Hi Everyone,

I recently performed a compression test on my evo 8. The results were
180, 175, 150, 180 (left to right). I have had some people tell me only 9-10% variation between cylinders is acceptable- then some others say 20-25psi variation isnt too bad and i shouldnt worry

Wanted some opinions as to what you guys think. Rebuild soon?

I do have a spare motor on the side i plan to start building as well but probably wont be completed until around june or july.

Thanks!!

 

150 is pretty low if all the others are nearly identical. leakdown test will help pinpoint what's leaking (rings, valves, etc)

 

Agreed. It's not terrible but that 3rd cylinder will most likely get worse over time. A leakdown test is the way to go here.

 

Yeah i figured it will get worse, i dont drive too hard but i get a few urges once in a while.
Also, i did add a cap full of oil into cyl 3 and it jumped to 180psi. Is there still a chance it could be the valves or does that basically point towards bad rings?

Thanks for the reply guys!

 

Improving compression with oil points to rings.


Did you do the test hot or cold?

 

I drove 1.5hrs to my friends shop but car was parked outside in 20degree temp for about 30mins before it was brought it. I do believe it was stil hot.

Might be a dumb question but from your experience how long would you imagine the car could drive safely before seriously needing to fix the cyl #3 compression issue? My friend had said to do it asap since it can cause issues and he is a very reputable mechanic in the area...but i would like others opinions.

My car also hesitates when starting when hot. Cold starts are fine, just hot starts are shakey for the first few seconds then catches back up to 900-1k rpms. Hits completely lean on idle and shakes then goes back to normal. Seemed bizarre to me. Could this be related to the low compression in that one cyl?

Thank you.

 

E85 or pump gas?

 

93 pump

 

Sounds like a issue with the tune. You may need more latency with the injectors. But it could be a host of other things with the tune.

I wouldn't worry too much.

 

I really appreciate the help!

 

I'm on E85 and it takes centuries for my car to start. It usually dies 3-4 times before I can get it going. You and I may both need more fuel upon ignition

 

Yeah it seems like that is the issue, I was avoiding a tune right now with the one cyl that has low comp. Will probably wait for a tune when the replacement motor is complete.

I was stressed thinking i was the only one dealing with this start up issue. Haha.

 

One worry would be a bad injector in the low cylinder and that cylinder running lean and knocking.

 

Would that also cause that random rough idle? And how do I test for that?

Thanks

 

I do not have pics of the spark plugs but all of them looked normal. Cylinder #3's plug wasnt any different from the others.