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Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
Yes. Leak down test is very important. If the leak down comes back good, there will be no reason to pull the head. If it comes back bad, it will point you in the direction of it either being valve or ring related.
I already know there isn't compression in one of the cylinders. I could tell that as I was turning the engine over by hand. I just don't 100% know which one it is, or why it doesn't have compression. I'm 90% sure it's #6, with all other cylinders I could feel and hear the compression stroke, with that one I just heard a whoosh with no resistance. Edit: and I could hear the whoosh coming out the intake.
The leak down would tell you by sound if the leak is in the exhaust valve, heard at the tail pipe, the intake valve, or the rings heard through the oil filler. But that is when the leak down is done during the diagnostic tree before things come apart. If you are sure you heard it from the intake and not from the open oil drain back holes with the cover off, then you would be looking at head. If it was coming out the drain back holes you would be looking at rings.
Now that we know this, was there something in driving from before the problem that would shed light on what happened and how? Like the time a friend drove a pro swapped engine where the distributor was never set up and didn't know the severe pinging was a problem until a rod came through the side of the block. Was there work done, or bad gas bought, or was it struck by lightning shortly before it started acting weird?
I already know there isn't compression in one of the cylinders. I could tell that as I was turning the engine over by hand. I just don't 100% know which one it is, or why it doesn't have compression. I'm 90% sure it's #6, with all other cylinders I could feel and hear the compression stroke, with that one I just heard a whoosh with no resistance. Edit: and I could hear the whoosh coming out the intake.
Yeah, woulda loved to see the compression numbers but I guess it's water under the bridge now.
As discussed in the other thread, do the compression check.
I don't think a (completely) stuck open exhaust valve would limit RPMs, but a malfunctioning intake, or adjacent cylinder head gasket failure might. Listen at all leak points (throttle body, tailpipe or exhaust manifold, oil filler, bubbly radiator) for clues.
I already know there isn't compression in one of the cylinders.
Yeah but is it only one? Two? All 6? Zero compression? Or low compression?
Still time to check compression but if the head's now off and you don't find anything then you need to consider timing chain issues, like it jumped (Yes it can, if you break a tooth or 2!).
Yeah but is it only one? Two? All 6? Zero compression?Or low compression?
A brief anecdote:
Recently did a Honda 2.4L engine. Suddenly became incredibly hard to start but ran reasonably well when it did. Compression -0- across the board. Pulled timing cover chain obviously jumped. Pulled head and the 4 high lift intakes bent (although bent valves not a concern in an XJ 4.0).
In your new video you said the head was being "resurfaced". How much material are they removing? At any rate be sure to check the lifter preload after reassembly.
So what was the actual cause? Bad lifter, bad valve, rounded cam, cam timing, bad piston or rings? Just getting the head checked out and slapped back on, you still might not have fixed the actual problem.
I probably won't be fixing the original problem, but I talked to the shop Wednesday, (they finally got it looked at). and they said that the head is straight and didn't need machining for that, but that a couple of the valves were leaking, so they are doing a valve job on it, which is actually probably done, but I ordered new valve seals, and was sent the wrong ones, so had to order a different set. Once I get those, I'll be handing those over, and they'll finish it up.
and what do you mean "what's up with that" dave? are you talking about the clogged cooling ports? it had a head gasket leak and the PO put a head gasket sealer in there, and all the ports were clogged up. I've done my best to clean it out on the block (the shop is doing the head of course), and I'll be running some radiator flush through it when all is said and done. Hoping to not have to replace the radiator, but I probably will.
Leaking bad enough to cause your problem? Since you have the head off, why not pull the lifters out and see what the tops of the cam lobes look like? If the cam is rounded off, you got bigger problems to fix.
I cannot say. Bad enough that the PO stuffed it full of that stop leak crap. Cam looks good, Lifters look fine with no wear on them. and the push rods don't seem bent. Though I have new lifters and push rods to go in, just because.
Thanks for all the suggestions. So far my new valve stem seals haven't shown up yet, so I don't have the head back. they should be here monday I think? so maybe middle of next weeks i'll be able to start reassembly? I think I have all the parts now just waiting except that.
03-17-2021, 08:55 PM
