I have been following this forum for a few weeks now since I recently bought a 94 Cherokee with 150K miles. I have been working on getting some of the mechanical issues fixed and I am a little stumped by an oil problem.

The Jeep burns a lot of oil (1 qt a week) and I have white smoke coming from the tailpipe under heavy load. The tailpipe also has a black ring around it and puffs out soot when I get it up to 3000 RPM. I do not think I am burning coolant though because the coolant level has not moved in 3 weeks. I check the coolant overfill bottle and radiator level every other day and I have not added any coolant to it. I also used an engine block leakage tester and it did not show any signs of leakage.

I just finished up a wet and dry compression test. The dry numbers were 137 at the lowest and 150 at the highest. The wet numbers showed a 15 psi increase on all cylinders. I also just did a leakdown test and cylinders 1, 2, 3, and 6 held steady at 90%. Cylinders 4 and 5 were around 80%. There were no bubbles in the radiator and I could not hear any air coming from the tailpipe or the intake. I thought I could feel some air coming from cylinder 4 when 5 had pressure and vice versa but it was so slight that I'm not sure if I was actually feeling anything. I'm assuming the head gasket is bad but I'm not positive. I'm wondering if the rings might be bad on cylinders 4 and 5 but I've also read that 20% leakage on an old engine is not a bad thing.

Another area of oil leakage is the oil fill cap and the front grommet on the valve cover. I also get a little oil coming through to the air filter. I just finished draining the oil and it does have a strong gas smell to it and it was pretty dirty. I am dropping the oil pan tomorrow morning to see if there is any debris in it and also change the rear main seal. I cleaned the engine up and there is a small but noticeable leak coming from the bottom, rear part of the engine. There does not appear to be any oil dripping down from the valve cover and I keep it wiped down to help isolate leaks.

Again, thanks for any help!

 

The vacuum line from the intake to the MAP sensor may be messed up in some way. If so, the engine will run quite rich because reduced vacuum to the MAP and it will tell the ECU to open the injectors for a longer period of time.

 

If your model uses a transmission modulator valve that hooks into an underhood vacuum source, pull the vacuum hose and inspect. If fluid is present inside the hose, you have found the cause.

White smoke can be either coolant (actually white steam) or transmission fluid. A bad modulator valve is usually the cause.

If you're seeing blue smoke at cold startup, suspect worn valve guides. This often disappears when the cats warm up and start burning it off. A quart per week is massive; are you sure there are no external leaks that have avoided detection?

If you do have a fuel problem, and/or an oil control problem, expect early catalytic converter death as well. The rings sound fine - keep looking.

 

I'd recommend rebuilding your CCV system. Anytime you have oil in the filter and decent compression results, the CCV system is suspect. It is a very common failure on the 4.0 engine. Remove the valve cover, pop out the grommets, clean the valve cover until you can eat off it. Replace grommets. Install new valve cover and after that, install new CCV hoses. Total hardware cost for this is probably under $75.

Oil contaminated with gas could also be a leaky fuel injector. Be sure that the vacuum line leading to the fuel pressure regulator isn't contaminated with raw fuel. If it is, the regulator has a ruptured diaphragm.

 

Thanks for all the help! I just finished replacing the rear main seal, flushing the coolant and the transmission fluid and changing the trans filter/screen. The trans fluid looked like motor oil and was pretty nasty. I also drained and serviced the transfer case fluid. I will get to the diffs next weekend.

The valve cover looks pretty good along with the CCV valves, hoses and grommets. I was able to pull them out without any trouble and everything looks like it has been replaced within the last few years. I popped them back in without much effort.

Are both CCV valves supposed to look the same? The front and rear valves look identical with the rear one going to the intake manifold and the front one going to the airbox.

As far as the fuel injectors, I haven't pulled them yet to inspect them. I plan on getting a loaner fuel pressure tester from the local auto shop and see what I'm getting.

 

You are in supper company here, I just have a quick question. Where the exhaust crosses over to the right, there behind the pan, what does the pipe there look like?

 

The pipe looks like it's been soaked in oil but I don't see any visible cracks. I plan on replacing the exhaust soon because of a cracked exhaust manifold. When I replace the manifold I will install a new exhaust.

 

OK. Oil can blow back from hardened oil filter adapter O rings, (common), and mimic a leaking rear main. Also driving down the road, that pipe gets hot and leaves a smoke trail if it's peeing well! Just a thought. It helps to look there before you even leave the car wash, or right away before it blows around, then you can't tell where it came from!

OIL FILTER ADAPRER O RINGS http://www.myjeepxj.com/cherokee-rep...filter-adapter And a link with torx.. https://www.cherokeeforum.com/f51/oi...o-ring-127359/

 

Thanks for the advice! Looks easy enough so I should be able to accomplish this after work one day this week.

 

Keep an eye on the oil pressure sender while you are checking.