Compression

[87we410877]

did a compression test except for cylinder# 5. All came up about 105 psi. Is that about right? I have TRW forged pistons, cast iron heads(o-ringed), and its bored .030 over. I called andersons but Bill wasn't in at the time. Any help?

 

[EightSecV6]

did a compression test except for cylinder# 5. All came up about 105 psi. Is that about right? I have TRW forged pistons, cast iron heads(o-ringed), and its bored .030 over. I called andersons but Bill wasn't in at the time. Any help?

Why didnt you do #5? all within 10% is good. A compression test isnt a good tool unless it is a major problem, a leakdown test is more accurate for ring/valve seal.

 

[VadersV6]

Was the engine warm?
Were the injectors disabled?
Were you at wide open throttle during the cranking?
Is the gauge good? Sometimes the ball valve can be a little sticky. You can pour a few drops of oil in there.

 

[87we410877]

It was not warm, it had been sitting a month or so, it was the type of guage that you crank the motor and it displays a reading. I would like to do a Differential leak down but do not have the guages. #5 is pretty hard to get to w/ the TH 3" and i was already having one of thoes days where you feel like the car is winning. So, thanks for the input but is 105 any good?

 

[bison]

It was not warm, it had been sitting a month or so, it was the type of guage that you crank the motor and it displays a reading. I would like to do a Differential leak down but do not have the guages. #5 is pretty hard to get to w/ the TH 3" and i was already having one of thoes days where you feel like the car is winning. So, thanks for the input but is 105 any good?

You mean the #6 right?

 

[87we410877]

I was told that # 1,3,5 are on the pass. side no? if so then yes #5 if not then its # 6 i didnt do. still do not know if 105psi is good or not??????

 

[Steve V]

That's Ford's GM's are 1,3,5 on the left and 2,4,6 on the right. I would think 105 is low,but your engine is cold so maybe it's okay. I do the test with it warm.

 

[bison]

1,3,and 5 are on the(left) drivers side. 105 isnt that good. They should be around 150psi with the stock cam, compression and a good battery, testing when the engine is hot, no spark plugs installed in any of the cylinders, and fuel injector fuse removed or harness unplugged. If you tested under these conditions and came up with 105 then id consider it low. Especially if the cylinders are not within 10% of each other. A leakdown test is more accurate as stated before.

 

[VadersV6]

Front of motor.
1-----2
3-----4
5-----6

Ford V8 (front)
5-----1
6-----2
7-----3
8-----4

Did you have it at WOT, and were the injectors disabled?????
If not, you arent getting much air into the motor. You need alot of air in the cylinders to get a real pressure reading.
If the injectors are firing, you're washing oil off the walls with gas, which will increase leakage. Disable the injectors by disconnecting the big connector on the side of the ignition module. Comes off with a 1/4" socket.
If the motor hadnt been run in awhile, you practically have no oil on the walls....more leakage.
If the motor is cold, the piston to wall clearance is bigger...more leakage.
Your test was totally invalid if you didnt do it that way.
Also, given what you thought the cylinder numbers were, your firing order is probably all wrong.