2.5L backfires?!?

I've been working on my '86 TBI 2.5L Cherokee for a while and I can't seem to figure out why or what it is doing. First off, it doesn't like to start on a regular basis despite my efforts in changing and fixing everything. Second, occasionaly right after trying to start it it will backfire, but into the oil cavity instead of the intake, causing pressure in the motor and smoke to blow out the oil pan gasket and ruin the crappy plastic valve cover at the same time. Furthermore, the compression seems o.k., 130psi +-5psi, but the motor has 308k on it and has never been gone through.
Because of my budget(or lack of monies thereof) I would like to fix it, but I think it's toast this time.
Anyone ever put a dodge SB in a jeep?
All help is apriciated.

perhaps I should restate the question, does anyone know what the problem is with my 2.5L?

Sounds like you have shot rings. Not enough compression to start well so the gas vapors end up getting pushed into the oil pan. Then when it starts, it ignites the gas in the pan. I'm surprised you haven't blown the pan off and ended up on fire?

Do a compression test and I bet you have numbers below 100psi.

Sounds like time for an overhaul.

I have had similar problems in the past. Does yours backfire through the exhaust or through the intake? Mine was thru the intake.....sort of a "hiccuping" with a power loss while driving.....never had a starting problem though.... BTW, it's an 87 MJ 2.5 with TBI


edit: oop -re-read your original post and it sounds different than mine...g/l

old_man said:

Sounds like you have shot rings. Not enough compression to start well so the gas vapors end up getting pushed into the oil pan. Then when it starts, it ignites the gas in the pan. I'm surprised you haven't blown the pan off and ended up on fire?

Do a compression test and I bet you have numbers below 100psi.

Sounds like time for an overhaul.

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Too late, just blew it up this morning, she sure did go out with a bang. All that happened is it blew the valve cover(which I JUST replaced :banghead: ) into smitherines. Luckily no fire or other damage, but I think I'll be changing to my burnt 4.0 this weekend
BTW, do you know if the 2.5 guages will recognize a 4.0, or do I have to change everything, even with running a carb.?

BlueMJ said:

I have had similar problems in the past. Does yours backfire through the exhaust or through the intake? Mine was thru the intake.....sort of a "hiccuping" with a power loss while driving.....never had a starting problem though.... BTW, it's an 87 MJ 2.5 with TBI


edit: oop -re-read your original post and it sounds different than mine...g/l

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I never got to drive mine on the road because it never had enough power, but yes, when it did start it "hiccuped" through the intake like it was backfiring. Check your oil for gas.

crazyoffroader said:

I never got to drive mine on the road because it never had enough power, but yes, when it did start it "hiccuped" through the intake like it was backfiring. Check your oil for gas.

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That would mean bad rings? Its intermittant...happens sometimes, then goes aay, then comes back, then goes away...it can last for 5-10 minutes then not rear up again for a few weeks.

BlueMJ said:

That would mean bad rings? Its intermittant...happens sometimes, then goes aay, then comes back, then goes away...it can last for 5-10 minutes then not rear up again for a few weeks.

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seems odd that it's intermittant, but most likely bad rings or worn out cylinder walls. Someone with more expertice will have to chime in to figure this out for sure.