KJamesJR

Decided to change out my failing CPS during my lunch break today at work. However I noticed, an immediate missfire after doing so. My engine lights are gone. I did not reset the computer after doing so... I'm thinking maybe I should have.

So yeah... 20 minutes prior to the CPS swap, the firing sequence is fine. After I change it, I get a noticale missfire. could this be the comp trying to play catch up?

I'm going back to work. I'll check back later on the subject.

KJamesJR

Nevermind. It went away... Strange, a problem the Jeep can actually fix itself.

KJamesJR

Aaannnd it's back... I'm thinking I may have to reset the ECU. Or will it set itself? I literally wasn't getting this misfire with a old CPS. 20 Minutes later and a new CPS... misfire.

Cap, rotor, wires, plugs... All new.

ZINGGG

Doesn't hurt to reset the ECU whenever replacing anything electrical. Do that first and then we'll go from there.

KJamesJR

Okay... How do I do it correctly? Read a lot of things online... All different techniques.

ZINGGG

If I remember correctly (I don't have the information in front of me at the moment) it's:

1. Disconnect the negative battery cable and touch it to ground for 30 seconds
2. Reconnect the cable
3. Get inside and turn the key to the "on" position (WITHOUT starting it up)
4. Turn headlights on
5. Turn headlights off
6. Turn key back to the off position

And that should do it.

KJamesJR

Is there someone who can confirm this? Because this one is new to me.

captainwoot

Don,t know if it really makes a difference in the xj, but on later model vehicles they call it a capacitive discharge....remove both batt cables and touch them together for 10 seconds then reinstall.....

tjwalker

Where did you buy your crank sensor? It is NOT unusual to have issues with some (not all) aftermarket crank sensors.

And to complicate the issue, sometimes those sensors test good electrically, but have a SPACING problem, which is very important with the hall effect crank sensor.

Because of the above, I install and recommend crank sensors purchased directly from Jeep for the best reliability and longevity.

You really should not have to reset the computer after a simple crank sensor swap.

KJamesJR

I got it from Rockauto.

I did read up on the spacing issues prior. However I sat it side by side with the stock cps and they did look identical in form and size.

The misfires seem to have subsided. Drove it for a good hour and it has not occurred. Engine light has not come back on... And oddly enough, my small evap leak appears to be gone as well.

I didn't reset the ECU. It was getting dark and I had to run out for things anyways.

ZINGGG

For future reference, I did have one thing backwards. Instead of the negative battery cable, it's the positive one. Mr. Walker is a smart guy so I'd go by his word and say you don't have to reset the ECU. But here is the correct way of doing it:

1. Disconnect the positive battery cable and touch it to ground for 30 seconds
2. Reconnect the cable
3. Get inside and turn the key to the "on" position (WITHOUT starting it up)
4. Turn headlights on
5. Turn headlights off
6. Turn key back to the off position

Then you can go ahead and start her up. And then set your radio presets