No Compression in Cylinder

Hello Car Talk Community,

About a week ago I was driving my Pontiac 2003 Grand Am V6 and it began to violenty shake and the “check engine light” came on and started blinking. I then immediately took it to the mechanic It has been with the mechanic for 6 days and they were unable to locate the problem. They called me today and I was told that I have no compression in one of the cylinders (I have done business with them before and felt comfortable in that I wasn’t being taken advantage of). They quoted me $1,600 is that a fair price? It comes with a 2 year or 24,000 mile warranty? Also, is there any problems in the future with getting a cylinder replaced i.e. other parts of the engine that might correlate?



Do you mean getting a piston, or piston rings replaced? Could you be more specific about the proposed repairs?

What ecactly does the quote say they intend to do? A cylinder with no compression would indicate a failed set of piston rings (VERY expensive to fix) or possibly a blown head gasket at that cylinder. Not quite so expensive. I’d be interested to know what they want to do exactly.

Your symptoms are consistant with losing compression in a cylinder, however in a family car that generally means something has happened to something in the valvtrain, not to a cylinder. Generally it may require removing a head but nothing with the cylinders. Exactly what did they find and what are they quoting $1600 to do? You don’t say how many miles you have on the car, but I’m going to take a wild guess that your timing chain popped and you bent a valve.

Post the details from the quote.

" They quoted me $1,600 is that a fair price? "

Fair price for what ? You haven’t mentioned what has caused the problem . . . valve(s), rings, head gasket . . . ? What needs to be repaired ?

Also, why would it take 6 days ( “they were unable to locate the problem” ) to diagnose low compression in a cylinder of an engine that was shaking violently ? That should be found in the first 15 minutes.


Dear Car Talk Community,

Thank you for your comments so far. My car has 100,000 miles on it. They said that I need a head gasket set and that the valve is either broken or bent, or burned. It needs to be taken to a machine shop to be fixed and around 3 days to fix it. Labor is 1,000 and the rest is parts, fluids, etc. Also, Does anyone know how long it takes to replace or fix a valve usually? Again, thank you all so far for the help. I am new to this stuff. Is there any other questions that I should ask?



Usually a head gasket and valve repair can be done in a day, but it is more the constraints of the machine shop. Certainly ask, they should be able to let you know. Price I will defer to others. You can ask if they thought there was a reason for the failure.

Yup, that all makes sense. They’ll need to remove the head, check it over, and replace at least that valve, which will mean at the very least “seating” the new valve. That’ll take a bit of machining to the valve seat. If the head isn;t flat, it may even require “lapping” (taking off just a bit of metal to make the surface flat). And, if the springs are weak, they’ll probably want to change those also.

Add anytime the head gets removed, it needs a new headgasket. They are not reusable.

Most important is figuring out why the valve bent. My guess is that the timing chain broke. Did they mention anything about this? Another possibiity would be a broken spring. Which is why I mentioned the “weak spring” comment above.

By the way, if it’s the rear head the cost escalates. In a FWD V6, the rear head (callled a “bank”) is against the firewall. They may have to pull the entire engine to remove the head. Perhaps someone here knows for sure.

No compression and a bent valve could definitely cause this kind of problem but I’m going along with mountainbike about wanting to know why this valve is bent.

There would need to be some definitive info about this problem before proceeding with a 1600 dollar repair that might go sour immediately after being completed.

The fact the car was apparently fine one minute and bad the next along with taking 6 days to determine this comes across as a suspect diagnosis.

I bet you have a valve problem

I assume they did a leakdown test and that’s how they know there’s a valvel problem likely, and limited to one cylinder. $1600 seems a very fair price in my opinion to get this fixed. But the question is, that’s what the above comments mean I think, will doing this really fix it? There may be hidden problems remaining, which won’t become apparent until the head is removed. Or at 15,000 miles after the fix is done and paid for. Maybe a good idea to get a max $$ amount you’ll have to pay in the event to fix the whole thing becomes too expensive for you, and buying a new car makes more sense. Doesn’t hurt to ask anyway.

Now we are talking about a bent valve. Peobably not. How about a broken valve spring?

This might also be a burned valve. Some models are more susceptible to this than others.

How does the engine run otherwise? ANy oil use/smoking? If not, go ahead and fix.


i agree that 1600 seams to be pretty fair. if you are unsure call a machine shop that also does auto work and ask them how much a valve job on one cyl. and new head gasket would be on your vehicle.

This is hard to believe, but a guy I know bought a '94 Beretta about 3 years ago, and it was missing on one cylinder. After spending around $300 for a tuneup, it still missed. I was sure it was a valve stuck or burned up. After driving it a year or so it quit missing. After about another 6 months, it blew a head gasket.

V6 motor is 3400? U could have a bad coil and 1 of the cylinders is not firing. That will give you misfire code and cause rough running. Yes shop can say cylinder is bad but do u trust them? A bad head gasket will usually leak coolant which may show up a 1 or 2 cylinders using coolant or worse yet, hydrolocking motor and causing bad things. So u remove intake, 1 cylinder head and replace gasket. U might not even need to spiff up head. And shop is doing 1 head and not replacing both head gaskets? And new intake gaskets which are prone to failure on GM v6 motors.

alot of good things have already been said i would add that you can remove both cylinder heads on this car w/o pulling the engine,stoveguyy the op said she has delt with them before and felt comfortable and at 100,000 miles if it were mine i would have both heads removed and and reworked it will cost a little more in labor but they are already there why take the chance on having this same issue come up on the other head say 10,000 miles down the road and end up out another 1600 dollars.

A severe misfire will cause engine code for sure. Ur cel light was on? Ok, all mechanics are honest. Pull head and inspect.