low compression
 

My buddy has an evo 8 and we recently did a compression test on it and got 185 on all cylinders except number 2. Number 2 showed 100 psi the first time and we repeated the test 5 times and each time it showed a higher number until the last time which showed 155. My question is what can cause this to happen? Could it be a valve no closing all the way do to carbon build up? He has pretty loud lifter tick so can there be a chance that a lifter is semi collapsed and not closing the valve all the way? Idk im trying to think what it can be before pulling the head off. I figured if it was the bottom end the results wouldnt change like that. Also car runs awesome. No smoke, no misfire, and pulls pretty good. He has full bolt ons. Your opinion would be greatly appreciated guys.

Photos of sparkplugs?

185 is too high which is just as bad as too low.
The cams could be "out" or there could be oil in the cylinders.

If there are any vacuum leaks on the intake manifold then that would cause less air to go into the cylinder when you crank.

I did a compression test on an Evo and the numbers were all over the place. Then I did a boost leak test and found leaky injector seals. Replaced the injector seals and compression numbers were improved and the variance between them were minimized.

Try a boost leak test before you pull it apart.

Rightsaid Fred what do you mean by cams could be out? They’re bc cams which are ****ty but car runs fine. That’s the weird part, no signs of any damage. No smoking or misfire. It pulls hard. Did the compression test for the hell of it and look what we found. I did a boost leak test on it couple weeks ago and it was fine. Now numbers one 1, 3, and 4 were the same but 2 was the only one different. I’m going to do it again and put oil down the cylinder to see if compression changes. Then I guess it would tell us if it’s rings. I just don’t understand how I did the test on the same cylinder 5 times and each time it read higher. That tells me it’s something in the head. I’ll take pics of spark plugs for y’all.

FIrst to last cyl 1 - 4...

lol build time, yolo

The valve spring closes the valve but there could be something stuck on the seat. Take it for a short drive and test again.

Wrong thinking since lifters self adjust to keep rockers in constant contact with lobes. Rockers also keeps valves from slamming shut on head (because of valve spring pressure) by connecting them to cams at all times.

So if lifters are soft, valves will close early and could slam shut based on valve spring rate....ignore original post.

Check intake cam lobes for cylinder 2 to make sure it is making full contact with rocker arms. If it does make tight contact, try to compress HLA under those two rocker arms. If they compress, HLA is probably leaking and not holding rocker arms fully up and allowing valvesprings to not fully open. This can also be the source of your lifter ticks.

The cams weren't degreed when they were fitted.

The plugs show no signs of oil which is good but it's running too rich at low load and quite lean at high load.

But that all fits in with your previous posts.

Well, got a compression tester from autozone and all cylinders showed 153 except that one which showed 90 - 100. Poured a cup of oil and and it jumped to 120. :sigh: Will do a leak down test today. I still don’t understand how a cylinder showing this has no effect on the cars performance. No smoke, no misfire, nothing. Hopefully, leak down points to the head but what do you guys think about the cup of oil showing higher compression?

Cup? Or cap?

If a cup you now have a bent rod.

I'm sure he meant cap.

ah sorry a cap lol...

Ok so did a leakdown test and results were good. Being confused as hell we did another compression test and was now better than last time, Actually it was pretty good. Wtf is going on? We’re thinking a lifter maybe? If a lifter is not functioning correctly can it be causing mixed results like this? I know a bad ring will not change results. It’s obviously something in the head. I’m thinking replace all lifters since there’s a hella lifter tick anyway and getting better cams with springs and retainers. I’ve heard mixed reviews about gsc zero tick. Map told me to buy itm lifters which is an oem revised lifter. What do you guys think? Also thinking gsc s2 cama and get rid of the bc cams. What do you guys recommend for springs and retainers? Was thinking kiggly? But damn those sob are expensive.