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Loss of HP Frequent Misfire

2002 Chevy Monte Carlo SS 6cyl 100,000 miles

Symptom, loss of horse power (from a stop and going uphill), surge or lunge forward when accelerating (misfire?), rough idle (occasional knock).
Maintenance, regularly change all filters and fluids, recently had the m.a.f cleaned and changed air filter, spark plugs and wires, oil.

There have been times in the past year or so when the car would crank but not start. Especially when the car was hot. Wait a couple minutes and it would start. Also a couple of times the car would shake fairly hard when started, get up to speed and it was fine.

I have had people tell me anything from a clogged catalytic converter to bad fuel injectors or fuel pump.

Scanned the car last week. No codes showed up. Never had a Check Engine Light.

**I forgot to mention that every once and a while the car will jerk when accelerating. I have a coworker who said his truck started to jerk forward and later would not start at all. Our mechanic said it was the fuel pump. I I will see what that does for him.

Has The “Check Engine Light” Illuminated ?
Have You Had The Car Scanned For DTCs (Diagnostic Trouble Codes ) ? What Were The Codes ?

I had the car scanned last week. No codes showed up. I have never had a Check Engine Light.

Check your fuel pressure regulator for the presence of fuel/vapors in the vacuum line. should be none.

I’ll do that. I had the fuel pressure regulator changed about a year ago.

This is either a fuel or ignition related issue. You can test fuel pressure pretty easily and would do so ASAP. A failing igition coil or coil on plug setup can cause the same symptoms. Both a failing fuel pump as well as a failing ignition coil can cause just the symptoms you describe.

How many miles are on the car? Have you changed the fuel filter regularly or not? If not, change this ASAP and see what happens to the performance. If it comes back to normal, you may have a failing pump and this will give you a temporary reprieve. Start saving to replace the pump as the problem WILL come back and WILL STRAND you eventually.

Many GM’s from this era are notorious for going through ignition coils although they are otherwise excellent cars. I had similar symptoms from one of my GM’s and found that I had both a failing fuel pump AND a failing ignition coil. I replaced the pump first which helped but was still having problems that I traced to the coil.

My first step would be to check on the fuel pressure. You can do rental gages for free from most larger chain parts stores and this is an easy first thing to check.

Really bad O2 sensors can cause similar problems when driving but I doubt that would cause any issues at startup.


I do change the fuel filter regularly. The car has about 101,000 miles. I plan to have the fuel pressure and coils checked soon.

Good idea! The fuel pressure is something you can check yourself very easily at no cost other than some time. Honestly, it might be cheaper to just replace the coil pack by yourself rather than pay a shop for diagnostics. Many of these GM’s seem to eat coils about every 100k miles so you might be due based on your mileage. I just checked the cost of the coil and they are like $35 for a lifetime warranty one at Autozone. I assumed you have the 3800 engine since you have an SS when checking.

Also, does this car use a distributorless ignition? If not, you are definitely due for a new cap and rotor. I didn’t see this in your list of repairs but this could easily be causing problems if your car has that setup. For $35, I would replace the ignition coil. I hate to to replace parts to replace them but that is an easy job for lower than the cost of a diagnostic. If you are at all familiar with cars, this will take 5-10 minutes. Easier than changing the oil…


@cwatkin that 3800 engine doesn’t have a distributor

It has 3 coil packs

if your catalytic converter were in terrible shape, I would think you would have codes P0420 and P0420
A misfire would have caused a P0300 code

I agree with the others . . . hook up that fuel pressure gauge

Thanks everyone I will let you know what happens.

My mechanic said the fuel pressure should be between 53 and 58 I believe. He said it was 48 the day he tested it. Also I read the temp of my cat converter after a short trip. It read 190 front-150 back. What do you think?

I think you have one bad injector, it is leaking. You should be getting a P030x code with the x being a number between 1 and 6 that identifies the cylinder with the misfire. The reason that yo may no be seeing the code is that this may be intermittent and that this is a two trip code (DTC). On a first trip, the code is only stored for one more drive cycle. If a second trip does not occur, then the DTC is erased.

Either you have to wait till the problem gets worse and it trips twice, which will turn on your check engine light (MIL) and store the DTC for at least ten drive cycles, even if the MIL turns off, or you have to get the code read immediately after you get a serious misfire.

You mechanic could also pull all you sparkplugs and see if any of them show an over rich condition.

If this is the 3.8 engine, it is also possible that you have either a bad intake manifold gasket or a cracked lower intake manifold. This engine has a history with these.

Try this next time it wont start, hold the gas pedal to the floor for 30 seconds, then with it still down, crank the engine for up to 15 seconds, if it doesn’t start. lift your foot off the gas and crank it one more time. If it starts anytime during this procedure, that points to an injector, if it doesn’t, that is bad news becaue repairing the intake is not cheap.

Thanks for the info! Since I last replaced the plugs and wires it has been starting pretty good. The main problem now it jerking/bucking during acceleration. My mechanic said that my fuel pressure was between 5 and 8 psi low. Could this be the cause?

Fuel pump could be giving out.