Hey guys,

I've been working through the p0171 and p0174, problems still. I thought it was the o2 sensors. Turns out not. When I connected the autoTap software I found that the TPS is not giving the proper range of 0.5-4v signal. Replaced the sensor and same thing, I'm convinced it's the wiring, but given that I am getting a voltage range it's not shorted.

Can someone send me a link as to where the wiring from the sensor terminates? In the VCM I believe? Where is that and what do I have to do to check the wiring?

Thanks,

 

Have you checked input voltage at the tps?

 

I worked on a 1990 olds something-or-other that had a shorted out coolant sensor that sucked the 5v ref down to 2.xx volts. Acted just like a bad TPS.

 

Crackers, thanks for the response. Yes since the post I did exactly that, checked for 5v on the source to the TPS. And yes all is good. Actually there must of been a gremlin or something in there, because after I re-attached everything, and tested, I get a good range 0.5-4.4 WOT. Weird.

The problem as is that the short term trim levels on bank1 and 2 are still around 22-25%. Back to square 1. I'm going to check the EGR and attempt to clean.

Also I'm starting to go back to the MAF sensor, so far the thing that makes the biggest difference is when I unplug it. what should be flow be across that? Lastly, I'm missing the screen at the front of the MAF sensor, I think the Canadian tire mech must of removed it to try and get more airflow.

Any help on this P0171 is greatly appreciated.

 

if the maf makes a difference when you unplug it,id pick up a can of maf cleaner and spray the inside down. Dont use brake cleaner or tb cleaner.

 

Yes, that was the very first thing I did, it did make a difference.

Actually, one thing I noticed was the short term trim values on both banks drop to -1% when the MAF sensor is disconnected.

Normally, despite all my messing around, the short term values usually are around 15-20% on bank 2, and 25% bank1, consistently.

I know this probably indicates a MAF sensor failure, but I've already replaced two sensors unnessarily. The o2, and the TPS (although this one was 50/50 if needed replacing)


I'm going to head to the wreckers and see if I can find just the screen for the MAF sensor which is currently missing.

Thanks,

 

25% fuel trim is maxed out, that's all the PCM will do. If those figures are positive, (not negative) it is definitely running lean and the PCM is trying to richen it up. Have you checked fuel pressure and leakdown? Low fuel pressure can cause those DTC's to set in memory.

Key ON, engine OFF, fuel pump running: pressure must be 60psi to 66psi and it must remain above 55psi for at least 10 minutes after the pump shuts off. If it fails one or both tests, it means there's a problem with fuel delivery and further testing is necessary to determine what the problem is. Post your results.

EDIT: Keep in mind that all sensors, except the O2's, are monitored continuously when the ignition is ON. If there's a problem with the PCM not receiving the correct data from a sensor, (i.e. your TPS) it WILL set a DTC in memory, no DTC = no problem.

 

Success! Hit the wrecker's, found a new MAF, 40$. Finally the short term trim levels are oscillating around -4% to +5%. Both sensors, running really nice too, and alarms gone.

I agree no DTC=No problem.

Thanks for the input guys.