MS Fowler

Greetings,
I am a newbie here. Used the "search" and looked for FAQ etc, but can't find this info.

One of the company's work trucks --(1998 Cherokee 4.0 L) has been diagnosed with a bad engine.

History-- Truck was in daily use this past summer until the gut using it was laid off. He said it wouldn't go over 40 mph on the trip to the office. It started right up, and would easily rev to 3000+ rpm. A minute later the top was 3000 rpm, and as it warmed up the revs dropped to under 2000 then it stalled out, and wouldn't restart until it cooled for an hour or so.
I had no time to do any other diagnostic on it and so it sat. We finally had some time and drove it to the "company approved" repair facility. The trip was eventful --odometer would flicker and then the gauge readings would go crazy--fuel at 1/4 tank, then E then fuel light comes on ad off, then 1/2 tank etc. Oil pressure gause varied but generally dropped the longer it ran. Down to about 10 psi at speed.
Repair shop said it took 3 hours to cool enough to start. "Engine was toast."

Options I have a few repair options--what do you think?
1) rebuild the existing engine
2) Replace with a junkyard ewngine.

JunkYard Options
1) Local Pick and Pull ( Crazy Ray's) sells engines for $200. However, they have no way to start them, and will not allow customers to start engines. I would look for a wrecked Cherokee that had clean oil and clean valve cover, and no oil in the coolant. Anytrhing else to look for to have a better chance to get a good one? I'd also plan on replacing the bottom end bearings as a matter of routine. Anything else?

2) Another Junkyard engine at $600 with short warranty that runs.

Questions:
1) How do these engines wear out? What parts become suspect at what mileages? I have heard that they are generally quite robust, but what parts would you routinely replace whenever the engine was out?

2) Any other advice/ suggestions. All help is appreciated.

About me--I am an "ole f**t" having passed 60 years. I have been turning wrenches for over 45 of those years, but with very little Jeep experience. I have restored a few cars, and rebuilt more than a few engines. I always defer to experienced opinions when I have that opportunity, and this forum provieds that opportunity for me--THANKS!

zjrog

Personally, to me it sounds like some serious electrical issues are at play. First check all grounds.

Next up, rather than look at the engine for the bad running, really sounds like a possible fuel pump issue. Not all of them fail completely.

mycherokee

I think its the cat. My sister had an issue where her car wouldnt go very fast at all and it was a clugged cat. Id replace the cat with a cheap universal.

MS Fowler

Wow! You guys are fast. Some forum ( fori?) can takes days to get a response.

One more piece of data....
While listening to the engine as the rpm dropped. If I went WOT, there was a sound like the secondaries opening up on an old 4 bbl carb--that deep wahhh sound, but the engine speed remained constant.

Abovetimberline

Do a compression check to make sure the engine is ok and check the cat.

whowey

Compression test.. leakdown test and a flow test on the Cat... I have a feeling you are going to find that your engine isn't "toast"....

98 JeepJeep

dought the motor is toast...when you say has to "cool" before it will start. does that mean turn over??? if so it sounds like your starter is heat soaking and needs replaced.. and the warmed up "shut" off issue sounds like it could be a COIL. was this engine Over heated? i would do a compression test on it before i say any thing is toast....do you know exactly what was done to the Engine for the shop to say its done? and secondly is this heep for sale? im local and would be interested?

P.S i know crazy rays JY PM me i know of a MUCH!!!! cheaper JY in VA but alot of the current 4.0 XJ'S are cash for clunkers!!!

MS Fowler

I wasn't very clear on that, was I?
The engine turns over just fine, hot or cold. It is difficult to start after it gets fully warmed up, but cranks and cranks.
The gauges did not indicate any above normal temperatures while I was driving it. The oil pressure gauge did fall to about 10 psi , at road speed, but that may have been a false indication as the fuel gauge was also giving wacky readings as I stated above.
The shop did nothing, AFAIK.
There is a fair amount of valve train noise.

It is not for sale, at this time. If the repairs get to look to be too expensive, the company may decide to sell it, but I hope to be able to get it on the road for company use.
I want to get it to my house/shop so I can have a turn at it. When that happens, I'll post my findings. I'd probably prefer to repair this engine if possible.

98 JeepJeep

well if it has alot of valve train noise than you could very well be low on oil pressure because they are hydraulic lifters but in general jeep have noisy lifters........next thing i would do is put a mechanical guage on it so i know for sure.....how many miles on this engine?

zjrog

See what the fuel pressure is, with a GAUGE. If it is low, you aren't going to have much in the way of RPMs. A fuel pump can get hot, and quit. Takes a while to cool down and it works just fin for a bit. Like others say, I doubt its the engine itself.

kswiencki

Whats the temp gauge saying during this eventful ride?
how's the coolant/oil look?
I've seen/repaired a 2000 that had a cracked head that sounded very similar... (the customer drove it till it was almost glowing.. the water pump impellers ROTTED off!)

MS Fowler

As noted before, the temperature gauge never strayed above normal. But with the other gauges fluctuating, I do not trust it too much.

4.0cherokee

I would say go with the advice that everybody else has given. I had a car and the cats were plugged and it would work ok until 3k rpms then it just wouldnt go past that. I would have to wait a long to time to even try to resart it or it wouldnt fire up. It was a 95 tbird and it had 3 cats. One off of each manifold then one at the joining of the two. Well the drivers side destroyed itself and it blew back into the one at the conntecting and It could not breath. I thought the motor was toast it woudnt run it sounded terrible, then I guy said here let me try to fix it. If it works you can pay me 80$ if it doesnt no worries you are not out any money. we cut the pipe where it connected and removed all the destroyed cat. and it started right up like it had been driven the whole day. (Disclaimer) (IT HAS THE CATS NOW SO NO BODY JUMP ON ME. WE JUST STARTED IT AND SMILED AND IT WAS FIXED WITHOUT DRIVING ANYWERE). The gauges were nore going crazy like you said in your jeep, but the cat is just held on with U bolts. Would be an easy thing to test and see.

MS Fowler

Thanks for all the responses. This is an ACTIVE board!

I need to get the Cherokee to my place before I do do anything else. I want to pull the cat and see how it runs. Maybe I'll start it before pulling the cat ans use an IR thermometer to see how hot it gets, and how quickly.
After that I will do a compression test and post my numbers.
Of course, with the snow in the local forecast, I can't say how quickly I can get it. Besides, I expect that with snow most of the members here will be outside playing in it.

zjrog

Don't forget to check the fuel pressure before spinning wrenches...