'06 3.8 dead cylinder

'94Blackbird · #1 04-11-2009, 11:32 AM

I have an '06 Grand Prix 3800 V6 with 60,000 miles. The check engine light came on I took it to the dealer and they told me there was only 20lbs compression in the no. 4 cylinder. We have babied this car switched to synthetic at 30,000 miles,regular oil changes.What could this be and what could have caused it,thanks for any help.

BNaylor · #2 04-11-2009, 05:58 PM

Thats a bummer for such low mileage. What was the code (DTC)?

Compression that low could indicate a defective piston or piston rings but I would not rule out a bad head gasket although not too common. How does the car run as far as driveability. Any overheating, bad misfire?

'94Blackbird · #3 04-11-2009, 11:15 PM

No overheating no blue smoke, the engine is a little ruff but no ticking. You can hear a sputter or a kind of put put put out of the exhaust. I drove it home on the highway 55 to 65 mph then to the dealership.I'm hopeing it is an exhaust valve or valve seal or spring.I can buy an 07 motor with 5000 miles for just over a 1000 dollares, so maybe thats the best way to go. I'm not sure.

doctorhrdware · #4 04-11-2009, 11:25 PM

That is a dam good price for a motor with 5K on it. I wish I could had found a engine with that mileage and for that price. I paid over $1500 for a engine with a little over 97K miles on it.

tblake · #5 04-12-2009, 01:21 AM

Get a second opinion!!!!!!!!!!!!!!

You could have a bad plug wire and the "stealership" could be trying to sell you a "rebuild" which would consist of a new set of plugs and wires for thousands of $$$$$.

Take it to an independant repair shop, tell thim its misfiring and just have them diagnose it.

Or you could do a compression check on it yourself. Number 6 is going to be sort of hard to get to, but it can be done.

doctorhrdware · #6 04-12-2009, 01:32 AM

tblake, you are right about getting a second opinion. With the way the economy is I would not put past a stealership to do that. That would be a nice profit for them to lie about a engine rebuild and just to put in a set of wires.

'94Blackbird · #7 04-12-2009, 07:51 AM

Yeah I went and got the car from the dealership and it is at an independent garage now. I nave used this guy for a couple of years and I trust him 100%. He is going to look at it first of the week. The dealership said they switched plug and wire but made no differance. Does anybody think this could be a valve or head problem or is it most likely rings thanks again.

doctorhrdware · #8 04-12-2009, 08:47 AM

It is possible that the head gasket may have a problem.

BNaylor · #9 04-12-2009, 08:50 AM

Best thing to do is see what the results of the second opinion are. If the compression test is done properly I don't see what the spark plug or wires have to do with the issue if what the dealership found is true.

On any other cause for low compression we would just be speculating. Also, if you get the code(s) please post it.

tblake · #10 04-12-2009, 10:38 AM

Quote:

Originally Posted by '94Blackbird

....The dealership said they switched plug and wire but made no differance...

Bob, I was just thinking that same thing...

Why in the He11 would the dealership replace the plug and wire after a compression test determined a mechanical issue? Would just be a waste of money and time.

94blackbird, either the dealership is feeding you crap, or they are trying to milk you for money. The fact they replaced the plug after they diagnosed low compression leads me to believe they are in it for the money.

Did you get a print out or anything that shows their diagnostic procedure and conclusion of a "dead cylinder"? If you could scan it in, I'd like to read it.

BNaylor · #11 04-12-2009, 10:42 AM

Yeah Tim. Its

He definitely needs a second opinion. If it were me I would run the compression test myself.

tblake · #12 04-12-2009, 10:46 AM

'94Blackbird · #13 04-12-2009, 12:49 PM

I don't know what the code was but I can check Monday. I think it said something was wrong with no. 4 so they changed plug and wire and when that did not help they did the compression test and found less the 20 lbs compression in no. 4 but that was the only one they checked. I think myself that there is a defect that caused this because this car has not been abused in any way. Thanks for your posts I will post when I find out more. Does nobody think this could be a valve problem or a worn lobe on the cam. Just thinking out loud I guess.

tblake · #14 04-12-2009, 01:06 PM

Warn exhaust came lobe will still show compression beleive it or not. Not true for the intake lobe. You could pull the valve covers off and observe the action of the rocker arms as you rotate the engine by hand.

20psi of compression huh? I would think that would be noticible when you crank the starter if it were true. Do you notice anything like that? (ie, as your cranking it, and you hear the engine turning over, do you hear it cranking sort of quick then slow, then quick then slow) indicating a weak cylinder not needing much torque from the starter?

I still think if I were in your shoes, I'd pull all 6 plugs and just do a quick compression test. It wouldnt hurt, and you might be able to get a better idea whats happening.

20psi, I wonder if almost it dropped a valve seat or something.

BNaylor · #15 04-12-2009, 01:10 PM

On this one I think a leak down test would be best.

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