I have an 84 2.5L Indy....
Due to the problems I have been having with the car and due to another problem I will go into later, we decided to get a compression tester and check the compression on all the cylinders. What we came up with was: all cylinders were doing the same, the maximum readout was between 110-120. Had a normal immediate bleed-down. After bleed-down, it was between 100-110. Is that good compression for this engine?

[This message has been edited by redraif (edited 08-28-2006).]

if you didn't have the throttle plate open then that's ok for a engine with any miles on it.
so i guess keep looking for your problem

I don't know what the factory compression was but depending on your mileage does not sound to bad. The biggest thing is how balanced the cyl. are. Since all four are close to each other that is a good thing.

It sounds like the engine's got a fair bit of wear to it, but doesnt have a serious problem like a blown head gasket.

Ideally at sea level your pressure should be around 132 psi, and assuming no blow-by. 110-120 isnt too bad at all for any worn engine.

You didn't say if it was a hot or cold test. Here's how you give the results " # 1- 120 # 2- 116 # 3- 110 #4 121. The throttle should be held open for the test, Hot, a certain amount of compression strokes for all cylinders, 5 or 6, fully charged battery. I dint know what your talking about, leak down the tester should have a schrader valve in it. When you do one cylinder release the pressure and do it again on that same cylinder.

quote Originally posted by Kekipi: You didn't say if it was a hot or cold test. Here's how you give the results " # 1- 120 # 2- 116 # 3- 110 #4 121. The throttle should be held open for the test, Hot, a certain amount of compression strokes for all cylinders, 5 or 6, fully charged battery. I dint know what your talking about, leak down the tester should have a schrader valve in it. When you do one cylinder release the pressure and do it again on that same cylinder.

It was a cold test due to the fact that we were testing for bad threads in the cylinder head at the spark plug hole. Throttle plate was not held open. Ignition was bumped long enough to get a compression reading. I didn't think I needed to list each cylinder since each one tested identically. The battery was fully charged. The compression tester had a push button on the side that released the pressure - did 4 tests on each cylinder.

This was the first time I have ever done a test like this, so could you please explain the differences in doing the test hot vs. cold and with the throttle plate open vs. not? Just for future reference. Since mine was done cold with the throttle plate closed, does this mean that I need to repeat the test to get accurate results?

i've never done a "hot" test myself.
i've always done it at room tempature.
all spark plugs removed.
throttle plate wire-tied wide open.

crank over about 5 or 6 times (that should be enough for the gauge to stop going up.)
make note of it.
and move to the next one. and repeat.

if i find one more that about 10% lower than the others then i retest it.

then repeat all cylinders with about a teaspoon of motor oil pored in the spark plug hole and recheck.
if it comes up by 20psi or so then i know the cylinder walls or rings are weak in the cylinders.

about the lowest test i've ever seen on a running engine was 85psi. and i double checked it because i didn't believe it.

120ish is just fine as long as all of them are close to that.

Ideally, you'd run this test "hot" so that you're measuring things as close to "normal" engine operating conditions
as is possible. I'm with you in that I usually run the test "cold" since I usually do this at the same time I'm fixing
other things with the car!

You want to keep the throttle open so you get consistent results. Especially with computer controlled engines,
you can't be sure things like the IAC are remaining constant during the test. With the throttle wide open, things
like the IAC moving around won't affect the results at all.

I'd agree with the previous posters that your numbers sound pretty good for an engine with a few miles on it. As
mentioned, as long as the cylinders are reasonably consistent between themselves, I wouldn't get too hung up
on the overall value.

Don't take this the wrong way but I have never seen a compression test where all the cylinders were perfectly even. The reason you test with the engine running temp. is the pistons expand and the rings seal better than on a cold engine. When you crank the cylinder plugged will have a compression sound, count those and do the same amount for every cylinder. Some people even record the first compression stroke. I Know it's a PITA but some of us would like to see the results. As well as a wet test ( I rarely do them my self) there is also the leak down test, piston held at TDC and compressed air forced into cylinder, Tool tells you how much leak down by % and where its going.

Be carefull doing a wet test on a newer car it will kill the front o2 sensor and catalytic converter! Fieros are old enough too do one on though.