EEVEE

Ok so since i did my tune up i decided to do a compression test as well. Anyways every cylinder was either 154 to 156 except cylinder 3 that one scored 124 psi.... Is this any cause for concern? Would it make it idle rough or kill gas mileage? Purrs like a kitten when its running with a very very slight miss but barely noticeable until you actually pay attention to it. But what would cause this for one cylinder?

'90Cherokee

Didi you test more than once to verify?

Bugout4x4

If it's a 99 and it is the original gasket this would be the first sign that you are getting a bad head gasket. I would try to get this done as soon as possible before it fails and gets hot to cause more damage... Here's the order...

First the seal between number 3 and number 4 start to leak compression to each other, not coolant yet, but compression.

Next comes the coolant exchanging cylinders and this is when you really start to have more major problems.

Then when it gets hot, number 1 blows out also and is prone to cracking. On mine it cracked through the valve seat and into the exhaust port so I had to get another head.

Please let me share something with everyone I discovered about mine that I just tore down. There is a design flaw with how the water jackets in the head, the water jackets in the block and the gasket all mate with each other. It causes the block to rust and swell in height against the gasket and head and over time ends up trying to "push" the head off.

I actually had to put a flat file on my block to reduce these rusted raised areas even though there is no "flow though" galley there. There was no way the head was going to tighten down with an even crush on the gasket and seal the cylinder seals around the bore.

I would suggest getting this changed before the issue gets worse and be sure and deal with the raised areas before you put it back. And if you need help with cleaning up these raised areas drop me a line. It's touchy and you have to be patient.

s346k

id retest to confirm. ideally you don't want more than about 10% variance between the cylinders. with that being said i've driven engines with weak cylinders for a LONG time. closely monitor fluid levels/condition as always. check compression every time you change the oil.

EEVEE

Yes its a 99 and about 8 to 10 years ago (kinda forgot) i did change the head gasket and valve cover gasket AND intake gasket (did scary stuff when starting it only to have it instantly redline) when i got it since it overheated to the point it shut off and wouldnt restart till it cooled down (yup i understand bad bad bad) but this was the previous owner he gave it to me for free and been fixing it ever since. To my knowledge the head gasket is good and it does lose coolant from what i noticed lately but i suspect thats due to the attachment to fit a hose and flush the system easier on the hose going into the heater core as i found a few drips from there. But when i got my oil change i did lose a quart of oil in 4k miles. What should i test for? like put oil in the spark plug hole and retry the test? because i did crank that specific cylinder 6 times just to make sure and stayed at that from what my grandfather said as he was looking. This is the first time i ever did a compression test on it but overall the engine seems healthy nonetheless with a little ticking once in a while from the lifters but with 205k miles cant complain lol. Sorry for the lack of info btw. I may add that the parts were brand new when i put them in along with the entire cooling system but it sat for 8 years before i finally actually put it on the road about a year ago.

Bugout4x4

Keep an eye on it... This is exactly what mine did and being experienced I watched it happen play by play. I pushed it as far as I could and then got stuck in a situation where I had no choice but to continue on to get home.

Seriously... These spots that raise themselves on the block are a problem. when it starts to use more coolant you might want to nip it in the bud and get it done.

EEVEE

Alright i will keep an eye out. If need to be might as well fix it before it gets worse just cant have it down for a long time since i cant miss work

EEVEE

may even do a leak down test to make sure as well.

Tbone289

Did you try pouring a little oil in cylinder 3 to see if compression improved? That would at least cover rings as a possible source.

Bugout4x4

^^This is a very good suggestion.

Bugout4x4

The worse it gets the longer it is going to take to fix it, example... In my case it trashed the rod bearings because the oil got too thin while it was hot so now I am into the bottom end too.