Thought i had a burnt valve for sure.
#1
10-14-2016, 09:43 PM
Thought i had a burnt valve for sure.
I have a '99 S70 with 175K miles on it, which I put about 60K miles on over the last two years. Prior to that it was a one-owner, a little old lady, who had Volvo service it at every oil change and every service interval. I use only Mobil-1 10W30 and try to use mid-grade to premium gas whenever I can.
A week ago, while idling, the engine began to run rough and the CEL came on. A local Autozone said the code was a mis-fire on cylinder 2 and probably just a bad plug. I replaced the plug with an NGK, but the roughness (like running on 4 cylinders) and the CEL stayed. The exhaust smelled like a combo of rotten eggs and raw gas.
I then replaced the other four plugs, but no change. On the recommendation of a local mechanic, he loaned me a compression test kit and said it was the best way to know whether the condition was terminal or not. He speculated that it was a burned valve or a blown head gasket.
The compression test showed psi's of 152-160 on cylinders 1,2,4,5 and 125 on cylinder 3. I was now convinced that the compression discrepancy between cylinders was the cause of the rough running and the compression loss was due to a burned valve.
Thankfully I talked to a Volvo technician and he said that a discrepancy that small, although somewhat concerning, would not create the situation that I had, and also that a blown head gasket would cause a loss of compression on two cylinders, not just one. He recommended replacing the number 2 coil pack. I ordered one from Amazon for $35 and it came today.
As soon as I cranked the engine with the new coil, the rough idle was gone. After about an hour of driving, the CEL went out and now I have my normal car back. I know I still have some concern over the loss of compression on cylinder 3, so I am deciding now whether to sell it or not.
A week ago, while idling, the engine began to run rough and the CEL came on. A local Autozone said the code was a mis-fire on cylinder 2 and probably just a bad plug. I replaced the plug with an NGK, but the roughness (like running on 4 cylinders) and the CEL stayed. The exhaust smelled like a combo of rotten eggs and raw gas.
I then replaced the other four plugs, but no change. On the recommendation of a local mechanic, he loaned me a compression test kit and said it was the best way to know whether the condition was terminal or not. He speculated that it was a burned valve or a blown head gasket.
The compression test showed psi's of 152-160 on cylinders 1,2,4,5 and 125 on cylinder 3. I was now convinced that the compression discrepancy between cylinders was the cause of the rough running and the compression loss was due to a burned valve.
Thankfully I talked to a Volvo technician and he said that a discrepancy that small, although somewhat concerning, would not create the situation that I had, and also that a blown head gasket would cause a loss of compression on two cylinders, not just one. He recommended replacing the number 2 coil pack. I ordered one from Amazon for $35 and it came today.
As soon as I cranked the engine with the new coil, the rough idle was gone. After about an hour of driving, the CEL went out and now I have my normal car back. I know I still have some concern over the loss of compression on cylinder 3, so I am deciding now whether to sell it or not.
#2
10-17-2016, 09:40 PM
Did you do both a wet and dry compression test? For piece of mind you can redo the compression test. Assuming the wet test bumps compression - you can try going to a heavier oil (ie 10-40) or consider a Seafoam treatment etc, but assuming the car is running fine and there's no other symptoms you probably have some wear on the rings but nothing worth tearing down the engine for. If the wet test doesn't change the compression, then you probably have some valve seating issues.
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