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how to diagnose this

1K views 5 replies 3 participants last post by  PTaylor 
#1 ·
2001 Jeep Wrangler, 4.0l
Last week driving down the highway at 55, the jeep jerked, like it hesitated, and then continued on as if nothing happened. Very quick, say 1 second of time passed. When it first jerked, I looked down to see the instrument panel for a check engine light or something, only thing I saw was my voltmeter dropped down to around 12 volts or so and went back up.
Checked for codes when I got home and nothing came up.
Today, it jerked again, like it just lost power for less than a second. Again, no codes. didn't get a chance to see the instrument panel it was so quick.

So something is going on, and it doesn't seem to be a fluke with it happening twice.

I hate to go chucking money at changing sensors, would really like to know where to start with this one or if anyone else has had something like this.
 
#4 ·
Thanks for the replies.
this morning when I pulled into the parking lot at work, I stopped and was going to back into a spot. It died while backing up, but started right back up.
So this will get worse with time.

Think you got the nail on the head about the crank position sensor.
I was able to pull the codes and got a P0320, which is:
"320 Crankshaft position sensor reference signal cannot be found while the engine is cranking."

I'm confused on pulling the codes. Referring to this thread:
http://www.wranglerforum.com/f210/tj-error-codes-358.html
it states that one must hold the odometer button while turning the key to the ON position and then releasing. This will give firmware version, give codes, test the gauges.
Doing so this way in my Wrangler gives no codes, it states "no faults"

However, doing the key three times in the on position within f seconds did yield a code.
 
#5 ·
My TJ is too old for all of that but the truck does it with the 3 turns.

If you do replace the CPS please make sure you disconnect the battery before you plug or unplug either of the sensors. Had a friend that fried his PCM plugging in a new CPS with the battery connected. Was an expensive lesson for him.
 
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