Does my 96GT have a blown headgasket or what?

keithnra · Jan 11, 2011

My 96 GT is running really rough, it wont hardly stay running at idle its running so rough. I checked to make sure the firing order was right, and is, i checked to make sure all coils are firing, they are, and i checked oil and no milkshake. Does a blown headgasket have to have milkshake oil? i cant figure why its running so bad.

joshjwc9 · Jan 11, 2011

If you hold the throttle halfway open does it start and stay running slightly more than if it doesn't?

It already sounds like your IAC is going.

trinity_gt · Jan 11, 2011

Check or codes in the PCM, specifically, P03xx codes... This may point you to a specific cylinder (e.g. P0301-P0308) or a systemic problem (P0300).

Do a simple cylinder balance test (while running, unplug each plug wire at a time and make note of cylinders where there is no difference between plug wire connected and disconnected states).

Pull the plugs. What do they look like?

Do a compression test.

Check for corona discharge in the ignition wiring (e.g. get the car in a pitch-black garage with the hood up; start it, close the door and let your eyes adjust to the dark.) Look for arcing and light "dancing" on the plug wires indicating a loss of spark energy: Is it worse when it's damp out? If you take a plant mister and spritz a bit of water on the wires, does it get worse?

keithnra · Jan 11, 2011

ok so heres what ive found out this afternoon.I pulled all the plugs and no 6,7,8 were all carbon fouled. No 5 had lots of gas on it so i started to do a compression test.the test was kind weird cause some of them had really good compression and no 5 had no compression. i tried it several times with no luck.i put a rod in to see if piston was moving up and down and it is, but the cylinder is full of gas. what do u guys think is wrong, maybe broke rings, i dnt know what else it could be.

nyuk98gt · Jan 11, 2011

keithnra:

Weekend mechanic's diagnosis: fouled/stuck injector. Injector sticks open or does not close fully so too much fuel gets into the cylinder at the wrong time, washes oil off the cylinder walls and the rings are trashed.

I don't know how to test injectors but I am sure you could find it somewhere on the 'Net.

In any case, I suspect that it is time for new rings and a honing.

Please post an update.

Chris

joshjwc9 · Jan 11, 2011

I definitely need to be completely awake when I post in the morning! I totally don't remember reading half of the OP. Defintely sounds like it isn't getting any spark in that cylinder and/or your injector is stuck open.

keithnra · Jan 12, 2011

I think i got most of the gas out so im going to put some oil in the cylinder and see if compression comes up at all. right now its a zero.

trinity_gt · Jan 12, 2011

keithnra said:
I think i got most of the gas out so im going to put some oil in the cylinder and see if compression comes up at all. right now its a zero.

The engine sounds badly hurt. Zero compression means either a hole in the piston or a bad valve (e.g. burnt, valve being held off the seat by debris, broken spring, bent due to PTV etc etc).

Can you explain a bit of the back story here:

When did this bad-running start?
What were you doing with it?
What are the mods on the car? Nitrous? Blower?
Mileage?
Any signs of trouble leading up to the "bad running"? (Puffs of smoke? Knocks/taps?)

keithnra · Jan 12, 2011

I just took the valve cover and found one of the rockers setting in the head. There is a little nick on it and on the cam. its hardly noticeable but i think i may change the cam and put it back togther, do u guys think it hurt something else. It was the second rocker from the front that was off which explains the no compression i would think. any suggestions

trinity_gt · Jan 12, 2011

keithnra said:
It was the second rocker from the front that was off which explains the no compression i would think. any suggestions

Only indirectly.

If the follower is lying on the head, what's to hold the valve open to produce zero compression?

The fact that the rocker was lying on the head may be a symptom of another issue, such as an over-rev or a severe PTV event. Inspect the valve spring and the height of the valve tip or retainer compared to the other valves in the head. If the retainer or tip is "lower" it's likely that the valve is bent (likely from PTV) which is (a) causing the zero compression reading and (b) the cause of the follower being tossed: when the valve failed to close to its normal height after being bent, the follower was left hanging there, free to move about and was tossed by the cam lobe as it came around again...

keithnra · Jan 12, 2011

so do u think i should go ahead and pull the head? ?I actually have another head, spare, that i could use. Can the head be pulled with the motor in the car?

trinity_gt · Jan 12, 2011

keithnra said:
so do u think i should go ahead and pull the head? ?I actually have another head, spare, that i could use. Can the head be pulled with the motor in the car?

1) Can you answer the questions I asked a post ago re what led to this? If you say "I accidentally shifted into 2nd at 75MPH" or "I hit the nitrous button and heard a bang and then it started running like crap..." etc it may help to confirm what are currently only suspicions.

2) Did you measure the valve height and compare it to other valves in the closed-state as I suggested? If so, what did you find?

I'd hate to counsel doing a ton of work when there are still one or two things to be done to rule in, or out, a bent or otherwise damaged valve.

Before pulling the head, I'd at least put the follower back in and see what the play is like and, if it seems reasonable, see how the car runs.

Do you have a source of compressed air? If so, you might think about borrowing or buying a spark plug adapter, setting the regulator to, say, 30 psi or something and and applying air pressure to the cylinder in question through its spark plug hole. Make sure the good valve and follower are on the base circle of the cam so that valve is closed. If you hear air rushing out the exhaust or intake, you'll know that the related valve is baffed and the head is coming off.

And yes, the head(s) can be removed with the engine in the car.

keithnra · Jan 16, 2011

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I pulled the engine and tore it apart and look what i found underneath the exhaust valve where the rocker was off at. think this is why i didnt have any compression on this cylinder, i bought this motor from a guy that thought it had a blown headgasket so he swapped motors. I got some work to do but it was worth 20.00. It came with ps pump, ac comp, TB, hoses, wiring harness and injectors so i came out pretty good. Ive never really seen this but is the piston trash. The cylinder is good with no scoring what so ever. the valve is bent and not closing so i have to replace the head, there was more damage to the head than the piston.

trinity_gt · Jan 16, 2011

keithnra said:
I pulled the engine and tore it apart and look what i found underneath the exhaust valve where the rocker was off at.

That's the intake valve. I suspect the manifold was off at some point shortly before it ended up in your hands -- perhaps for a PI swap or to be replaced due to a leaking crossover -- and whomever had the thing apart was careless and dropped a bolt into that intake port.

What a waste of an engine.

nyuk98gt · Jan 16, 2011

keithnra:

LOL at the bolt! Good work getting the head off and finding the problem. You don't waste a lot of time, I see.

Are you putting PI heads on (or has that been done and you are just replacing the hurt one)?

Chris

Does my 96GT have a blown headgasket or what?

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