OntarioTurbo

Lapping day at the track today. Car running good until sudden loss of power. Pulled into pits, car running on 3 cyl. Checked plug wires, injector wires, vacuum hoses etc, all OK. Limped home slowly and did compression check:

#1 - 145 #2 - 60 #3 - 0 #4 - 120

#1 - 155 #2 - 65 #3 - 0 #4 - 130 With oil added

Yes those are "ZEROS"!!!

No coolant in oil or oil in coolant. No smoke from exhaust. #1,2,4 plugs tanish greyish, #3 oily black.

I have spark and fuel at all cylinders.

At fist I though head gasket with #2 and #3 low, but a ZERO? Could a valve be burned or stuck open? there is no unusual valve train noise.

Looks like the head is coming off at the very least. Anyone seen this before?

JohnKoaWood

Sounds like buggered head at the very least, maybe burnt valves on #2 and #3... my guess is fuel related issue... 2 and 3 shoot together I believe (1-4 and 2-3 if I recall correctly)... injector harness ate it and took out your valves with massive shots of fuel or spray after valves were closed?

I'm just making guesses at this point... Sorry for the dammage, but post pics and writeup of the cause and aftermath...

Travis - sflraver

All stock injection is batch fire. All injectors fire every time. 3 times against a closed valve, once against an open valve. If you follow the injector wires back to the DME they bridge on a trace on the board. Just to correct the above...
Don't know what it could be but I would pull the head and take a look.

JohnKoaWood

TY for the correction, I thought it was batched in pairs, not all 4 together... damn, get the head pulled and let us all know..I'm still on burnt or bent valves...

sebastian944

That's terrible. How many miles do you have on your car?

Techno Duck

Sounds like burnt exhaust valve(s). #2 is probably has a very tiny piece missing causing slight compression. You can do a leakdown test and listen for where the air is escaping from. Most likely it will be out of the tail pipe.

If its just a burnt valve, find replacements and then find out why it happened.. most of the time i have not seen collateral damage as a result. My friend (Jeeper31) recently burnt a valve on the #1 cylinder last year, replaced the valve and redid the headgasket this winter and the car is back out on the track again.

Rock

I must be terrible to these cars because for like the past week every problem people have had with 944's has happened to me at some point.

I had this same thing happen to me on the same cylinder too, number 3. Zero compression in that cylinder. The car sounded like a clankey diesel truck. The vaccuum line popped out of the intake manifold, screwing up the fuel pressure which resulted in, yep John called it, a burnt valve.

Here is a pic of my zero PSI valve.

OntarioTurbo

Thanks for the replies and support guys.

That's terrible. How many miles do you have on your car?
__________________
215,000 Kms (133,000 miles)

Thats a good chunk out of that valve rock. Where did all the metal go?

When I got the car in the fall, #3 was already slightly low. During the winter I had replaced all the vacuum lines and found some that were quite ratty. Looks like I just finished off the weak link.

Van

John's right - the 4 injectors fire in pairs - 1 & 4 and 2 & 3. One firing is against the back side of the intake valve when it's closed, the other when it's open.

It could also be a mechanical problem - like a broken valve spring and a retainer that failed...

Either way, time to pull the head!

Chris White

Sounds like a burnt valve - typically that will be accompanied by a ‘chuffing’ noise at idle and some occasionally back firing.
Its one of the least expensive fixes when it comes to a zero compression reading!
Burnt valves are usually caused by high EGTs….which are common with the combination of lower AFR and retarded ignition timing.

sebastian944

Just curious, where are you going to send your block too? Are you going to use someone in canada?
How much will that cost?

Rock

At the time, the engine had ~3000 miles on it when this happened.

OntarioTurbo

Rock: Did you ever find the cause of the burned valve and how did you correct it?

Sebastian: I'll let you know as soon as I figure that out. I'm pulling the head this weekend so I'll know what I'm dealing with and then decide from there. Hopefully cylinders are in good shape and just need to repair the head.

Mike Lindsey

"John's right - the 4 injectors fire in pairs - 1 & 4 and 2 & 3."

Actually, 1 and 2 are wired together, as is 3 & 4.

OntarioTurbo

If I understand correctly, the injectors fire on the intake valve side. How does this contribute to the exhaust valve being burned? Just by an over rich mixture? If so, you would think #2 plug would look black as well. #2 looked the same as #1 & #4.