GitRDunn

I tested the compression of my 1996 Jeep Grand Cherokee 4.0 both dry and wet and here are the results (This engine has 256,000+ miles)

Cyl 1 2 3 4 5 6
Dry 160 165 155 160 140 165
Wet 160 165 160 165 135 160

It seems they are within spec but I would like suggestions

The head has had oil seepage on passenger side for years. It starts and runs fine but lacks power. Injector seals were replaced about 30,000 miles ago. Fuel pressure still @ 49 lbs. I just replaced both O2 sensors, the Cat (generic) original old one was clogged, muffler (Walker Sound FX). Those changes made a difference. I have a K&N air filter in the stock air box. It has a generic throttle body spacer. It does not have any smoke out of exhaust of any color. Rear main seal was replaced from leaking and the bearing looked new. The exhaust manifold has been cracked for years. I have a new APN header to replace it and a 99+ intake to install as well. I got these parts in anticipation of replacing the head gasket for the oil seepage. MPG is about 13-15 in city and get be close to 20 on HWY only. But has been progressively dropping. Has all new tune up, Crank position sensor and cam sensor have been replaced. Oil changed every 3,000 with Lucas oil additive and once in a while Motorkote. I usually add one extra quart due to the oil seepage of the head. Oil pump has been changed and stays between 40-50 on hwy. I replaced the timing chain (with 1/2" slop) about 30,000 miles ago along with radiator, water pump, hoses and added a transmission cooler. Replaced output seal on Trans and input seal of 242 transfer case. Plus a slew of front end parts including u joints on the front axles and hub bearings.

My question is with the compression test what should I expect when I remove the head? I ran seafoam thru a couple of times in the past but still has carbon by the test results. Should I expect to have to a valve job done?

My goal is to maintain the vehicle and help MPG.

kjc

With that many miles, you can bet that your valve guides are worn. If the head's coming off, it'd be a good idea to have it rebuilt (new guides, valve grind and re-surface it) My '93 only had 150K miles on it when I had my head rebuilt. It made a noticeable improvement in power. My compression numbers were similar to yours, except for one cylinder, due to a blown head gasket. With all the 'love' you been puttin' in it, you'll really appreciate puttin' a "like new" head on it. ;-)

GitRDunn

Thanks for the advice. I will look into re-doing the head. With the compression test results should I worry about my rings?

kjc

Worry about them? You know they're pretty worn after 200K+
With the head off, you should be able to inspect the bores for scratches or unusual wear that might indicate a broken ring but I don't think that's very common. (who knows?) New rings would of course improve compression/performance, but if you're going that deep into it, you might consider a complete rebuild. All that new compression would stress those old rod and crank bearings. I guess it just depends how much work you want to do to it. I didn't replace rings when I had my head rebuilt.. looking back, I wish I would have, but I just didn't want to invest the time and dough at the time. (this old '93 has lived in the 'salt belt' for 20+ years so the rust is pretty severe) I'm pretty sure the engine will outlast the body/frame. Let us know what you decide.

GitRDunn

Thanks for the information. If I had the money I would rebuild it. I have other cars with issues including a 1996 Buick Roadmaster Collectors Edition that the LT1 blew up the rear end with 170K on it I still have to fix after being down for 6-7 months. So I will save up money to get the head redone at the local machine shop. About $300 with 3 angle valve job, shave, magna flux, new valve seals, etc. Plan on getting a Felpro gasket kit from rockauto along with new head bolt kit. The head gasket was changed at least once by previous owner so I don't want to take chances on the head bolts. With the head redone, APN Header, 99+ Intake and new cat and muffler hoping to make a difference. I may pop the $60 for a reman dist also. The shaft has lots of play in it and could cause different issues. Once that is complete then I will look at changing the tranny fluid vs getting it flushed. The tranny fluid is a little burnt. Already changed the fluid in the Transfer case. Was waiting to figure what's best with the tranny until I got the head done and I just replaced the output transmission seal. No use putting good ATF in until those are resolved. Then there is the issue with buying offset ball joints to get the camber correct. All in good time. so open to any suggestions... otherwise I can give an update once I have the funds to redo the head. great forum!

dave1123

I don't know your location, but watch the frame for rust. ZJs like to tear out rear lower control arms.