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Stumped .. Smooth idle, runs rough with any touch of the gas

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Old Sep 17, 2016 | 01:46 PM
  #1  
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From: Santa Cruz Ca
Year: 1999
Model: Cherokee
Engine: 4.0 HO
Default Stumped .. Smooth idle, runs rough with any touch of the gas

96 4.0 auto

Just swapped a 91 block and head over to this 96 and swapped the appropriate sensors for obd2 engine harness as well. Been driving fine for 2 weeks. Was driving and came to a stop light. When I went to take off I had a crazy rough running jeep and couldnt get past idle speeds
Will start up and idle rough as hell, eventually the idle smooths out and is around the 750 rpm mark. ANY touch of the gas it with sputter and run like absolute crap.

I do have a scanner with live data

TPS voltage - 5.17 FEED 3.98 at WOT and .8 at closed.. smooth transition throughout
49 psi at idle fuel pressure and when attempting to gas
MAP "hg" 4.5 at idle
Swapped map with a known working one from another jeep
Swapped TPS from another jeep
changed the coil
changed IAC
changed plug wires and inspected spark plugs
changed cap
removed distributor and verified timing
changed fuel injectors
Tried unplugging o2, coolant temp sensor

Can't really think of anything else

Need to get this rig back rolling ASAP
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Old Sep 17, 2016 | 06:37 PM
  #2  
CCKen's Avatar
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From: Canton, MI
Year: 1999
Model: Cherokee
Engine: 4.0
Default

Originally Posted by 831xj
96 4.0 auto

Just swapped a 91 block and head over to this 96 and swapped the appropriate sensors for obd2 engine harness as well. Been driving fine for 2 weeks. Was driving and came to a stop light. When I went to take off I had a crazy rough running jeep and couldnt get past idle speeds
Will start up and idle rough as hell, eventually the idle smooths out and is around the 750 rpm mark. ANY touch of the gas it with sputter and run like absolute crap.

I do have a scanner with live data

TPS voltage - 5.17 FEED 3.98 at WOT and .8 at closed.. smooth transition throughout
49 psi at idle fuel pressure and when attempting to gas
MAP "hg" 4.5 at idle
Swapped map with a known working one from another jeep
Swapped TPS from another jeep
changed the coil
changed IAC
changed plug wires and inspected spark plugs
changed cap
removed distributor and verified timing
changed fuel injectors
Tried unplugging o2, coolant temp sensor

Can't really think of anything else

Need to get this rig back rolling ASAP

Did you keep the '96 distributor?
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Old Sep 17, 2016 | 06:44 PM
  #3  
97grand4.0's Avatar
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From: syracuse ny
Year: 1997 230,000 miles
Model: Grand Cherokee (ZJ)
Engine: 4.0, new lifters valve job with new springs and exhaust valves, preload set with shims
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Shooting from the hip, sounds like my cam sensor when it started to go.
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Old Sep 18, 2016 | 08:36 AM
  #4  
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I did keep it, accidentally broke the fork tab off it tho when fumbling stuff around in the garage
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Old Sep 18, 2016 | 10:29 AM
  #5  
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Originally Posted by 831xj
I did keep it, accidentally broke the fork tab off it tho when fumbling stuff around in the garage
Did the distributor move at all?
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Old Sep 18, 2016 | 12:03 PM
  #6  
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From: Santa Cruz Ca
Year: 1999
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Engine: 4.0 HO
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The distributor and timing have been set again. Same issue is still going.

#1 tdc on compression stroke rotor was just at the tail end of #1 spark plug on diz cap
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Old Sep 18, 2016 | 12:07 PM
  #7  
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From: Santa Cruz Ca
Year: 1999
Model: Cherokee
Engine: 4.0 HO
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I do notice the timing advance a lot on my scanner .. from 10* to 29ish tops
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Old Sep 18, 2016 | 08:28 PM
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From: Canton, MI
Year: 1999
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Originally Posted by 831xj
I did keep it, accidentally broke the fork tab off it tho when fumbling stuff around in the garage

I think I would replace that distributor.
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Old Sep 19, 2016 | 09:51 PM
  #9  
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Year: 1999
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Originally Posted by CCKen
I think I would replace that distributor.
It's in the garbage can... was never installed.
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Old Sep 20, 2016 | 05:44 AM
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From: Lost in the wilds of Virginia
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
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Okay.... so what distributor is in there?
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Old Sep 21, 2016 | 05:18 PM
  #11  
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From: Santa Cruz Ca
Year: 1999
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It's fixed. Trans bolt was forgotten to be torqued and had backed out causing a gap. Damaged the CPS. New bolt and CPS and it runs great. Flexplate was fine... was worried about that.
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