Seth U

Hi guys,

I kinda think I know the answer, but wanted to run it by you for confirmation.
1997 Cherokee Country 4x4 4.0

Today was a hot day, AC on, and while in a long drive through line the "check gauges" light came on. Engine temp had just crested into the red, no big deal, just turn the AC off. A couple seconds after I turned the AC off, the engine died as cleanly as if I were to turn the key off. Wouldn't restart. Once I got a push to a parking spot I plugged in my code reader and it showed crankshaft position sensor not reading. Let it cool for a half hour or so (back down to 210°) and it fired right up and drove home flawlessly.

I've spent a fair amount of time reading through threads. Some real good info, but can't find a clear answer to my question, so here it is...

Does the computer have a fail safe feature that shut the engine off until the temp returned to normal, or is that not a feature and the CKP sensor likely heat soaked to temporary failure?

If the sensor is the likely culprit, would a new one suffer the same consequences or likely eliminate this issue in the future?

(Yes, I'll look into why it overheated too )

Thanks guys.

-Seth-

DFlintstone

Welcome. You should fill out your info.

No. There are cars out there that will shut off the fuel pump with no oil pressure, but I'm pretty sure you are cleared to bake a 4.0 in a Jeep.

The CPS does seem to be temp sensitive. Try just unplugging it and plugging it back ans see if that does anything.

"AC on, and while in a long drive through line" Is Line a town? Point being....if you are not moving with air speed, the Electric fan needs to be working to help with air flow. Also the shroud around the main fan needs to be there.

Is the E-fan running while it's hot? Is there a fan shroud around the main fan?

Seth U

I read something about an "auto shutdown relay" which suggested to me there might be an auto shutdown fail safe feature in the ECU, but when it wouldn't start I could still hear the fuel pump prime when keyed on. So, I'm guessing that's not the case and it was pure coincidence that it shut off within seconds of the "check gauges" warning light coming on.

It re-fired once it cooled, without futzing with anything. My main inquiry is, will a new replacement sensor act the same way or is this occurrence any sort of indication that the current sensor is sub par and on it's way to complete failure?

Don't want to get too side tracked as to how or why it overheated. That part I can figure out.

"AC on, and while in a long drive through line" LOL Yeah, I suppose that could have been written better... In-N-Out, That's What A Hamburger's All About. A long line, waiting for my 4x4 animal (no pun intended) at the drive through window. It's a fast food joint, for those of you that may not be in the Western States.

E-fan runs when the AC is on, no matter the engine temp. Shroud is factory and intact. But, like I said, I can solve the overheat issue. Just wanna know if replacing the sensor will change anything... or that the ECU does or does not, in fact, have an auto shut down feature for an overheat situation.

I appreciate the reply. Thank you.

DFlintstone

Oh lord, stuck in Lodi again!

I don't think there is any auto shutdown for overheat. CPS can be temp sensitive. If the problem is indeed the CPS, a new one may well solve it. Going to the dealer is a good idea there. For our Renix some of us trust the Echlin from Napa, no Idea for your HO though.

In your shoes I might check spark while it's hot and not starting.

Cheddarnut

My 95 did the hot day fail a couple of times when I lived in AZ, similar to yours. Mine was the cps, bought two from the dealer, swapped it and still have the spare. General consensus seems to be that the mopar part is more reliable.

jld66

last summer when it was hot. i had a crank sensor problem also. my 97 would not start sometimes if i shut it off and tried to start it in 30 minutes to a hour. once it was running though, would not shut off on it's own.

Seth U

That's good news. I'll replace the sensor then. Thanks for sharing your experience.

Did a new sensor solve your problem? I had a similar issue a few years back, but on a restart attempt the engine wouldn't even turn over. A quick rebuild of the transmission range sensor (neutral safety switch) was the solution. Another indication that lead me to this solution was that the reverse lights didn't work, which is also a function of the same sensor. Took it apart, gave it a good cleaning, sanded the contacts, greased it up, reassembled it... it fixed the reverse lights and the intermittent failure to restart issue.

Anyway guys, I really appreciate the input. I'll replace the crank position sensor and report back if the problem persists. If I don't, assume it's a solved issue.

All the best,
-Seth-

Oswalla

I had a similar shut down several years ago with my '90. My temp gauge was just about pegged out in the red when it just shut off like turning the key, on the interstate. Called the misses to bring some water, about an hour later with some water back in system, she fired right up and drove 5 miles or so home. I always assumed it had something in the ecm to tell it to shutdown at a certain temp, never looked into it though. I never had the urge to replicate .