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Mysterious Chevy Caprice Ailment

My Dad has a 1991 Chevy Caprice Classic he dearly loves, but it has lately been stranding him for no reason that our mechanic (yes, he’s honest and capable) can find. It happens only sporadically - hesitates a bit, and occasionally just dies. Or, after an episode of hesitating, if he stops and does an errand, then it won’t start again. They’ve tried all the diagnostics, changed fuel filter, etc. It will run fine for a while, then strand him again. Mechanics can’t duplicate the phenomenon, even after keeping and using the car for several days. Any ideas?

What happens when he tries to restart? Does it crank at full speed?

What needs to be determined when there is a no-start situation is what is missing: fuel or spark.

“What needs to be determined when there is a no-start situation is what is missing: fuel or spark.”

Two cheap things available at any auto parts store can help him figure this out. First, he can get a spark tester (though a spare plug also works) - when it won’t start, pull one of the plug wires, plug in the tester & check for spark. The second is a can of starter fluid. The next time it won’t start, if there is spark, spray some of the fluid into the intake and see if that gets it to go. If so, then the problem is fuel.

Thanks for your response. Car does not crank at all. Also has a new battery, BTW.

Mechanics have checked for spark - not the problem, apparently. Acts like a fuel problem, they say, but can’t find it. Someone else suggested an O2 sensor problem, but no indicator has been triggered there, either. I’ll pass on your starter fluid suggestion, though, on the off-chance they haven’t tried that. Thanks!

fuel pump pressure and fuel filter, return fuel pressure to tank, solenoid to the fuel pump can intermittently fail. Plugged or failed EGR system and other emmissions devices. this can be checked easily. dirty or sticky fuel throttle plate can be cleaned, sometimes they wear a groove in them and need replacement. a decent mechanic should find this one out pronto.

Thanks! Will pass this on to Dad’s mechanic.

hesitates a bit, and occasionally just dies

Mechanics have checked for spark - not the problem, apparently. Acts like a fuel problem, they say, but can’t find it.

Thanks for your response. Car does not crank at all. Also has a new battery

It appears to me you may be looking for 1 solution to 2 different problems. Hesitates and dies indicates to me injector, fuel pump or carb problem, maybe even a vacuum line.

Does not crank indicates starter motor or cable problem.

Thanks! Latest update: back at the garage, they replaced the starter, which at least got it going. However, it finally misbehaved for them like it has for Dad. They re-checked the Oxygen sensor, and discovered that although it was working well enough not to trigger any diagnostics, it wasn’t exactly 100%, so they replaced that. Also found evidence of moisture in the distributor cap, so took care of that, too. They had previously checked fuel lines, fuel pump, etc., and had replaced fuel filter. We’ll see what happens next!

Sounds like you may be good to go soon!

Color me skeptical (extremely) here but I don’t see that O2 sensor as being the cause of the car dying at all. Expect it to quit again.

Random dying is likely a fuel pump problem; especially if the pump has never been changed and even more so if the fuel filter that was changed was also filthy.

I have a 1993 Caprice, but have not experienced any similar problems. I had the same problem with a 91 Ford Taurus. After an hour or so of driving, the fuel pump would quit. After 30 or 40 minutes the car would start with no problem. The mechanic determined it was the fuel pump by connecting it to the diagnostic machine and leaving the car running for 45-60 minutes.

When I got the Caprice in 2002 from my late Father-in-Law (it was his baby), I had the coolant, trans fluid and filter, fuel filter replaced and a fuel system cleaning (Motovac) done. I replaced the plugs, wires, and distributor cap and rotor myself. The spark plug charge interval is 50k miles on mine.

I’m leaning toward the fuel pump myself, but a complete tune-up (plugs, wires, dist. cap and rotor) wouldn’t hurt. The good news is that a fuel pump for a TBI motor is fairly inexpensive http://www.partsamerica.com/ProductDetail.aspx?MfrCode=MST&MfrPartNumber=E3268&PartType=52&PTSet=A

Good luck with the Caprice,

Ed B.

When does it hesitate a bit? Does it happen when taking off from a stop? If so, and the car still has the metal air cleaner with the old style filter with the thumbscrew on top; see if the heat pipe is missing from the exhaust manifold to the snorkel on the air cleaner. If you see the perfectly round hole on top of the exhaust manifold, the pipe has to be found and put back in. If the pipe is lost, a three inch long (or whatever length) piece of exhaust pipe can go into the hole and that flexible silver tube stuff can go over it and connect to the air cleaner.

Thanks for your reply. Our mechanic, too, thought of the fuel pump first thing, and replaced it. Still not the problem, apparently.

I was reading the shop manual and there is a oil pressure switch tied into the fuel pump. If the switch indicates low/no oil pressure the fuel pump is disabled. My Caprices’ oil pressure was replaced recently since it was leaking. I’m not sure if this is the same switch though.

Ed B.