PontiacBonnevilleClub.com

2005 GXP with just under 95,000 on it. The car has been in the family since it had 3000 miles on it and it has always been one of the "good" ones.

Past few days it has started each day by running rough for the first minute or two after starting, then smoothing out. Last two restarts were accompanied by a blinking check engine light. I now have codes P0300 for multiple misfires - no code for a specific cylinder, and a P0442 code for a leak in the evap system (I think the filler neck is rusted - why are those so *dang* expensive?)

So far no coolant loss observed, no bubbles in the tank, oil looks fine - I am checking them after every drive.

Clearly I am thinking head gasket by the Northstar reputation and the way the idle smooths out after running for a couple minutes. Otherwise no misfires, still runs great, still goes. Is head gasket the most likely cause for misfires with this self recovery mode?

Has anyone used something like this http://www.amazon.com/Lisle-75500-Combu ... B0007ZDRUI - Lisle 75500 Combustion Leak Detector on a GXP to confirm/rule out head gasket issues? I was wondering if it would still work given the remote pressure tank setup in these cars.

Worst case I did locate a place in Cleveland (spoken of on Cadillac forums) that works the Northstar engines with issues - http://www.powertrainautomotive.com/cad ... repair.htm

Thanks!

Lets rule out normal, basic stuff before throwing both feet in the water that you have a headgasket/stud issue.

On cold startup, in open loop operation, a small amount is normal. If it were a true misfire, it would set a P030x, the "x" referring to the cylinder(s) affected.

harofreak00 sells any parts you would need (filler neck) and his prices are very reasonable. Check out his site www.bonnevillesunlimited.com or PM him on here.

Or you could just put a light coating of grease/vaseline/etc, around the filler neck and the rubber o-ring on the cap...

It is pretty clear to me that something is amiss as far as that start-up misfire goes. It lasts for a bit and then clears itself up - but while doing so the engine clearly stumbles more than I've ever felt in the four years I've been driving it. It flirts with stalling but hasn't done that yet.

Hopefully ruling out head gasket was why I wondering about the combustion leak detector as a way of potentially telling me one way or the other what I am looking at repair-wise.

Lane is right, I would start with the small stuff but just my 2 cents.

All 3 cars I've had that have headgaskets go had the P0300 multiple random cylinder misfire. Because of the coolant leaking into the cylinders. And it did smooth out after it runs a bit. But I didn't notice any coolant loss either, well until it overheated and boiled over that is.

But the tell tale of failure is when the car starts overheating on long trips....the fat lady has sung by that point....

I would look into the evap issue and maybe pull the plugs and see what you've got going on and go from there.

"Some circumstantial evidence is very strong, as when you find a trout in the milk." - Henry David Thoreau.

"Daddy, why does the smoke from the car smell so sweet?" - my daughter this morning.

Oil still looks okay. Down on coolant from yesterday. As the idle smoothed out this morning I got massive, billowing clouds of white smoke out of the exhaust - looked like a sub-zero winter morning rather than a summer one. Guess the symptoms are progressing.

Feeling the resignation setting in.

Hate to say it.....

Sounds like tell tale signs of blown headgaskets.

Again, still exhaust all simple things before diving in and "assuming" the worst.

You've got 95k on it. Have the plugs ever been changed? Could be a bad plug. Could be a bad coil/sleeve assembly, although anything ignition typically would be constant and cyclical, funny things happen when heat causes parts expansion. What about a bum fuel injector? at 95k, running cheap gas, could cause pintle corrosion in the injector causing it to not fire properly...

When you "smell" Dexcool, it's usually because it's leaking or the system is somehow open... NOT burning. And we all know N*'s don't leak coolant either, right???

The small amount of Dexcool that will initially filter into a combustion chamber, lit by an HEI ignition system, in addition to the heat of compression, and previous ignition events in any of the affected cylinders will pretty much burn off anything in terms of odor. A trained nose (like mine), can sometimes smell it, but to the average person, much less a child, probably not.

Well, finally took the car into a place that does a fair amount of Northstar work. I've got head gasket issues and a fair number of oil leaks. Good thing I really like the car and figure I can't buy as nice a used car for what it will cost to fix mine. I will be getting the Northstar Performance studs installed as well as getting the oil leaks addressed.

Make sure that they reseal the midcase and oil pan. I would highly recommend Midwest Cadillac Repair. Did the inserts on mine and completely resealed the bottom end, etc for $1,000. Very happy with the repair.

Now to put it back in the car.