North American Turbocoupe Organization



Compression testing time I think...
ianbfromct Offline
Senior Member
#1
Yesterday my car was running like it was missing a cylinder and had much less power. I was running 87 and had the boost up around 16 psi didn't hear detonation but that does mean it was happening. I had a recent tune up done when I bought the car a few weeks ago but I went out and bought new wires and plugs anyways, I haven't put them in yet. The car has high miles around 170k and might be on the stock head gasket for all I know. I figured I might as well check the compression before I jump to conclusions. So what should I be looking for with the compression is it 140 psi?

Also is there a way to tell the difference between a blown head gasket and a major engine failure IE-rings, hole in the piston..
88 5 speed TC
-3" DP,lowered, 255 Walbro, Gillis valve, Cobra R's, bondo/rust, Stinger's PIMP Ecu
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ianbfromct Offline
Senior Member
#2
Oh yeah if it is a head gasket do you re use the bolts or get new ones? And which head gasket should I be using for a stock head/bore?
88 5 speed TC
-3" DP,lowered, 255 Walbro, Gillis valve, Cobra R's, bondo/rust, Stinger's PIMP Ecu
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Jeff K Offline
Administrator
#3
140 PSI is fairly typical with the stock cam, but more important is variation between cylinders. All should be within 10% at the maximum.

Bolts: The stock 12 point bolts can be reused. The new 6 point bolts (either Ford or aftermarket)are TTA (torque to angle) and should only be used once.

Post up your compression numbers when you get them and we can go from there as far as what is wrong. After the initial compression test, put a little oil in each cyl and rerun the test. Report back with both sets of numbers.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
11 Crown Vic Interceptor
14 Toyota Camry (wifes car)
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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ianbfromct Offline
Senior Member
#4
Thanks for the reply..

Do I need to leave my throttle body open the whole time?

Do I need to leave the spark plugs in on the cylinders im not testing at the time?

How are you dropping in the oil just a regular old funnel?

I know you are supposed to do this on a warm engine but I already pulled the TMIC and the plugs and by the time I get home its gonna be late. Not to mention getting it run long enough to warm up might be a pain. Will doing this on a cold motor really screw things up??

thanks again
88 5 speed TC
-3" DP,lowered, 255 Walbro, Gillis valve, Cobra R's, bondo/rust, Stinger's PIMP Ecu
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Pete D Offline
Posting Freak
#5
See this for testing procedure: http://turbotbird.com/techinfo/Compressi...n_Test.htm
Pete Dunham
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ianbfromct Offline
Senior Member
#6
Pete D Wrote:See this for testing procedure: http://turbotbird.com/techinfo/Compressi...n_Test.htm

Appreciate it..ill let u guys know what happens tonight!
88 5 speed TC
-3" DP,lowered, 255 Walbro, Gillis valve, Cobra R's, bondo/rust, Stinger's PIMP Ecu
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ianbfromct Offline
Senior Member
#7
Does anyone pull the fuel pump fuse before doing this so your not tossing a bunch of fuel in the cylinder or is it not enough to cause a issue?

If so which fuse is it to kill the Fuel Pump?
88 5 speed TC
-3" DP,lowered, 255 Walbro, Gillis valve, Cobra R's, bondo/rust, Stinger's PIMP Ecu
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Stang8u Offline
Senior Member
#8
If you hold the pedal to the floor the pump will not prime
:mad:
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ianbfromct Offline
Senior Member
#9
So here's what I got 1st without oil and 2nd with.

Piston/psi
1= 50
2=60
3=130
4=150

With oil added
1=60
2=70
3=150
4=190

What do u guys think.. I obviously have a problem
88 5 speed TC
-3" DP,lowered, 255 Walbro, Gillis valve, Cobra R's, bondo/rust, Stinger's PIMP Ecu
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Tbird-fanatic Offline
Senior Member
#10
With the compression being low on 1 and 2 and not changing a whole lot with oil Im thinking you have a blown headgasket between them. Looks like its time for you to pull the head. Either that or if you can introduce air into one of the 2 cylinders and have the plug pulled on the other you can see if the air is leaking into the other one.
1988 Tbird TC - in pieces - barn find - mods beginning while restoring
2000 F250SD XLT CCSB 7.3 Powerstoke - Daily Driver - AFE intake, Swamps tunes, straight piped
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