Sad Day A 4.0 Died today

It's sad day when a 4.0 dies. and today is no different. Cash for clunkers claimed far to many Cherokees, and most where still in there prime.

Overheated My 1992 Cherokee today. In the process some serious damage was done. :explosion It's fighting to live, after it cooled down I didn't see any signs of coolant in the oil, the Jeep did start, but bit of a clanking and rough running. later as it cooled down it would start to quiet down. Oil pressure steady at 40lbs at idle

It still ran rough, like a couple of plugs where fouled out. Plugs swapped out for fresh, and they where worn but no signs of oil fouling. still ran rough sounded like a an exhaust leak, perhaps I cracked the header.

Run the throttle up slowly to see how everything sounded, engine smoothed out, no signs of missing.

decide to take the Jeep for a quick trip around the block, by now the temp gauge was at normal operating temp. The Jeep is lacking power, and I start to hear some noise. rattling and light knocking, Limped the Jeep back home and shut her down.

If not for the noise I heard I would chalk it to a blown head gasket. after all the oil pressure is decent... The question now is how much time do I spend trying to figure out if the 4.0 can be saved? the Jeep is a 1992 with 214k on the clock. The Jeep WILL live again, perhaps with a different engine. I have regretted getting rid of my last cherokee, and I like how easy it is to work on.

If the rattle is a bearing (I wouldn't bet on this) you can figure out which by running it with each cylinder's plug removed and injector unplugged one at a time. When the rattle dies down or goes away, you have found a cylinder that was causing problems.

I just discovered that the head gasket on my '98 is blown between cylinders 3 and 4 today. Strangely it is the only 4.0 I've ever owned that I *haven't* abused in some way, and the rest are all alive and running to this day. Did a compression check and got 150 on all but 3/4, which have... 30psi compression and it comes out the other cylinder.

CAP has a decent compression gauge for around 50 bucks and a Fel-Pro head gasket for under 30. I bought both today but haven't started putting the gasket in yet.

Its not dead, it just needs some love.

When i found my Dad's old XJ it had 2 melted pistons! The owner that bought it from my wicked stepmother drove the thing 30 miles with no coolant left in it.

I thought for sure the 4.0 was dead but our local machine shop owner laughed when I dropped it off. Even with #3 and #4 pistons melted down and scared cylinder walls it was easily fixed and better than new!

I have about 1800 in a fully rebuilt 4.0, that included new pistons, polished crank, new cam, new rockers/fulcrums, bored 40 over, decked 40, milled 40, 3 angle valve job, melling oil pump and much more!

NEVER GIVE UP ON A 4.0!!

xjtrailrider said:

Its not dead, it just needs some love...


...NEVER GIVE UP ON A 4.0!!

Click to expand...

With this being My daily Driver, and now 2 dead vehicles in my driveway, time is limited. I no doubt it can be repaired, even If I turn out to not be the one doing so.

The thought process as of right now is to run a compression check and see where the issue is. Then to try and locate the source of the noise I am hearing after it warms up again.

Then I will be in better place to decide fix it, or pull it to be rebuilt as a spare and swapped in a different 4.0

If theres coolant in the cylinder it will be cleaner than the others. Also the plugs will be cleaner. Yank off the head and do an inspection. Thats the only way to know for sure. At 214k with good oil pressure its still worth fixing.
Good Luck
Ron

4.0liters dont die.. their owners give up on them..

I have a 4.0 in my jeep and when it starts to show its age i'm looking at getting the mopar 4.7 stroker. Then once I change out motors the 4.0 will be rebuilt and repurposed for an offroad crawler that will evenually be built

4.0? Dead? A 4.0 will smell a can of premium fuel in your truck bed and crawl up onto the trailer by itself once the jeep is locked in 4...

Well, just order up a new Fel-pro head gasket, and pull that head off. I'll bet you just blew the gasket between 3 & 4... Pretty common, and I have see it 4 times now.

Compression test. Half hour of your time and valuable data point.

yup. Wish I'd done the test on mine a long time ago.

The compression tester from harbor freight doesn't have a long enough threaded section to fit into a 4.0 head properly, don't bother buying it. The one that Advance Auto / CAP have is good though.

Well, its a bit more serious then a head gasket...

Compression test showed was extremly low, but I also chalked it up to a crappy compression tester. the oil was starting to get milky and I had water comming out of the #4 sparkplug hole when I pulled it.

Tonite I pulled the head, hoping to find it was nothing more then a cracked head. couple of head bolts where alot looser then I expected, between the #1 and #2. I have not checked with a straight edge yet. but I suspect I will find it warped there.

#2 piston and cylinder wall is messed up, melted part of the piston and Galled the crap out the cylinder wall.






And what looks like a crack in the #4 cylinder wall.

The head actually appears to be in good shape, I don't see any visible cracks and I check with a straight edge. and it appears to be flat. gasket was blown between the #1 & #2 and the sealing ring around #4 was gone.

If the #2 piston wasn't trashed, I would just put it back togather. Engine will be getting swapped this comming weekend.

Im not kidding when I say use some JB weld on that scuff... Iv used it in VW TDI engines with much the same damage. Try it... you will be surprised!

I lucked out and found a 4.0 with low miles. I do need to replace the header since it is cracked.

Since I could only really work on it over the weekends, I spent the down time cleaning all the electrical connections and greasing them, and replacing seals.

I also ended up replacing the intermediate shaft on the steering column. I had alot of play and a clunking. turns out it was hitting the mechanical stop in the "rag" joint in on direction due to the rubber being shot.

It was great hearing the newish engine come back to life when I hit the key.