Compression

Bunta · 07-25-2007

Me and my buddie did a compression test on my car a few days ago and I was just wondering what these numbers sound like to you guys

120,115,125,145 (I don't quite remember if these were the exact numbers but it was something to that matter)

**1ViciousGSX** · 07-25-2007

Looks like an engine with some miles on it, usually 4g63/64 engines are a little higher than that, assuming you have a 4g63/64 since you didn't say.

Bunta · 07-25-2007

yeah 4g63.

1990 Eagle Talon TSI AWD.
123,XXX miles on it.

**Shane@DBPerformance** · 07-25-2007

Something like 164psi is factory compression. You are probably close to the service limit on some of those cylinders.

niterydr · 07-25-2007

Cylinder with 115 worries me, 120 is also a bit low.

The varience between the cylinders is the key thing, max varience between cylinders shouldn't be more than 15psi.

I'd redue the test. Did you do it warm or cold?
Leakdown test?

Bunta · 07-25-2007

well I guess you could say I did it when it was kind of warm. I guess I'll wait till the car has been sitting for a while and the weather out there isn't so nasty.

xveganxcowboyx · 07-25-2007

You want to get it up to full operating temperature. Drive it pretty hard. Make sure the throttle is all the way open when you do the test. Redo it with a cap full of oil in each cylinder when you are done.

**Shane@DBPerformance** · 07-25-2007

If you put oil in each cylinder, it will give a false higher reading. DSMs have dished pistons with will hold that oil, which will make the combustion chamber smaller and raise the compression. His numbers aren't good, still high enough to run and everything, but a step away from being done.

Bunta · 07-25-2007

Engine rebuild? head gasket? or what should be done in this situation?

Pushit2.0 · 07-25-2007

I would do a leak down test to see where your compression is going, valve seats, rings, head gasket. Does the car run funny? why did you do a compression test?

~John

Bunta · 07-25-2007

Well I'm assuming the reason why the car wasn't running right was because it wasn't tuned and it needed a FMIC.
So I called up my buddie so we can change some spark plugs on it. Than we decided since the spark plugs were off we miles well do a compression test.
The car kind of feels like when one of your injectors go bad and your car just kind of lags for a while than later on everything starts to kick back in inconsistently. You can here the car spool and everything but the car just has the feeling where it's just not getting enough of something.
As of right now I'm going to just get the fmic put on and then get a new head gasket in there and then get it tuned. Hopefully that solves it.

xveganxcowboyx · 07-25-2007

Leave the front mount alone for now. That isn't your issue. Focus on the basics. Do the proper compression test. Check for boost leaks. Check plug wires. Change fuel filter, etc...

Pushit2.0 · 07-25-2007

The compression is not your problem, it sounds like a wiring/grounding issue.

~John

**JET** · 07-25-2007

Is it blowing coolant out? Why change a head gasket out just for the heck of it? Get the thing tuned and go from there. You can't modify a car and not tune it.

DWs97GST · 07-25-2007

First off the numbers being that low ALL the way across probably means ur tester is off a little. BUT it doesnt make a diffrence because you have to much of a diffrence between compression therefore there is a problem somewhere. I would suggest a rebuild. NOW if it kinda takes off slow and gradually get better it could be because as u go you build compression. If one of your cyl is not sparking because the compression is too low then once it build up a little from moving then you will get spark and gain that cyl back.

**JET** · 07-26-2007

You just totally pulled that out of your ass, didn't you? Physics says otherwise, not to mention how it works in the real world. Ignore the above post.

Bunta · 07-26-2007

Yeah like I said most likely I'm going to get this thing tuned and go on from there. I'll keep you guys updated. Thanks for all the input though.

**1ViciousGSX** · 07-26-2007

Do yourself a favor. Just run a real compression and leak down test. Then take it from there.

niterydr · 07-26-2007

Quote:

Originally Posted by DWs97GST

First off the numbers being that low ALL the way across probably means ur tester is off a little. BUT it doesnt make a diffrence because you have to much of a diffrence between compression therefore there is a problem somewhere. I would suggest a rebuild. NOW if it kinda takes off slow and gradually get better it could be because as u go you build compression. If one of your cyl is not sparking because the compression is too low then once it build up a little from moving then you will get spark and gain that cyl back.

Umm wrong.
Post started okay then turned into a rambling mess of useless brain spew. I'd suggest to do a bit more research before giving technical "advice".

Pushit2.0 · 07-26-2007

I would look into your flamitation valve, when they get old and stick stuff like this can happen, I would try to get the car tuned that will point you in the right direction.

~John