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Unread 11-21-2012, 11:39 PM   #1
Freestyle713
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RPM's drop while driving

Randomly over the past couple weeks, my RPM's have been dropping while cruising down the road, usually under 3000 rpms. While parked, the idle is erratic, usually when I start it in the morning it will jump up to 1500 and stay there for a while. CEL is a code 21, but I replaced the o2 sensor a couple months ago, and the cat is less than 2 years old. I just replaced the TPS on monday, because I had symptoms telling me thats what it was. Well, I still have the same problem.

Ex: I was driving home from the movies tonight and all was well. I was on the highway and I felt a sort of "slip". I say that because it feels like the transmission is slipping, but its not. I can see the rpms drop. It got worse within the next 30 seconds and my CEL came on. After that, it was "slipping" every couple seconds, and the only way to get out of it was to floor it.

I have done:

Disconnect/clean PCM
Replace o2 sensor
Replace cat
Replace TPS

I think the MAP sensor would be next on my list, but I don't want to keep driving down a dead end road here. Plenum repair needs to be done, and I dont think I have any vaccum leaks.

I am at a loss here. Couldn't seem to find a solid answer in the search.

Edit: forgot to mention I got a code 32 yesterday, which is egr is bad, after I replaced the TPS. I got it a few months ago when I replaced my o2 sensor, and didnt get it again until yesterday, and it hasnt come back since.

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[B]94 Grand Cherokee 5.2[/B] [SIZE="1"]33in. Federal Couragia M/T's on Procomp Steelies, np231 swap, IRO Hack n Tap SYE, Carolina Driveshaft, 4.5 in. lift, RE front upper/rear lower ca's, RC front lowers, Ironman rear uppers, IRO 4.5 coils in rear, 3.5 and 2" bb (no isolators) in front, Bilstein 5100's, Clayton/JKS adj. track bars, KOR rad support and SS, Magnaflow/Flowmaster exhaust, clear corners, custom light bar w/ Hella 500's[/SIZE]

[CENTER][COLOR="Yellow"][URL="http://www.jeepforum.com/forum/groups/zombie-outbreak-response-vehicles/"][COLOR="Yellow"]Zombie Outbreak Response Team[/COLOR][/URL][/COLOR][/CENTER]
[QUOTE=elcorvino;14544406]Yea... It's kind of like the fat chick who lives around the corner. You aren't trying to get caught with her, but you know she'd be a good time.[/QUOTE]

[QUOTE=ScottD16;14460352]I had a dream my entire family was attacked by a giant polar bear. The crazy part was he attacked us with a giant spoon. Best dream ever.[/QUOTE]
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Unread 11-22-2012, 01:29 AM   #2
BobbyDean
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Can't say for sure. But I can say I had similar issues. I wasn't going to search for the issue until after i fixed an intake issue I had going on (Replaced the plenum gasket). Well I never needed to because it hasn't happened since.
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Unread 11-22-2012, 07:47 AM   #3
ZeeJay1997
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Quote:
Originally Posted by Freestyle713 View Post
I can see the rpms drop.
How much? A bad brake switch can cause 100-300 rpm rise by unlocking the TCC intermittently. But there are generally no codes associated with this.

I cant help you much on the codes, just thought this would be something to keep in mind in case you have more that one problem.
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Unread 11-22-2012, 10:56 AM   #4
TallyZJ
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I had an issue similar to this (sudden and quick RPM drop) and it didn't go away until I replaced the cam sensor in the distributor. I too had replaced everything there was to replace other than the PCM.
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Unread 11-22-2012, 11:07 AM   #5
Freestyle713
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Quote:
Originally Posted by ZeeJay1997 View Post
How much? A bad brake switch can cause 100-300 rpm rise by unlocking the TCC intermittently. But there are generally no codes associated with this.
If I'm at 2500 rpm, it will drop to about 1500, and stay there until I either let off the gas completely or floor it.

Quote:
Originally Posted by TallyZJ View Post
I had an issue similar to this (sudden and quick RPM drop) and it didn't go away until I replaced the cam sensor in the distributor. I too had replaced everything there was to replace other than the PCM.
How quick were your drops? Going from 2500 to 1500, it takes about 3-4 seconds. Almost like I'm easing off the gas. I'll keep the cam sensor in mind for when I do my plenum, hopefully over winter break.

