Intermittent No Start, Not CPS

N

Nevada City Sparky

Jeeper
Location
Nevada City, CA
Brand new CPS put in to solve an intermittent no start. Worked great and car started and ran fine for a day, next day, it wouldn't start.

A few times when this happened, rocking the car fixed it. I'm thinking shift cable needs adjustment first. Anyone got a link to instructions (lost myFSM).

Could be the nSS needs cleaning again (done 60k miles ago).

I noticed the ignition key cylinder is loose. Any possibility this is the issue? How to adjust the interlock.

... Damn. I wish I could fine my manual. :(.
 
Year? Transm?
 
Usually if it spins it's not the switch, I would check the CPS wiring, personally I've never had a bad CPS, but I've had 2 renix cherokees with bad CPS wiring (usually just above the connector on the main harness, replacing the connector fixes it).

If you think it's the switch, the start switch on renix cherokees is fairly easy to get at, it's on top of the column behind the dash, there is a control rod that moves the switch back and forth, you can usually carefully pull out the switch and then unthread the control rod, at this point you can move the switch manually and see if that's your issue. I think it's likely #1.
 
Sorry, this is an 89 XJ 4.0 w/ AW4 tranny.

Looked at the lock cylinder again and I think it's fine, but I'll check the rod this morning to make sure it works.

Pretty sure the wiring on the CPS is solid, so I'm getting ready to move to the NSS and clean that.

What's frustrating is it will run perfect for days, and then just not go. Of course, now that I'm ready to work on it, it's running fine. Started right up yesterday where I'd parked it a week ago when I couldn't start it.
 
I would assume it is cranking, but not firing up?

If true, then you need to check for fuel at the fuel rail (several things in the wiring can cause the pump not to run), and spark at a plug wire.

No spark means the new CPS is bad or needs to be remounted closer to the flexplate-fllywheel to get a better signal. After market CPS's are hit and miss on quality, some have bad lose connections inside the CPS, work one minute and not the next, and most need to be drilled out with a larger hole size drill bit, one size larger than the stock hole so the CPS can be pushed closer to the flexplate to boost the signal voltage to at least 0.50 V AC on a digital AC volt meter setting. Renix will often not start if the cranking voltage is lower than .5 V AC.

Here is a great thread on the 3 month ordeal I went through over an Autozone CPS that worked when it wanted to. I now use Rockauto "Standard brand" CPS from Italy. Cruiser54 and others only use dealer CPS.

http://www.naxja.org/forum/showthread.php?p=245940774#post245940774

Here is a great thread on de-gremlinizing Renix rigs:

http://www.naxja.org/forum/showthread.php?t=1072534

PLease confirm if this is a no spark, no fuel or no crank (starter) issue now.
 
Thanks Mike,
Engine cranks, no spark, fuel at rail.

I replaced the CPS with a NAPA one, and it went intermittent after a bout a week. Took it out and replaced with a new MoPAR one.

The CPS from NAPA was putting out .1V on a Harbor freight meter, so I thought I had it licked. Worked for a day, then dead on the next. Wait a week and it started right up, without touching or moving a thing.

When I removed the Napa CPS it had grease on it from not cleaning the top of the bell housing. I cleaned that area before putting the MOPAR one in.

Pulled the inspection plate and it looks clean inside. No crap on the flex plate or in the cavity.
 
The voltage rises rapidly as the rpms (cranking or running) go up. So a slow crank will not spark!!!! Battery cables and starter must be like new condition. Then the CPS must be closer to the flex plate. The new CPS sensors just don't seem to have the muscle they need.

Losses in the harness connection drop the voltage the ECU sees too.

We fixed ours by moving it about 1/16" closer to the flexplate which is what most everyone else has done.
 
Nevada City Sparky said:
So, you don't see the NSS as being a likely culprit?

If the NSS is fubar, does it prevent cranking?
Click to expand...

NSS is not involved in a no spark problem. But it can cause no cranking, keep the starter from turning.

People forget to say if it is a no crank problem, or cranks and no start, which is critical info when asking for diagnostics help.

No spark, 95% of the time is the CPS.
 
Disconnect the CPS and test the cranking voltage of the CPS. If it is zero it is bad, if it is under .50 V it needs to moved closer with the MOD.

You can also test the battery cranking voltage, it should be at least 10.0 volts post to post while cranking. If below 10.0 volts that is a problem too, battery or starter.
 
Ecomike said:
Disconnect the CPS and test the cranking voltage of the CPS. If it is zero it is bad, if it is under .50 V it needs to moved closer with the MOD.

You can also test the battery cranking voltage, it should be at least 10.0 volts post to post while cranking. If below 10.0 volts that is a problem too, battery or starter.
Click to expand...

Battery and starter are known good. The NAPA CPS I replaced with the MOPAR version was only putting out .1v. Didn't check the MOPAR one yet. I'll do that this morning after the wife's chores are done.

Not sure how drilling out the CPS holes one size bigger helps. Do you push down towards the center of the flex plate then against the slop that was created by the oversized holes to get it closer?
 
Not sure how drilling out the CPS holes one size bigger helps. Do you push down towards the center of the flex plate then against the slop that was created by the oversized holes to get it closer?
Click to expand...

Yes, about 1/32 to 1/16" closer moves the voltage up about 300% (at least mine did). I used the next drill bit in my bit set that would not fit the part hole in the new sensor.
 
Renix CPS Testing and Adjusting
　
　
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out the upper mounting hole to 3/8" from the stock 5/16", or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.

　
　
Revised 01-26-2013
 
Ok I tested the new MOPAR CPS and got no voltage or just a tickle when I cranked. That's weird.

There was grease on the other new napa CPS I put in, so maybe I need to bump the flex plate around and see if there's crap somewhere on it.

Obviously, I'll be pulling out the CPS again.
 
Nevada City Sparky said:
Ok I tested the new MOPAR CPS and got no voltage or just a tickle when I cranked. That's weird.

There was grease on the other new napa CPS I put in, so maybe I need to bump the flex plate around and see if there's crap somewhere on it.

Obviously, I'll be pulling out the CPS again.
Click to expand...

Meter set on AC volts, low scale?
 
^^i better start there. It's been a while since I noodled around back there.

<sigh> I guess the honeymoon phase of the complete rebuild I did 60K miles ago is now officially over. Back to tracking sh!t down again..... :(
 
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