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post #1 of (permalink) Old 12-31-2002, 12:56 PM
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Engine problems 97-4.0, need help diagnosing

I am having a problem with my 1997 Grand Cherokee that my mechanic can't diagnose. At highway speeds (65-75 mph) after driving for long periods of time (3 hours plus), the transmision (?) slips out of gear. It does not rev at all. I just lose power to the engine even when my foot is flat on the accelerator. Sometimes, after a few seconds it kicks right back in with a jolt, sometimes it just coasts on along and I need to pull over. After pulling over, I shut the engine, restart, and all is fine, but the problem recurrs after a few more miles. My mechanic can not reproduce this effect in the garage or on a test drive at highway speeds and can not diagnose the problem. I would appreciate any leads/help anyone can offer.

Many thanks.
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post #2 of (permalink) Old 12-31-2002, 04:50 PM
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Re: Engine problems 97-4.0, need help diagnosing

if i didnt know better, id say this was a vapor lock issue... but i have never heard of vapor lock on suck a new vehicle...
i would check to see if the catalytic converter is clogged....
did you do the obd II diagnostics?
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post #3 of (permalink) Old 12-31-2002, 05:37 PM
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Re: Engine problems 97-4.0, need help diagnosing

No codes???

...and ...

something doesn't quite add up. Are you sure it "slips out of gear"?

When you pull off to the side of the road ...is the engine idling ..or is it stalled (hence you turn it "off" and restart it)??

The engine should remain turning even if it loses power ..since the trans is engaged. You would have no throttle response but I believe that viturally everything else would appear to be working (power steering etc.) until you slowed down enough to get into Low gear where the trans is able to overrun the engine in the coast mode.

Please clarify. [img]images/graemlins/confused.gif[/img] [img]images/graemlins/confused.gif[/img] [img]images/graemlins/confused.gif[/img]

If that's the case it makes a little more sense. You're just losing fuel or spark or both. You should still get something out of the PCM ..or so I would reason.
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post #4 of (permalink) Old 12-31-2002, 06:28 PM
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Re: Engine problems 97-4.0, need help diagnosing

1. Check to see if it has speed sensors to sence clutch speeds.
2. If so, replace them...
3. Just replace 'em and see if that helps.
4. The computer can't tell what gear to put it in as the speed sensors may be sending the computer garbage.
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post #5 of (permalink) Old 01-01-2003, 12:03 PM
 
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Re: Engine problems 97-4.0, need help diagnosing

Agree with Leve, Have the trans controller checked for codes. Most likely it is the output speed sensor, causing the trans to go into limp-in mode. I have seen many bad.
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post #6 of (permalink) Old 01-01-2003, 12:31 PM
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Re: Engine problems 97-4.0, need help diagnosing

But [img]images/graemlins/confused.gif[/img] [img]images/graemlins/confused.gif[/img] [img]images/graemlins/confused.gif[/img] Why would this render his engine null and void? Heck ...let's say he puts it in neutral and floors it ...why would that prevent him from having the engine rev??? Is there some electronic rev inhibitor built into the RE trans ....like the MB traction control????

I think the "jolt" that he feels (sometimes) is the engine "reacquiring" fire.

Or did I read something else?
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post #7 of (permalink) Old 01-02-2003, 08:23 AM
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Re: Engine problems 97-4.0, need help diagnosing

Thanks

The engine in fact remains turning the whole time, I just get no power when pressing the accelerator. When I pull over, I brake to a stop, shift into park, and then shut and restart the engine. Will ask my mechanic about the codes.

Thanks again.

David Sack
post #8 of (permalink) Old 01-02-2003, 11:46 AM
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Re: Engine problems 97-4.0, need help diagnosing

Hockey (okay)

The only definitive element that I'm missing is ....if the engine is in fact idling when you put it into park and turn the key to the off position and then restart it. Or is it stalled (idiot lights all on and zero rpms)??? Your responce still leaves that in question.

The engine will turn as long as the trans is engaged. When you take your foot off the gas ....the trans is turning the engine. The only difference between a running engine and a dead one is that when you push down on the gas pedal on a dead one nothing happens.......yet the power steering will still work the oil pressure will still be fine.

Watch your tach the next time it happens. If it tracks your road speed until you reach a certain low speed and then drops dead ..you've got an engine problem. If you see it drop to idle or whatever and it remains in that state until you turn it off on the side of the road and restart it (reset something) ......then it could be anything (trans - yes).

I'm just trying to isolate the symptoms just in case that one simple element is missing. You may infact have a trans problem ...but I'd want to eliminate the engine ..which by your description ..it could easily be.
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