93 Jeep cherokee won't run right please help!

muddyrunner02

Active Member
Joined
Dec 13, 2007
Location
greensboro
Hey so i have a 1993 Cherokee 4.0 HO 2wd that i recently converted to a 4wd that is having some problems while running. so when i start it up it will drive fine i can stomp on it and it'll go hit rev limiter no problem (i was testing it to see haven't even wheeled it yet), when I'm driving around town it does fine as long as i stay below 2700-2900 rpms but if i have to step on it at all it starts struggling and won't rev past 3000 rpms, and once it starts getting up to temp it starts having the same problem just driving it normally though and bogs down almost to the point where its about to shut off when you have to keep a steady rpm. when i say struggling it acts like it doesn't want to go like it's not getting enough fuel, 3000 it's becomes "redline" and begins to sound like its back firing through the intake when i just hold the pedal down. however if i cycle the key off and then back on i can get maybe 2 or 3 good pulls out of it before it starts acting up again. heres what i have done so far it has a new fuel pressure regulator, i swapped the fuel rail and injectors as well from my old jeep, it has a new distributor when i swapped the new one in it seemed as if the problem went away for a little bit, its got a new map sensor, new TPS, and a new CPS. all the cylinders are holding compression within 5 psi of each other (dealer recommended 120-150 compression), i swapped the ECU out of my old jeep that had 4x4, I've disconnected the O2 sensor it does not have a catalytic converter(had to cut it off). Any input helps and is greatly appreciated.
 
Disconnecting the o2 sensor isn't going to help anything, but may put the ecu into limp home mode. You need the o2 to run properly, especially after engine warm-up when it goes into closed loop fueling.
The 3k RPM rev limit and backfire is an obvious sign of that. Limp home mode usually fuels the engine stinky rich for conservative engine safety.

So you haven't mentioned if this behaviour occurred before converting to 4WD...?

Have you checked the coolant temp sensor for the ECU? They're easy to test.
 
Have you actually checked the fuel pressure with a gauge? While it's acting up, as in installed a fp gauge and drive around with it duct tapped to the windshield? Could be the pump is getting hot and failing. I'd check the basics before throwing a wheelbarrow full of parts at it.

Sent from my XT1254 using Tapatalk
 
Another vote for the fuel pump. Had many pumps fail at hot delivery, low volume which in turn creates low pressure. My xj had a pump do exactly that, put a gauge on it and found that hot pressure under load was under 20psi. It wouldn't pull a greased string out of a cats ass going down hill.
 
If it's a fuel pump, the problem will be load based and not as much RPM based. High load at lower RPM should have problems, more so than higher RPM with very low load, and it wouldn't run OK but then stumble and bog at idle which is the lowest load operating condition the engine ever sees.. I'm really not convinced that it's fuel system based, especially when a key cycle will slightly reset the behavior.
 
Key cycle primes the fuel system. 4.0s typically run fine without 02 sensors, although not optimum. Won't hurt to put a gauge on it and rule out the pump.
 
Yes i have hooked a fuel pressure gauge up and tested it, no i have not duct tapped it to the window and drove around (i will try that tomorrow and let you know), from what i was told unplugging the O2 sensor on it should make the computer revert back to a stock tune even with it making the computer go into limp home mode? either way my next guess was the O2 sensor. It ran fine before i converted it but i drove it up the street and back before pulling it onto the lift so i never really gave it a chance to mess up. A coolant temp sensor for the ECU? The coolant temp gauge for the motor is registering that it's operating at normal temp so I'm guessing the coolant temp sensor is working? Also all the parts I swapped either I had or were life time warranties from Orielly's/Auto zone. Also it does not bog down at idle it idles fine it's only under throttle does it act up, and after it's been driven or it has gotten to a quarter of the way on the temp gauge. Thank you for the feed back ill update you after I test the fuel pressure again.
 
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