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  #1  
Old September 13th, 2006, 04:13
lawlopez lawlopez is offline
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'98 4.0 engine smokes on hard acceleration

Yesterday I noticed that while I was doing 70 MPH if I gave it full throttle my '98 Jeep Cherokee Sport AT 4.0 was putting out some smoke.

It has almost 150,000 miles on it. Inline 6 cylnder.

It went away when I stopped giving it full throttle.

It is know that it uses some oil although I don't know quite how much.

I'm wondering what this might be caused by and how to fix it and if it is worth fixing.

Thanks.
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  #2  
Old September 13th, 2006, 06:45
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Dr. Dyno Dr. Dyno is offline
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Re: '98 4.0 engine smokes on hard acceleration

The problem is piston ring/bore wear so the only cure is to rehone the cylinders and replace the rings.
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  #3  
Old September 13th, 2006, 19:52
lawlopez lawlopez is offline
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Re: '98 4.0 engine smokes on hard acceleration

Nuts. I was afraid of that.
That probably means I should start hunting for a used engine.
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  #4  
Old September 13th, 2006, 19:53
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MogifiedXJ MogifiedXJ is offline
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Re: '98 4.0 engine smokes on hard acceleration

Quote:
Originally Posted by lawlopez
Nuts. I was afraid of that.
That probably means I should start hunting for a used engine.
Don't run it hard and abuse it and it should last you another 50,000 with proper maintanence.
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Old September 14th, 2006, 10:39
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Dr. Dyno Dr. Dyno is offline
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Re: '98 4.0 engine smokes on hard acceleration

You could try adding a can of Restore in the crankcase to see if that reduces oil consumption. It could buy you some time but I don't think it'll be anywhere near 50k miles though.
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Old September 14th, 2006, 11:46
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Blaine B. Blaine B. is offline
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Re: '98 4.0 engine smokes on hard acceleration

It could be an overfilled trans leaking out the vent, or your rear main seal is leaking. Check the seal around the oil filter as well.
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  #7  
Old September 24th, 2006, 20:55
lawlopez lawlopez is offline
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Re: '98 4.0 engine smokes on hard acceleration

I'll check for leaks but I don't think that's it.
It's seems to be coming from the tail pipe.

I'll just baby it ...

I don't really want to go fast in it.
That's what I have a Prius for.
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  #8  
Old September 25th, 2006, 06:22
Frank Z Frank Z is offline
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Re: '98 4.0 engine smokes on hard acceleration

Use a can of SeaFoam to clean out that motor first.
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  #9  
Old September 25th, 2006, 19:56
YosemiteXJ YosemiteXJ is offline
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Smile Re: '98 4.0 engine smokes on hard acceleration

What color is the smoke? Internal smoke will be bluish and outside dumping of oil will be whitish. Like the others posted, smoke can be caused by oil getting into cylinders from above via leaking through wornout valve guide seals or below via worn out rings.

A common prob with 4.0L's is a leaking rear main seal or the seal around the back of the crankshaft. Mine leaks when the engine is stressed and higher pressure is created inside by heat etc., oil shoots out; and lo and behold the crossover of the exhaust is right there under the leak, producing mucho smoke.

I was towing a tow dolly with a 1970 Cadillac convertible behind my '88 XJ and was leaving a smoke screen all the way up a steep hill. Knowing what it was I didn't worry about it... as long as a CHP wasn't around!

Look to see if oil is coming out between the engine and trans. That is where a rear main leak shows.

You can check the cylinder pressure of all 6 cylinders with a pressure gauge to see if you have tired tubes. If your pressures, dry and with a squirt of oil, are all high, you probably have no prob with the valve guides or rings.

Gary
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Old September 25th, 2006, 20:11
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Re: '98 4.0 engine smokes on hard acceleration

Just for reference:

Smoke on hard accelleration is caused by rings. Vacuum is very low.

Smoke at idle or under decelleration is caused by valve guides. Vacuum is very high.
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  #11  
Old September 25th, 2006, 20:12
lawlopez lawlopez is offline
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Re: '98 4.0 engine smokes on hard acceleration

This may take a few weeks to get around to.
I think I have a compression gauge somewhere.

This isn't a daily driver unless it is snowing !!!
I think the smoke was white.

Ran all day with no problem. But I was generally gentle on
the throttle.

I'll get a passenger to check the color some time.

I do get some pinging too.
Again not much.

Thanks !!!
Larry
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  #12  
Old October 22nd, 2006, 21:09
Zoro Zoro is offline
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Talking Re: '98 4.0 engine smokes on hard acceleration

Quote:
Originally Posted by lawlopez
I don't really want to go fast in it.
That's what I have a Prius for.
Don't mean to resurect a dead thread but that's the funniest thing I've ever heard HA!
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  #13  
Old October 22nd, 2006, 21:31
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Blaine B. Blaine B. is offline
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Re: '98 4.0 engine smokes on hard acceleration

I vomited with my lips closed.
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