Bad exhaust valves, or more?

I have been dealing with a CEL for a few months now and thought I would post it up for the professionals.
Consistently get, p0303,p0304,p0300 on my '99 xj, 4.0, 0630 head, thing runs great, just low on power.
After chasing down literally every sensor I had a leak-down done which resulted in,
Cyl1 - 145
Cyl2 - 149
Cyl3 - 50
Cyl4 - 55
Cyl5 - 150
Cyl6 - 150
Shop said exhaust valves, they would do valve job for $1600 :wow:

My vacuum diagnosis tells me bad rings but: 1) plugs are dry as a bone, 2) no smoke out the exhaust whatsoever.
My question is this, when I pull the head to have it redone is there a way I can check if the rings in 3 and 4 are still OK?
thanks :wave:

has this jeep ever been overheated? that seems odd that both the center cylinders have low compression, and pretty close to each other.

I bought it with 89K, the PO had some aftermarket temp control on the radiator, and what appeared to be a new radiator. So I suspect it had a previous life of overheating.
That being said, I got it for cheap, it had the AX-15 (hard as hell to find around here!) and I saved it from cash for clunkers. Maybe I should have thought a little harder than I did!

has this jeep ever been overheated?

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Anyway, yes, I know what you're thinking, I may have just finished off the 'burning the valves' job that the PO had been doing.

that seems odd that both the center cylinders have low compression, and pretty close to each other.

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I agree, and I suspect one possible problem is the head gasket is blown, just between those two cylinders, which is possible even though I do NOT have oil in antifreeze, or antifreeze in oil.

Is it consuming coolant? When the head gasket on my 97 went, it leaked coolant into the cylinder... In my case, the #1 cylinder.

Sounds like you had a compression check done, not a leak down. Prob a cross blown head gasket, could do a leakdown to pin point. Heck a head gasket is cheap, a head 400 or less.

Any idea if this is the original head? If not is it possible its a valvetrain issue? Cam lobes wiped off, bent pushrods, bad lifters, etc?

I do agree that with both cyl 3 and 4 showing low compression that its more than likely the head gasket at the least.

If you pull the spark plugs out of both cyl at the same time and pump compressed air into one listen for air leaking out into the other cyl or hissing thru the exhaust/intake.

Is it consuming coolant?

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Not consuming any coolant. Besides the low power it starts, idles, runs fine.

Sounds like you had a compression check done, not a leak down.

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Both tests were done. Posted comp #s were from compression. The shop's leak-down revealed exhaust valve. They also looked in through the plug hole in cyl 3 and 4 and told me they noticed cross-hatching still on the cylinder walls.

Prob a cross blown head gasket

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I like this, would cost me the least!

Any idea if this is the original head?

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Definitely original head, based on visual inspection, #s check out, no paint on head bolts. Everything looks stock and ~ 100k wear.

If you pull the spark plugs out of both cyl at the same time and pump compressed air into one listen for air leaking out into the other cyl or hissing thru the exhaust/intake.

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I would like to try this, my question is this, is there a point during engine rotation where both cyls 3 and 4 intake AND exhaust are fully closed. If this is possible, I could rig up an adapter to push compressed air into one, and listen for it coming out the plug hole of the other.

thanks

Just do one cylinder at a time, TDC compression stroke. Use a piece of nylon tubing small enough to go into the spark plug hole. Apply air to the cylinder at TDC and listen through the tubing for escaping air into the other cylinder, down the intake, and into the exhaust manifold. Repeat for the other cylinder.

Not a big fan of "miracle in a can", but you MIGHT have a couple of carbon covered valves not sealing correctly. Rumor has it that the 4.0 engines will carbon up. You could try some MCCC or SeaFoam in the engine, but this would be a long shot.

As said, a head gasket is cheap DIY; even a new, ready-to-go head from Alabama Cylinder Head is only $400 + head gasket DIY.

Way better than $1,600.

joe_peters said:

Not a big fan of "miracle in a can", but you MIGHT have a couple of carbon covered valves not sealing correctly. Rumor has it that the 4.0 engines will carbon up. You could try some MCCC or SeaFoam in the engine, but this would be a long shot.

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You could also try ATF. I've seen some of the old timers at shops do it to a hot engine. With it running pull a small vaccum line off that feeds near the 3/4 cylinders. Suck SMALL amounts of cold ATF thru the hose. It shatters the carbon buildup off of everything it hits. I've had good luck doing this to an old 258 in an AMC Eagle wagon I had to get it to stop pinging under heavy load.

joe_peters and wheeling365,

Thanks for the advice. I failed to mention when I had the shop do the leakdown they also tried some treatment to clean the carbon, with no luck.

I just got an adapter from car quest for connecting my air compressor to the plug hole. Tomorrow I am going to pull the valve cover again, to look more closely at springs and pushrods for 3 and 4, and I figure when I take the rockers off to do this the intake/exhaust will be closed - perfect time to fill up the CC with air.

Got my fingers crossed for ONLY cross-blown HG.
(Great excuse for me to put on my new APN header while I'm in there)

thanks again for the great advice.:wave1:

To answer your question about figuring out if the rings are bad/good some oil into the suspect cylinder and retest.If the numbers are higher then rings are bad.
I tend to agree with the blown head gasket diagnosis though....

OK. Got this thing solved.

cross-blown between cyls 3 and 4. clear as day in the photo.

Bottom end looks great! No oil, crosshatching, I'm gonna bolt it back together with a new gasket.
Phew!
Thanks everyone for all the help.:cheers:

Check the head and deck for flatness.

Any paint on the headbolts--if so they have already been used twice and need to be replaced.

Don't forget to use sealer on bolt 11 where it passes through the water jacket, and it gets less torque than the others. Make sure and clean out those bolt holes too.