My pontiac is missing, from a complete stop, she hesitates a second before she goes…and in the driving, I can feel a misfiring, not a noise, but it’s not smooth, it’s hesitating as I’m driving her too. We have replaced the fuel filter, air filter, had a tune up & trans serviced, it seemed to be better for a while, but now it’s back…driving my husband and I crazy. She’s an oldie, but a goodie, and we want to keep her, please help if you can…thanks!
Could be anything, but if you haven’t replaced the PCV in a decade or two, I suggest you do so. It’s cheap and a new one just might solve your problem.
Thanks SteveF, but did replace that part, she’s still missing.
There’s much more info needed to even be able to make a wild guess at this.
Mileage on the car, which engine (some are TBI, others are carbed), the exact definition of “tune-up” as to what was done, etc.
A great deal of information is needed to even get started on that one. If the engine is carburated and the CEL light does not come on the engine will be running full rich at all times with no spark advance. Fill us in, Honey.
It’s a Citation with nice upholstery, right? How many miles on it?? Perhaps the HEI ignition system system needs a little work…I mean, 31 years…
You might want to check if the timing chain has jumped time. Your vintage of GM has a camshaft sprocket with teeth made of plastic. Over time these plastic teeth break off and fall into the oil pan and the timing chain jumps time. This then causes the valve and ignition timing to be off causing the missing.
A quick way to check for this is drain the oil and inspect the drained oil for bits of plastic.
Tester
This was Pontiac’s version of the Caprice. Could be the things mentioned above, along with plugs, cap, vacuum leak, etc.
The HEI ignition needs a complete review, high voltage burn-threws, the two wires connected to the module, the vacuum and centrifugal advance mechanisms, everything…Then the EGR valve for sticking and leaks…A quick check with a timing light will reveal if the timing chain has jumped…The timing will be way off…
“It’s a Citation with nice upholstery, right?”
Actually, it’s a Chevy Impala/Caprice with nicer upholstery.
It is also very similar in body/chassis/mechanics to an Olds 88 and a Buick LeSabre.
Thanks everyone for your comments, here is more info. She has a 305 chevy engine and the timing is a chain, not plastic to my knowledge. The tune up was full, new spark plugs, dist. cap, wires, etc. Mileage on the car is around 130,000, when we bought it several years ago it only had 60,000 on it, garage kepted and fully maintained. The engine is carburated, but she’s not running rich. EGR valve has been replaced…will try some of the suggestions, more advice as to what to check would be greatly appreciated.
Tester was referring to the possibility of plastic teeth on the camshaft sprocket, not the timing chain itself. Plastic teeth or guides combined with a steel timing chain can indeed cause the chain to “jump timing”. This is something to have your mechanic look into.
If it’s just a slight miss, then a decent mechanic with a scope should be able to narrow it down as the where it is (which cylinder, or random, etc). That will point towards which parts you need to check next.
Unfortunately, just because the parts are new, doesn’t mean they’re performing as expected or designed.
HTH,
Chase
Sounds like its time for a compression check.
transman
Check this…Remove the distributor cap. Locate the kidney shaped ignition module. It has two small wires that lead outside the distributor…Since this part moves with the vacuum advance plate, the wires are continually being flexed. Thy can and do break INSIDE their insulation! Very hard to spot…But if you GENTLY pull on each wire and observe where it enters the module, see if it stretches a little, that’s a sure sign the wire inside is broken…
As long as the ignition timing checks normal with a timing light, the timing chain has not jumped time. (they DO use plastic covered cam gears to keep the chain quiet)…
The carburetor used in 1985 is a NIGHTMARE and you better hope it never needs rebuilding or replacing…