Compression test numbers

Chipdog · 03-02-2001, 12:03 PM

Ok I am trying to find where my extra horses have gone. I think I an missing about 40 or so. I just finnished doing a compression test and here are the numbers.

1-140
2-135
3-140
4-150

5-125
6-132
7-135
8-120

I also noticed that all of the plugs on the right side were white. Lean? While the right side seemed to be more oily. All of the plugs seemed to have oil on the threads.

------------------
92 GT Convertible
K&N, Hooker Headers, H-Pipe, Flow Masters, B&M Holeshot 3k converter, 4.10s, BBK 1.5 drop, 73mm Vortech Mass air, 65 FMS TB, B&M Super Cooler trans cooler, FMS Aluminum radiator

And a Small Blow Job

Rick 91GT · 03-02-2001, 03:52 PM

Did you put a tsp of oil in each cylinder turn the motor over and the re-run the test? That will tell you if it is your rings or heads. I think 120 is a little low but it is with in range, 130-150 is more optimum.

I just did mine I had

180
185
180
175

180
110
170
100

I was really happy with my results except for those two low readings. After I did the test and re-ran it with oil it didn't change, so I know my rings were OK. I pulled the heads off and found I had bad valve seals and guides. Cylinder #8 which read 100 the valve seal was gone and a piece of it was stuck in my drain hole in the back of the head. The seal from #6 was stuck up out of it's seat in the retainer. Holley is sending me new ones no questions asked....they have had a rash of problems a rise with bad valve guides and seals.

If your compression goes up after adding the oil it is the rings, if it doesn't change then it is in the heads.
Hope this helps

------------------
My Ride Check Out My Site 91GT, Holley SysteMAX II Kit-Heads 2.02" x 1.60",Full MAC exhaust 1-5/8" Long tubes, 2-1/2" O.R H-Pipe, 2 1/2" cat back, 12" K&N Filter, RNH PERFORMANCE Ram Air, Ron Davis Radiator, Full Suspension,3:73's, Welds, Best on new motor-12.60 @ 108, no traction 1.98

[This message has been edited by Rick 91GT (edited 03-02-2001).]

FivepointOH · 03-02-2001, 06:26 PM

How exactly do you run an compression test?

------------------
92 AOD GT, K&N, ram air, pulleys, 2 ch. flowmasters, 4:10's, shift kit, 1 5/8 mac longtubes and offroad hpipe 14.249 @ 97.34 mph before the headers and hpipe

Capri306 · 03-02-2001, 08:18 PM

With a warm (not hot) engine, pull all of your plugs, disable the fuel pump (inertia switch) and the ignition system (DO NOT just pull the coil wire, disconnect the plug going into the coil!). Then you screw the end of the gauge's hose into a cylinder, hold the throttle open about ¼ of the way, crank for about 4-5 seconds, then see what the gauge says. Repeat for all cylinders. Oh, here's my numbers I got today:

172-172-174-172-172-176-172-172

Not too shabby for an all-stock engine with 110,000 miles, eh?

Chipdog: it seems you have a vacuum leak, and it sounds like it's in your PCV system. Let's keep the possibility of bad injectors on the back burner for now. Replace the PCV valve & screen under it, check that and ALL other vacuum hoses for leaks, and pray for the best. BTW, what oil pressure do you have at idle and cruising? What grade of oil are you using?

As to your low compression numbers, do as directed above and try pouring 1-2tbsp of oil into the cylinders to see if compression is raised. Good luck.

------------------
Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch

[This message has been edited by Capri306 (edited 03-02-2001).]

03-02-2001, 12:03 PM	#1
Chipdog Registered Member Join Date: Apr 1999 Location: Miami,Fl USA Posts: 297	Compression test numbers Ok I am trying to find where my extra horses have gone. I think I an missing about 40 or so. I just finnished doing a compression test and here are the numbers. 1-140 2-135 3-140 4-150 5-125 6-132 7-135 8-120 I also noticed that all of the plugs on the right side were white. Lean? While the right side seemed to be more oily. All of the plugs seemed to have oil on the threads. ------------------ 92 GT Convertible K&N, Hooker Headers, H-Pipe, Flow Masters, B&M Holeshot 3k converter, 4.10s, BBK 1.5 drop, 73mm Vortech Mass air, 65 FMS TB, B&M Super Cooler trans cooler, FMS Aluminum radiator And a Small Blow Job

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03-02-2001, 03:52 PM	#2
Rick 91GT Procharged! Join Date: May 1999 Location: Hanover, PA Posts: 1,539	Did you put a tsp of oil in each cylinder turn the motor over and the re-run the test? That will tell you if it is your rings or heads. I think 120 is a little low but it is with in range, 130-150 is more optimum. I just did mine I had 180 185 180 175 180 110 170 100 I was really happy with my results except for those two low readings. After I did the test and re-ran it with oil it didn't change, so I know my rings were OK. I pulled the heads off and found I had bad valve seals and guides. Cylinder #8 which read 100 the valve seal was gone and a piece of it was stuck in my drain hole in the back of the head. The seal from #6 was stuck up out of it's seat in the retainer. Holley is sending me new ones no questions asked....they have had a rash of problems a rise with bad valve guides and seals. If your compression goes up after adding the oil it is the rings, if it doesn't change then it is in the heads. Hope this helps ------------------ My Ride Check Out My Site 91GT, Holley SysteMAX II Kit-Heads 2.02" x 1.60",Full MAC exhaust 1-5/8" Long tubes, 2-1/2" O.R H-Pipe, 2 1/2" cat back, 12" K&N Filter, RNH PERFORMANCE Ram Air, Ron Davis Radiator, Full Suspension,3:73's, Welds, Best on new motor-12.60 @ 108, no traction 1.98 [This message has been edited by Rick 91GT (edited 03-02-2001).]

03-02-2001, 06:26 PM	#3
FivepointOH Registered Member Join Date: Jan 1999 Location: Sugar Land, Tx USA Posts: 478	How exactly do you run an compression test? ------------------ 92 AOD GT, K&N, ram air, pulleys, 2 ch. flowmasters, 4:10's, shift kit, 1 5/8 mac longtubes and offroad hpipe 14.249 @ 97.34 mph before the headers and hpipe

03-02-2001, 08:18 PM	#4
Capri306 Moderator Join Date: Sep 1998 Location: Grand Rapids, Michigan, USA Posts: 1,001	With a warm (not hot) engine, pull all of your plugs, disable the fuel pump (inertia switch) and the ignition system (DO NOT just pull the coil wire, disconnect the plug going into the coil!). Then you screw the end of the gauge's hose into a cylinder, hold the throttle open about ¼ of the way, crank for about 4-5 seconds, then see what the gauge says. Repeat for all cylinders. Oh, here's my numbers I got today: 172-172-174-172-172-176-172-172 Not too shabby for an all-stock engine with 110,000 miles, eh? Chipdog: it seems you have a vacuum leak, and it sounds like it's in your PCV system. Let's keep the possibility of bad injectors on the back burner for now. Replace the PCV valve & screen under it, check that and ALL other vacuum hoses for leaks, and pray for the best. BTW, what oil pressure do you have at idle and cruising? What grade of oil are you using? As to your low compression numbers, do as directed above and try pouring 1-2tbsp of oil into the cylinders to see if compression is raised. Good luck. ------------------ Capri306, Moderator, The Mustang Works Online 1979 Mercury Capri, 5.0L -- C4 -- 2.73 1987 Mustang LX Notch [This message has been edited by Capri306 (edited 03-02-2001).]