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I burned my exhaust valve, now what?

garagecouple

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Hi Everyone,

Finally have some peace of mind that I diagnosed the issue with the cylinder 3 misfire. Literally checked every component, every sensor, and turns out its my exhaust valve on cylinder 3. Any recommendations on how I should go about this repair? Buy a reman unit fully assembled or take mine apart and have it machined?

Thanks for your time! Appreciate all recs, wouldn't have been able to diagnose without this forum and all the amazing help!
 

Flivver250

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If you have a good local machine shop, let them take a gander. They can give you a pretty good idea of cost and outcome.
 

Chris

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You could replace the valve itself. However, that's going to involve removing the head, and since you're doing that, it would be a good time to just refresh the entire head in general (i.e. new lifters, valve job, etc.).

That being said, you could buy a fully remanufactured head which I suspect would run you around $1000 give or take. Or you could just take your head to a reputable machine shop and let them rebuild it and refresh the entire thing.

I would do one of those two options personally as oppose to just fixing that one valve and putting the head back on. Might as well refresh the entire head while you're at it!
 

Boinked

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Maybe someone who remembers what the bad head used on the 4.0l was. @Chris .

Might be worth changing the head completely. If its the good head just rebuild it.
 

Chris

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Maybe someone who remembers what the bad head used on the 4.0l was. @Chris .

Might be worth changing the head completely. If its the good head just rebuild it.

Oh yes, the 0331 or TUPY head casting found on the earlier 2000 model TJs.

More on that here:

 

Goatman

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I would either rebuild it completely or replace. All that labor for 1 valve when all the others should be in similar shape seems silly. Edelbrock has a new aluminum head for the 4.0 and I would love to see a write up on it.😉😉
 
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garagecouple

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I would either rebuild it completely or replace. All that labor for 1 valve when all the others should be in similar shape seems silly. Edelbrock has a new aluminum head for the 4.0 and I would love to see a write up on it.😉😉

So I plan on doing a complete head job. While I am at it, I will change the intake and exhaust manifold gaskets as well as the head bolts. Is there anything else I should change while I have everything torn apart on my 260k mile 4.0? Besides burning the exhaust valve, the jeep was running perfectly, not a single complaint.
 

Goatman

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I'd replace anything that moves in the head. 260,000 is awesome but valve guides, studs, all the wiggly bits have been working long enough. If you can check the cam lobes and be sure they are still all the same lift (all the intake the same, all exhaust the same) then you should be pretty ok. If you can pull and replace the cam then you could get a little bump in h.p. and torque.
 
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garagecouple

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I'd replace anything that moves in the head. 260,000 is awesome but valve guides, studs, all the wiggly bits have been working long enough. If you can check the cam lobes and be sure they are still all the same lift (all the intake the same, all exhaust the same) then you should be pretty ok. If you can pull and replace the cam then you could get a little bump in h.p. and torque.

So...Today before preparing to rip things apart I did a leak down test and got perfect results. No apparent leakdown in each cylinder. Redid compression test and all cylinders had perfect compression. At this point, I have no idea what to check next. I am going to just start throwing parts at it.

MAP sensor
O2 sensors
Fuel pump relay..
 

Goatman

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If the valve had a miracle of a rebirth and you haven't pulled the head off then I would put it back and run it until it scraps out again. May be a day, a week, 10 years.
 

oconnef

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So...Today before preparing to rip things apart I did a leak down test and got perfect results. No apparent leakdown in each cylinder. Redid compression test and all cylinders had perfect compression. At this point, I have no idea what to check next. I am going to just start throwing parts at it.

MAP sensor
O2 sensors
Fuel pump relay..

Interested to hear how you concluded it was a burnt valve? Maybe just stuck? I have an 06 TJ with 276k miles, presenting a cylinder 1 misfire for months. Finally did a compression test and saw 1 was well below all the others @ 65 vs 120psi for others. Did the "paper test" over the exhaust and it's clearly sucking in the paper, so I figure the exhaust valve is stuck open, not sure if I should bother with leak down or skip ahead to pulling the valve cover and taking a look. Car still runs, albeit poorly, so I'm in a bit of confusion on next steps...
 

freedom_in_4low

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Interested to hear how you concluded it was a burnt valve? Maybe just stuck? I have an 06 TJ with 276k miles, presenting a cylinder 1 misfire for months. Finally did a compression test and saw 1 was well below all the others @ 65 vs 120psi for others. Did the "paper test" over the exhaust and it's clearly sucking in the paper, so I figure the exhaust valve is stuck open, not sure if I should bother with leak down or skip ahead to pulling the valve cover and taking a look. Car still runs, albeit poorly, so I'm in a bit of confusion on next steps...
I don't seem to hear much about burned valves on here. I'd probably pull the cover and look for a stuck one, but a leak down test isn't hard to do, either. I think I rented the tool from the parts store.
 

jjvw

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Interested to hear how you concluded it was a burnt valve? Maybe just stuck? I have an 06 TJ with 276k miles, presenting a cylinder 1 misfire for months. Finally did a compression test and saw 1 was well below all the others @ 65 vs 120psi for others. Did the "paper test" over the exhaust and it's clearly sucking in the paper, so I figure the exhaust valve is stuck open, not sure if I should bother with leak down or skip ahead to pulling the valve cover and taking a look. Car still runs, albeit poorly, so I'm in a bit of confusion on next steps...
I don't think you'll be seeing much of garagecouple around here. 🤣
 
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roverhi

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With that many miles the engine is on borrowed time. I’d go for a total rebuild with new bearings, pistons, cylinder bore as well as head rebuild. If it’s your daily driver, a reman. Engine would be the least downtime though not as cheap if you did a DIY. Maybe time for that 4.6 stroker.
 

Apparition

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Wait, is that Yogo Pants?
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1652988481634.png
 
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