I need help with a 4.0 that doesn't idle well (long)

vanguard

vanguard

Well-Known Member
Joined
Oct 19, 2005
Location
Apex, NC
My buggy has a Jeep 4.0 from a 99 Grand Cherokee. When you first start it cold it runs like a champ. After warming up it doesn't idle well. At first it just doesn't rev quickly and eventually it will stall. If you need high RPM it usually does that well for a long time. Here are some of the things I've done or checked lately but so far nothing has fixed it.

1) New fuel pump
2) Fuel filter flows great
3) New TPS
4) Cleaned up Idle control motor
5) Sprayed a bunch of throttle body cleaner into the throttle body
6) New CPS

Does anybody have any idea as to why it wouldn't do well at low RPM after it warms up?
 
Does it act like its getting too much fuel?
 
The times i have heard it run rough it does sound and seem too rich. I don't have any ideas other than things you have already checked though.....
 
I don't know what everyone else is running but you might wanna change the E2000 out for a stock fuel pump. Just a thought. Those things push a shit-ton of pressure and it sounds like its ok when you're using the fuel but while idling it can't handle the load. You might also consider a fuel pressure regulator. I would find a way to check just how much fuel pressure you have and compare it to stock specs.
 
Can you pull codes on it? That would be where I would start. Also, it's easy to stick in inline pressure gauge on it to see what the pressure actually is. That little gizmo proved invaluable in diagnosing a fuel delivery issue I had on a TBI engine.
 
I can't pull any codes, there is no OBDII harness. As for the fuel pressure, IIRC it's around 45 PSI. I think it's right about where it's supposed to be. Also, the E2000 fuel pump worked well for years in this setup. It would be odd if it suddenly wasn't appropriate for it.
 
Hmmm...Sorry woody but thats all I know to tell you.
 
IIRC, there should be a pressure regulator on the fuel rail... that may not be working right, and causing it to run rich...

I would try to check the pressure in the system, before & after the regulator...
 
Back
Top