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Unread 08-15-2013, 07:14 PM   #1
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Join Date: Jun 2013
Location: tulsa, Oklahoma
Posts: 9
Please help!!!

i have a 98 cherokee 4.0 4x4 limited 220k miles

its running very rich DARL BLACK smoke from pipe when in good acceleration.. i cant find out how to fix this?!?! It idles terrible never dies but the engine shakes terrible when idling and my mpg has dropped by X3

replaced MAP sensor, IAC, TPS, 02 downstream sensor and upstream are new within 6 months , new cat and seafoamed the thing correctly... i've checked all the vacuum lines and they look fine. New injectors and spark plugs also

recently borrowed a fuel pressure gauge and while idling it jumped drastically from 40-50 in the same pattern as it idles bad

i'm thinking the fuel pressure regulator might be the cause but im exhausted of throwing money at it trying to find these problems

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Unread 08-16-2013, 04:03 PM   #2
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1996 XJ Cherokee 
Join Date: Feb 2010
Location: Gurnee
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any CEL?
1996 Jeep Cherokee- Project-- Rusty's 8in long arm, SYE kit, Teraflex driveshaft, Cragar soft 8's 15x10 with 33x12.5 Firestone Destination MT's, Eaton Tru Trac in the front
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Unread 08-16-2013, 06:46 PM   #3
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1993 XJ Cherokee 
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fuel pressure regulator, pull the vacuum line and see if its wet and smells like gas if so then replace it. engine coolant temp sensor could be faulty too..
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Unread 08-16-2013, 07:04 PM   #4
Real Jeeps have dents.
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2000 XJ Cherokee 
Join Date: Apr 2002
Location: out in the garage - Minneapolis, Minnesota
Posts: 21,614
Originally Posted by xjdantheman View Post
fuel pressure regulator, pull the vacuum line and see if its wet and smells like gas if so then replace it...
If it was an 1995 or older Jeep, this might be true. Not so much with an OBD-II Jeep.

Why were all these parts replaced, routine maintenance, or some issues you were trying to shotgun cure ?

Poor running, and severely decreased gas mpg's often points to O2 sensor issues or exhaust manifold issues. Has you checked/tested the O2 sensor fuses and wires ? Have you tested the O2 sensors ? Are they BOSCH O2 sensors ? Have you inspected for cracks in the exhaust manifold ? Have you hooked up an OBD-II trouble codes reader and checked the live data ?

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