Compression

[blaze12]

Did a running compression test today does this sound normal, 100 psi on startup and then hit the throttle and it drops to 50 psi on every cylinder?

 

[Calan]

http://www.dsmtuners.com/forums/articles-engine-fuel/338152-compression-leak-down-testing.html

 

[blaze12]

I've read the article and it basicaly telling me i have verry low compression on all cylinders and there all almost exactly the same , so do i have a faulty compression guage or what ?

 

[Jezza]

Did a running compression test today does this sound normal, 100 psi on startup and then hit the throttle and it drops to 50 psi on every cylinder?

Wait... Your not doing this while the car is running, are you? Remove all the plugs so the car won't start. I'd think that trying to do a compression test while running one cylinder down won't give the most accurate results.

 

[blaze12]

why would a running compression test be inaccurate just wondering?

 

[rlacasse1]

Yeah, you need to do that again without the car running.

 

[Jezza]

why would a running compression test be inaccurate just wondering?

Cranking compression is usually about double of idling compression.

 

[blaze12]

Ok ,so dont i have to pull the fuel pump fuse and ignition fuse?

 

[Jezza]

Ok ,so dont i have to pull the fuel pump fuse and ignition fuse?

Pulling those fuses is the best way to do it. That way you don't have to worry about killing your ignition module (very small chance any ways) and wont end up with gas in the oil.

You can do a comp test without removing the fuses if you want though. If you don't crank the car for 20 seconds a cylinder, you should be fine. You should crank it typically for no more than 10 sec. per cylinder.

 

[Calan]

Ok ,so dont i have to pull the fuel pump fuse and ignition fuse?

From that article up there that you read:

2. Pull the MPI fuse on the positive terminal of the battery. This keeps your injectors from spraying fuel during the test.

3. Unplug the coil connector on the back/right side of the block.

 

[Tyeler18]

Cranking compression is usually about double of idling compression.

what?

Yes pull the fuses, you really only need to pull the fuel pump fuse since all your plug wires should be disconnected. Just make sure to move them somewhere they won't jump spark.

 

[GsXdSmKingGsX]

Cranking compression is usually about double of idling compression.

Whaaa?? I would love for you to attempt to explain this to me.