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No Start - Troubleshooting Help...

N

notamos

NAXJA Forum User
Location
Fort Collins, CO
OK - my '99 (4.0/aw4) has been sitting for about 3 months. About a month ago, I tried to start it when it was REALLY cold, wouldn't start. The next day (warm), fired right up. Now, after doing more work - the same thing is happening again. I finally got the suspension buttoned up and went to start it, no luck. Perhaps something is temperature sensitive? ;-)

-The battery has been on a tender and is charged/new.

-The engine turns over strong but seems like there is no spark

-I tested the CPS (15k on a Mopar CPS), tests fine. (I have a spare that I verified my testing on)

-I put a test light between the coil and the distributor, NO light/blink.

-The fuel pump (15k on a new Bosch unit) primes when the key is turned on and holds pressure at the rail.

What would you do next? Test the input voltage to the coil? How is it supposed to act when 1) ignition is on and 2) when cranking?
 
I'm not sure the camshaft sensor inside the dizzy would prevent the coil from sparking. I think of it as used to fire the injectors. I could be wrong. I also tend to think coils are more likely to fail when they heat up, or run crappy all the time, rather than fail only when cold. I also have a spare camshaft sensor under my drivers seat in case it fails. I figure its cheaper to have a spare than get a tow and a hotel room. I am using a NAPA Echlin with success can't speak to the others. Relays may stick when cold. Was the crank sensor test done at the same condition (i.e. temperature) as the problem? If not, it is suspect. They are more known to fail when they heat up, i.e. stalling at stop lights, but who knows. I keep one of those under the drivers seat too. ;-)
 
Last edited:
What is missing at the cylinders, spark or fuel ?
 
Pull connector off coil and put a test light across the 2 pins. Crank motor and observe. If it flashes but you have no spark, suspect coil. If no flash, verify power to coil. If ok, you likely have a sync problem. If your ckp was good then could be in distributor.
 
Temperature definitely can play a factor in part failure. Sensors, computers, coils, relays... can fail cold or hot.

-I put a test light between the coil and the distributor, NO light/blink.
Click to expand...

maybe a typo on your part but that is not a valid test.

While cranking, there should be 12v on one wire (greenw orange stripe, if memory serves) from the ASD relay. The other is the trigger wire from the PCM (gray?)
The gray wire when probed while cranking will cause a test light to flash very brightly, if everything is working. It will be solid on while cranking if the PCM is not triggering it (either bad pcm or no signal from the CPS)
If the light stays off always on the gray but power on the green, suspect the coil.
 
The cam (aka sync) sensor times the injectors. If the PCM does not receive a sync signal it will shut off the ASD relay after about 10 seconds of cranking.

This action will not effect spark at the beginning of cranking, but will turn off spark after the ASD shuts off.

A no spark condition is 'usually' either the CPS,the PCM, or the coil.

I assume you are checking for spark at the coil.
 
Digger87xj said:
Temperature definitely can play a factor in part failure. Sensors, computers, coils, relays... can fail cold or hot.



maybe a typo on your part but that is not a valid test.

While cranking, there should be 12v on one wire (greenw orange stripe, if memory serves) from the ASD relay. The other is the trigger wire from the PCM (gray?)
The gray wire when probed while cranking will cause a test light to flash very brightly, if everything is working. It will be solid on while cranking if the PCM is not triggering it (either bad pcm or no signal from the CPS)
If the light stays off always on the gray but power on the green, suspect the coil.
Click to expand...

Maybe I wasn't clear. I picked up an inline spark checker (http://www.harborfreight.com/90-inline-ignition-spark-checker-69023.html) and put it between the coil and the distributor. I was using that to see if spark was even reaching the distributor, it wasn't.

I tested my CPS again. 6.27 megohms. My older, used, CPS measures at 5.6 megohms. Both of those are fine, I'm assuming.

As for testing the wiring harness (2-pin) that connects to the coil. I don't get *any* power to either pin, either when sitting or cranking. I tested my test light and it works. ;-)
 
Also, only the renix 87-90 CPS can be tested with an ohm meter

91+ are different and testing with a meter is moot due to the electronincs inside the sensor.
 
I just tested the coil plug w/ my multimeter to see if I'm getting anything (even small). When cranking, I'm getting about .3 volts to the plug (both wires).

Another thing to note. I've cranked this thing a million times in the past 48 hours. I just put my meter on the battery and I'm only getting 11.6V.
 
If the PCM does not see CPS trigger during crank, it will not turn on the ASD relay.

The ASD feeds 12v to the coil, injectors, fuel pump relay and O2 sensor heater coils.
 
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And, just for others who read this in the future. This thing has *fairly new* Mopar MAP/IAC/TPS sensors on it as well. They were more of a preventative measure - replaced 6 months back.
 
notamos said:
Alrighty then! Going to pickup a new CPS.

Out of curiosity, is there not a way to test a new CPS?
Click to expand...

No practical way. The PCM feeds 5v to power the electronics in the sensor to 'turn it on' so to speak.

testing it unpowered with an ohm meter tells you nothing.
 
The RENIX sensors are essentially a electro-magnet. a coil of wire around a metal core.
One can measure those for continuity. Very simple.

The HO sensors are hall-effect sensors and need to be powered to function.
The only valid test is not actually testing the sensor, but that the PCM is providing 5v, and a ground, and 5v carrier on the signal wire. If the PCM voltages check out, it is assumed the sensor is bad.
 
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