2000 Buick Regal - 3.8L PCM Issue - FIXED!

[Tim Martin]

This 2000 Buick Regal (253,000 miles) with a 3.8L (K) engine/auto trans came in on the hook. Customer reported engine cranks over fine but will not start. I get in and the engine starts and immediately dies. If I hold accelerator pedal slightly it runs, although somewhat rough. Connected scan tool - no codes. The only thing I saw was both short term and long term fuel was -20%. Fuel Pressure is 52psi KOEO. Thinking we have a IAC issue, I removed the throttle body. Cleaned it, installed new IAC. No change. Checked system voltage to PCM Fuse and PCM - 9-10 volts. So we have an issue. I see on my Mentor Scan tool Repair Tracs as well as on IATN there was some comment about the ignition switch giving out, creating this situation. I replace ignition switch. Now I can get the engine to run and have battery voltage to the PCM although it floods itself. I am thinking that the low voltage to the PCM caused the PCM to fail and needs to be replaced. Is it possible that the low voltage ruined the PCM?

[ricmorin]

First thing I'd check is engine vacuum and exhaust backpressure. From your explanation it sounds like it came in running rich and still is. If both of these are good, check the MAF and the boot. Something is causing this to run rich. Low voltage doesn't usually kill PCM's that I've seen. It's possible.

[steven kiser]

A quick question here. When you say flood do you mean it's rich or it fouls out the plugs at idle. See if there is an impulse at the injector. It there is no break then i think the p.c.m. is bad. Is there any history on this car?

[Tim Martin]

A quick question here. When you say flood do you mean it's rich or it fouls out the plugs at idle. See if there is an impulse at the injector. It there is no break then i think the p.c.m. is bad. Is there any history on this car?

Flood to the point of not hardly running. Black smoke can hardly exit the tailpipe fast enough.

History? If I don't do it to this car, it don't get done. In other words, I do all the work except tires. Car has been serviced and maintained regularly since he got it.

Yes, I suppose I need to be checking the pulse at the injector with my noid light. Good point steve. Thanks.

[steven kiser]

I know this is way out there but is there a chance the customer topped it off with dsl fuel?

[Tim Martin]

By installing noid light there is good pulse. So, I have to conclude we got a bad PCM.

[Jeff @ Able Auto]

Tim...I would check the Mass Air Flow and temp sensors if not already done. I have also had fuel pressure regulators bleed gas thru the vacuum line. Is this the model of 3.8 that had the issue with the intakes leaking? Just some thoughts.

[steven kiser]

Good thought on the regulator.

[Tim Martin]

Tim...I would check the Mass Air Flow and temp sensors if not already done. I have also had fuel pressure regulators bleed gas thru the vacuum line. Is this the model of 3.8 that had the issue with the intakes leaking? Just some thoughts.

MAF readings are right on the money. No fuel leakage at the pressure regulator. Intake temp is ambient temp. ECT is within 5 degrees of Intake temp. No codes.

[steven kiser]

When you turn the key off during the pressure test how fast does the pressure drop? If it drops rather quickly you may have a stuck injector. Just a thought.

[Jeff @ Able Auto]

One more thought...is one of the O2 sensors stuck lean? I just hate replaceing controllers w/o being 99% sure thats the culprit.

[Tim Martin]

Ok. For an update including the fix.

I installed another PCM. Obviously there was an issue with the original one because now it idles but as soon as the throttle is touched it shuts off. Well, even though initially I had checked the MAF, I began being very suspicious about it. So I put my scanner on lab scope function and saw a very weird pattern even though the data numbers on the scanner pid were within specs. As soon as the engine got off idle, the MAF numbers went way out of specs. So, I replaced the MAF and now we got us a very nice running engine again. I am supposing that the low voltage from the faulty ignition switch affected both the PCM and the MAF even though I physically cannot prove it except that in replacing both, the engine runs fine.

Thanks guys for the help.

[steven kiser]

It's fixed, on to the next head slammer. Thanks for posting it.

[Tim Martin]

Ahhhhhhh steve. Thant's why my head has been paining me lately.

[Jeff @ Able Auto]

Good job Tim. Thanks for the follow up.