I think I'm gonna take off my throttle body tomorrow and give it a good cleaning. I mean, It can't hurt, right?
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[B]94 Grand Cherokee 5.2[/B] [SIZE="1"]33in. Federal Couragia M/T's on Procomp Steelies, np231 swap, IRO Hack n Tap SYE, Carolina Driveshaft, 4.5 in. lift, RE front upper/rear lower ca's, RC front lowers, Ironman rear uppers, IRO 4.5 coils in rear, 3.5 and 2" bb (no isolators) in front, Bilstein 5100's, Clayton/JKS adj. track bars, KOR rad support and SS, Magnaflow/Flowmaster exhaust, clear corners, custom light bar w/ Hella 500's[/SIZE]

[CENTER][COLOR="Yellow"][URL="http://www.jeepforum.com/forum/groups/zombie-outbreak-response-vehicles/"][COLOR="Yellow"]Zombie Outbreak Response Team[/COLOR][/URL][/COLOR][/CENTER]
[QUOTE=elcorvino;14544406]Yea... It's kind of like the fat chick who lives around the corner. You aren't trying to get caught with her, but you know she'd be a good time.[/QUOTE]

[QUOTE=ScottD16;14460352]I had a dream my entire family was attacked by a giant polar bear. The crazy part was he attacked us with a giant spoon. Best dream ever.[/QUOTE]
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Unread 11-22-2012, 11:24 AM   #6
TallyZJ
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Quote:
Originally Posted by Freestyle713 View Post
How quick were your drops? Going from 2500 to 1500, it takes about 3-4 seconds. Almost like I'm easing off the gas. I'll keep the cam sensor in mind for when I do my plenum, hopefully over winter break.

I think I'm gonna take off my throttle body tomorrow and give it a good cleaning. I mean, It can't hurt, right?
Mine was just a quick stumble. It also did this at idle sometimes too. I didn't lose speed, just noticed the RPM drop.
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Unread 11-22-2012, 11:43 AM   #7
ratmonkey
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how fast are you going that you're cruising at 2500rpm with 33's and 3.73 gears? are you using overdrive at all?
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Unread 11-22-2012, 12:01 PM   #8
Freestyle713
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Quote:
Originally Posted by ratmonkey View Post
how fast are you going that you're cruising at 2500rpm with 33's and 3.73 gears? are you using overdrive at all?
At highway speeds, so like 70. I'm sorry, cruising rpm is lower than that, but what happens is rpms drop, I press the pedal up to where it engages the kickdown cable (where the pedal gets harder to press), and the torque converter unlocks, then its at about 2500, maybe a little less. Then they drop again. I said 2500 because that seems to be the barrier. If I'm above that, the rpms dont seem to drop as much, if at all. I'll have to see if I can duplicate it, and take a video.
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[B]94 Grand Cherokee 5.2[/B] [SIZE="1"]33in. Federal Couragia M/T's on Procomp Steelies, np231 swap, IRO Hack n Tap SYE, Carolina Driveshaft, 4.5 in. lift, RE front upper/rear lower ca's, RC front lowers, Ironman rear uppers, IRO 4.5 coils in rear, 3.5 and 2" bb (no isolators) in front, Bilstein 5100's, Clayton/JKS adj. track bars, KOR rad support and SS, Magnaflow/Flowmaster exhaust, clear corners, custom light bar w/ Hella 500's[/SIZE]

[CENTER][COLOR="Yellow"][URL="http://www.jeepforum.com/forum/groups/zombie-outbreak-response-vehicles/"][COLOR="Yellow"]Zombie Outbreak Response Team[/COLOR][/URL][/COLOR][/CENTER]
[QUOTE=elcorvino;14544406]Yea... It's kind of like the fat chick who lives around the corner. You aren't trying to get caught with her, but you know she'd be a good time.[/QUOTE]

[QUOTE=ScottD16;14460352]I had a dream my entire family was attacked by a giant polar bear. The crazy part was he attacked us with a giant spoon. Best dream ever.[/QUOTE]
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Unread 11-23-2012, 11:49 PM   #9
Freestyle713
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So here's how it ran when I started it this morning. I'm in the process of changing the fuel filter just to see if thats the problem, but I broke a connector, so gotta wait till tomorrow to finish. I still think its electrical, though. BTW, that's me revving it in the middle of the video.

Edit: and no, I don't have shaky hands. Thats the engine.

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[B]94 Grand Cherokee 5.2[/B] [SIZE="1"]33in. Federal Couragia M/T's on Procomp Steelies, np231 swap, IRO Hack n Tap SYE, Carolina Driveshaft, 4.5 in. lift, RE front upper/rear lower ca's, RC front lowers, Ironman rear uppers, IRO 4.5 coils in rear, 3.5 and 2" bb (no isolators) in front, Bilstein 5100's, Clayton/JKS adj. track bars, KOR rad support and SS, Magnaflow/Flowmaster exhaust, clear corners, custom light bar w/ Hella 500's[/SIZE]

[CENTER][COLOR="Yellow"][URL="http://www.jeepforum.com/forum/groups/zombie-outbreak-response-vehicles/"][COLOR="Yellow"]Zombie Outbreak Response Team[/COLOR][/URL][/COLOR][/CENTER]
[QUOTE=elcorvino;14544406]Yea... It's kind of like the fat chick who lives around the corner. You aren't trying to get caught with her, but you know she'd be a good time.[/QUOTE]

