evest Posted February 27, 2015 Share Posted February 27, 2015 Hi folks, Just about to change my rocker covers so took the opportunity to do a compression test. Car is a 2004 GT with approx 130K on the clock, road driving only, not been tracked or otherwise abused. I did the test twice just to er.. do it twice... Run 1 Run 2 Cylinder 1 171 180 Cylinder 2 182 184 Cylinder 3 190 188 Cylinder 4 190 190 Cylinder 5 172 174 Cylinder 6 178 191 All seem roughly within 10% of each other. Interestingly, cylinder 5 is down a bit... Cylinder 5 is why I'm changing the rocker covers, as I had oil in the spark plug aperture, which I was told would be a leaky seal on that rocker cover. Could there be another issue - the compression doesn't seem to be significantly worse than the others. (I did a wet test on cylinder 5 and compression went up to 220 - piston rings? Will wet test the others tomorrow) Cheers Quote Link to comment Share on other sites More sharing options...
evest Posted February 27, 2015 Author Share Posted February 27, 2015 Forgot to mention - testing was on a cold engine. Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted February 27, 2015 Share Posted February 27, 2015 The fact that the two tests show pretty different figures is a bit odd, especially cylinder 6, how did you conduct the test? normal procedure would be to use a fully charged battery, in the case of the Z pull the fuel pump or injector fuse, wedge the throttle fully open and remove all plugs, and make sure you turn the motor over at least 6 times for all cylinders. The fact that cylinder 5 went from 174 to 220 with oil (how much did you use?) is rather worrying, the figures themselves are not bad for a cold engine and the mileage, I usually run a hot and cold test to see how much change there is. Quote Link to comment Share on other sites More sharing options...
GT4 Zed Posted February 27, 2015 Share Posted February 27, 2015 That's not bad going for a cold compression test. Tbh you should expect an improvement on compression with the wet test as a130k engine will have expected ring wear. Because you are within 10% that's fine. A hot compression test is better as expansion is accounted for and representative of true ring leak. Reassemble that baby and keep motoring👠Quote Link to comment Share on other sites More sharing options...
GT4 Zed Posted February 27, 2015 Share Posted February 27, 2015 Look like you beat me to it RIcky and your questions are pertinent👠but I've assumed the OP know what he is doing. There you go op. Quote Link to comment Share on other sites More sharing options...
evest Posted February 27, 2015 Author Share Posted February 27, 2015 (edited) Procedure was pretty much as you said Tricky Ricky - although I didn't wedge the throttle open. Will run through it few more times tomorrow to ensure I've done it consistently across each cylinder, and will run a hot test when I've re-assembled everything. Used just a cap full of oil for the wet test but will compare to the other cylinders tomorrow. Car feels good when driving so no worries - was just interested to see how it's doing. Edited February 27, 2015 by evest Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted February 27, 2015 Share Posted February 27, 2015 Doesn't hurt to double check things, no disrespect to the OP, yes wedging open the throttle allows maximum air flow into all cylinders, I just found the 45psi difference on cylinder 5 a bit excessive, so could well be worn rings, however given the mileage I would have been inclined to wet test the rest just to see, however as I said its a pretty good figure for the mileage. a leak-down test would give a more comprehensive idea of the condition. Quote Link to comment Share on other sites More sharing options...
evest Posted February 27, 2015 Author Share Posted February 27, 2015 Cheers mate, will go through the tests again tomorrow. Unfortunately I don't have the kit to do a full leak-down test. Does anyone know what the compression should be when brand new? Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted February 27, 2015 Share Posted February 27, 2015 Std =185 psi minimum =142 psi maximum difference between cylinders 14 psi. Quote Link to comment Share on other sites More sharing options...
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