01 LeSabre: Poor drivability and P0102

[DrRadar]

Son is complaining of low power, poor acceleration, and surging, which I confirmed. Read code P0102. Disconnected the MAF electrical and drivability improved. So, need a new MAF sensor, right?

To test that theory, pulled the MAF sensor from my 99 Grand Prix and installed in the 01 Buick. (RockAuto shows they use the same part number.) But the drivability problem remains...disconnected the MAF sensor and improvement. Go figure.

Put the MAF sensor from the Buick into the Grand Prix and it drove fine, at least for the 5-10 minutes I drove it.

I did not clear the codes at any time. Would that result in the poor drivability in the Buick when installed with the supposedly good MAF sensor? I don't think so.

My thought is a potential wiring problem or something other than the MAF sensor tripping P0102. But if this is the case, why would disconnecting MAF sensor improve drivability?

As always, any help is appreciated.

[maxwedge]

When the maf is disconnected the pcm goes to a default back up setting. Which in your case is better than a failed circuit. Google that code for multiple causes.

[Tech II]

Do you have access to a scan tool that can read data?

[DrRadar]

I have a dongle that Bluetooth connects to phone app that can read some data.

[Blue Bowtie]

The MAF wiring harness is always suspect. On this vintage Buick 231 V-6 the CTS, TPS, and IAC connectors and harness are also suspect. Most chain parts stores sell MAF connectors, and it isn't due to coincidence.

[Tech II]

I agree with Blue....could be one of the MAF connections in the harness or one of the wires to the connector could be broken inside the insulation.

Need to check data to pre O2 sensor....but you would need a scan tool to read O2 data......if data is skewed hi or low, but data is ok, when the MAF sensor is disconnected, then you need an MAF sensor....

[DrRadar]

I'm out of town for a couple weeks. He'll have to limp along with the MAF sensor disconnected until I get back. Thanks for the feedback.

[DrRadar]

Disconnecting the MAF seemed to help initially, but my son said the drivability problems returned.

Drivability seems to be getting worse and the P0102 remains; also comes back after resetting it. Verified +BAT voltage an MAF connector and continuity to ground at MAF connector; the signal pin on connector indicated +5VDC, which I suspect is provided by PCM. So it appears that there are no wiring problems to/from the MAF sensor.

I inspected vacuum lines and found a cracked boot which I repaired with no subsequent improvement. No obvious indications of other vacuum leaks although I haven't put a vacuum gauge on it. Replaced PCV valve with no improvement. My Android scan app (ScanMaster) does provide live MAF data; it was showing 0.8-1.0 lb/min in park at idle with increase to as much as 8.0 lb/min (that I saw) while driving. I need to learn how to interpret the quantitative measurements but the MAF does seem to be measuring the air flow. My next thought is to check the PCM/ECM by switching with the 99 Grand Prix GTP....I'm hoping the programming is sufficiently compatible.

Could a failing transmission cause a P0102 and these symptoms? It really seems that the tranny is reluctant to shift and I see RPMs go up to 3000-3500 without the expected acceleration. But putting it in neutral doesn't really improve the behavior. I don't have a scan tool that reads T codes; I hope to "borrow" one from O'Reilly.

As always, any guidance is appreciated.

Happy Memorial Day,

[DrRadar]

Originally Posted by Blue Bowtie

the CTS, TPS, and IAC connectors and harness are also suspect.

The signals at MAF sensor connector appear OK. If wiring problems existed for CTS, TPS, or IAC connectors, would these result in P0102? Or a different code?

[Blue Bowtie]

They all use the same 5VDC reference supply in the wire harness, and it's not uncommon to find connection problems on these Buick 231s. The IAC only has two stepper drive signals from the PCM and does not use the local ground nor the 5VDC reference supply.

The kicker is that the CTS and TPS are a bit more forgiving, with perhaps a couple of seconds of tolerance by the PCM for signals out of range before an error code is set. The PCM watches the MAF inpuf very closely, however, with as little as 600mS for an out-of-tolerance signal before an error code is set. Thus, a 5VDC supply problem will almost certainly be picked up as a MAF error and may not be picked up as a TPS/CTS error.

[DrRadar]

Disconnecting the pre-cat O2 sensor did not change performance. The more I drive it to test theories, the more I think it's transmission related. I'll limp to my transmission shop this week and let them check it as I don't have a scan tool that reads trans codes.

Any recommendations for a good "shade tree" scan tool that reads "all" codes (PCM, trans, ABS, body) and live data. I guess freeze frame data would be nice although I have never had access to it so can't say I need it. I realize control functions (like cycling the ABS when bleeding) are likely only in professional models out of my budget. I might be convinced to spend a few hundred dollars on a good tool.

[Tech II]

Sorry, I wrote some misinformation in Post #6, and have corrected it....

As for driving the vehicle with the MAF disconnected, that is not a good idea.....running it with the MAF disconnected, is just for testing....

Beware of cheap aftermarket MAF's.......have had a lot of problems buying those, right out of the box.........

[DrRadar]

Found a couple of holes in the intake plenum that were underneath the wiring harness and fuel lines. One hole is in the gasket trough and the bigger hole is in the top of plenum behind throttle body, directly above the hole to the lower intake manifold. I'm suspicious that whatever is blowing out of the lower intake is hot enough to melt the plenum gasket. Is this common? Is it indicative of another problem that should be addressed?

Photo: https://drive.google.com/file/d/0B5Z...ew?usp=sharing

[Tech II]

It looks like hot gasses from the EGR tube are melting the top of the plenum.....that should not be happening......gasses are only allowed when the EGR is pulse-width modulated, while cruising....this looks like the EGR is wide open, and sending too much exhaust gasses into the plenum, which will cause no power.....I have seen this happen because of a partially plugged cat, builds up too much back pressure, and it unseats the pintle in the EGR, allowing too much exhaust gasses to enter the upper plenum....it will get to the point where it will actually blow a hole in the top of the plenum.....

So I would have a back pressure check done on the exhaust....this is usually done by removing the pre cat O2 sensor and installing a pressure gage.....rule of thumb is less than 1 psi at idle, less than 3 psi at 2000 rpms....

[DrRadar]

Got the replacement plenum this week. I'll look into exhaust backpressure once that is installed.