Help, I’m outta ideas. My 1996 Cherokee was running great. Then just quit while I was driving. Towed it home and found the distributor shaft bushing was so worn, it caused the rotor to hit the cap and break. So I secured a new distributor with cap and rotor (ORiellys, Spectra brand), put it in, double and triple checked the timing position, cleaned the fouled plugs and after a little cranking it started up. Seemed to run fine. Moved it to garage to button up a few items, went to start it and all it would do is crank. Checked coil it tests fine. Checked spark and it is weak so I went ahead and replaced the coil. No change. Cps checks good. Finely figured out I can get it to start after lots of cranking by holding the throttle about 1/3 open. Then it idles smooth, but when I open the throttle smoothly it misses and backfires. Jab the throttle open and it’s smooth. Load the engine in gear and it seems to load smooth but don’t want to try driving it for fear of being stranded. I tried swapping the old camshaft position sensor to make sure I didn’t have a bad part, but it made no change. I really don’t want to just start throwing parts at it, but I’m lost. It’s actually my sons Jeep and he’s on a very limited budget. Any ideas, help would be greatly appreciated.

 

Kind of has the hallmarks of a low-voltage problem. Do you have a multi-meter? Have you tested the battery voltage while engine-off and with the engine running? When was the last time the battery connections and various ground connections were cleaned up?

Are you certain that the rotor/cap was actually the cause of the original problem? Or just something you noticed when trying to find a cause?

 

The battery is a bit weak. We jumped it to up the voltage. Also cleaned the terminals and the main ground. There is no doubt the distributor caused the no run condition. The shaft has at least 1/4” side play. The rotor was broken at the base and twisted on the contact point. The cap has grooves where the rotor was rubing on it before it broke. It cranks very fast when jumped and the voltage only drops to about 11 volts after cranking a while. It was running great before the distributor broke, very smooth with great power.

 

As added info, it is VERY hard to get started, if we can get it to start at all. But when it does it acts as described in my first post.

 

I'm assuming you didn't mess with many things while you were in there, so I'll stay focused on the distributor/cap/rotor. Have you double-triple checked that the spark plug wires went back on in the correct order? Generally speaking, when standing on the passenger side of the engine looking at the cap, the #1 plug will be about the 5 o-clock position and continue clockwise in the 1-5-3-6-2-4 order.

Do you still have concerns regarding a weak spark? If so, what method are you using to determine that?

 

I have been working with Baddad on this one. And its a weird one. Have to feather the throttle to get it to start, then its running on 3 or 4 cyls, then when kind of playing with the throttle all of a sudden kind of a bang and its idling smoothly. The weird part is the snap throttle works fine but light throttle makes it fuss something awful. Shut it down and try an immediate restart and its back to 3 or 4 cyls. Battery is weak, but we jumped it with a running car and no change in the condition. Spark is weak. I think the next round we can slip a loaner battery in there for good measure, buy why all of a sudden would it snap to and idle nicely? I am certain the thing flooded while diagnosing the first no start, but I cannot think what that would mess up.

 

I’ve checked the firing order so many times, I’ve forgotten how many. The “weak spark” is by looking at both a used and new spark plug while cranking and observing a mostly yellow, small spark.

 

Has the wire from the coil to the rotor been compared for spark quality against the spark quality on a plug wire to see if there is an observable difference pre/post distributor cap?

 

Get a whole bunch of the same spark that way. Also, just exchanged the new distributor for another one. No difference.

 

Fixed it! Omg, when you put a distributor in these, point the rotor just PAST the #1 cap post! Not right at it! It seemed like it was a tooth off but the new distributor came with a plastic post holding the rotor just past #1. I thought it was screwed up so I put it in like I’ve done a 100 times before on SBC, fords, etc... I guess that’s not the case with 4.0’s! Thank god it’s fixed now! It was driving me crazy!

 

Thanks for the update, it may help someone else in the future.