Compression Test

PittSpeed Automotive
1

I’ve been tryin to contact the kid who installed my motor. Not sure of the pistons in it.

So, i’m gonna try to do a compression test. Any instructions on how to… OR should i take it to the stealership and have them do it???

I know it involves removing spark plugs, and a pressure gauge, but i gotta find directions on how to.

Any ideas?

2
  1. disconnect coil
  2. remove plug
  3. insert guage
  4. crank engine
  5. read compression
3

Compression test wont directly tell you what comp ratio you have, if that is what you are looking for.

That being said, you just pull the plugs, disconnect the coil, screw in the gauge, crank the motor with the key for several revolutions. Basically, you want to watch the guage while cranking. Just crank until the guage stops moving, or peaks out.

Check here for more info: http://www.motorage.com/motorage/article/articleDetail.jsp?id=16170

4

everything above is correct, but 2 obmissions.

1- pull out all spark plugs. if a cylinder is leaking through to another one, it can build pressure back into the cylinder your checking. w/ all plugs out, no chance of this happening. because it will leak out the adjacent plug hole.

2- do compression check w/ throttle wide open. engine is an air pump, so let it breathe in air. thats what your testing…

5
6

x3

7

Sorry…it was assumed by the following statement:

And YES, I forgot to add that the throttle must be wide open.

8

no offense meant, your stating was vague. i know that you can do a compression check.

9

None taken…Thanks.

10

For what it’s worth, I’ve seen very similar (within 5 PSI) readings from a cold to warm motor. I only mention this because everyone always seemed to stress to me how important having a warm motor is, and I don’t see it as that big of a deal.

11

warm motor, wot, all plugs pulled, disconnect FUEL!, crank till needle stops.

12

i wondered if anyone was going to mention this, or if the poor guy was going to get an eye full.

13

If the fuel system is not opened up (on an EFI motor), this should not be a problem.

14

unless you interrupt the signal that fires the injectors then yes, it will be a problem. the above only states unplugging the coil, some systems fire the injectors based on rpm signal calculations either from the ecu direclty or from some kind of a transistor pack.

15

stole the words right out of my mouth…

I did a compression test once, (i forgot to put it at wot while cranking :doh:)

16

Whatever…

As I had mentioned before, if you do not open the fuel system up on an EFI system, you should be fine. Aeroking has a Syclone with Multi Port EFI. The injectors are mounted in the intake manifold. The other end is attached to a fuel rail. If fuel is going to spray out of a “closed” system, than you have other problems. Fuel is not going to spray out of the spark plug hole. Fuel is not entered into the combustion chamber as a liquid. It is normally atomized by mixing with intake air. The injector is upstream of the intake valve.

Maybe your statement would be true on a “direct” injected vehicle, but this is not what the original question was about. It was about his Syclone.

17

^^the man has spoken^^

thanks to all

:owned:

18

no. i would say if you had gotten a mouthful of gasoline you would have been owned.

sorry people were trying to look out for you and that not everyone knows off the top of their head what type of vehicle you have… hope everything works out with your compression.

19

lol i am trying to be grateful. and i appreciate everyone’s help.

20

Maybe this picture in his sig would have helped you. You don’t even have to involve the top of your head…It’s there in plain sight. It is a 1991 GMC Syclone (pretty much the fastest production pickup ever built).

No problem…Anytime