Hey guys, I have always done my own work and searched and researched everything i could to do it right. Now i am at a loss and don't know what could be going on.

First I have a 99 classic, 4.0, AW4. All regular maint. done. Tune up done. Full Headers back exhaust, new throttle body, spacer and Cold air intake. New MAP sensor.

Now when my jeep is driven and at regular temps, when turned off it will not crank back up. New-ish battery, new starter. It cranks and cranks, but will not run. Every now and then it will run for a few seconds roughly and die....
This only happens when it is warm..it will crank up and run fine when cold...

Also, sometimes while going down the highway at a steady speed 50-60 mph, it will jerk. Acts like it don't want to stay in overdrive or something. I have adjusted the transmission cable.
Today I went through checking the wires and could not find any kind of burnt, or damaged wires...all the harnesses i could get too were good.

Before the weather got too bad I went ahead and picked up a new CPS for the $70 and plan on trying that cause i had read that they can be heat sensitive when going bad...

So that is it...
Any and all help is greatly appreciated. I just don't know what it could be...

 

Thought I heard a rumor, don't know if it's true, something about lowering the tranny a bit, to help reach the CPS. No idea.....

 

you've definitely done your homework. Nice work.

My opinion is you hit the nail on the head. The most common failure of the crank sensor is thermal failure. That's definitely what I would start with.

Here's a fantastic guide I wish I had when I had to replace mine:
http://greatlakesxj.activeboard.com/...picID=24211453

 

I also agree... A bad CPS is notorious for causing thermal related, and intermittent running issues. Just as a heads up... when installing the CPS make sure you keep the wire away from the exhaust manifold. Either zip tie it out of the way, or route the wires in a way so it won't come in contact with the manifold. I unfortunately learned this the hard way haha

 

thanks guys I really appreciate it...I replaced the CPS...still no crank except now it won't crank cold...
Is it possible to buy a brand new one that is already bad?
Or is there something else i am not finding...this is really startin to **** me off. To the point i even checked to see how much it would cost to just have the shop tell me what is wrong with it, lol...
but the $100 bucks they want to just tell me what it is then whatever the part/malfunction is... not to mention i would have to get it down there, and possibly back...I still prefer to do my own work...

any more ideas?

 

yes it's possible to get a bad one from the parts store. Try moving it slightly one way or the other - position on the bellhousing is key.

 

ahhh ok, going to go and give that a try.
Thanks i really appreciate it.

 

ok, it don't really move much at all, but i did it a couple of times and held it while securing it and still a no-go.

I was wondering though, on the accelerator bracket on the throttle body, what is the center wire for? when the bracket is moved that wire don't... i adjusted the one for the trans and it is perfect, but the center one has nothing but slack when the accelerator is pushed...
that most likely ain't my problem right now, but you never know.

 

You wrote you did the regular maintenance. I guess that included a fuel filter?
Good to have that ruled out while you are chasing the problem.

 

Country.........hmmmm.....seems from what you are writing it is an automatic transmission ya?

Besides the possibility of a bad CPS right out of the box (yes, as the other gurus here have said, it does happen), maybe your NSS (Neutral Safety Switch) is gummed/corroded/stuckish/slipping causing the issue your having.

lots of posts here on that particular problem! do a search and you'll find lots on it! excellent writeups and how to's to refresh it.

other than that, could be fuel delivery, pump getting weak, fuel pressure regulator starting to go out, check pressure at rail during idle and high (2000) rpms.

checked all your grounds? should be clean and solid contact.

best I can do from here sir, I wish you much success, as we all know what its like when something confounds the ***t outta us!

cheers!

cpnwrench

 

addendum.......forgot to ask, if you have same starting symptoms in both park and in neutral (provided you have aforementioned automatic transmission).

cheers!

cpnwrench

 

center wire on throttle assy is more than likely the cruise control wire.

that wont come into effect until your rollin' down the road


cpnwrench

 

thanks guys i appreciate it.
fuel filter has been replaced. And as far as the NSS I have never had a problem with reverse lights and it started only not cranking when warm, so not sure if NSS would be that. Will check anyways though.

As far as fuel pressure not sure how I'd check that, but a side note its been difficult troubleshooting as i am alone. Family visiting back home and buddies have gone to Big Dogs down in VA. I don't know anyone else since i am Army and not from around here...
First i wanted to check for spark, but can't do that alone, lol.

I have smelt gas though after a few mins of tryin to crank and giving it some pedal at the same time...

Edit- it is an auto though.

 

ya but......do you have IDENTICAL symptoms when trying to start in PARK and when trying to start in Neutral?

sorry for the dumb question...


fuel pressure gauge you can get at autozone, and you can do it yourself.

also thought of something........

seriously.....( i do think at times, when there is no Rum involved).......

how are your plug wires? remove each plug and check gap ( should be around .035 or REAL close to it). plug wires, doe they visually look ok? no cracks or separation? does the snap in doo-hickey inside the boot "click" when you put them on? check to be sure. Rotor an cap ok? not a lot of wear?

just puttin it out there Soldier! (by the way God bless! I am retired Navy, so I know the feeling of being waaaay alone is!)

think and study, and thanks for serving!

cpnwrench

 

Dang! forgot to say you can RENT one at autozone....

(might even be able to check in parkin lot of store....see what reading you get at idle, then use the throttle body and rev it up for 10-20 seconds see what reading you get.. both should be steady lower press at idle, more press at rev, not fluctuating but steady.)

again, my 2 cents worth.

crap! forgot its friday., I AM drinkin Rum!

good luck, let us know!

cpnwrench