of knowledgeable people!

[ZiggyPA]

Originally Posted by JESSICAR

I find it very hard to believe that this 18 year mechanic couldn't find this problem. But I believe that my husband and I are victims of a scam.

This sounds pretty normal, I've seen and heard things like this happening all the time. Some mechanics overlook things or just aren't good enough.
Doesn't sound to me like he was trying to scam you. I am glad though the problem is fixed now.