[QUOTE=ScottD16;14460352]I had a dream my entire family was attacked by a giant polar bear. The crazy part was he attacked us with a giant spoon. Best dream ever.[/QUOTE]
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Unread 11-24-2012, 12:51 AM   #10
johnridesjeeps
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What about replacing the IAC?
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Unread 11-24-2012, 06:46 AM   #11
ZeeJay1997
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It looks like the battery is weak. I would do whatever it needs to fix the CEL and check charging system before i pursued other possibilities.
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Unread 11-24-2012, 11:05 AM   #12
ratmonkey
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yeah, your charging system isn't working well at all. i'd get that sorted out before tackling anything else. it will cause running issues.
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Unread 11-24-2012, 01:13 PM   #13
Freestyle713
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I just put a new alternator in, and the battery is only about 3 years old, but ill test everything. I pulled a spark plug and it was black, so its running rich. Could it be my ignition coil or distributor?

Edit: Just tested it and it checked out fine.
__________________
[B]94 Grand Cherokee 5.2[/B] [SIZE="1"]33in. Federal Couragia M/T's on Procomp Steelies, np231 swap, IRO Hack n Tap SYE, Carolina Driveshaft, 4.5 in. lift, RE front upper/rear lower ca's, RC front lowers, Ironman rear uppers, IRO 4.5 coils in rear, 3.5 and 2" bb (no isolators) in front, Bilstein 5100's, Clayton/JKS adj. track bars, KOR rad support and SS, Magnaflow/Flowmaster exhaust, clear corners, custom light bar w/ Hella 500's[/SIZE]

[CENTER][COLOR="Yellow"][URL="http://www.jeepforum.com/forum/groups/zombie-outbreak-response-vehicles/"][COLOR="Yellow"]Zombie Outbreak Response Team[/COLOR][/URL][/COLOR][/CENTER]
[QUOTE=elcorvino;14544406]Yea... It's kind of like the fat chick who lives around the corner. You aren't trying to get caught with her, but you know she'd be a good time.[/QUOTE]

[QUOTE=ScottD16;14460352]I had a dream my entire family was attacked by a giant polar bear. The crazy part was he attacked us with a giant spoon. Best dream ever.[/QUOTE]
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Unread 11-24-2012, 02:07 PM   #14
Freestyle713
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Ok, so while my boss was checking it out under the hood, I moved the PCM connection and the idle freaked out. On the way to work (AAP), it ran like **** and the cel was on. But then after I moved the pcm more it was fine. And its still fine now. So at least I know where the root of the problem is if it happens again.

My boss was telling me about someone that had this problem and was told about a screw somewhere in the actual pcm that was touching something inside it and had to be trimmed. Has anyone ever heard of this problem?
__________________
[B]94 Grand Cherokee 5.2[/B] [SIZE="1"]33in. Federal Couragia M/T's on Procomp Steelies, np231 swap, IRO Hack n Tap SYE, Carolina Driveshaft, 4.5 in. lift, RE front upper/rear lower ca's, RC front lowers, Ironman rear uppers, IRO 4.5 coils in rear, 3.5 and 2" bb (no isolators) in front, Bilstein 5100's, Clayton/JKS adj. track bars, KOR rad support and SS, Magnaflow/Flowmaster exhaust, clear corners, custom light bar w/ Hella 500's[/SIZE]

[CENTER][COLOR="Yellow"][URL="http://www.jeepforum.com/forum/groups/zombie-outbreak-response-vehicles/"][COLOR="Yellow"]Zombie Outbreak Response Team[/COLOR][/URL][/COLOR][/CENTER]
[QUOTE=elcorvino;14544406]Yea... It's kind of like the fat chick who lives around the corner. You aren't trying to get caught with her, but you know she'd be a good time.[/QUOTE]

[QUOTE=ScottD16;14460352]I had a dream my entire family was attacked by a giant polar bear. The crazy part was he attacked us with a giant spoon. Best dream ever.[/QUOTE]
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Unread 11-24-2012, 03:51 PM   #15
ZeeJay1997
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Quote:
Originally Posted by Freestyle713 View Post
My boss was telling me about someone that had this problem and was told about a screw somewhere in the actual pcm that was touching something inside it and had to be trimmed. Has anyone ever heard of this problem?
That's a web rumor associated with the 96-98 PCM. Even if were fact, it doesnt apply to your PCM.

I'm not very familiar with the earlier ECM, there might be a screw somewhere on it, but I haven't seen reference to it on this forum. The first thing to do would be use some contact cleaner and soft brush to clean the connector and plug. If that doesnt help, take the backshell off the connector and use some needle nose to grab each wire and move to see if you have a bad socket.

The most common problem this ECM is bad capacitors that are cheap and easy to fix, but what you have sounds like a connection problem rather than failing electronics. See the link in my sig, there's a link to the cap replacement writeup at the bottom of #1
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