Hi my name is David I have been looking through this forum for some time now. It has a lot of great info. I am new to using forums. any way to my question I have a 90 xj 4.0l that i got dirt cheap (now i know why) It will idle fine but when you slightly touch the throttle it back fires threw the exhaust give more throttle it backfires threw intake. I have changed and checked:
timing ( not sure what it should be its about 12 at idle jumps when gas applied)
plugs, cap, rotor
distibutor (distributor is at #1 tdc comp stroke)
module
tps (replaced with used one checked voltage good now)
cps
computer (replaced with used one)
found low vacuum 8lb at idle 0 when gas applied ( should be higher)
intake/exhaust (found a leak around #6 after replacement vacuum still same even with all ports pluged can not find a leak now)
compression is around 120 in all cylinders.
map sensor (used one)
checked all grounds that i know of
this is what I know about this jeep. the motor is out of a 90 xj 4 door auto and is now in a 88 xj 2 door man i do have both xjs wire harness from 90 was used ( also have an 85 xj it wants a v8)
any help would be great if I had much hair I would pull it out
Thank you for the help

 

Did you check the IAC ?

 

Sorry yes i replaced that to

 

I also cleaned intake when i had it off
I guess what is really got me is the vacuum

 

Plug wires to?

 

have not checked wires they looked fairly new

 

My wife car did that,would be fine at idle,once you gave it gas it would back fire and miss bad.Bad plug wires.

 

Just cuz they look good don't mean poop.

 

I will change them and see if that helps so far everything i have done no charge at all oh when it is cold it idles rough but when it warms a little smoothes out
i did check egr also

 

when I did my wifes car it was like that,changed everything I could think of,ended up being just the dam plug wires.Thats my 2cents.

 

i read a post on here I think it was titled timing what else could it be it sounded alot like my problem but there was no end results

 

I will try wires and let you know thank you

 

the timing is fixed, so it couldn't be that.

 

My first thought was timing tried to turn dist. but no luck then saw the ears on it I felt dumb
Do you know what the timing should be at when you put a light on it

 

I don't off hand, hold on.