99 SSEi stumbling under load

[blye]

Hi.

My 99 SSEi is running poorly these days. It stumbles under load (climbing hills, accelerating).
Or if I rev past 3000 rpm when parked - very fast vroom, stumble, vroom, stumble.
I also got the P0442 code pop up recently (I've have not had any other codes for years)

The car has new spark plug wires, recent plugs (NGK platinum), new air filter, cleaned MAF sensor, new gas cap. no rust.
Also has a 2 year old evap solenoid.

Checked the cat, and I dont hear any rattling really, and the temps are about 300F engine side and 200F exhaust side.

Checked the vacuum lines with carb cleaner and did not hear any change in engine idle sound.

I'm going to replace the fuel filter (did it 2 years ago) but I dont think that will fix it.

Any ideas? what further diagnostics I should do?

Thanks

[MKMike]

You're on the right track.
Typically, the issue is with the ignition or fuel.
Did you carefully inspect the vacuum fitting beneath the supercharger snout?
It's common to find the rubber fitting cracked or broken--which will lead to driveability issues.

Did the problem start before or after you replaced the spark plugs and wires, etc.?
Sadly, it isn't all that unusual for brand new parts to be defective.

Did you use a special MAF sensor cleaner to clean the MAF?
If not, know that many cleaners leave a residue that has an adverse affect on MAF function.

In addition to replacing the fuel filter, there are a few things you can do.
Check to make sure the wires are fully seated at both ends.
Check the coils carefully for any cracks--you may see thin carbon tracks.
A failing coil may first present itself as a stumble under load.
You can check their resistance
http://www.pontiacbonnevilleclub.com/fo ... c1683.html

If you hook up a vacuum gauge , you can test to make sure the catalytic converter hasn't gotten clogged.
Normal vacuum at idle is around 17-21 inches and steady as a rock.
Hold the engine at 2500 RPM and watch the vacuum gauge, it should be slightly lower than the idle reading but remain steady.
If it's dropping, then your converter is clogged--or there's a restriction elsewhere in the exhaust--but most times it's the converter.

As for the P0442 read this https://www.obd-codes.com/p0442

[blye]

Hi thanks for all the great info.

The stumbling problem started after I replaced the spark plugs (about 6 months after). But the wires were replaced after the problem, but did not solve the problem.
But I replaced the fuel filter just now... no difference.
I checked the coils.. all were about 6k ohms on the secondary, and 2 ohms on the primary.
I checked around for the vacuum leaks as you suggested but I see nothing wrong.
The MAF sensor was cleaned with the special MAF cleaner.

So next thing on my list is the vacuum gauge test, as soon as I buy one.
Other than that I will take out each spark plug to inspect, but its such a pita.

Thanks

[MKMike]

If they're really reading 2 ohms on the primaries, then they're bad.
0.9 is the upper limit
It would seem unusual for all to fail at once, though.

I should have said to check all the vacuum fittings and that the one beneath the supercharger snout is often the bad one.

Fuel pressure is another thing to check.
A failing fuel pump will not be able to deliver enough fuel while under a load.

[TrueWildMan]

Howdy.

Did you ever find out what the issue was? Mine's doing the same thing and I've replaced every vacuum line and sensor in this sucker.

Thanks.

[96 SSEi]

hi, since you have already done lots, I would suspect the cat and pinpoint or eliminate it by removal of down pipe to cat/resonator bolts enough to let exhaust escape to bypass the cat - rev that bad girl and see if your issue stays(not cat) or is gone(check cat flow).

but, since your issue started after plugs, what plugs did you put in and what gap were they?

[blye]

Howdy.

Did you ever find out what the issue was? Mine's doing the same thing and I've replaced every vacuum line and sensor in this sucker.

Thanks.

Haven't had too much time between all the rain here..

resistances in the wires and coils were pretty normal.

hi, since you have already done lots, I would suspect the cat and pinpoint or eliminate it by removal of down pipe to cat/resonator bolts enough to let exhaust escape to bypass the cat - rev that bad girl and see if your issue stays(not cat) or is gone(check cat flow).

but, since your issue started after plugs, what plugs did you put in and what gap were they?

Yeah I am suspecting the cat. I can hear loose metal fragment sounds from the cat when I bang it.

Spark plugs are NGK Iridium. I didn't check the gap, since the box said not to change the gap, they were pre-gapped


I'm probably going to have to get rid of it. If anyone wants to buy this car and fix it, I can send you a list of problems with it and you can make an offer. PM me. Located in Vancouver BC.

[Roadrunner]

Sad to hear about losing interest in car.
Sounds to me like bad coil or ICM may be next things to check.
I have had them go intermittently and also sometimes they can still be bad even if test OK.
Only real way to confirm is substitution with known good ones.
Cheapest way is try your luck with junk yard (used original ones are often better than new aftermarket).