Cranks but won't start (I'm so sorry for posting this!)

F

FilthyLlama

NAXJA Forum User
Location
Montana
Hey folks.

I've searched and searched on this, but can't find definitive answers so apologies for this:

1990 Jeep Cherokee 4.0 5spd 4x4

Symptoms:
Cranks, but doesn't start. No Spark at coil.

Tests and work done:
CPS tested bad, so replaced it (see notes below)
Still no spark, so had ICM tested and it tested good.
Cleaned and put dielectric grease on ICM contact points, they were really gunked up from being such a new rig :)
Replaced Ignition Coil
Cleaned all plugs I could find with electronics cleaner.
checked grounds, but didn't reground and clean yet, will do this soon, they are tight though.

Oddities:
This XJ WILL turn the starter when it's in gear without pressing the clutch in... is this an issue? I've seen mixed things here and from fellow wrench turners... the safety switch just kills the starter ground, right? Shouldn't affect the spark? I've only seen good answers to this question for AW4 transmissions.

It did start once while loading it onto a trailer with the starter creeping it up the ramps, and scared the holy crap outta me. This is why a buddy thinks perhaps the NSS is the issue.

More Oddities:
I'm going to test this again tomorrow, but my newly installed CPS tests like this...
230ohms resistance
1.0 VAC (that's ONE, not pointOne)
This is way higher than all the tests online tell me it should be, which is 0.5 vac.
The last CPS tested 290ohms and .25 VAC.

Did I somehow install this CPS incorrectly? Is more voltage here a problem?


AT the ICM I'm getting:
11.5-12volts at the "A" wire and the one wire connecter is 5 volts if i remember correctly. The outside plug on the 3 plug connecter, if this makes sense, is pulsing .25ish DC when the motor is cranked (like I think it should be, telling the Coil to spark, right?)


I have done nothing to the PCM.

Previous owner was using as a DD until it died and they couldn't get it running. They were not mechanically inclined and I fear what they may have done. However, everything looks ok from staring at the beast for a few hours. There is one mystery plug under the dash near steering column, and one mystery vaccuum line on passenger side of motor, though.

Any help is appreciated. If you live near Missoula and are up for a challenge, I've got beer!! :cheers:


PS: I've had this for months; was waiting to work on it until after I found out if I won the Giveaway XJ. Was hoping to not have to fix it! lol
 
CPS voltage is way low.

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
 
The test text you pasted and that I've read in many places states 0.5 vac (half a volt).

Am I reading this wrong?
 
The way I troubleshoot no spark, I measure the voltage at the large yellow wire going into the ignition module (with the key in the run position). Then I measure the test point on the coil (should be no difference between the large yellow wire and the test point on the coil, but the voltage into the ignition module is often a volt or so less than battery voltage). The small yellow wire going into the ignition module is your trigger wire, the coil is triggered through the ignition module by the ECU. The trigger signal is a square wave most meters can't read, sometimes you get a twitch or erratic reading from your meter, but in most cases they can't read this signal well if at all. The ECU shuts down the spark when the ECU receives no pulse signal from the CPS. The ECU triggers the coil to ground through the ignition module (collapsing the electromagnetic field in/around the coil and creating high voltage), when it gets a good pulse signal from the CPS (with sufficient RPM's). The ground for the ignition module is right next to the module and needs to be checked. One reason I always make a jumper from battery negative to the radiator cross brace, so the chassis has another ground path besides the rear head to firewall ground.

The problem may be the CPS, it may also be the connectors or wiring between the CPS and the ECU (moderately common). It may be the trigger wire between the ignition coil and the ECU (but this is rare). It may be a poor connection between the coil and ignition module, this is a relatively high amperage connection and can test good for volts but not pass enough amperage, making for iffy spark. It may be the high voltage spark is reaching ground before it ever gets to a spark plug. I've never had a Renix coil or ignition module fail, but have heard it happens.

A common failure is the connector between the coil and the ignition module. It is exposed to the elements, gets corroded, heats up and relaxes. A poor connection between the coil and the ignition module can make for a weak spark. A very weak spark can be hard to see. I use a an old spark plug and hook it up to a spark plug wire, ground it well and watch (and listen) for the spark. The spark should be clearly visible, blue/white, make an audible crack. If the spark is thick yellow it is likely moderately weak, barley visible and it is likely very weak. Word to the wise, make sure the test spark plug is grounded well, don't rest your crotch on the fender while making the test. A good place to test is the coil to cap wire (with a spark plug) and again at a spark plug wire at a couple of cylinders. You can also use a timing light, just aim it at something dark and see if it pulses when and where you expect your spark to be.

