1994 Buick Lesabre 134k running low on options to repair constant stalling...

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#1
This car is starting to really stump me. . .
1994 Buick Lesabre 134k

QUICK FACTS: Car stalls once it warms up AND is idling.
1. No fuel coming from the return side of the fuel rail
2. Already replaced the oil pressure switch, fuel pump, pcv valve, fuel pressure regulator, air filter, plugs and wires, coil packs, Stopped vacuum leaks.

The car will idle for about 10 to 15 minutes, very smooth, and then begins stalling. And when it begins to stall it doesnt take long. From running fine to actual stall takes about 30sec to a min, (you can hear it coming). Then it stalls. Then it becomes very difficult to restart. I don't believe its a fuel issue because even if I keep putting ether in the intake it wont stop if from stalling.

Originally I was getting low fuel pressure at the schrader on the rail (14psi), I then replaced the fuel pump and the regulator and nothing changed. I used the schematic to come up with replacing a leaking oil switch which should fix low output at the fuel pump by ensuring that it is getting 12 volts. (traced the low fuel pressure all the way back to the hard line attached to the tank, the haynes book says it should be getting 43psi, and when the last hose is taken off before the gas tank the fuel does not spray out hard, just like its being poured out. I think the fuel pressure is higher now after replacing the oil switch but my gauge broke so I don't have a new reading. Also there is no fuel coming out of the regulator end of the fuel rail.

Here is what I have yet to do,

Replace the crankshaft position sensor (owner is convinced there may be a problem with CPS, but does anyone know if it can work when egine is cold and then fail once the car is warm?)
Clean the intake
Replace the Idle control valve.

The owner said she would drive on the highway totally fine, (seemingly limitless range) but when the car slows down to say a gas station or a stop sign, it begins to stall and either won't restart or is exceedingly difficult to restart. I think she is getting it on the highway BEFORE its fully warm, which allows her to
drive quite a distance until she slows down and lets the car idle.

Somehow I am convinced temperature is playing a role here somehow, and my next move and best guess is the CPS is failing once the car is warmed up .
Going to replace the crankshaft position sensor.

This is basically a pro bono job to help an old lady with her car, but its really startin make me wonder. . .

Thanks in advance!
 

Gus

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#2
Who in the world checks fuel pressure on the return line? It's open ended....

Get your fuel gage fixed, AND CHECK IT AT THE SCHRAEDER ON THE FUEL RAIL.

No codes?

Need to check fuel pressure when vehicle won't start.....also check for spark and injector pulse.....will it start if the MAF is disconnected?

Have you tried a tap test on the PCM? Does it have he infamous red, white, and blue harness connectors?
 
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#3
Re:

Who in the world checks fuel pressure on the return line? It's open ended. . . . Posted by: Gus
------------------------------------------------------------------------------------------------------
Its all used up? That's what you mean by open ended? you never see fuel come through, or only at higher throttle?
Havnt found flash codes for this vehicle and scanner is only communicating with ABS and airbag. Posted by Mechanic in Training.




I will post more later
 

Gus

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Can't communicate with ECM?

Does the CE light come on with a bulb check?
 
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CE light comes on, yes, when doing a startup selfcheck.

I plan to check fuel pressure when car stalls, (before it was 14psi when it stalled, but I think pressure is higher now).

will try tap test too.
 

autodr

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#6
Re: 1994 Buick Lesabre 134k running low on options to repair constant stalling..

Tap on the ECM while idling, see if that makes it stall.
 
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ok will try that too. . .

I have till tommorrow to figure out if I can change a part out

either

TPS
CPS
IACV

i think TPS is the most expensive. . . .
 
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#8
Re: car starts but does not run with MAF disconnected

after taking off the throttle body I noticed that there might be a leak in the gasket that blocks out the coolant , which could either be dripping on the wire connector to the fuel injectors or could be leaking into the throttle body, so I am going to replace the gasket and see if that helps.

I tried starting the car a few times with the MAF disconnected and it will start and run for about 1 second and then dies right out which I am assuming is normal.
 

Gus

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#9
No, it is not normal.....

Let's get back to basics...

First, turn the key to the on position, but don't crank the car.....look at the SECURITY light, does it stay on, or does it go off after 5 seconds? If it stays on, you have a PassKey problem....

If it goes out, are there any powertrain codes? Or you still can't communicate with the PCM?

If none, check for spark(all six cylinders with a spark tester), injector pulse(noid light), and fuel pressure(should be above 40 psi).......if you have good spark from ALL cylinders and it won't start, spray carb cleaner into the intake....wait a few seconds and then crank the vehicle to see if it will start....,.
 
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#10
still no communication with PCM/ECM or tranny, only airbag and ABS. I have tried different keys, connectors, model years, different modes etc, so far nothing.
I am hoping its not the ECM, but before an ECM replacment I want to confirm it has a failure inside the unit and/or whether it has a failure or high resistance going to the unit (which could cause a replacement ECM to just do the same thing).

cars current condition is that it will crank and run only for a few seconds if you don't fiddle with it.

yesterday I was able to keep the car running fairly smoothly if I occilated the intake throttle control from 0 to 40% at a certain frequency. ENGLISH: by wiggling the the throttle on the intake a certain way the car did not stall. This leads me to believe the TPS could be the problem. I measured the voltage coming out of the TPS (while connected) and I could not get the voltage to vary with throttle movement, another reason I suspect the TPS. I have reference voltage 5. 2V going to the TPS, and each terminal (while unplugged from TPS) gave me 5. 2V/0. 03/0. 03 (i am assuming the 0. 03V coming from the PCM/ECM is meaningless noise from my DVOM. )

I noticed oil from leaking valve covers running down the split loom to the oil switch, and found oil in the connector. I am going to work on stopping the oil from interfering with the oil switch. I did clean out the connection but it hasnt improved the situation yet that I can see.

