Well I had a compression test done on my Evo 9 with 86k miles this past weekend and cylinders 3 and 4 were only at 100 and 70. Cylinders 1 and 2 were fine. Could this be because of the head gasket being that they are adjacent. And being that I live in Phoenix, AZ its very hot during this time of year so is it possible that I burnt up the valves by running 91 oct and driving in this 105+ degree weather as well? Thanks

 

Heat and 91 octane no, blown head gasket between cylinders is possible.

 

Did u add oil to see if compression goes up? U need to do a leak down test.

 

did you put the car on a charger when you did the test... also a leakdown would identify any issue that may exist.. a cap full of oil or two will tell you if its the rings...

 

It doesn't smoke, knock or anything like that so in that case i'm hoping its not the block.

 

agree with this

 

Check your oil for coolant

 

This does not matter in your case.. U have uneven compression with one cylinder showing very poor results, its only a matter of time before it shows its face.

 

yup leak down test time, try the 2 caps full of oil first to see if the test results raise

sounds like a blown head gasket to me, had a talon with similar results on 2 and 3 cylinders, the head decided to warp on me ( PO got it pretty hot)

got it re decked, new head gasket and fresh headstuds and great compression across the board minus a 10% loss on cylinder 4 -- lol that motor always burned just a bit of oil -- heck it ran after all the work and pulled fine under boost ,, I considered it a win

good luck


just a question for everyone ( not to thread jack or anything ) what should the evo 8/9 compression numbers be ?

 

I'd listen to the guys above.. prevention is better than cure is the saying.... so before things get too bad take the necessary steps to fully investigate and repair now

 

Really good question lol. I just know mine were no where close...

 

91oct and az heat is all you can do sometimes when you live here and aren't converted to e85. Unless you have more than one car. Just try to stay out of boost....

 

did some searching on the compression numbers at warm operating level

fresh rebuild or new motor -- 163psi
can go all the way down to 138 psi ( mitsubishi service still considers this a healthy motor )
no more then 14psi difference from cylinder to cylinder

now all of this depends where your at as well, if your well well above sea level then your numbers are gonna be different then someone at sea level

 

It will have much more to do with density altitude than pressure altitude. That's also why Mitsubishi and other manufacturers have such a wide range for "healthy".

 

Leakdown test. Find out what is the problem before you make the plan to fix it.