post #1 of Old 02-17-2015, 09:50 AM Thread Starter
obcean
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1993 YJ Wrangler 
 
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Crankshaft positioning sensor and what else?

(I apologize for the length, I tried to include the pertinent information..) Three YJ's drove to Death Valley on Friday and two drove back on Monday towing the third...mine.We went through Steel Pass between Saline Valley and Death Valley on Sunday and on good gravel roads I could hear and feel a little hesitation, but couldn't figure it out. On the gawdawful washboard and driving through the wash before the pass, it REALLY was hesitating, but seemed to shake itself out when there were long relatively smooth stretches. Once we hit the pass, forget about it. We had to stop navigate a waterfall just before the pass, and not only was their hesitation but the brand new muffler sounded like crap as it was gunned up a loose dirt/gravel hill immediately after the waterfall. It really started to miss a short while later but we attributed that to needing gas because when we fueled up it sounded a little better when it ran. We had to stop about 25 minutes later as one of the other jeeps broke a tie rod on a rock. After maybe an hour and a half it didn't want to start at all and sounded BAD...like maybe it was running on two unhappy cylinders. We made it down 3 waterfalls with no power and then were towed to the dunes. After a lot of discussion, we thought it might be the CPS, and if it ran well on pavement then that had to be it for sure. Sure enough, after being towed on miles of washboard, when we hit pavement it ran like a Jeep is supposed to...until we went up a grade. After a few of those, it wouldn't even start any more. At that point we were towed all the way to the turn off for Scotty's Castle, and we tried to start it once more. Got it started after a struggle, but it would not go into gear. Actually, the it went into gear, but giving it gas accomplished nothing. It was a long tow back to Las Vegas.
So. if it is the crankshaft position sensor, what ELSE is it? Why would it progress from being an apparent cps issue to refusing to have forward momentum? Any and all helpful input is gratefully requested.


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post #2 of Old 02-17-2015, 09:56 AM
mike134
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I'm wondering if your clutch is disengaging properly. It seems to be happening when you are crawling slowly, maybe half clutching or shifting gears slowly?

Otherwise, I'd check the fuel pressure at the rail. Grab the fuel pressure gauge from autozone, free to borrow. Check pressure with the key in the ON position and again at idle.

You may as well check for vacuum leaks while you're at it, provided you can get the thing to start up and idle a bit.
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post #3 of Old 02-17-2015, 10:20 AM
Que89YJ
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Could be a lot of things. You always need to start by checking fuel and spark. The other thing I noticed is that it was happening on grade. You said you heard noises. Do you still have your cat on? Trailing it with the cat will bust it up and the pieces will block the flow of exhaust. Remove the O2 sensor and see if it makes a difference.
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post #4 of Old 02-17-2015, 11:41 AM Thread Starter
obcean
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Quote:
Originally Posted by Que89YJ View Post
Trailing it with the cat will bust it up and the pieces will block the flow of exhaust.
Thanks for the help. Do you mean the stuff inside the cat shakes loose and blocks flow? That is what I understand, but I just want to make sure I get what you meant.
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post #5 of Old 02-17-2015, 12:05 PM
Que89YJ
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Yep. Start by checking 1) fault codes 2)spark on all the plugs 3) fuel pressure 4) back pressure on the exhaust by removing the O2 sensor
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post #6 of Old 02-17-2015, 03:35 PM Thread Starter
obcean
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Quote:
Originally Posted by mike134 View Post
I'm wondering if your clutch is disengaging properly. It seems to be happening when you are crawling slowly, maybe half clutching or shifting gears slowly?

Otherwise, I'd check the fuel pressure at the rail. Grab the fuel pressure gauge from autozone, free to borrow. Check pressure with the key in the ON position and again at idle.

You may as well check for vacuum leaks while you're at it, provided you can get the thing to start up and idle a bit.
Thanks, Mike! I can't wait to leave work to try the suggestions you gave. I really appreciate it. I will update as soon as I have more of a clue what is going on.
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post #7 of Old 02-17-2015, 04:10 PM
mickcollinsb16b
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wasnt clear if you had problems on hills vs flat. but one thing you said made me think of this. that when you filled up it ran a little better. i had a friend that changed the fuel pump with a Crown replacement and about a year latter he had really hard starts and hesitations but it always ran. we explored all options until we finally decided something might be blocking the feed tube of the sending unit. upon dropping the tank we found out the rubber hoses that came on the sending unit had rotted out already. cheap china hoses almost looked like vacuum hoses had come on the sending unit/pump! not to bash Crown i still use there products but wow. replaced the short sections of hose and no problems again and its been years. something to think about.

RoknRoll, beer & Jeeps
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post #8 of Old 02-17-2015, 09:46 PM
Que89YJ
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Good call on the fuel pressure.
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post #9 of Old 02-18-2015, 09:28 AM Thread Starter
obcean
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Update: Towed it to the mechanic yesterday, and he started it right up and gunned the hell out of it and drove it into the shop. Seems the forward momentum issue had to do with engine compression. His initial thought is the fuel pump.

I will give another update just in case someone else ever has a similar issue. Thank you so much for all of the advice!
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post #10 of Old 02-18-2015, 12:43 PM Thread Starter
obcean
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Final update....definitely the crankshaft positioning sensor. Thanks again for all of your help!
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post #11 of Old 02-18-2015, 01:34 PM
Que89YJ
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Usually see stalls from a failed cps not stumbles. Thanks for posting back the fix.
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post #12 of Old 02-18-2015, 01:59 PM Thread Starter
obcean
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Quote:
Originally Posted by Que89YJ View Post
Usually see stalls from a failed cps not stumbles. Thanks for posting back the fix.
Just to be completely clear, it was definitely stumbles first, then flat out stalls.
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