Gas mixing with oil in crankcase

[TerraWombat]

Old post, but I finally just got around to sending the injectors out to be cleaned. I'm in close contact with the guy who will be servicing and cleaning the injectors and he should let me know if they are leaking while under pressure. This would mean after the truck is shut off, the pressure in the rail will force fuel to exit a leaky injector and it will run into the cylinder (if the intake valve is open at the time) and will most likely seep past the rings and into the crankcase.

Anyway, I'm hoping that's the problem and that cleaning the injectors will sort this all out. If this works, I'll be doing this to my newly acquired Comanche ('88 w/77K) as it has the same problem, just not nearly as bad as my other truck.

 

[JJacobs]

Wait- now you have FOUR vehicles with the same unusual problem?

 

[Blaine B.]

You sure the 3 stooges didn't put gasoline in your radiator on accident, and you have a headgasket leak at the same time?

lol.

 

[TerraWombat]

Well, a lot has happened in the last six months that I neglected to mention. The 1986 MJ with the Chevy 2.8L V6 took a turn for the worst and lost compression in one of the cylinders. Pulled the engine and tore it apart and found some very interesting things. Decided it wasn't worth the money to rebuild it, so I sold it to a guy down the street who has a use for it and plans on dropping in a rebuilt engine.

The 1990 MJ had the gas mixing with oil problem, but it wasn't nearly as bad as the 1988 MJ I bought six months ago. There was definitely a little bit of gas present in the oil whenever I changed it and I also got 6 3/4 quarts out of the engine whenever I changed it so somehow the engine is producing oil rather than burning it But in all seriousness, it was definitely gasoline in the oil - you could just tell by the smell and how much thinner it was. Anyway, I sold the 1990 MJ too and notified the buyer of the problem, but he didn't seem to mind too much as long as the oil pressure was within spec (it was) and the engine still ran fine (it did). He was just using it as a work truck around his ranch so he wasn't overly concerned with the problem, plus the price was right

Now, with all of that said, I was left with just one 1988 MJ. This one had the gas mixing with oil problem BAD. I'm talking 8-10 quarts drain out on oil changes and I have to change the oil every 100 miles or so. It comes out super thin and it smells very bad. I'm having the injectors cleaned as we speak, and hoping it solves the problem...only time will tell.

Since I only had one MJ and I'm not used to only having one, I went out in search of another and came across a 1988 MJ w/77K. Full details on that truck can be found here: http://www.naxja.org/forum/showthread.php?t=902646 This truck has a similar problem to the 1990 MJ I had. There is a slight mixing of gas and oil in the crankcase, but nothing bad that it's dropping oil pressue or making the car run like crap. If the injector cleaning service solves the problem for my one 1988, I'll be cleaning the injectors in this truck too.

I'll keep you all informed.

 

[89Daytona]

What kind of gas mileage are/were you getting with these vehicles?

 

[TerraWombat]

What kind of gas mileage are/were you getting with these vehicles?

I never kept track of anything like that. The first 1988 MJ only had Farm Use plates on it, so it only traveled from farm to farm and it also has a hole in the gas tank so we can't fill it past 3/4 tank.

I could, however, keep track of the new 1988 MJ I just got once I get a set of plates for it.

 

[Jess]

Sorry to dig up an old thread, but I'm having the same problem on an 89 4.0. Is there any updates or has anyone else experienced this problem and/or solved it?

 

[TerraWombat]

Wow, this IS old! But, that same '88 MJ with the gas/oil mixing problem still remains in my shop waiting to be stripped of its paint and hit with a new coat. I had the injectors cleaned and the truck fires up and runs smooth, but I still haven't run it long enough to see if the gas and oil mixing problem has been solved. But, just thinking about where and how gas could ever mix in with the oil in such large quantities, the injectors are the only culprit I can think of.

 

[TerraWombat]

2-20-09 Update: The injector cleaning did not solve my problem as I'm still getting gasoline in the crankcase. The truck IS running rich...VERY rich. So rich that I already blackened my brand new tailpipe within 15 minutes of running the thing. I just located my multimeter last night so I'll be doing some ohm readings on all of the sensors today to try and figure out if one of those is the culprit.

 

[JeEpXjSaM]

anyone ever figure out what was causing this? my 89 4.0 cherokee is doing the same thing. i drive 40 miles every day and changing the oil every week is getting really old. so please help

 

[joe_peters]

One of the things noted early on by the OP was "fuel in the vacuum lines".

Well, that is likely coming from one place--the fuel pressure regulator is leaking fuel at the vacuum port, and that fuel is being sucked into the intake via the vacuum lines.

Good luck.

 

[JeEpXjSaM]

i just got it fixed and it now goes into closed loop and no more gas in the oil. what i did was took all the exhaust pipes off and fixed a few holes, cleaned the O2 sensor ( with an old toothbrush and compressed air), replaced the fuel pressure reg with a used one i had (wasn't closeing all the way and failed the leak down test. lost all pressure in less than 5 min), and cleaned the throttle body. not sure what fixed it but it was one or more of these.

 

[oldseddie]

Sorry I didn't see this earlier. If it has a mechanical fuel pump. The diaphram has a hole in it. Replace pump and change oil.

 

[Talyn]

What XJ has a mechanical fuel pump?

 

[old_man]

Before spending a ton of bucks, pull the plugs and show them. Also do a wet/dry compression check. That way you can see what is happening before you spend the bucks. If you are gas washing the cylinder walls, the bores may be shot.