I pulled the fuel rail and watched conical streams of fuel pulse out of the injectors while cranking the engine. There is also fuel squirting from the schrader (when I push it in) right after the car has stalled. All of the coils are firing. Car will run for a couple of seconds ok then just goes out. If you give it gas while its running it will immediately begin to stall. Pumping the gas or tapping the gas makes the problem worse. Again TPS. . . .

I have to return my fuel pressure tester for repair so I can get another reading on the car, in the meantime I will try to use my other pressure tester to get a reading at the fuel filter.
 

autodr

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#11
Re: 1994 Buick Lesabre 134k running low on options to repair constant stalling..

Concentrate on the lack of communication issue.

Check powers and grades at ECM connector, then ohm the communication wires from PCM to diag. connector. If all good, replace the ECM.
 
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#13
ok, just had the security light checked by the owner yesterday. She said the light does in fact go out after a short period of time. Thats what I remembered also.

Today I checked the voltage of the TPS and it seems fine. I connected to the middle wire and read the voltage as I moved the throttle and it ranged from . 48v to 4. 8v or something similar.

I do not have an accurate wiring diagram of the vehicle, only what Haynes has, and a SnapOn fuel injection book that only goes up to 1992, two years shy of what I need. I was trying to find the wire that goes to the ECM, I was running out of time but on my first attempt, the dark blue wire that I checked at the ECM connection had 11. 7v. The battery is low, not holding a charge very well, and seems to be showing signs of a bad cell, its not old but has been used for cranking many many times.

Pretty soon I am going to have to urge the owner to buy a new battery.

I am going to check the MAF and IAC voltages and begin checking the wiring back to the ECM.
 
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#14
Currently biggest problem is:
it stalls right after start up, unless I wiggle the throttle a certain way.

before it would Idle smooth for anywhere from 10 to 30 min then stall. No communication yet with the Soluspro scantool. The ECM/PCM is dismounted and the DLC moved closer to the ECM. 5 wires are going out of data link connector port. I think the orange one is to the airbags or ABS, (which I can communicat with the scantool anytime I want) but not tranny or ECM/PCM.

orange wire (ABS or Airbag) does not go to ECM/PCM
green (ABS or Airbag) does not go to ECM/PCM
tannish?
black (ground connect to the ECM/PCM)
black with white stripe. will check again with DVOM. Coming from the the ECM to the DLC.

is there a way to tap right into the ECM bypassing the DLC? Risky?
I hate to just be a parts swapper but with the junk yard parts being so cheap its hard to resist.

change out wish list: "Throttle Body" sensors TPS(even though the TPS voltage was seen moving from . 48v to 4. 8 volts with the throttle, with no drops I could see) ,IACV, the ECM, Crankshaft position sensor, battery.


I am going to go back and recheck the fundamental 3. spark,compression fuel.

1. recheck fuel pressure
(I know I should have done that by now my own vehicle took a dump on me (blown head gasket) so its eating my time on this. 14 psi was checked over a month ago at the rail and 9 psi with two testers at the fuel filter. I have battery voltage at the four wire terminal to the fuel pump just past the fuel filter. Sender gauge is around 7v.

2. Play around with the coil packs,
swap em out, I have 3 or 4 laying around. Retry the original again.
Wonder if I could get what seems to be a good coil pack from induction test, but something could be
faulty with the wires to it or a command is given to kill them thats stalling the engine.


3. recheck compression
I had decent compression when I checked it months ago. I got from 90 to 120psi from the front three cylinders and the back right near the master. Anyone think the remaining two cylinders could cause a problem like this, is worth a check? they are damn hard to reach.


I did find four greenish wires going from the Idle air valve had a spotty brown (like they had heated up a little) patches all the way back to the fire wall. They ohmed out good at 0. 3 - 0. 4v.

I'm not ready to shoot this horse just yet. . .
 

Pestco1

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#15
Re: 1994 Buick Lesabre 134k running low on options to repair constant stalling..

Wow, Tough diagnostic. I have been in your position when I first started out. My advice is not going to be specific to your vehicle, more to your state of mind. Forget all of your assumptions, the wiggling of the tps and such. Stand back, take a deep breath and start over with a good check of all of the basics. For starters, I would find a good reference manual w/ the specs. you need. About and almost won't do in this situation. If you need for instance 20 PSI in the fuel rail and you only have 10 then you have a real issue. Since it is not you personal vehicle I can see why you would not want to invest in alldata but hit the local library or beg a shop to at least get the basic fuel pressure, voltage specs. The reason you check the fuel pressure at the rail and not return is that the return is not pressurized. You can drive yourself ( and your customer ) crazy if you skip around to different points and not follow a systematic approach, carefully checking basic things first. Have seen guys replace expensive sensors and ECMs when all it needed was a fuse or a connector replaced.

Good luck