94 lesabre starts, immediately stops

My daughters 94 lesabre, 3.8 will start immediately, then stop. Everytime key is turned off & on again it will do this. If key is held on, ie after it starts it will still start, then stop. Last week it did this a couple of times, but eventually ran. Now no go. I seem to recall this happening a couple of years ago. It needed a new computer. Any other ideas? Thanks Cliffw

You may be just priming the pump here, get a fuel pressure gage on it and confirm fuel pressure when it stalls. 35-40 psi.

Thanks. I'll try that. If it's fuel I should be able to nurse it along by spraying gas into tb, right?

Correct.

same problrm two weeks ago on my son's car and the computer was the problem even though it had a passkey code when diagnosing the check engine light.

As MAX mentioned, first check for fuel pressure during prime. If the pressure checks OK, then you need to check for injector pulse using noid lights. After you let go of the ignition switch and engine starts, the injector pulse is controlled by the PCM. If no injector pulse, you can suspect the PCM. :uhoh:

BTW, you can pick up a set of “noid lights” at most major part supply stores for about 10-20 bucks.

Thanks, guys. It definately is a fuel problem. I can keep it going by spraying gas into it TB ( not easy with the horizontal intake) Also it keeps sparking after stalling out. I have the feeling it is being shut down as opposed to fuel pump problem. I looked at the wiring diagram. It looks like oil pressure switch could shut it down. The other possibility ( the one I suspect) is the PCM. I'm wondering about hot wiring directly to the relay. This should get me going I think. I'm just not sure which relay is for fuel pump. The problem is the car is at my daughters work 40 miles away. I'd just like to get it home. Thanks again Cliff

Thanks, guys. It definately is a fuel problem. I can keep it going by spraying gas into it TB ( not easy with the horizontal intake) Also it keeps sparking after stalling out. I have the feeling it is being shut down as opposed to fuel pump problem. I looked at the wiring diagram. It looks like oil pressure switch could shut it down. The other possibility ( the one I suspect) is the PCM. I'm wondering about hot wiring directly to the relay. This should get me going I think. I'm just not sure which relay is for fuel pump. The problem is the car is at my daughters work 40 miles away. I'd just like to get it home. Thanks again Cliff

Do you have pulses to the fuel injectors continuing after the cutoff like what Z28 asked about.

Is there a wire to check the fuel pump that you supply battery plus to? It's close to the battery area IIRC. Could you connect that and start the motor to verify the fuel pump isn't cutting out on you. That would narrow it down to the control of the fuel injectors.

That's what I'm thinking. I haven't checked for pulses. What I'd like to know is which of the relays is fuel pump. I could run wire to fuel pump directly, but would prefer not crawling under the car if I don't have too.

That's what I'm thinking. I haven't checked for pulses. What I'd like to know is which of the relays is fuel pump. I could run wire to fuel pump directly, but would prefer not crawling under the car if I don't have too.

Of the hundreds of posts describing this problem over the years that I've read this board, I can't remember a single case where the problem was the fuel pump. Keep that in mind.

Thanks. that's been my experience also with other vehicles. I'm almost certain it's the PCm, but want to make sure before springing for a new one.

Thanks. that's been my experience also with other vehicles. I'm almost certain it's the PCm, but want to make sure before springing for a new one.

You need to get a service manual for this car or subscribe to alldata.com for this car and run the tests that would give you an exact diagnosis for the problem before buying any parts (unless you could get them very, very cheaply).

I changed computer - no differance. Also pulled gas line. It's spitting out gas , but I'm not sure of pressure. My next step will be to check pressure at fuel rail, & check injector pulses. I also will check connectors at PCM. Any way a low oil pressure could shut it down? Oil level is good. At least it's nice weather. Cliff

I changed computer - no differance. Also pulled gas line. It's spitting out gas , but I'm not sure of pressure. My next step will be to check pressure at fuel rail, & check injector pulses. I also will check connectors at PCM. Any way a low oil pressure could shut it down? Oil level is good. At least it's nice weather. Cliff

You already have the answer. Read previous posts. Your answer is NOT to guess at the cause and replace parts or waste time chasing the most unlikely problem (fuel pump). Yes, you need to check the fuel pressure. Go to an auto parts store and buy a fuel pressure gauge and get to it. Once you likely find that your fuel pressure is fine, move on to diagnosing the car by either paying a mechanic to do it, or by investing in the information and tools necessary to diagnose it. Right now you don't appear to have either.

just a reminder that the pcm needs the signal from the anti-theft module to allow injectors to fire(if you have a resistor in the key)

Thanks Steve I had trouble a few years ago that I traced to the antitheft module. After working all morning to try to get at it under the dash, I bypased it. That cleared up the problem. So I don't think that's my problem.
As for the suggestion I don't have the information or equipment, you're right otherwise I wouldn't be asking. However I do have a method to my approach. I also know that other things can cause problems besides what the manuals suggest. That's why I'm asking for your experiences. The answer may or may not lie in what has already been suggested. Having said that I will follow through.

Forget about the oil pressure switch. It does not interrupt power to the fuel pump. It is there only as a redundant path for power to the pump. If the FP relay fails, the pump will still run on the pressure switch. Study your schematic.

What happens to the "Security" light when the ignition key is inserted and turned to the RUN (not START) position?

Thanks. That's what I thought, however Haynes said something about oil pressure light shutting it down. I have found Haynes lacking in some areas. I've rebuilt several Chrysler motors, & found Haynes fine for most mechanical issues, but lacking regarding diagrams &electronic/ electrical issues. I have much less experience with GM products, but Haynes seems to have same limitations. I don't have a security light - maybe burned out bulb. I'll keep plugging away. Thanks for all the help. BTW some time ago when we had a problem with intermittent gauges & headlights my daughter took it to a dealer to fix. After $200.00 they said it was a shory & they would need more time & $ to fix. I knew it wasn't a short, so cut my losses. I eventually traced it to the antitheft module, which I bypassed. I am no longer anxious to trust these things to a mechanic.

If there is an anti-theft (VATS) module, and the ignition key contains a resistor pellet near the bow end, there should be either a "Security" or "Anti-Theft" warning lamp on the instrument panel.

This might help your diagnosis:

VATS/PassKey System (http://72.19.213.157/files/VATSSystem.html)

http://72.19.213.157/files/flag.gif

Got 'er. Turned out to be bad connection at fuse. First time through I checked fuse, ok. Figured it must be something common to injectors, since not were passing fuel. Traced back to PCM fuse. Fuse was fine, but noticed contacts badly corroded. Cleaned them off, & fired up right off. This is a new one for me. Thanks again for all who helped. Cliffw