• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

rough running at 1500rpms

R

rebelcherokee

NAXJA Forum User
Location
Huntsville, TX
I got my miss fire problem fixed and it idels great but when I try to give it any gas it stumbles and wont get over 1500 rpms and when it starts to stumble my tach goes to 500. if I ease in to the throttle some times it will go over 2500 put it dont have any power
I sorry if there is another post on this I could not find it
 
Yeah sounds like it could be the TPS. By the way have you removed your distributor lately? I only ask cause that is one of the issues I had when I bought the 87 and alot of work from people who didn't know the system caused me alot more work. If you haven't then yeah points to the TPS. There is an adjustment procedure in the manual I sent you. Also while you are at it check you ground potential to battery ground. If it is anything above 0 then you may want to splice in a connection to lower the gnd potential. Also check your grounds the renix years are hard core about having a proper ground. good luck.
 
yes i put a new distributer in it when i changed the motor but I have already indexed it the rotor is pointing at 5 0'clock at tdc the motor has brand new bosch platnums in it. I know that the 4.0 likes the champion plugs I'm just broke right now but if that will correct the problem I will put them in ASAP
 
Have you checked you TPS? What are you getting? If that does not fix it then reindex the dizzy. Remember the 5 O'clock is when you are standing on the passengers(6 O'clock) side facing the drivers side (12 O'clock). The guy I bought my 87 off of had done it from the grill facing the firewall. I had the same symtoms oh plus a cherry red Catalytic converter (which was peelin and baking paint).
 
tps checked out ok, when I put my timming light on it tonight at idle i noticed that my timming mark was at about 12* before tdc is this correct? when i give it throttle i can't even see the timming mark, is this normal?
 
i would re- index the distributor properly and not rely on setting at 5 o clock. if it ran well before the engine change. i would bet that can help. also i would check for a loss of vacuum at higher rpm's, the convertor may be getting clogged
 
Try using a set of NGK's. Basic plugs no platinum iridium super nova plugs. I really dont know but I doubt its the distributor.
 
This is a process of elimination and most things on a RENIX are easy to verify functionality with a meter and a manual. (factory service manual is by far the best) Have to narrow down whether your problem is fuel, ignition, or sensor related. Some things to think about would include:

*Test Fuel Pressure
*Verify EGR valve operation
*Test Ignition coil and ignition control module
*Test Map sensor
 
Last edited:
OverTheHillsATTW said:
Try using a set of NGK's. Basic plugs no platinum iridium super nova plugs. I really dont know but I doubt its the distributor.
Click to expand...

I'm curious why you say NGK's. Personally, I use them for all my other vehicles and dirt bikes, but I've never changed the plugs on my new (to me) Cherokee. The strong consensus on this forum is to use Champions, but they seemed to foul out on my older or oil burning vehicles. I'm sure that evedryone will say that the vehicle was developed by Chrysler with Champions so that's what you should run.
 
are the computers the same from an automatic to a manual? I have the chance to change out the computer it comming from the same year model 89 xj but it has a manual trany and i have an auto trany
 
the computers are not the same however it will work. I have used the one from my 88 which is a manual to test on my 87 and vice versa and the both worked. O am pretty convinced that its gonna be your dizzy
 
Like was said, it still sounds like distributor indexing. Rather than rely on 5 oclock, crank the engine until it is approximately 15 degrees before TDC on the compression stroke. Pull the cap. The rotor should be pointing at the #1 plug wire. It is possible to get your wires indexed wrong on the distributor cap, so this method gets rid of any uncertaincies.

As for checking the TPS with a voltmeter, what you did is a good start, but you need to manually rotate the lever arm while looking at the voltage. It should smoothly change with no jumps or dips throughout the range of motion.
 
I looked at the dizzy this morning and the rotor is pointing at #1 plug wire and the wires are on correctly I even cross checked it against another 89 4.0 XJ and every thing is the same. And yes the other XJ does run
 
I wonder if it was placed at the exhaust stroke and not where it should have been the compression stroke like old_man said. There are two TDC positions, I went through the same thing with mine while it was raining and snowing out which pissed me off worse but I learned the hard way that day.
 
You must log in or register to reply here.

Similar threads

J
Cranks, Fires, Dies - 1991 Briarwood Restoration
Replies
17
Views
3K
Jam Master Jay
J
N
Severe stumble, misfire and no start issues
2
Replies
27
Views
4K
maxbraketorque
M
S
2000 STFTs stuck at 98% ??
Replies
8
Views
2K
RCP Phx
R
G
1997 Sport running rough after warming up
Replies
8
Views
2K
Gilpine
G
W
Error codes: p0123 and p0122
Replies
5
Views
2K
Unclewolverine
U
Back
Top