Low Compression Before SC Install
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From: Ann Arbor/Hell, MI
Low Compression Before SC Install
I ran a compression test last night on my 86.5 manual trans car. I ran the car on the driveway at idle until it was on stat control and pulled it back into the garage (had not been run since November). Removed the intake to get easy access to the plugs, removed all the plugs, both coil wires, and the fuel pump relay (took about 30 min). Had my son crank the engine and hold the throttle wide open while I took readings. I got a fairly good grouping of 139 +/- 6psi on all the cylinders except #7, which came in at 100psi. I checked it a couple times to make sure the gauge seal was fully seated. This may be one of the reasons that I only pulled 240rwhp on the dyno.
The battery was fully charged before the test and I didnt put any additional oil in the cylinders during the test. The car only has 50k miles on it so this is worrying me. Let me know what you think/additional checks before I tear it down further to install my SC.
The battery was fully charged before the test and I didnt put any additional oil in the cylinders during the test. The car only has 50k miles on it so this is worrying me. Let me know what you think/additional checks before I tear it down further to install my SC.
Captain Obvious
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From: Cambridge, Ontario, Canada
Hmm, 100psi is a little low. You should try pouring s little auto trans fluid in that cyl. And see if the pressure rises. If it does, the compression rings are worn but it doesnt then it would be an indication that the head is the problem (burnt valve, cracked head, etc.).
What type of gage are you using, the screw in or the press on type? Test it a few more times, just to make sure the low reading is not equipment/procedure related. At 50K that engine should be as good as new.
What type of gage are you using, the screw in or the press on type? Test it a few more times, just to make sure the low reading is not equipment/procedure related. At 50K that engine should be as good as new.
928 Collector
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Imo, truly you are one of the nicest people I have ever talked to. Despite the fact that I unjustly kicked your rear when I didn't know you a long time ago, you were gracious. That, and you used to have a Ferrari in your avatar 
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You have problems. Hopefully one of the pros will chime in on why your numbers might be so low on a 50k car. I wouldn't SC it till you have this figured out. 
Originally Posted by Sharks
I ran a compression test last night on my 86.5 manual trans car. I ran the car on the driveway at idle until it was on stat control and pulled it back into the garage (had not been run since November). Removed the intake to get easy access to the plugs, removed all the plugs, both coil wires, and the fuel pump relay (took about 30 min). Had my son crank the engine and hold the throttle wide open while I took readings. I got a fairly good grouping of 139 +/- 6psi on all the cylinders except #7, which came in at 100psi. I checked it a couple times to make sure the gauge seal was fully seated. This may be one of the reasons that I only pulled 240rwhp on the dyno.
The battery was fully charged before the test and I didnt put any additional oil in the cylinders during the test. The car only has 50k miles on it so this is worrying me. Let me know what you think/additional checks before I tear it down further to install my SC.
The battery was fully charged before the test and I didnt put any additional oil in the cylinders during the test. The car only has 50k miles on it so this is worrying me. Let me know what you think/additional checks before I tear it down further to install my SC.
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Burning Brakes
Joined: Jul 2003
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From: IL
Your only 4hp off on your dyno from where you should be with a stock 86.5 manual. I think its the gauge, but the one cylinder does bother me alittle bit. Maybe you had alittle dirt caught between your o-ring and the threads on that cylinder. Dunno, but your dyno is right in there for hp. I know some say the 85-86 is very underrated.
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Joe Kucinski
Burning Brakes
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From: Suburban St. Louis in Illinois.
Hate to say it...but if the car hasn't ran since November...and you warmed it till it was "on stat control"...you probably didn't run it long enough, to get everything fully warmed and run in....before you pulled it into the garage for disassembly, and testing. I always prefer to run the engine and drive the car for 20-30 minutes before a compression test,that way the motor was run under load for abit, and like these guys have said...there is significant variation in the quality of the compression testers available at the local AutoZone, vs a professional mechanics tool for this purpose. I always oil to the sealing oring at the seating flange of the compression tester, or coat lightly with vaseline... to prevent the oring from binding or sticking while tightening the threaded schraeder valve fitting into the spark plug hole, this assures a proper seating and sealing of the oring to the the spark plug threaded bore.Also...dumb question...but you did have someone hold the throttle fully open while cranking...right ??? if not...that would explain the very low numbers you got..
if not...that would explain the very low numbers you got..
Nordschleife Master
Joined: Jul 2003
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From: Minneapolis
Originally Posted by Warren928
I think its the gauge, but the one cylinder does bother me alittle bit.
I'd drive it a few days and then re-check when warm. Do two or three cylinders (or all) to get a feel for if there was an overall improvement.
Three Wheelin'
Joined: Nov 2003
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From: Los Angeles, CA
#1: There's nothing wrong with 240rwhp
#2: When I did a compression test on my motor before the SC install, I had 150-160 on all cylinders except one which gave me around 100. After 20K miles of boost, I did another compression test and the numbers were pretty much the same.
#2: When I did a compression test on my motor before the SC install, I had 150-160 on all cylinders except one which gave me around 100. After 20K miles of boost, I did another compression test and the numbers were pretty much the same.
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From: Ann Arbor/Hell, MI
I will rerun the test later this week after I put some miles on it. Next few day look like snow flurries and low 30s but the roads are dry and the dirt/mud roads that we live off of are frozen.
Just got back from purchasing a new compression tester (lets see how this one compares with the one Andrew lent me).
BTW, the car pulls great, better than my automatic, but that may be gearing. No smoke and does not use oil so I am hoping that it may be something just with the test.
Mike, the reason I said that I only got 240rwhp on the dyno was that it had a chip, no smog hardware, no cats, and dual electric fans. I thought I should have got at least 250rwhp. It was running very rich though as I had the FPR cranked to make sure that the future SC would start out on the rich side.
Jeff, I actually ran the test twice on all cylinders. The first time I forgot to tell my son to go to WOT. The second time I ran it he had the peddle to the floor. I got slightly better numbers on the first test, but that may have been due to the lube on the cylinder walls. Cylinder #7 was around 100 psi for both tests.
I did a search on compression test and someone mentioned a wet test.
How much oil do you put into each cylinder to run that?
Just got back from purchasing a new compression tester (lets see how this one compares with the one Andrew lent me).
BTW, the car pulls great, better than my automatic, but that may be gearing. No smoke and does not use oil so I am hoping that it may be something just with the test.
Mike, the reason I said that I only got 240rwhp on the dyno was that it had a chip, no smog hardware, no cats, and dual electric fans. I thought I should have got at least 250rwhp. It was running very rich though as I had the FPR cranked to make sure that the future SC would start out on the rich side.
Jeff, I actually ran the test twice on all cylinders. The first time I forgot to tell my son to go to WOT. The second time I ran it he had the peddle to the floor. I got slightly better numbers on the first test, but that may have been due to the lube on the cylinder walls. Cylinder #7 was around 100 psi for both tests.
I did a search on compression test and someone mentioned a wet test.
How much oil do you put into each cylinder to run that?
