87Comanche

Howdy,

I've got an interesting problem with my 88 Cherokee. First of all, a little background on this rig. It's got a 4.0 with an auto trans. I picked this up from a shop that had started changing the timing chain when the owner decided he didn't want to pay for the job after it was halfway done so he just abandoned it. When I got it, the timing chain cover was off as well as the valve cover and had been off for who knows how long but I suspect it had been at least 3 years. I flushed out the pan and rockers as best as possible and installed a new timing chain. The thing fired up right off the bat and idles well. Here is where the problem is though. When you start applying throttle the thing starts to misfire, backfire and do all kinds of bad things for the majority of the throttle throw. Once it gets to WOT, it will start to smooth out. I have no vacuum leaks that I can find, I have replaced the throttle body assembly with one from a known good running motor, installed new dist cap, rotor, wires, plugs, coil from known good runner, and computer from a known good runner. None of this has solved the problem. Now when I put the new coil on, it ran right for a short period of time, then went back to the same thing.

Any ideas?

87Comanche

Anybody??

huntingman2706217

uumm i got a 89 that i recently got and noticed they run a balast resistor... cheap less then $10 part that could be the problem... mines mounted on the inner fender... has one wire in one side and one wire out the other side... made from ceramic... i doubt it but its worth a try... mine doesnt and i doubt you have any kind of points but i would check unless someone gets on soon and says im stupid for thinking its possible... Also could be the distributor itself... buddies was acting like that but hes got a 350 and thats pretty much all different but im just trying to throw you acouple more ideas... Goodluck man!

tampaviking

You should probably start with fuel next. If it sat for as long as you think then the stuff in the tank might be bad. Gas and the fuel pump. The connectors on the pump could be corroded or the rubber line in the tank could be rotted.

huntingman2706217

aahhh... yes i forgot you said it sat for along time... i would check the fuel system also... hookup a fuel pressure guage and test it out... i have a 96 motor and not sure if there all the same but mines at 31psi and with the vacuum line taken off the regulator its uuhh... i forgot... like 49 i think... that doesnt really matter as much... just helps tell you if the regulators working right or not...

87Comanche

Well, I changed the fuel filter and it made it better. It still has a bad case of runslikecrapola off idle. I pumped all of the old gas out and replaced it with new fuel and put a can of Seafoam in the tank. I imagine it will take a while for it to dissolve all the shelac that has built up in the injectors. I don't have a fuel pressure gauge to test pressure so I probably will have to get one.

87Comanche

Got it figured out. Plugged up Cat. Kinda suprised me as it was not the original one and looked to have been recently replaced.

aa7kn

my 91 XJ was the same way, it started and ran ok at idle but when I went to drive it, wow, all sorts of crazy things went on...chugging, backfiring, and one time I got mad and floored it...she ran bad at first than kicked in and ran great....I tried everything, but when I changed the Fuel pump assembly that is in the tank, it fixed all ( well most of) my problems. so maybe you have a fuel pump issue...worth checking into, there's allot of info out there on how to change the pump so I won't go into it, but it is only maybe a 30 min. job....worh the effort in my case for sure.

DFlintstone

You might be better off with your own thread. 91 and later are way different that 90 and earlier. Yours, you might start with getting the codes read, assuming it's tuned up, plugs, cap, rotor, wires, ect. Good luck!