This is a loaded question so go easy on me.... My 97 xj has an on and off miss for some time now. I've usually been able to correct it but this time I can't fix it.

I recently took it to mechanic and got a compression test and leak down test. They said It likely needs a valve job or new head. I got the car back home and I'm going to pull the head this weekend and take it to a machine shop this week.

Any other must do's while I've got everything off? I'm kinda unsure about the state of my rods and lifters and not sure If I should replace when I get the head in working order(assuming that is the problem)

Any further advice will be appreciated.

 

Before you jump whole hog into this, what were the compression numbers and the result of the leakdown test? Doesn't seem to me that an intermittent miss would be valves. I'd start by looking at plugs, wires, and cap/rotor, Inpsect the wiring harness from the injectors back to the firewall for damage, wiggle it and see if that affects the idle. Inspect the vac lines for any breaks, or manifold leaks. $100 will get you a set of matched, refurbished Bosch 4-hole injectors if you think they are suspect.

 

Yeah, an intermittent misfire can be just carbon buildup on valves or spark plugs. Not uncommon with this engine since it pulls crankcase vapors into the intake to be burned at a constant rate, not like a true PCV valve does. Try pouring a couple of glasses of water slowly down the throttle body while keeping the engine running at about 2500 rpm. The water will be absorbed by the carbon, boil, and flake it off. And it won't cost you anything.

 

I can't find where I wrote it down but 50 and 70 come to mind. The leakdown test said the the air was coming out of the valves(maybe I'm not saying that correctly). Anyways, I'm going for it. As long as the valve job isn't a ridiculous price, I'll give er a go. If the valve job comes back way too expensive, I'll just consider sharing a car with my wife for a while.

Thanks guys.

 

I had my Clearwater head reconditioned for my new shortblock swap last year and it cost me $300 for 2 new exhaust valves, reseat all the valves, new valve stem seals, new springs, grind valve stem heights, and a .010" head cut to true it up. Not in that particular order, just things that were done. That's when I found out the Clearwater head has inserted hardened steel valve seats.

Chances are it's the exhaust valves that are bad. This engine tends to burn exhaust valves if asked to produce lots of power with heavy throttle at low crankshaft speeds. They also will carbon up if never run over 2500 rpm either.

I would suggest not replacing the lifters because they are wear-matched to the cam now and new ones could possibly wear the cam prematurely. Inspect the pushrods for straightness and the rockers and pivots for abnormal wear. I put all new valve gear in my engine swap because....252K miles on them. They still looked good. I put new lifters on a new cam.

Make absolutely sure the lifter preload is set right. Since there is no valve lash adjustment on this engine, the lifter plungers need to be at about .040" inside the lifter body. The tolerance is .020" to .060" and is adjusted by using shims under the rocker pivots. If the shop doing the valve grinding does it right, everything should be bolt together, but check it anyway. It should be zero lash, then no more than 3/4 turn to reach 21 ftlbs. Here's a printout I made that explains how to do it;

 

Try the water trick.................

 

Got a little ahead of myself...Looks pretty nasty no? 200k Miles

 

Looks like 3 and 6 had incomplete combustion.

 

Yes, and the gasket between 3 and 4 was leaking and #2 exhaust valve is burnt. At least it looks that way.

 

dude what kind of meth was you on since when can water be compressed and burned 💀 and it’s rare they have valve problems

 

 

Dave never stated water could be compressed and burned.

He outlined EXACTLY how slowly pouring water into an engine will release the carbon.
This procedure has been used for decades very successfully since before you and your meth were born.
Check with your supplier. I think he's cutting yours with some bad ****.

 

Dangerous and shouldn’t be done there’s a reason sea foam exist

 

False. Been in use for years.

 

People also pour Seaform down the intake, and about the same rate so you don't hydro-lock anything.