I've had the high voltage ground, between the coil and the distributor cap, through water in the spark plug boots. The spark ground inside the distributor through water. It can even ground through a crack in the coil to cap wire or inside the the cap through carbon dust (rare). I mud a lot and have a lot of experience with missing spark that had nothing to do with the CPS, coil or ignition module.

The green wire coming out of the ignition coil is your tach wire, you can test there for pulse, works better with an analogue meter.
 
Last edited:
FilthyLlama said:
Not trying to argue with you... just confused :) I appreciate the help!
Click to expand...

My error. Sorry. .5 AC volts. 5 AC millivolts.

1.0 is great.

Here is one of the things 8Mud is referring to below. Double check the connector for the CPS as he suggested also.

Renix Jeep ICU/Coil contact refreshing
　
　
The contacts between the coil and the ICU on your Renix Jeep can become corroded and loose causing a complete or intermittent no-start condition. I recommend the following procedure as a maintenance precaution to insure this is eliminated as a possible cause now and in the future.
The coil is attached to the ICU by two T20 Torx bolts. Remove these two bolts and lift the coil up off the ICU. You will see 2 pins and 2 sets of contacts. Clean both the pins and springy contact pieces with a good electronics cleaner and some fine sandpaper.
Squeeze the springy contacts closer together with some needlenose pliers. Bolt the coil back on to the ICU.
While you’re right there, unplug the connectors from the ICU and inspect the pins in the harness connector. Make sure the pins are not retracted into the connector. Spray out the connector and the receptacle of the ICU with the same good electronics cleaner you used earlier.
I feel this procedure should be performed at least once in the lifetime of a Renix Jeep.
　
Revised 04-04-2013
 
Thanks. You've given me some things to check that I'll get to today. I'll refresh the grounds, as well. And create a new ground from battery to frame.

don't rest your crotch on the fender while making the test.
Click to expand...

That should be in a sticky somewhere :)

What about the clutch / nuetral safety switch? Do I need to worry about this seemingly being in a failed state since it cranks in gear with the clutch out, or can I ignore this since it's a manual and it's cranking over (whereas I believe a failed switch would prevent crank on an auto, right?)
 
It is a de-facto sticky in that renix no-start gets you a post from cruiser.

One thing I'd like to add... in the past when I've had CPS issues the CPS wasn't the issue and instead it was the wiring harness leading up to the connector. I ended up cutting a few inches off the end, and re-terminating it with a waterproof molex connector, as I wasn't able to find the original connector. If you have a spare/old throttle position sensor it should have the right connector on it, it's the opposite of this one:

http://www.napaonline.com/Catalog/C...-Sensor-TPS-Connector/_/R-ECHEC117_0334779084

You only use the A&B wires.
 
Here's the latest.

Retested the CPS after checking a ton of wires. It was read .2-.3... weird. I obviously tested it wrong the other night. So I replaced it with another new one. Twice. Then I went to NAPA, drilled the top mount hole and walla! .7 vac.

So now...I have extremely weak spark. Still no start. I'm refreshing grounds as the dipstick ground was odd and welded. Found a broken wire at the ground. Hopefully fixing these grounds will make him start up.

Frustrating. Thanks for the help.
 
Is your rear main seal leaking? A buildup of oil and grit on the tone ring/flex plate can cause CPS issues. If the grit buildup upon the flex plate tone ring has metallic content it can bridge the gap between the CPS and the tone ring.. The CPS has a tiny magnet in it. This is just something to look at if all the normal problems are addressed.

I usually ohm test the CPS and volt test it. Also the CPS can be temperature sensitive and the values can change from a cold motor to a hot motor. Make sure the connector is clean, really clean as it doesn't take much, like an invisible coat of oil, to mess with a half volt signal. Also clean off the ends of your volt meter leads, the oil from your fingertips can mess with the ohm and very low voltage values.

I don't think the CPS is going to mess with the strength of your spark, you may get no spark or sporadic spark, but if you get any spark, a weak spark is likely IMO something else than the CPS. ohm test the coil to distributor cap wire, flex it like a snake while you are ohm testing it, look inside the distributor cap for carbon/flash trails and moisture under the sync sensor mounting plate. Make sure the contact ends of the coil to cap wire go all the way in, the wire can slip up into the boot and may not be making full contact.
 
Last edited:
FilthyLlama said:
Here's the latest.

