Took my car to a dealer today and after a $89 diagnostic fee they said there was "no compression in cylinder 4." They want $1330 to pull the head off and investigate whats wrong, this does not include repair costs. Anyone have any alternate suggestions of what i can do to figure out whats wrong?? Thats quite a bit of cash!

 

You didn't post the year or the miles on the car, but I would say its probably time to find a good vette mechanic in your area and talk about an engine rebuild or a new short block. If it is an older or high milage engine it would seem to be a waste of $ to have the stealership do the work. My .02.

 

I would get out of the dealer right now. No compression can have a few different causes, but my .02 says it is a piston. Get busy shopping around for a local, trusted Corvette friendly repair shop that is comfortable with engine rebuilds.

$1400 to pull a head off ? Man, I am in the wrong business.

 

45k miles...is a bad piston common in a engine of that many miles?

one more thing, it threw a code of P0300 with is a RANDOM misfire, if cylinder 4 has no compression and is constantly misfiring wouldn't it throw a code of p0304, where the 04 is means cylinder 4?

oh and does any one know which cylinder number 4 is? i.e drivers side or passenger side front or back?

Thanks guys

 

2nd hole from front on passenger side I believe. The misfire code is more about the spark so you might not see one (1 PO304 that is). Easy test, pull the spark plug, disconnect the fuel pump by pulling the fuse and have someone crank the engine with your finger over the spark plug hole. If you have no compression, you'll know 1 or 2 revolutions.

 

No. A bad piston is not common in an engine of that many miles. If it's a bad piston, it probably has a hole in it from something catastophic. I wonder if a valve spring broke and you dropped a valve.
Assuming you have a bone stock car, did you over-rev, i.e. missed shift? If so you could have floated a valve and punched a hole in the piston. OR you could have a bent valve that isn't closing all the way. My money is on that one.
Did you drive through deep water and possibly hydrolock the motor?
A bent valve can be verified without removing the head. One of the stems won't come up all the way if it's bad enough to prevent compression. And you could put a boroscope into the cylinder through the spark plug hole to do a visual inspection without removing the head also.
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You are correct about P0300 and P0304.
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Cylinder # 4 is the second cylinder bask from the radiator on the passengers side.
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As suggested above, run away from the stealer and find someone that is friendly to Corvettes.
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I see you are in Delaware. I suggest you call East Coast Superchargers and talk to them. They aren't too far away from you. They are straight shooters and stand behind their work.

 

would i be able to notice a screwed up exhaust valve by just pulling the valve covers?

 

I would gather my own info on the situation before starting to panic
You didn't say what you took it to the dealer for. You should have "heard" a valve drop if that is was issue

 

i took it to the dealer for the p0300 code. To me the engine doesn't feel any different than before, thats the strange thing, but there is a shutter at idle so there has to be a misfire. I'm fairly sure that i didn't hear any obnoxious noises like a valve hitting the piston, but if its not a valve was else is there? connecting rod going bad on a bone stock ls1 with 45k miles?

 

was the car running when you took it to the dealership?


what kind of noise did you here when things went wrong?



what was going on when things went wrong?


how hot is it where you are and was it when this happened?


For that price the dealership wants you could fly out an expert CF member... pay them/feed them for a day or two and get better results than the dealership probably would give ya...

Seriously though... at this point you've spent $90... cut your losses with the dealership if it doesn't fall under warranty and walk away... if you have a garage you can do it all yourself... You can buy a full tool set (black powder coated/ laser etched with torqe wrenches for less than $500 ( lifetime warr)which is far less than they want to pull the head... whats funny is it's probably just one head they are referring too..

if it's stoock i'm gonna guess you have a better chance of it being a valve than a pistion or something more damaging...

i'd maybe think about checking your coolant tank/oil and see if you see either of the two in the wrong container... Ie. coolant in oil pan, or oil in coolant tank... This would indicated a blown head gasket...

as stated above there are ways to look inside the cylinder to inspect without removing the head.. dealership is playing with ya (stupid vette owner) as i'm sure they have the ability to see inside without removing the head as well..

 

if your car shakes at idle (misses) and has obvious misfire issues at low speed load, and a compression test shows NO COMPRESSION on cylinder #4, then it can be a piston. I doubt that you had catastrophic breakage of the piston as you should have heard something indicating that something blew. On the other hand, issues with overheating or detonation can cause ring lands to blow on any mileage car.

Pull the rocker cover and inspect for any obvious valve issues, and if not there, pull the spark plug and inspect. I would bet that you find oil on the plug. Pulling the head is the only way to know for sure. Good luck.

 

Assuming the techs were marginally competent and accurately diagnosed no compression, it could be from a broken intake rocker arm, as well. Lots of reasons to get your baby home and dive into it yourself.

If you don't feel confident doing this solo, I bet there are some CF members close enough by to give you moral support.

HTH, and have a good one,
Mike

 

A fast way to diagnose where the problem lies is to put the bad cylinder at TDC (valves closed) and pressurize the cylinder through the spark plug hole.Listen to where the air is escaping. (Throttle body =intake valve, exhaust= exhaust valve, crankcase=hole in piston). This will give you a big heads up as to where to attack the problem. Chuck.