Hey guys (and gals).

I have a 98 TJ 4.0 5 spd with some engine problems.


Background: (skip if you want, the pushrod problem and questions are below)
As I was driving down I-95 last Friday the engine went from "runnin' just fine" to "runs like S#$%^!" in about a blink of an eye (seriously). Symptoms were a REALLY rough idle and NO horsepower or torque. I had absolutely no warning that anything was going to happen (noises, "feel" of the engine, etc.) I couldn't find anything on the side of the road so I limped it two miles down the road on the shoulder to the exit and a couple miles more to the nearest AutoZone for an OBD-II scan. The scan came up with just one code, P0301, indicating a cylinder #1 misfire. So I did all the usual stuff like replace cap & rotor, plug and wires all to no avail (not ignition system). The #1 plug WAS very black though with carbon build-up.

The Real Issue:
So I then run a compression test when I get back home and find that cylinders 2-6 are in great shape (all 150-155 psi) but I have ZERO compression in #1 - obviously not a good thing. After pulling the valve cover and the rockers off of #1, I quickly noticed that the pushrod for the #1 exhaust valve is bent all to hell and scored where it passes through the head (likely from the bend). I reckon that the bent pushrod is just a symptom of the real problem, which I assume is either a lifter or a valve problem. Everything else, including the #1 intake pushrod and both valve springs appear perfectly normal.

I swapped the pushrods from # 2 to #1 and there was still ZERO compression. I didn't place much hope in doing that, but I figured I might as well try it. I'm going to pull the valve spring so I can check it and the valve stem. Also, I did verify that the piston is moving, but I’m sure that if it were a piston rod I would have noticed much bigger problems.

At this point I think it has to be either a burnt or bent valve. I really don’t want to pull the head, but it looks like that’s all that’s left. Am I missing anything here?

Questions:

1. How much damage did I do driving it ~200 miles in this condition? I never went over 55 mph but I was out of town with my wife and 2 yo daughter and had to get home.

2. What are the pitfalls that I should be carefull to avoid when pulling & replacing the head?

3. Should I take the head to an automotive machine shop to have cleaned up or anything?

4. Anything else I should do while it's all apart?

This is my virginal voyage into working with internal engine parts so please be relatively gentle. :flipoff2:

There are pictures of the bent pushrod and the valvetrain on my Webshots page at http://community.webshots.com/user/floridatj1


Any help would be GREATLY appreciated!

Jason

I've seen bent pushrods in 4.0Ls before.
hopefully, you didn't damage the lifter in the process.
amc straight 6's require you to tear the engine down to the short block to get the lifters out. a real bitch of a job.

do a visual of the lifter top and the rocker bottom, and if it looks ok, replace ALL the pushords. you'll probably find a few other that are bowed out.

if the lifter top looks damaged, tear down the engine.
get a new cam kit with lifters and an engine gasket kit. it's about a weekend job.

So a screwed up lifter could cause the loss of compression?

Yeah, the 4.0 requires teardown to get at the lifters. I guess the fact that you can get to the lifters with out a teardown would be the one redeeming factor of the 2.5.

Thanks,
Jason

Originally posted by Florida TJ
So a screwed up lifter could cause the loss of compression?

doubtful

try removing both pushrods on the #1 cylinder and check the compression. if there's still no compression i'd be willing to bet you blew a hole in the piston or broke a valve.

sounds to me like a bent valve or a shot piston. the reason i think it is a bent valve is that when a valve bends it gets stuck, then the cam pushes up on the rod and bends it. that would also explain the 0 compression.

a way to check if you have a bent/stuck valve is pull the rockers and put a straight edge across the valves, it one is lower than the others (just hair will do it) then you know you need to take the head off on replace a valve (fairly cheap to do.)

Originally posted by Chrisjeep7
sounds to me like a bent valve or a shot piston. the reason i think it is a bent valve is that when a valve bends it gets stuck, then the cam pushes up on the rod and bends it. that would also explain the 0 compression.

Makes sense.

Originally posted by Chrisjeep7
a way to check if you have a bent/stuck valve is pull the rockers and put a straight edge across the valves, it one is lower than the others (just hair will do it) then you know you need to take the head off on replace a valve (fairly cheap to do.)

THAT'S what I was looking for - a way to determine if it was the valves BEFORE I pulled the head. Of course, I'm pretty sure the head is coming off at this point anyways. Thanks for the tip. I'm heading home to check that out right now.

good luck, that is how i found my toy had a bent valve...:(

The good ole ruler test confirmed that the #1 exhaust valve is definitely not right. So it's "off with her head!" on Saturday.