94 Cherokee 2.5 excessive smoke after changing plugs?
 

Hey fellas! I recently joined CF and bought a 94 Cherokee two door 2wd with the 2.5/manual trans combo. Yeah, I'm already looking for a wrecked 4wd donor truck, but in the meantime, I brought I'd get this one running better.

I knew it had high miles (174k), but when I bought it, it seemed to run decent. It just had a squealing throwout bearing. I drove it 40 miles to my house and suddenly (imagine that), it wasn't running so well anymore. I pulled the valve cover, and found that the engine was the absolute DIRTIEST engine I had ever seen. It was pretty obvious that the PO had seriously neglected the poor Cherokee. I simply put the valve cover back on and left it there for a week.

Today, I decided to at least TRY to do something productive. I changed the spark plugs and wires. Well, it didn't surprise me a bit to find the plugs in VERY bad condition. The electrodes were almost burned off! But after installing the new set, it immediately ran better an idled better.....BUT, there was TONS of smoke coming from the tailpipe. Not really a blueish smoke, but rather a white/gray smoke that smelled of something burning. I drove it around the block anyway, then let it idle for about an hour. Still producing massive amounts of smoke. My wife followed me on the way home after I bought it, and reported that it only smoked a little when I shifted. NOTHING like what it's doing now!

My first suspicion (hope) was that it's just burning oil residue out of the exhaust or something to that effect, but when I removed the oil filler cap while it was idling, I noticed there was a lot of pressure inside the valve cover. Is that all blow by? Do you guys think it might be time for a new engine?

Thanks in advance for your help!

I'm hoping you don't have a fudged head gasket. Are you low on coolant, have coolant in the oil or oil in the coolant, or any gurgling in the radiator?

There are some other things to check that can create your symptoms:
Check the crankcase vent/PCV system. I'm not that familiar with the 2.5 and can't tell you exactly what system it has, but I suspect you'll find two hoses attached in some manner to the valve cover, one providing clean air from the air cleaner box and another connected to engine vacuum to draw blowby out to burn.
Either or both can clog and cause problems. See if they're plugged. One should have engine vacuum, put your finger over the end to check. I'm not certain if the 2.5 has a PCV valve or fixed orifice on the vacuum side, make sure whichever it has isn't clogged shut.
I'm betting there is an obstruction in the crankcase vent system if you have noticeable pressure behind the oil filler cap. It should vent back to the air filter box worst case instead of pressurizing the block.
If it can't escape it blows past the rings on the intake stroke, past the valve seals and lord knows what else and creates smoke. Vapor blowing out the oil dipstick is a common symptom as well.

If your oil is contaminated with fuel and moisture, that'll result in white/gray smoke when it burns... and contaminated oil sneaks past the rings and burns easier.
If the engine has been neglected, moisture/fuel in the oil is pretty likely...it accumulates when the engine is run short periods without a good heat-up to burn it back off. Dump a slug of solvent in there (MMO, Rislone, Seafoam), run it a while and change the oil.

If those don't fix the problem, check cylinder compresson dry, then wet.

Great info! Thanx bud! I have been suspicious of that PCV anyway! Im gonna check the stuff you mentioned and I'll get back to you guys ASAP. Btw, I once saw a guy remove a spark plug from a v6, get a funnel, an FILL the cylinder and combustion chamber with seafoam™.... Cranked it and it smoked just liked mine for a couple hours before it burned it all out! Lol I'm just bringing that up because mine looks just like that!

Not unusual for owners of older Saturn 1.9's to give that a try when the inevitable oil burning starts. Fill the cylinders with solvent and let it sit overnight hoping to unstick the oil control rings. Make sure the cylinders are empty again before reinstalling the plugs and cranking....:w00t:

Haha no kidding!

I have considered trying the old school "kerosene engine flush". I figure at this point, I really have nothing to lose!
And if inevitable happens, the cheapest reman 2.5 I can find is $987 plus $200 core. Does anyone know of a place to buy one cheaper?