Retested the CPS after checking a ton of wires. It was read .2-.3... weird. I obviously tested it wrong the other night. So I replaced it with another new one. Twice. Then I went to NAPA, drilled the top mount hole and walla! .7 vac.

So now...I have extremely weak spark. Still no start. I'm refreshing grounds as the dipstick ground was odd and welded. Found a broken wire at the ground. Hopefully fixing these grounds will make him start up.

Frustrating. Thanks for the help.
Click to expand...

Grounds are super important. Did you do the ICM contacts and plugs yet?
 
I'm not getting a spark out of the coil (much of one anyway) so haven't touched anything beyond the coil such as the cap/rotor/plugs/wires. I suppose it could be the main coil wire to cap as I've been using that to check spark.

Only time I see spark is if I put an inline spark tester on the wire and ground it to the negative battery cable.

And yes, there is a rear main leak. I may have to drop the transmission to clean the flex plate and fix the seal while I'm there. Just trying to get it running and now that I have a spark (even a diim one) I think I've tackles the cps and am having a ground or other issue.
 
For folks searching in the future, here's my troubleshoot:


  1. CPS tested bad on non-running 1990 jeep xj I just purchased.
  2. Replaced CPS - 3 times, final CPS was with Eichlan from NAPA and I drilled out the top mounting hole to get it to sit closer to the tone ring to help my CPS send more VAC (Is now sending .7 VAC)
  3. Cleaned up the ICM to Coil connections with cleaner and applied dielectric to all connections I could find.
  4. I had spark, but VERY WEAK SPARK now... so
  5. I checked the grounds, and the grounds leading to the oil dipstick were all FUBAR.. 2 were completely off the stud, one was gently wrapped around another. Cleaned these up and replaced stud that had been tack-welded together...GREAT SPARK at coil
  6. Removed cap and there was a thick coating of oil on the rotor that was appearing to drip down from the coil contact on the cap...odd, replaced the cap/rotor. then had great spark at spark plugs.
  7. Still no start, however. Fuel rail pressure valve spits fuel and I can hear fuel pump turn on with key, so seems like I have fuel
  8. Removed air intake from throttle body. Tried to start, still no-joy.
  9. Squirted Starting Fluid into throttle body while little bro started and he fired right up!
  10. Now, however, it won't start unless I have someone spray starting fluid into the throttle body... so new problem.
But at least the CPS and SPARK are working, and refreshing the grounds had to have helped. I need to do the ground refresh under the steering wheel as well.


Thanks to Cruiser and 8Mud. I'm now off to figure out why the darn thing won't start without starting fluid. I've read so far that it could be a power to the fuel pump while cranking issue, or fuel pressure. But it ran real nice the other night until it got hot and I realized I needed to change the thermostat as the upper radiator hose almost burst on me! Changed the thermostat and started it, but this time he wouldn't stay running long enough to get to temp, just died and I've been unable to start or troubleshoot. I'll do this tonight.



I want to like this jeep so bad... he's making it difficult, however.


If you happen to read this and have any ideas, feel free to offer up your sage advice! :helpme:
 
Went to troubleshoot with a fuel pressure tester and multimeter and little brother last night. Figured I should be thorough.

So first: checked spark. And back to extremely weak spark. Ugh! CPS still tested fine. Ground is good on ICM and Coil. 12.1 volts to ICM and test point on coil.

The only way I see spark is with one of the inline spark lights. No spark on plugs, even just on the coil wire.

So I'm back to chasing my tail. And hating this xj. Might be a parts candidate if it keeps this up.

Yellow plastic box under steering wheel? with AMC embossed on it and three adjustment wheels... is this the ECM?
 
I'm tempted to replace the ICM but at $120~ I don't want to be wrong. And O'Reillys tested the ICM I have and told me its OK ... starting to have my doubts though.

I've got two coils. Both behave the same way.
 
FilthyLlama said:
Went to troubleshoot with a fuel pressure tester and multimeter and little brother last night. Figured I should be thorough.

So first: checked spark. And back to extremely weak spark. Ugh! CPS still tested fine. Ground is good on ICM and Coil. 12.1 volts to ICM and test point on coil.

The only way I see spark is with one of the inline spark lights. No spark on plugs, even just on the coil wire.

So I'm back to chasing my tail. And hating this xj. Might be a parts candidate if it keeps this up.

Yellow plastic box under steering wheel? with AMC embossed on it and three adjustment wheels... is this the ECM?
Click to expand...

That's the cruise control box.
 
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