Will not start, no coil grounds

Tiny
DAZLE1
  • MEMBER
  • 1997 PLYMOUTH GRAND VOYAGER
  • 3.3L
  • V6
  • FWD
  • AUTOMATIC
  • 189,000 MILES
Vehicle will not start. I have battery voltage at the coil while cranking but no ground on any of the three coil driver wires from the PCM. If I wait about an hour the vehicle will start and run for five to ten minutes and shut off again. This will happen over and over again. I have a code for a crank sensor but I have battery voltage at the coil while cranking so I think that eliminates the sensor. I do not want to replace the PCM if it is not the problem. Why do I lose ground on all three circuits after five to ten minutes of operation and then regain it after an hour of sitting only to repeat? Why does it keep coming back? Anyone ever had this condition before? I opened the connector between the coil and PCM, seems fine, moving it while running makes no difference. Thank you for your help.
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Monday, September 18th, 2017 AT 11:26 PM

7 Replies

Tiny
STEVE W.
  • EXPERT
Sounds like a failed camshaft sensor.

What do you have for test equipment? Both the cam and crank sensors send out a square wave signal that runs from.3 volts to 5 volts.
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Tuesday, September 19th, 2017 AT 1:08 AM
Tiny
DAZLE1
  • MEMBER
I appreciate the attempt to help, but from the shop manual it says the ASD will not energize until the PCM receives a signal from the camshaft position sensor. I get continual voltage to the coil from the ASD while cranking, indicating both a camshaft and crankshaft position sensor signal. I have found my same problem online but no answers and some have replaced their PCM's without resolution. Of course that could just be a bad replacement but I want to be sure. There are some tests at the PCM connectors in the diagnostic manual but they do not make it clear which connector or what is top and bottom of the connector. Plus I believe the test have to be done with the battery in and you cant get to it without removing the battery.
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Tuesday, September 19th, 2017 AT 9:49 AM
Tiny
STEVE W.
  • EXPERT
You said you get voltage while cranking but that the engine shuts off soon after starting. That indicates that it is losing the signal as a sensor fails.
The ASD turns on with a signal from either the cam or crank signal, The PCM only needs to see one or the other to activate the ASD.
So you start the engine, the sensor gets warm, the signal degrades and the engine shuts down when the PCM kills the ASD relay.

The only way to tell for sure which is dying is to put a scope on them and see which is dropping out or sending a corrupt signal. A standard meter will not work because you cannot watch the actual waveform.
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Tuesday, September 19th, 2017 AT 11:21 AM
Tiny
DAZLE1
  • MEMBER
Actually what I said was " Vehicle will not start. I have battery voltage at the coil while cranking but no ground on any of the three coil driver wires from the PCM" I also said "I get continual voltage to the coil from the ASD while cranking, indicating both a camshaft and crankshaft position sensor signal."
So I have made it clear that when the vehicle will not start I get continual voltage to the coil from the ASD, thus eliminating the 2 sensors. You cannot get battery voltage at the coil while cranking if the sensors arent working. The PCM must 1st have a cam sensor signal and then a continual crank sensor signal for the ASD to be energized. The fact that the voltage is continual while cranking shows the ASD is staying energized while cranking, if the grounds were there, it would start, and does start after about an hour when the grounds come back. So the PCM isnt "killing the ASD" because it is continually working and sending voltage to the coil.

Again, the problem is that when it wont start I am losing the ground on the 3 coil driver circuits from the PCM. When it does start, the grounding is obviously there and I get spark. Ive never heard of an intermittently failing PCM or all 3 coil driver circuits failing intermittently together(doesnt mean that its not), and I am wanting to know if anything else could be causing the PCM to stop grounding the 3 coil circuits. I checked the coil to PCM wires and they have infinite resistance to ground and very little resistance from coil to pcm, so I dont see a short, ground or resistance problem with the wires of the 3 coil drivers. Both ground wires from the PCM to ground are grounded when it wont start, #'s10 & 50, so the PCM isnt losing its ground. What I havent been able to find in my research, if there is something else that the PCM controls, or is controlled by that would stop it from applying ground to the coil driver circuits.
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Tuesday, September 19th, 2017 AT 7:27 PM
Tiny
STEVE W.
  • EXPERT
No what you wrote is -
"I have a code for a crank sensor but I have battery voltage at the coil while cranking so I think that eliminates the sensor. I do not want to replace the PCM if it is not the problem."

An issue on that system is for a code to set when either sensor fails but the engine is not running, but it can set for the wrong sensor. So a bad cam sensor can send a signal to the PCM even though the engine isn't turning. The PCM expects to see both cam and crank signals so you get a crank sensor error.

NO: 18-24-97

GROUP: Vehicle Performance

DATE: Aug. 8, 1997

SUBJECT:
No Start Diagnostics Cam/Crank Sensor
$01 and $28

MODELS:
1997 (FJ) Avenger/Sebring/Talon
1997 (GS) Chrysler Voyager (International Market)
1997 (JA) Breeze/Cirrus/Stratus
1997 (JX) Sebring Convertible
1997 (LH) Concorde/Intrepid/Vision/LHS/New Yorker
1997 (NS) Town & Country/Caravan/Voyager
1997 (PL) Neon

NOTE: THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 2.0L DOHC/SOHC (NATURALLY ASPIRATED), 2.4L, 3.3L, 3.5L, OR 3.8L ENGINE.

