IslandXJ

Just changed my oil and went for a 60 mile drive. Now my oil smells of gasoline. The jeep starts and runs great. Does not burn oil and gets 18 mpg. '99 4.0 126k AW4. I just did a dry and wet compression test:
Cylinder Dry Wet

1. 179 221
2. 151 192
3. 168 210
4. 180 224
5. 160 201
6. 181 224

First time checking compression... Warm engine, removed pump and asd relays, WOT, removed plugs. For the wet test I used a turkey injector to put 1/2 oz of oil. These numbers don't look good but I'm looking for some guidance.

IslandXJ

There is 30 psi difference (~20%) between the cylinder 2 and 6. All the cylinders had higher psi when wet, from 18%-27%

wildbill1

I don't think those compression numbers look too bad at all. A little more consistency wouldn't be bad, but there are no real low ones and no indication of leakage between cylinders. Your gas/oil issue could be a bad injector leaking.

offroadordnance

Pull #2 plug first and see if it's fuel fouled or wet. Then #5, then #3, and the rest in no particular order.

IslandXJ

I didn't notice that the plugs were wet but all 6 of them had an ashy grey deposit on the electrodes. I put them in about 1000 miles ago and haven't checked them since the test.

DFlintstone

Seeing how your fuel pressure drops when it's sitting might clue you to injectors leaking. Less than 20# drop in 30 Min would be pretty good IIRC.

I never tested, but with my old stock injectors, sometimes it would miss a few beats, starting it warm after sitting 1/2 hr or so. I think one or two cyls were flooding.

This is how I learned to check for sure. (photo). Comp #'s could be better...wonder what's up with #2. I guess if it was me I might repeat the wet test....that's just me. I'd want to make darn sure a potential problem # was correct. Oil pressure?

IslandXJ

Okay, fuel rail pressure test done. 52 psi from ignition and while idling and with some throttle. After 10 min. it was @30psi, 15 min.@25 psi, and 25 min.@22 psi.

xjsnake

As others have said, cylinder 2 is barely within spec but shouldn't be causing you any major problems. Every 4.0 I've owned or worked on has had a slight smell of gas to the oil. I wouldn't worry about it as long as you haven't noticed any major problems.

offroadordnance

Provided you empty the cylinder to avoid hydrolock prior to installing the sparkplug, an over night piston soak with Seafoam might bring up #2.

IslandXJ

I just bought the jeep in may and I don't remember the oil smelling. This seems to be a recent problem. I may just buy a set of injectors from Precision and see of that helps.

IslandXJ

How would Seafoam help my compression?

DFlintstone

I don't mean to put words on offroads mouth. I have been through more then a few engines. As clear as the specs seem, there always is something on the edge.

Rings can get gummed up. Deposits in there can "hinder" them from floating/seating perfectly. There ARE solvents that really "talk" to stubborn deposits. Berymans B-12 Kemtool comes to mind. Loosening a bunch of gunk at once might ruin it. Meltdown.

Interesting thought....at only 120+K. I guess if it was me, I'd double check my #'s.

DFlintstone

I'll try to dig into some FSM for #'s in the a AM. Salad! where are you! That sounds a little swift to me.

salad

Lol

I'm still in early morning braindead mode but IIRC 49 PSI should hold for like half an hour.

By the way the FSM method for measuring cylinder compression is to take it on the 3rd compression stroke. Sounds like you just kep going until the numbers stopped going up. Not really "wrong", per se, but all of the troubleshooting etc is based on the FSM method. Using that procedure you should only see a max of 160 PSI per cyl.

I like DFlintstone's pic of popping the assembled fuel rail off and lettin it leak over a piece of cardboard.

Leakdown test?

offroadordnance

I've always used seafoam and just dumped it in, let it soak, and changed oil after a fee days of running. It's okay to add to oil, I'm not sure about B-12's lubricity or if it eats gaskets/seals when it ends up in the oil. Mopar 4318001AD "combustion chamber cleaner" is another option. I'm pretty sure that's what the dealer techs use when low mileage 3.8L's start drinking a quart every 500 miles.