jeep 4.0 wont rev up

[offroadin 88xj]

i just rebuilt my 4.0 in my xj its bored .30 over it runs fine at idle but wont rev up just spits and sputters and pops does anyone know what my problem could be

 

[mattb6679]

Timeing may be off. by 1 tooth.

 

[offroadin 88xj]

ive checked the timing and its all good

 

[Jweezy]

misfire or switched up plug wires? not getting fuel?

 

[jtbenfie]

I would start by pulling codes and checking fuel pressure.

 

[offroadin 88xj]

its got a new fuel filter and pump and my book says the wires are on right

 

[Jweezy]

check throttle position sensor, and idle air control valve.

 

[offroadin 88xj]

alright ill try it and let you know

 

[hadfield4wd]

Is this an 88? If so it's the Renix fuel injection. They have a ballast resistor for the fuel pump. It knocks down the voltage for the fuel pumps from 12v to 6v. Mainly for noise reduction. When a pump goes it will lose pressure. Bypass the resistor.

 

[offroadin 88xj]

yeah its a 88 were is the resistor and how do i bypass it

 

[offroadin 88xj]

my o2 sensor is broke off would that have anything to do with my problem

 

[amajeepman]

The o2 sensor could be it. Also check your map sensor

 

[jtbenfie]

An o2 sensor usually will not keep the engine form revving, it will just prevent it from going into closed loop. Make sure the wires from it aren't touching each other.

Did you try pulling codes? Did you check the fuel pressure?

 

[Pinkston]

My 4.0 does something similar to what you are describing when the CPS gets out of whack.... something to lok into.

 

[Jody Treadway]

How did ya check the timing? Timing is not adjustable. It can however be off a tooth either way and still run, just poorly.

Make sure the vacuum line from the intake to the MAP sensor isn't cracked. Also make sure the nipple on the MAP sensor isn't cracked.

 

[offroadin 88xj]

i made sure the dots on the timing sprockets were lined up with each other

what is the cps and how does it get out of wack

 

[Jody Treadway]

Your cam timing may be ok, but what about your ignition timing? How did ya install your distributor?

 

[offroadin 88xj]

i set it to tdc and put the distributor in with it pointing to the number 1 cylinder wire

 

[Smokeater]

You can still have your Distributor off by one tooth. The rotor should be pointing to the lead of the terminal, I think the book says around 4:45. If it's on the trailing end of the terminal, when the timing is advanced the spark will occur too late almost or actually missing the terminal. Hope this helps.

 

[offroadin 88xj]

Wat do you mean by lead terminal

 

[Smokeater]

Well lets see if I can explain better. The rotor turns clock wise. At TDC the rotor should be pointing at #1 terminal but not straight at it. Meaning the leading edge of the Rotor should be at #1. If 1 tooth off (too far clock wise), the trailing edge of the rotor will be to far past the terminal when timing is advanced. Maybe these pics will help. The circles represent the terminal on the cap.
Correct position. the leading edge of the rotor is at #1 when TDC

Incorrect position. The trailing edge is at #1 when TDC. as you can see, when timing is advanced the rotor will be too far ahead. Move back 1 tooth

 

[offroadin 88xj]

Alright thanks ill check that when I get home and let you know

 

[offroadin 88xj]

it was right wdoes anybody have a code reader for a 88 cherokee that might be able to check it for me

 

[mattb6679]

I don't think it will throw a code, if anything its obd1, and the check engine light will be your code reader. Have you tried messing the Distributor? Ive worked on a lot of xj and had this happen a couple times. Easy fix.

 

[offroadin 88xj]

i have no check engine light on is there any way you might be able to come by and take a look at it some time