NA_VersionFC3S

I did a search but could not find the answer.

I have asked around and gotten a few different answers.

QUESTION: How do you do a compression test on our cars. Can you use a regular compression tester that you would use on a piston engine or no. I have heard both yes and no. I don't want to have to go to a dealer.

Thanks. Tim

TonyTurboII

Yes you can use a regual compression tester, but you need to hold the schrader valve open while doing it. Youll also need to remove the EGI fuse in the engine bay.

Then, when ready, hold the throttle fully open, making sure the motor is warned up. Your looking for 3 even bounces, atleast 90+ psi. Use the Trailing spark plug holes.

Itll also be next to impossible if no one is helping you.

Project84

yeah, have someone crank the engine while you watch the gauge. If it bounces too fast, you can video tape it and watch it in slow-mo.

1 low reading and 2 high readings =bad side seals

2 low readins and 1 high reading= bad apex seal

you will get three readings since there are 3 sides to a rotor. The reason you hold the valve open is cause on a piston engine, you do one piston at a time, and the check valve will not let the air escape so the gauge will hold a reading. You want the air to escape so the gauge can reset and read the next side of the rotor.

NA_VersionFC3S

2 questions.

1) What is the schrader valve?

2) Do I test the trailing spark plug holes 1 at a time?

Thanks. Tim

Black13B

iTrader: (1)

whats with people suggesting the trailling plug holes?

personally i would use the lead holes.. the trailling holes are closed up about 75% tapered at the housing as where the lead holes are almost totaly untapered..

Fingers

I'd imagine its a safeguard just in case the compression tester has a really long probe. You wouldnt want it taking out the apex seals

THe trailing one is alot longer, IIRC

Dan H

Make sure the batteries are fairly fresh for full cranking power.

Black13B

iTrader: (1)

ahh i see

yeah depends on the tester.. if you do the ghetto style test, definately use the lead holes

Digi7ech

iTrader: (1)

the schrader valve is the air release button. You know like on a bicyle? That valve is called schrader.(Presta owns joo!,lol)

Just hold it while doing the test so it will release the pressure instead of holding it.

Project84

Its not a schrader valve, its a check valve. Schrader is a company that makes valves, just like N.O.S. is a company that produces the equipment to use nitrous oxide (chemical designator N2O) on vehicles.

NA_VersionFC3S

Does someone have a pic of the schrader/check valve or can someone point it out to me in a picture.

And also again, do i test the trailing holes 1 at a time?

Thanks.

Project84

If you got a basic compression testor, its the only valve on there. If you go to check compression, and the gauge still shows a reading after you stop cranking the motor, then the valve is holding in the air. Open it, then do the test again.

Each rotor housing has 2 spark plugs. Remove 1 plug and put the tester in that hole. leave the other plugged in. Either one, leading or trailing. The tester shouldn't thread in any further than a spark plug does, but if it does, use the trailing plug hole (upper of the 2 spark plugs). Other than that, use either one you want. Hell, do it once in each hole and see if one reads different. Make sure you pull the EGI relay from the fuse box under the hood so it doesn't inject gas, and you'll want to disable the spark too.

NA_VersionFC3S

Thanks a lot, got both my questions answered.

Tim