94 Lesabre NO ONE CAN FIGURE OUT

Hi, I 'm hoping someone might have crossed this problem before. I am a mechanic with a 94 lesabre in my shop. The car has seen four other shops before me. I must say it is soon to see #6.
The car starts ,But It idles fast, the alt. does not charge, the a/c compressor does not turn on, and the electric fans do not kick on. the service engine soon light comes on, as well the abs brake light pops on and off. I looked for codes and found the computer to be bad. I put in a GM computer, as well tried one from Napa. NOTHING, I checked all the ground wires. NOTHING............car has a new battery and the alt.was bench checked and is good. The car straightened itself out a couple of times for about 2 min. when it straightened out the alt guage showed it was charging good, the a/c compressor kicked on, the idle slowed down, and the electric fans turned on.
I have about 80 hours total into this car. and could use your HELP on this one.
Thanks........Any help would be appreciated

OBVIOUSLY this is an electrial problem.
FIX VOLTAGE FIRST always.
Get the alternator and charging system working.

The other problems occur from bad voltage , ignore them for now.

* Bad cable or wires, grounds, (checked)
* Bad battery, (UNDER LOAD plate can seperate from post internally and during a charge it seperates and may cause the alternator to spike up. ) (checked?)
* Bad alternator. (field exciter voltage etc.)
{CORRECTION... I think I understand now NO FIELD EXCITER voltage is attached OEM to these alternators. There is a small red wire connection that goes to the PCM and then to the console indicators and is a grounding switch that lights the idiot light or guage when there is too high, too low, or no output. Bass}

As for discussion:

ENGINE MODES as an 3.8L evolves
*RUN Below 400rpm only uses 3 things RPM Temp and TPS .
*OPEN LOOP Above 400rpm
*CLOSED LOOP Sensors (O2 and such) are warmed up and all is well.

On the fast IDLE problem it sounds like the PCM isnt computing or may still think its in RUN mode, either from voltage or seeing what it wants and therefore later the TPS may be suspect. The voltage has to be stable, a different voltage source to a sensor puts a different value to the PCM.


Good luck

As for discussion:

ENGINE MODES as an 3.8L evolves
*RUN Below 400rpm only uses 3 things RPM Temp and TPS .
*OPEN LOOP Above 400rpm
*CLOSED LOOP Sensors (O2 and such) are warmed up and all is well.


Please explain this since I have never seen a 3.8L idle below 400 RPM. Niether does the open loop happen above 400 RPM's

BTW on a cold start the computer uses MAP, Coolant temp and IAC to control engine operation. Closed loop means the O2 senor is warmed up and the computer is using that data to control fuel/ air mixture.


This year Lesabre had a major problem with PCM's being bad you can tell when you see a red, white and blue connectors plugged into the PCM. But I don''t feel it is totally a computer problem since the alt isn't controlled by the PCM.

The most logical problem would be a bad, dirty or loose ground. Have you done a ground check with a volt meter. If you connect one lead of a meter to the negative battery cable and the other lead goes to the ground you want to test. If you have more than 1/2 volts showing on the meter you have a bad ground. Make sure you check the ground under the coil pak.

Also what code did you oull out of the PCM?

For discussion.. :)
I didnt say the engine was Idling below 400rpm.
I didnt know the 94' had a MAP sensor. MAF yes.
I would think as you (Flatrater) said "Niether does the open loop happen above 400 RPM's" you meant something else since OPEN LOOP is the state it is in before other conditions exist I will list, and is always above 400RPM.

Dusted off the book (S.M. Service Manual.)

When starting and the ignition is first turned on the fuel pump is supposed to get a 2 second fuel pump on (to the relay) from the PCM for fuel pressure then checks ECT and TP to determine mix. (interpreting the S.M.) Maybe thats not happening..

"When the engine is first started and engine speed is above 400 RPM the system is in 'Open Loop' operation. In 'Open Loop' the PCM ignores the signal from the Heated Oxygen Sensor and calculates the air fuel ratio based on inputs from the TP, ECT and MAF sensors" Quote from the S.M..
Sorry for the errors or confusion in previous post, it was off the top of my head. Hope this clears it up. I also figure the engine knows its speed at that time thus RPM sensor.

