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New distributor

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NAXJA Forum User
I was looking at my timing today trying to figure out why my Jeep runs so rough after about 3000 rpm. So I thought i would try that new search feature offered here, wow does that work great , it answered my question completely and 100 %. Well maybe 95%, I know i need to change something but unsure what. Do I need a new distributor or just a new gear. Also do I need a Mopar distributor or will an Advance auto dist. work?
Thanx Digger
 
Before you change the distributor may I ask how many miles on your vehicle? Sounds like you may be having the classical "cut out" and I'd recommend new cap, rotor, wires and see if that fixes the problem.

ON my 88 and sure on the post 90 4.0s it teh same way. There is a hall effect sensor in the distributor to "fire" the injectors. This sensor is called the sync sensor or the Camshaft position sensor.

There is a sensor on the bellhousing called the crankshaft position sensor (CPS). It determines when the spark plugs fire. The CPS is a part that does wear out even though it done not make physical contact. It is very similar to the ABS sensor on any vehicle.

Yes, you can use a rebuilt from the parts store but I purchased a new distributor for my 88 XJ from the dealership. I wanted a "new" sync sensor in my replacement distributor so i spent the extra money.

You also may want to make sure the hose from the throttle body to the MAP sensor is not borken. If you unhook the MAP sensor it runs bad - don't ask me how I know ;)

So I may do things in this order
1) Cap, rotor, wires
2) new CPS, just replace it if it has over 100K on it
3) new MAP sensor, same as CPS for mileage
4) replace distributor
 
Thanx for the info. Already ahead of you thou, Cap rotor and wires are new, cps is less than a month old.
I feel it it is my distributor because i put the crank on #1 TDC and my rotor was like 3/4" off. I also put a standard timing light on it and it show'd about 12 degrees instead of being at the 0 mark.
PS How much should I expect to pay for a distributor at the stealership?
 
At the time I think the distributor was 65 at Autozone but 180 at the dealership. To get the new sensor I was willing to pay it. I checked on the sensor and it was 70 bucks by itself so if you figure a autozone distributor & a new sensor you are 2/3 of the way to a dealer part with a 12 month warranty.

I recommend you take the rig to the dealer and have a mechanic who knows Renix XJs install it. It will cost you 1.0 hours of labor but well worth it. As part of the install the mechanic will hook up the test set and make sure all the sensors are working right. My guy let me watch him install it, so interview the mechanic, if they know who own's it then you get better service.

On the rotor position remember there a huge tip on the rotor so it will be able to bring spark to the stud on the cap.

The bushings in the distributor do get worn and that could explain what you have observed. While you are at the dealer pick up a High ALT CPS and install it. It will give you more advance which turns into more power. You should not have a ping problem since you have a knock sensor. If you get knock running 87 octane with a high alt CPS then you will need to replace the knock sensor.

OR you could take the rig into the dealer, tell them of your problem and let them figure it out. You may not need a distributor but one of the sensors I mentioned already.
 
Before you buy anything, do a search on distributor indexing. What you describe is a common symptom of a distributor that is indexed off by one tooth.
 
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