Hello folks, New issue for this jeeps life with me...

I was driving down the interstate the other day, and noticed that I was having a definitive miss. Now. I pulled the plugs, cap and rotor to check their condition,
- plugs are burning clean, maybe a little lean if anything, however the o2 was just replaced 3 weeks ago
- cap and rotor button had some build up, took a wire brush and cleaned them up to no avail
- plugs, wires are 1 yr old, give or take a month
- cap and rotor 2 yrs old
- injectors swapped with dflintstones Volvo injectors about a year ago.

Now what makes me think it's at least not a burnt valve is that when in overspool (coasting in gear, it is a 5 speed) the motor sounds absolutely normal, however at idle, and most noticeably under load, it has a clear miss, sounds almost like a diesel when that one cylinder misses.

Open to all suggestions, I'm going to replace cap rotor and plugs tomorrow just for good practice and because I want to run the good ol champions instead of these ac delcos

 

Bent pushrod, bad rocker?

Do a compression test.

 

Will do. Out of curiosity wouldn't a mechanical failure like that have some metal clanking associated with the miss?

 

You said it sounded like a diesel.....

But, a bent pushrod can become dislodged from the rocker and fall to the side. Nor real noisy...

 

Fair enough. I'll post results

 

Cruiser I love you and dislike you now haha
Cyl 1 105#
Cyl 2 140#
Cyl 3 100#
Cyl 4 30#
Cyl 5 135#
Cyl 6 120#

Cyl 4 obvious problem

 

Pull the valve cover.......

 

Ok, vc pulled, a few rods are deff bent. I suppose I should check oil pan next

 

For what?

Bent on #4?

Shine a light down in there.

 

Well, bent on 4, 3, and 6 was a little iffy. It was from mudding Bout a month ago. I'll give you more info tonight after work but I'm going to 're check compression, I'll take off the pan to make sure there isn't just a hole in the cylinder. I'm starting to think the skirt is shot

 

I'm not sure why you would want to pull the pan. Anyway the 4.0 is not an "interference" engine, (like some Honda and Subaru), where the piston can hit an open valve.

Since I have no idea (other than a valve stem or rocker seizing), I googled > https://www.google.com/search?lr=&hl...w=1173&bih=586

One thing mentioned was pre-ignition (pinging). I wonder if you had a bad wire to your knock sensor if it could cause that.

I might check and see if the bent are clogged up. The idea being if they are, the rocker was not getting oil and could have seized.

 

My knock sensor is actually broken, however the point is valid, except that still I'm only getting 30 psi in the cylinder...I'm thinking either skirts are gone, or the intake valve is seized and not allowing in air, therefore no air to compress so 30 psi is all I get

 

Compression will be low on a cylinder with closed valves.

It ain't the knock sensor.

I bet you revved the **** out of it bogging...right?

Don't be in any hurry to pull the pan.

 

When I was boggin yes. Fun day but it did suck water into the motor and cut out on me. Pulled plugs, put in wd 40, cranked her over. Changed oil, etc. But yes, it did have high revvs.are you thinking pull the head and inspect the valves or...?

 

See what others think. Hydro-Lock was mentioned besides pre-ignition. I might just change out the bent push-rods. (you role them on a flat surface to check). Agreed with Cruiser Btw, just pre-ignition was mentioned googleing, and that's what the knock sensor is there for. A stretch though. If I had sucked in water and had bent pushrods, I'd just install straight push-rods. (yes, likely the reason for low compression).

Oh, AND install a knock sensor.