I still think the proubability is that the computer is a little confused by voltage in imkatowing's post and possibly causing more sympoms.

Conditions needed for CLOSED LOOP.
* HO2S has a varying voltage.
* The ECT reaches a certain temp
* A specific amount of time has elapsed
* The engine stays above 800 rpm since startup.

Hope we get more info!


I agree on the ALT problem and think that needs to be addressed first and bad connections are best checked your way with a digital voltmeter.

Thanks for the discussion..
Could it be my book has been superceded?

Bass

[QUOTE=Flatrater]

This year Lesabre had a major problem with PCM's being bad you can tell when you see a red, white and blue connectors plugged into the PCM. But I don''t feel it is totally a computer problem since the alt isn't controlled by the PCM. [QUOTE]

What do the red white and blue connectors mean?

I could only guess that with the PCM since the male side is color coded with the female side, one being the cable and the other the PCM board its a simple way to connect the right cable to the right socket.

It would be interesting to know if colored connections identifys another characteristic of the PCM.

One might also note that the small red wire from the ALT goes to the PCM to check voltage status and report to guages and indicators. Its actually a somewhat hot wire that is being grounded in the alternator when the alternator stops or goes to high or too low. Some posts have mentioned a flickering ALT light indicator and this circuit is the source of the flicker.
READING the original thread post: This circuit, could be involved in the problem/solution.

Bass..

For discussion.. :)
I didnt say the engine was Idling below 400rpm.
I didnt know the 94' had a MAP sensor. MAF yes.
I would think as you (Flatrater) said "Niether does the open loop happen above 400 RPM's" you meant something else since OPEN LOOP is the state it is in before other conditions exist I will list, and is always above 400RPM.

Dusted off the book (S.M. Service Manual.)

When starting and the ignition is first turned on the fuel pump is supposed to get a 2 second fuel pump on (to the relay) from the PCM for fuel pressure then checks ECT and TP to determine mix. (interpreting the S.M.) Maybe thats not happening..

"When the engine is first started and engine speed is above 400 RPM the system is in 'Open Loop' operation. In 'Open Loop' the PCM ignores the signal from the Heated Oxygen Sensor and calculates the air fuel ratio based on inputs from the TP, ECT and MAF sensors" Quote from the S.M..
Sorry for the errors or confusion in previous post, it was off the top of my head. Hope this clears it up. I also figure the engine knows its speed at that time thus RPM sensor.

I still think the proubability is that the computer is a little confused by voltage in imkatowing's post and possibly causing more sympoms.

Conditions needed for CLOSED LOOP.
* HO2S has a varying voltage.
* The ECT reaches a certain temp
* A specific amount of time has elapsed
* The engine stays above 800 rpm since startup.

Hope we get more info!


I agree on the ALT problem and think that needs to be addressed first and bad connections are best checked your way with a digital voltmeter.

Thanks for the discussion..
Could it be my book has been superceded?

Bass

I erred in calling the MAF a map sensor. You are correct in the MAF sensor being an input for the fuel air mixture during a cold start. But I will give you a stat that GM drilled into me for years. And that stat is a manual only has to be 80% correct to print. Now are you in the 80% correct or the 20% incorrect. I rather use my time wrenching on cars as my basis to determine a likely fault. Granted I sometimes mis-state something but you have to consider 15 years of fixing GM cars over 3 product lines which equals to alot of different powerplants and body styles.

And we all need to dust of the book, not just you but me also. I understand we all err at times and that is why I asked for you to explain in depth what you meant.

I can't remember if the 94 3.8l has a heated O2 sensor or not. But if it is heated then you have less than a 2 minute warm up time for the PCM to go into closed loop. The temp of the O2 sensor is the determining factor on when the PCM goes into closed loop.

You the man!!... ::Raising my Bic Lighter "CLICK"::
Nice to see someone with the experience, knowledge and skill and here keeping a proper focus and direction.
Thank you.

This forum seems to attract many types of problems, typical and atypical, and bizzare. Symptoms can be strange and wide ranging until the problem is found and all makes sense. It also makes us think and that's a good thing.

Great info on the 02 sensor. That fills a gap. I frown often when so many posts that want to go to that O2 sensor for a fix. I think a bad O2 would mean either a solid code against it or bad gas mileage and not a halting and stopping and failing engine.


Bass