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Why might it stumble on light acceleration

Tiny
FRUSTRATEDWRENCH
  • MEMBER
  • 1990 JEEP WAGONEER
  • 170,000 MILES
I have a friend who has a 1990 jeep wagoneer, 4.0l, 6i. Also lack power. New cap, rotor, wires, fuel pressure tested and spot on, TPS ratio @.832v, throttle body cleaned, IAC cleaned, searched high and low for vacuum leak (found none), cleaned EGR, MAP vacuum line cleared. Car idles fairly smooth until put into gear, then idle becomes a little rough. Upon light acceleration, get a slight backfire or two, then it tries to go, but not with good get up and go. The car goes better upon hard acceleration, after a slight hesitation. Any ideas? Thanks !
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Saturday, January 28th, 2012 AT 2:37 AM

9 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,262 POSTS
Have you checked engine compression?
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Saturday, January 28th, 2012 AT 2:43 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
You sure the EGR is not opening too soon?
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Saturday, January 28th, 2012 AT 3:47 AM
Tiny
FRUSTRATEDWRENCH
  • MEMBER
  • 5 POSTS
I checked the compression (dry) and the cylinders were all within 5 psi of each other, but I don't recall what the actual reading was. I can run them again if you could tell me what an acceptable reading should be, either wet, dry or both. Thanks. As far as the EGR, how can I know if it's opening too early? Thanks for the responses!
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Saturday, January 28th, 2012 AT 4:51 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Disable the EGR and test drive it-
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Saturday, January 28th, 2012 AT 8:48 PM
Tiny
FRUSTRATEDWRENCH
  • MEMBER
  • 5 POSTS
Should I pull the unit off, or should I just pull the hose? Do the symptoms indicate to you and EGR issue? Thanks!
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Sunday, January 29th, 2012 AT 2:10 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
You have to make sure the EGR valve is closed completely then block of the vac hose to it-
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Sunday, January 29th, 2012 AT 3:04 AM
Tiny
FRUSTRATEDWRENCH
  • MEMBER
  • 5 POSTS
Rasmataz, I isolated EGR, plugged hoses, drove the car. Still idled rough as soon as engaged into gear, and still hesitated upon light acceleration. Could there be a vacuum leak or restriction that I have not located? What would you suggest as the best way to check? Thanks, Frustrated
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Tuesday, January 31st, 2012 AT 4:57 PM
Tiny
FRUSTRATEDWRENCH
  • MEMBER
  • 5 POSTS
There is also an additional issue, though I don't know whether it's relared or not. Any time you attempt to start the car, it takes about 8 to 10 seconds of cranking to start, then once started the previously mentioned issue exists. Why the long cranking time? Thanks
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Tuesday, January 31st, 2012 AT 5:24 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check the colant temperature sensor and IACV

Go to this link: https://www.2carpros.com/articles/engine-misfires-or-runs-rough
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Tuesday, January 31st, 2012 AT 8:08 PM

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