4wheeldrivenewbie

I have this cherokee and it cranks and cranks then fires. The other day after it snowed i tryed to start it and almost started but i let off and it was dead after that.

I assume it was from playing with the radio and car off and the cold weather drained it.

So i waited the next day and i slow charged it went from 6v to the 12v setting after a few hours next day i unplugged it in the morning yesterday.

Today i went out side and hit the key and varoom almost instantly i couldent believe how fast it started no 5-10 second start.

I have a excide battery and a microfarad cap for the audio, the system doesnt exceed 700w .

Anyone can chime in if u know something. I have herd that cherokee are known to crank hard.

I also have a brand new cps incase that helps anyone.

BatmanXJ

I would think Fuel pump
There is a one way check valve in the fuel pump that keeps fuel in the fuel line and fuel injection rail after you shut the engine off. It could be leaking back into the line. I would run a fuel pressure check before trying to crank the engine after it sits for a while. I think the only way to fix the check valve is to replace the fuel pump it self.

ss427ci

What are the CCA on the battery you have?

cruiser54

REnix likes a good strong battery and good grounds. Check out the link in my signature for easy and cheap improvements you can make. This one below is one in particular that you should do ASAP.


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.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.
　
　
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 12-04-2012

DFlintstone

Besides the fine advise above, you (and other Jeepers) might try the "poor man's prime". The pump only runs a couple secs when you turn on the key. Try doing that three times before you go to start it. If that makes it start allot faster you may well have a faulty check valve in your pump.

I might check that new CPS, especially if it's not from Napa or the dealer.

Firestorm500

I don't think I would recycle an old ignition switch 3 times just to get a faster fire-up. Plus you're zapping that hard-to-replace fuel pump too. And the computer. And the electrical system.

My '87 Renix cranks about 3-4 seconds before light-off. That's just what they do. Nothing is wrong with it.

Besides, it gives the oil pressure a little longer to come up.