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Unread 11-11-2013, 04:49 PM   #1
me_jeep
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1998 ZJ 
 
Join Date: Nov 2012
Location: emmett, michigan
Posts: 35
98 4.0 losing power

Hey guys, I have a 1998 Grand Cherokee 4.0 4x4. Recently the trans went on it. So, I got one from the junkyard, and it was bad. Took a crap after ten miles and wouldn't warranty it. But, while it was driving... It would lose power. Literally drop down to about 50 rpms, the engine sounds like it would shut off, but it would kick back in and lurch. The rpms would go from about 50-2500. I put in a new tps, cps, cap and rotor. Still did it. So I talked to a couple people and they said it sounded like a trans problem. So, I bit the bullet and got it rebuilt since it was bad. The original trans also not the junkyard. The owner of the shop called tonight... Took it for a drive and he said it was having the exact same symptoms. Anyone have any idea where to start? I'm kinda thinking its my ECM. But it's weird how it only does it when it warms up, besides once it did it at around 150 degrees. I love my jeep... But my dads got a nice 454 suburban 4x4 I could buy... But I want my jeep! Thanks guys, I'm stumped on this one.

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Unread 11-11-2013, 05:28 PM   #2
JasonStebbins
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1997 ZJ 
 
Join Date: Jan 2009
Posts: 3,137
Quote:
Originally Posted by me_jeep View Post
Hey guys, I have a 1998 Grand Cherokee 4.0 4x4. Recently the trans went on it. So, I got one from the junkyard, and it was bad. Took a crap after ten miles and wouldn't warranty it. But, while it was driving... It would lose power. Literally drop down to about 50 rpms, the engine sounds like it would shut off, but it would kick back in and lurch. The rpms would go from about 50-2500. I put in a new tps, cps, cap and rotor. Still did it. So I talked to a couple people and they said it sounded like a trans problem. So, I bit the bullet and got it rebuilt since it was bad. The original trans also not the junkyard. The owner of the shop called tonight... Took it for a drive and he said it was having the exact same symptoms. Anyone have any idea where to start? I'm kinda thinking its my ECM. But it's weird how it only does it when it warms up, besides once it did it at around 150 degrees. I love my jeep... But my dads got a nice 454 suburban 4x4 I could buy... But I want my jeep! Thanks guys, I'm stumped on this one.
Need a better description. It could be 100 different things. Dirty IAC/Bad coil/Timing issue/Fuel starvarion/Bad spark. When does it happen? All the time? When driving fast or slow? While idling? Does it ever actually stall? Have you checked ZeeJays stall thread in my signature? Did you use Mopar TPS and CPS? Have you checked the grounds and charging system?
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Unread 11-11-2013, 05:56 PM   #3
me_jeep
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1998 ZJ 
 
Join Date: Nov 2012
Location: emmett, michigan
Posts: 35
Ok, it has never stalled out completely.but always feel like it is going to but doesn't. Has never done it while idling. Has done it a few times while going slow, but much more while going fast. Around 50, or after shifting into overdrive. Idle is the same it has been, little bit of range around 800 but that's it idling wise. Doesn't happen all the time, but 9/10 times. Also when it wants to stall, the rpms shoot up and the jeep lurches forward.
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Unread 11-11-2013, 06:05 PM   #4
JasonStebbins
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1997 ZJ 
 
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Quote:
Originally Posted by me_jeep View Post
Ok, it has never stalled out completely.but always feel like it is going to but doesn't. Has never done it while idling. Has done it a few times while going slow, but much more while going fast. Around 50, or after shifting into overdrive. Idle is the same it has been, little bit of range around 800 but that's it idling wise. Doesn't happen all the time, but 9/10 times. Also when it wants to stall, the rpms shoot up and the jeep lurches forward.
What kind of maintenance have you done? Ever clean the IAC/throttle body? Sounds electrical. Did you use Mopar sensors? Original catalytic converter? Test the charging system and battery connections/grounds? Check the transmission fluid level while running warm in neutral? We'll track it down.
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Unread 11-12-2013, 04:59 AM   #5
me_jeep
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1998 ZJ 
 
Join Date: Nov 2012
Location: emmett, michigan
Posts: 35
Well it's still in the transmission shop, trying to figure out how to get it home. But never cleaned iac, never had problems with the jeep. Been my dd for two years. There was no cat converter on it when I bought it. Also the check engine lights not on. And weren't moose cps/tps, I got them from autozone.
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Unread 11-12-2013, 12:58 PM   #6
JasonStebbins
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Bingo. I'm willing to bet the AutoZone sensors are your problem. A bad TPS/CPS can sometimes have similar symptoms, so your best bet would be replacing both with Mopar/NGK brand.

These Jeeps are very picky about sensors, mainly because of the resistance. Mopar/NTK (OEM) have a different resistance then the aftermarket brands.

Especially stay away from Bosch anything (other then a fuel pump).

Also, having no converter is illegal and can get you banned from the forum, so be careful. You're losing back pressure without it anyway. Put on a high flow one when you have the time and money.

When you get it back, clean the IAC and where it mounts into, and clean out the throttle body. If you haven't done it in two years, it's definitely time to get it done.
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Unread 11-12-2013, 01:11 PM   #7
me_jeep
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1998 ZJ 
 
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Location: emmett, michigan
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Yeah the jeep needs whole new exhaust lol. It's on my list, it's a big list. So my original trans went, had no stalling issues before the trans went. After I swapped in the junkyard one it started the stalling symptoms. And after a rebuilt trans it's still stalling. My dad wants me to stop at the dealership ad have it "diagnosed" for $100. I'd rather not. I don't think it's going to tell me my issue sense it doesn't do it constantly. Would you think it's the cps, or the tps? A o2 sensor? PCM? Trying to limits spending money since the trans did a number on me.
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Unread 11-12-2013, 01:19 PM   #8
me_jeep
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1998 ZJ 
 
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Location: emmett, michigan
Posts: 35
Also, I don't really think it will be a fuel problem/spark because I can tear up to 50, now loss of power or anything. Until it wants to stall. And once I slow down it'll reset itself or something an be fine until the next time.
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Unread 11-12-2013, 01:27 PM   #9
JasonStebbins
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Well, if the problem started after the new transmission was installed, my money is on the CPS because it mounts to it. And it's aftermarket, so it's a problem by itself.

A CPS will cause starting/stalling/running issues all day long.

Put the original CPS back on or buy a new Mopar one and install it. I guarantee your problems will disappear.

The TPS can cause running/stalling issues, but usually won't cause a no-start. The oxygen sensor and PCM can have the same symptoms, but since you said it started after the new transmission, it sounds like it's definitely the parts store CPS.
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