Cranks, starts and dies immediately

[Ecomike]

I haven't tested the cranking voltage. I bought the CPS at Autozone. I wasn't aware about the CPS mounting customization, is it simple to do?

I haven't checked the grounds yet. I've been needing to do that anyhow for a while now (I drive a bucket of oil pretty much.) So I'm going to try that tomorrow and check the voltage for the CPS. You guys have been a great help. Keep the suggestions coming please!

The last CPS I bought at Autozone, Jan this year gave me no start problems for 2 months, but passed the meter voltage crank test, until one day when it was reading 0 volts for 2 cranks, then magically worked again, confirming poor electrical contact inside the plastic casting of the CPS. I bought the next one from Rock Auto (they had more than supplier in the 3 Standard products brand boxes I bought). The first one I tried worked fine. The CPS is a magnet and coil on the inside, and the coil wire is angle hair fine, while the lead to the connector is about 18 Ga. I took the bad one apart, and all I could figure is the mechanical crimp contact on the angel hair dia wire was bad. The mod is to drill out the CPS mounting holes using one drill size larger than the OEM hole, then while tightening the bolts, have something or someone force the CPS as close to the flex plate shaft (crank shaft) as possible. This will increase the signal strength, higher voltage output on the CPS.

 

[cruiser54]

If your CPS AC voltage is less than 3.5, you can have intermittent no starts.

 

[Ecomike]

If your CPS AC voltage is less than 3.5, you can have intermittent no starts.

I think you mean .35 V?

 

[blondejoncherokee]

everyone else hit all the usual suspects. i hope you cleaned the hell out of the grounds and checked all fuses and all sensor/electrical connections and checked all vacuum lines. how does the vacuum line to your map sensor look? i know when i broke mine without knowing it , the thing wouldnt start. check to make sure something weird like 02 sensor wiring or cps wiring didnt get burnt on the manifold.

 

[cruiser54]

I think you mean .35 V?

Yes. Many times I think faster than I type or vice versa.

 

[Orodreth]

So I took the bad boy to a Jeep shop and they determined it was a blown fusable linkage to the ignition. Took them a few hours to find out what was wrong.
I need to figure out exactly why the linkage blew.
Mainly because it blew again.
Any ideas?

 

[cruiser54]

Do this to insure all the grounds are good and not causing alot of resistance somewhere. Resistance equals heat which causes melted wires etc.

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

 

[Ecomike]

So I took the bad boy to a Jeep shop and they determined it was a blown fusable linkage to the ignition. Took them a few hours to find out what was wrong.
I need to figure out exactly why the linkage blew.
Mainly because it blew again.
Any ideas?

It is not a ground problem then, especially not if it blew one of the main fuse links. It is usually bad connections on the positive side that burn up wires, not bad grounds.

One of the main hot wires has grounded out, shorted to ground. Most likely suspect is the O2 sensor wires (heater wire to be exact, the large gauge one), got hung up on the exhaust or the front drive shaft. (Ask me how I know, LOL)

Time to check all the wires!!!!! Visual inspection to start with!!!!

 

[Orodreth]

Hahaha I take it you've had a similar issue, ecomike?
I tried to figure out what was going on the other day when I had a chance, but I didn't have any tools or anything and the cable went straight into the main harness.
:Not important backstory:
Now I bought it from this place (Ironman 4x4) that I took it to and it was the owners wife's Jeep. and they seemed to have it rigged in some places.
:End not important backstory:

The fusible linkage was actually replaced by a fuse holder, I replaced the fuse a few times but it just keeps blowing when I try to start it up. Like I said, I tried to trace the wire back to see if I could see anything, but it went into the wiring harness and I couldn't really see anything going on. I just don't really understand.
Luckily I'm |this| close to getting my dad's scrambler running so I can have a way to and from work while I'm tearing apart my XJ haha

 

[Ecomike]

Try pulling the O2 sensor heater relay, and see if the fuse stops blowing!