I have been reading around about the CPS and the long crank problem I have been having? I was thinking of changing the CPs.. Would it be Helpful to get this High Attitude CPS... Could there be benafits to this CPS... Because I did read it adavances the timing a little bit? Is that True?

 

Kindof interested in this also... never heard of a "high altitude"

 

yup its a real part the Mopar part # is 53005421 I may call the dealer tomorrow for one... depending how it goes according to the old parts book..

 

Cruiser just posted in another thread that it has the sensor mounted differently on the bracket.

 

hm... thats the differnce....i think there has to be more of a difference then that... i guess i will wait to see what he has to say about it...

 

Sorry, should be more clear. I'm making the assumption that it is mounted on a different bracket that would position it some degrees forward or behind a stock CPS.

I gotta wonder if it's just intended for extreme high altitude. Anyway, if our Jeeps are running as advanced as the knock sensor will allow already, I don't see what's to be gained with more advance. (if it is advancing, might be retarding would make more sense)

Was just thinking...they could have made a tiny "window" for it, but they didn't.

OK, found it, he does say it advances a bit.
https://www.cherokeeforum.com/f2/no-...113021/index2/

 

hm... that is a interesting point...

 

ok i see your edit now... so it defintely advances it 5 degrees... I wonder how much this helps...

 

A CPS is just a Hall Affect sensor. It is a magnetic coil that registers breaks within its magnetic field. so when the crank is rotated, the CPS picks up the slots that are positioned every 90 deg on the flywheel to determine its position. Altitude has nothing to do with how this sensor works. If your rig has trouble firing up at higher altitutes it's because of air pressure within the MAP. To put it in more simple terms, your enginer wants more air. I realize Mopar has another part number for the CPS, but when I pressed them for more info about the sensor, that admitted there was no difference between the two part numbers. For better starts at higher altitudes, make your engine breather better.

 

3 @ 60 degrees...right? Determines #1 and #6 i think...

 

Yea the cps (ckp sensor), tells the ECM (or PCM>90), when one of the three pairs are up. (1,6)(2,5)(3,4). 3x60=180* (one rev). (It's that other one that tells it which if the pair is firing).

 

On a 1987 4-cylinder XJ I replaced the CPS with the direct replacement in an effort to eliminate a rough idle. Didn't work. Replaced it with the high altitude one and it smothed the idle out. That vehicle is driven mostly at 8-10k ft elevation. There was no visible difference between them.

 

The sensor portion of the CPS is bonded on to the same bracket as stock but just off-set.

More important to address long crank times is the AC voltage output of the CPS while unplugged and cranking the engine over. Rooster, what reading are you getting?

 

subscribed.
I have the same problem.
https://www.cherokeeforum.com/f2/no-...7-4-0l-113021/
Long crank times. I would have to order a high altitude sensor in. (4-6 days) If it works I wouldn't care what they called it.

 

It's more important to drill the holes out as described in my write-up and get more than .5 AC volts than it is to have the high altitude CPS.

The engine/sensor grounding system neds to be in tip-top shape also in order to reduce cranking time somewhat. Have you
ever done this?

Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 11-28-2011
ever done this?