Intermitant No start, now RUNS with No distributor Hooked up!!!!!

Its an 89 Renix 4.0 w AW4, replaced the dist/CPS last year, worked fine then. Once in a blue moon it has not started due to no sprark but have letit sit 10 to 15 min and started like there was nothing wrong. Until Now!?!? Didnt start foe 3 days, low readings coming from CPS, replaced it under warrenty, still no start. Next day pulled spark plug to check for spark, the dam thing fired right up when i turned it over. But here's the thing, idles fine WOT fine but the first half throottle pops backfires and doe s all kinds of wierd stuff. Started checking wire continuity levels and volts. Showed 0.08 volts to CPS instead of 5v?? Output also low ofcourse. unhooked the plug from Dist/CPS measured harness plug, got 0.08v on BLUE wire & 4.99v on the GREY/Black wire wich is theRETURN signal wire? Same exact readings at the ECM itself. Better yet, Decided to turn motor over with Dist/Cps unhooked to see what it sounded like ( rollover noise sputter anything), AND THE DAM THING STARTED AND RAN JUST LIKE IT WAS PLUGGED IN!! still with backfiring at less than half throttle.

Please Help before all of my hair is Gone!

P.S. Renix EFI won't run without signal from CPS...My jeep sais thats a Load of Crap. Ithink my ECM is toast of course , please help and THANKS in advance.

The Cam Position Sensor ( CPS )


The Crank Position Sensor (CKP )


This info comes from my 2001 FSM...

So, even though my 2001 XJ is not RENIX EFI, I'm pretty sure those two sensors work the same way in both your vehicle and mine...SO, they won't run without a Crank signal, but will start and run like crap without a Cam signal...someone please correct me if I am wrong.

On Renix era XJ's you do not need a valid cam position sensor signal to start. That is why renix models take so long to start...most of them have bad sensors. Alot of vehicles are like this.
If you do not have a good crank position sensor, the engine will turn over but not start.

Hmmm, everything i've ever read sais that if the Cam Sensor goes out while in operation the motor will continue to run based on last signal but will NOT run once it has been shut off ( for RENIX anyways ), and that is the way mine acted when it went bad a year ago. Either way i am sure it's posessed.

I was thinking internal short in ecm creating partial reading from cps thats not really there triking itself into running.

Jess said:

On Renix era XJ's you do not need a valid cam position sensor signal to start. That is why renix models take so long to start...most of them have bad sensors. Alot of vehicles are like this.
If you do not have a good crank position sensor, the engine will turn over but not start.

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so you're saying that if you put in a new cam sensor there will be shorter crank times?

veedubshafer said:

so you're saying that if you put in a new cam sensor there will be shorter crank times?

Click to expand...

i got shorter crank times by upgrading the battery to a red top and upgrading the battery cables and ground strap.

89xj said:

i got shorter crank times by upgrading the battery to a red top and upgrading the battery cables and ground strap.

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The RENIX ecm needs to see 300rpm + at the Crank Position Sensor, located behind the head (top-right of Bellhousing if standing at the front of XJ) before it will fire.

Upgrading the batt + cabling and such will make it start quicker, yes. Less internal resistance = more voltage arriving at the starter for use.

You'll never totally escape the crank time.

The cam position sensor simply tells the ECU which stroke it is on. If the Renix ECU does not find the cam position sensor signal, it makes a guess. It will either be correct or 180 degrees out. If it starts, it guessed right that time. If it does not start, turn the key off and back on again before cranking. You have a 50% chance of getting it right each time. The sensor will not make it run crappy. It either runs fine or not at all depending on the guess results.