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1990 Oldsmobile Cutlass Engine quits after running.

Tiny
EYEWONDER
  • MEMBER
  • 1990 OLDSMOBILE CUTLASS
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 187,000 MILES
The engine will start normally, and run for some random amount of time, then just quit - no stumbling, chugging, bucking, or anything else. Just running normally, then quits as if the key was turned off. I could usually restart it and go on my way, but sometimes it would only run for 2 secs, then quit again. I could let it sit for 5-10 minutes, and it would run normally.

Thought the fuel pump was quitting, so replaced the fuel pump relay - problem still there. Plumbed a fuel pressure gage into the fuel rail on engine, ty-rap'd the gage to the windshield wiper to observe fuel pressure. Normal running pressure was ~37 PSI. Was watching the gage when it quit the next time, and fuel pressure was still ~37 PSI, so I assume that fuel system is good.

I replaced the coil driver module (the plate under the coils, that the 3 coils plug into) after the auto parts testing machine indicated it needed to be replaced. Problem still there.

Replaced the crank sensor - problem still there.

Replaced the computer module with one from the auto parts store, transfered the cal-pak from the old computer to the new one - problem is still there.

I'm looking for ideas to try next.

Cheers,
Steve
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Wednesday, June 25th, 2008 AT 9:49 PM

12 Replies

Tiny
MASTERTECHTIM
  • MECHANIC
  • 4,749 POSTS
Do you have 3 seperate coils or one big one with all 6 built in one?
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Friday, June 27th, 2008 AT 5:33 PM
Tiny
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This engine has the three separate coils that plug into the aforementioned driver module/base.

The car had been setting for a few weeks, while I drove my other vehicle. Last night I tried the Oldsmobile again, and had some slightly different symptoms. It would start & run when the key was in the 'start' position, but quit as soon as I released the ignition key. I was most likely depressing the accelerator pedal a little bit during this test. I was able to get the car to start and idle for a few seconds, by NOT touching the accelerator pedal. As soon as as I did press the pedal, the car would quit.

So at this point, I can not even get the car out of the yard, and into a (qualified) mechanic.

Thanks for the help.

Cheers,
Steve
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Friday, June 27th, 2008 AT 6:37 PM
Tiny
MASTERTECHTIM
  • MECHANIC
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If the vehicle has a mass air flow sensor, try unplugging it and see if you can now give it throttle. It still has 37 psi fuel pressure? If you have access to a ohm meter I would measure resistance across the coil towers and see if they are the same. If you have a coil with too high or low resistance it can shut down the entire ignition system.
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Friday, June 27th, 2008 AT 6:49 PM
Tiny
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I took off all three coils & measured them. All primaries measured 0.6 ohm, all secondaries measured 5.78 Kohms to 5.9K Ohms.

I found what I think is the MAF - in between the plenum & air cleaner (a distance of maybe 9 inches). It was a black square cover 2"x2", with a 3-position connector. I set the air cleaner element clear of its housing, un-plugged the 3-position connector, reattached my fuel pressure gage to the schrader fitting on the fuel rail.

At key on, fuel pressure came up to 35-40 PSI range. After a few tries, the engine started (no accelerator pedal). Fuel pressure maintained around 40 PSI. Slowly pushing in the accelerator got the engine to rev a little, but it would then die.

Is there a separate circuit on the ignition switch for the computer, that might be corroded? Just grabbing at straws floating by.

Cheers,
Steve
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Friday, June 27th, 2008 AT 7:44 PM
Tiny
MASTERTECHTIM
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I doubt that. Unplugging mass air flow did nothing? Was the check engine light on prior to this? Do you have any codes that you know of? How about spraying starter fluid or carb cleaner into intake when its dying and see if rpms pick up. Fuel pressure seems ok. Coils check out good, you must be losing injector pulse, which is how long the injectors are being commanded on from the ecm or we have restricted exhaust system like possibly a clogged cat converter.
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Friday, June 27th, 2008 AT 8:10 PM
Tiny
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I'll continue tomorrow, and get back

Cheers,
Steve
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Friday, June 27th, 2008 AT 9:11 PM
Tiny
TJEGZ
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I see thx.
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Friday, June 27th, 2008 AT 9:18 PM
Tiny
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I have found the problem - I think. I will be driving the car this weekend, and to work next week. If it makes it through Friday with no stalls, I will call it done. In any event, I will post back next Friday with a 'Yea-O-Nay'.

What it was.

I wanted to see if the fuel injectors were getting fired at the time of the stall. I pulled one of the fuel injector connectors, and hooked up my O'Scope to the connector terminals. At idle, I could see the pulses. As I slowly increased RPM I could see the pulses get closer together - as they should have. At some RPM, the pulses went away. To see if I was loosing +12VDC to the injectors, I jumpered battery plus to the +12 lead in the connector plug for the disconnected injector. According to the wiring diag I have, all injectors have +12 common, so this would ensure that all injectors were getting +12. The engine would still quit at some RPM.

Thinking that the injectors themselves might be a problem, I pulled all three connectors on the front of the engine. It would start, running rough as you would expect. I could rev it up without it quiting. So I started putting the connectors back on the injectors, one at a time. I found one that would cause the engine to quit. Its Saturday, and no injectors at any of the parts stores in this small town. I ordered an injector, and it will be in on Tuesday. In the meantime, I have 5 injectors hooked up, and the engine runs well enough to get around town. I'll continue to drive like this till I install the new injector when it comes in. And then drive till Friday, when I will report back whether or not it appears to be fixed.

Thanks for the help.

Cheers,
Steve
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Saturday, June 28th, 2008 AT 5:16 PM
Tiny
MASTERTECHTIM
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Double check the injector you think is bad. Before replacing I need you check the resisters for resistance. I think you will find that one injector will be reading lower resistance than the others and this is the problem injector. Not necessarily the one that you diswconnect and it runs fine, its possible its one of the others
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Monday, June 30th, 2008 AT 11:55 AM
Tiny
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The injector that I disconnected measured 5.2 ohm. The others measured 11.2, 12.7, 12.7, 12.7, & 12.8 ohms.

The new injector (new, not reman) should be in tomorrow after work. I will check resistance before installing, for a comparison with the existing ones.

By the way, any suggestions on how to physically remove the injector? It looks like a lot of unhooking of lines, and no way to get out just one injector.

Cheers,
Steve
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Monday, June 30th, 2008 AT 8:49 PM
Tiny
MASTERTECHTIM
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You definitely got the right injector. Lightly pry injectors out from base and use vaseline on the o rings to reinstall them.
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Monday, June 30th, 2008 AT 9:02 PM
Tiny
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It's Sunday, and I have been driving the car without it dying, since I located the bad injector. The car ran rough with only 5 injectors, but no stalls. I put the new injector in (turned out to be an easy job) on Wednesday, and the car has been running great since then.

Thanks for all the help.

Cheers,
Steve
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Sunday, July 6th, 2008 AT 9:10 AM

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