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Tech question for any of those mechanics/engineers out there


 
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monkeyman3875
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Joined: 06 Jul 2005
Location: Charlotte, NC

PostPosted: Thu Apr 06, 2006 8:42 pm    Post subject: Tech question for any of those mechanics/engineers out there Reply with quote

On my '97 Cherokee after a cold start if I kill the engine it won't start again for another 5 minutes, and if I drive it directly after a cold start, often times it won't shift into 4th at all (automatic tranny). However, when the engine's warm (210 deg.) I don't have that problem at all. My mechanic says it's the neutral safety switch; sound familiar to anyone? Thanks.
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ThePhantum
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Joined: 23 Jan 2004
Location: I knew it...I'm surrounded by Assholes!

PostPosted: Thu Apr 06, 2006 9:03 pm    Post subject: Reply with quote

That's a weird one. Usually when the transmission won't go into OD, it indicates that the ECU has activated "limp in" mode. Which is a condition that happens when the computer knows it's getting bad info from a sensor. It then ignores sensor data and "guesses" about how to run the engine so you can limp it in to a mechanic.

However, limp in mode is always accompanied by a check engine light. Plus, it runs fine when warm. It also doesn't sound like the NSS, that would not allow you to even attempt to crank it.

It does sound like a bad sensor someplace. Unless someone here has run across this one, the best piece of advice I can give is to have someone put a DRB scan tool on it when it's cold and see what the ECU is reporting.

Moving this to to Drivetrain to give it more exposure. Wink
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Renegadestang
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Joined: 07 May 2005
Location: Marietta, GA

PostPosted: Fri Apr 07, 2006 2:03 am    Post subject: Reply with quote

Kinda sounds like vacuum lock, until you get to the tranny part....
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1998 Jeep Cherokee Sport: 4.0L, AW4, 235/75 Wild Spirit's

1981 Jeep CJ-7 Renegade: 307-4V SBC, SR-4 4-spd., 31x10.5 Wild Spirit's

1966 Ford Mustang: 289-4V, C4 Auto.
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JeepinNH
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Joined: 13 Sep 2005
Location: New Hampshire

PostPosted: Sat Apr 08, 2006 4:22 pm    Post subject: starting Reply with quote

What does it do when it won't start? If the motor turns over but does not fire it would not be the NSS. A bad/dirty NSS will not allow the starter to engage. If it does turn over then you have to check sensors like the crankshaft position one. Not sure how many a 97 has, the 94 Grand I used to have had 2. It would intermittently start depending on the weather and of course never happened in my driveway for weeks. When it finally did I was able to see a bad sensor (under the distributor) with a volt meter. I wonder if the tranny issue is seperate, could be the computer doing both.
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Present: 99 Cherokee
Past: 86, 87 Cherokee; 94 Grand Cherokee
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monkeyman3875
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Joined: 06 Jul 2005
Location: Charlotte, NC

PostPosted: Mon Apr 10, 2006 10:39 am    Post subject: Reply with quote

When it doesn't start it doesn't do anything. No noises no clicking no nothing. Then about 4-5 minutes later it fires up no problem.
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ThePhantum
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PostPosted: Mon Apr 10, 2006 11:39 am    Post subject: Reply with quote

OK. That definatly sounds like the NSS. It also sounds like there's two different problems here. I would rebuild/clean the NSS first and once that problem is fixed, start diagnosing the tranny shift problem.
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