COMPRESSION TEST

1999 Saturn SC2

Tiny

RandyMI

November, 21, 2010 AT 1:54 PM

I have a 1999 SC2 that is idling rough. It does burn a little oil too. I did a compression test. I had never done one before. For the dry test, all 4 were 195 to 210. When I did the wet test the pressure increased significantly, 270 to 300. I did not expect that much of an increase. According to what I have read, a significant increase in pressure means the piston rings are worn. I am not sure that I trust the results of the test. Could I have added too much oil?

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9 Answers

Tiny

mmprince4000

November, 21, 2010 AT 2:01 PM

Don't really think you have a ring problem specs are 185-205 psi.

Tiny

RandyMI

November, 21, 2010 AT 4:50 PM

Thanks for the reply. If the rings are ok, what should I check next? Should I do a leak down test? I have never done one, but it does not look very hard.

Tiny

saturntech9

November, 22, 2010 AT 10:38 PM

If your compression is good then doing a leak down test is a waste of time the only time you would do a leak down test is when you had a low compression issue. So does the engine only run rough at idle?Also do you have any codes?

Tiny

RandyMI

November, 25, 2010 AT 1:47 PM

The engine runs rough at idle and seems to lack power. I do not notice it running rough when driving 30 MPH or above. I took it to Autozone and had them hook up the scanner. The guy said that cylinder 1 was misfiring. I did not actually see the code. I have checked the plug wires by doing a continuity check. The wire for cylinder 1 was just over 6,000 ohms. The rest of the wires checked ok too. I also recently replaced the plugs. I checked the resistance on the fuel injector, it was 12 ohms, which is in specs according to the Haynes manual. I also listened to the fuel injector with the engine running by using a long screw driver like a stethoscope, and I could hear it clicking very fast. Would trying a spark tester make sense next? Thanks again.

Tiny

saturntech9

November, 28, 2010 AT 4:19 PM

Doing a spark test would only help if the number one was a dead hole meaning it never ran. At idle you can determine that by taking off one spark plug wire at a time and see if the rpm's drop down to let you know if that cylinder is running or not. As far as the wire's go they they could test good and still be bad when put under a load. How are the plug's what kind are they?

Tiny

RandyMI

December, 3, 2010 AT 1:00 AM

I did as you suggested and there was no noticeable difference in rpm when I took off the plug wire from number one. I did put new plugs in when I first started. The plugs are AC. They were about $2 each. There was a more expensive plug, about $8 each, but I went with the less expensive ones.

Tiny

saturntech9

December, 3, 2010 AT 4:55 PM

As long as you don't have platnuim plug's in your engine you will be ok. Have you checked fuel pressure?Back pressure?Also have you made sure your plug wire's are routed correctly?

Tiny

RandyMI

December, 4, 2010 AT 2:57 PM

I pulled the plug last night, just to double check the gap and I noticed that the plug was wet with gas. When I went to check the gap, I noticed that the porcelain around the tip slipped down. I replaced the plug again and I think number one is firing now. I think it is good. Thanks for all of the advice.

Tiny

saturntech9

December, 5, 2010 AT 10:57 PM

Glad to hear you got it figured out that's what we like to hear.

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