DISCUSSION:

If a vehicle exhibits a no-start due to failure of the cam or crank sensor, the opposite sensor may be reported as the DTC (i.E. Bad cam sensor sets crank sensor DTC and vice versa). The faulty sensor may generate a signal strong enough (at key "ON") to be interpreted by the controller as a legitimate signal. Since the engine is not running, the opposite sensor will not be generating any pulses. The controller, expecting corresponding pulses from both sensors, matures a fault for the sensor that is not generating any pulses. In this case, the good sensor is reported as faulty.

To verify which sensor is at fault, use the DRB III and select DRB III Standalone, 1994 - 1998 Diagnostics, select Engine system, select Monitor Display, and No Start monitor. Under the No Start monitor the cam and crank sensors should display a no response or LOST on the display. If a sensor is reporting a signal at key ON", it should be replaced.

Then you are saying it will start and run for ten minutes and quit. Those are classic signs of overheating in a sensor or electronic component. So I gave you the options for testing the system. With either a DRBIII or a scope you can watch to see what is happening, without them to actually look into the system and watch the signals you cannot go any farther, unless you wish to start swapping expensive parts.

Any electronic component can fail from internal overheating. The most common ones are the cam and crank sensors followed by ignition modules and ECM/PCM.
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Tuesday, September 19th, 2017 AT 9:35 PM
Tiny
DAZLE1
  • MEMBER
If the sensors were not working I would not get voltage at the coil while cranking. Factory service manual pg 8d-10 Failure to Start Test, step 6.(This is the way Chrysler gives to determine if the crank and cam sensors are bad) two separate circuits, voltage and ground. To my knowledge no crank or cam sensor will cause the PCM to not ground the coil driver circuits. I know you are trying to help me but you doggedly ignore that I am getting voltage at the coil while cranking. You cannot get voltage at the coil if the sensors are bad, voltage means the ASD is energized which means the PCM is getting proper signals from the sensors and thus energizing the ASD. I can find nothing that says that a sensor can affect the PCM grounding the coil driver circuits. I also can find nothing ( other than a bad PCM), that says anything can cause the PCM to not ground the coil driver circuits. Do you know of anything officially that says there is something other than a bad PCM that will cause the PCM to not ground the coil circuits? This is what I really need to know. I would have already replaced the PCM if it were not for the intermittent nature of the failure. If I were not getting voltage at the coil I would have already replaced both sensors. Thank you
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Tuesday, September 19th, 2017 AT 11:54 PM
Tiny
CARADIODOC
  • EXPERT
Hi guys. I just stopped by due to interest in the topic, but I did not read everything. Allow me to add a comment that may be of value. You are one of the few people who understand how the ASD relay works and gets turned on, but starting somewhere around the late 1990's. It was possible for some Chrysler engines to run with one failed sensor, but once shut off, the engine would crank but not restart. It has to do with the spacing of the notches in the ring on the torque converter that are read by the crankshaft position sensor. Some use a varying number of notches in each group, and the computer can tell by the number of notches which pistons are coming to top dead center. On others, all three sets of notches have the same number, so the computer needs another input from the cam sensor to know which pistons are coming to TDC. That one, at least on the newer years, can continue running when the cam sensor fails because the back-up strategy for the computer is to simply calculate which ignition coil comes next, and next, and next. I am told those can also do the same thing by running on just the camshaft position sensor, but not once the stopped engine has to be restarted.

To add to the misery, there are some where the ASD relay will turn on during cranking when one sensor has failed, but I cannot remember what year that started or if it involved all engine sizes that year. The clue you might be overlooking is you may be stuck on the ignition coils. The injector pulses are also timed off the cam and crank sensors, so check if you lost those too.

You were lucky enough to get a diagnostic fault code for the crank sensor. Those often do not set just from cranking the engine. They need time to set, as in when a stalled engine is coasting to a stop. There are two real common problems with these crank sensors. First is either sensor on any car brand commonly fails by becoming heat-sensitive. Typically they fail during hot soak when a hot engine is stopped briefly, as in when stopping for gas, then they work again after cooling down for about an hour. This is where you may never get a fault code. The second is the crank sensor needs its critical air gap set with a thick paper spacer on the end, or, a lot of aftermarket sensors have a thin plastic rib molded on the end. If you remove and reinstall that style, you are supposed to cut off the remaining part of the rib, then use a paper spacer.

To show the importance of that air gap, when we got behind on transmission replacements at the dealership, I was asked a few times to take one on. My specialties are suspension and alignment, brakes, and electrical, but I am able to replace an engine or transmission. For the first couple of transmissions, (which require removing the crank sensor), I used the paper spacer, and everything went fine. Later I cut those spacers in quarters to use fewer resources and save the dealership a few pennies. For the last few, I became too arrogant to need the spacers. I just stuffed the sensor in all the way, then pulled it back a fuzz. Well, I heard through the grapevine that my thirteenth one developed a stalled engine about twenty miles from the shop. Another mechanic diagnosed the code as a failed crank sensor, replaced it, and there were no more stalling problems. I am convinced I caused that by not setting the air gap correctly.

To condense all this wondrous information down to something useful, you have the fault code and the perfect symptom for a failing crankshaft position sensor. A real easy way to verify that is by driving the vehicle with a scanner connected so you can view live data when the problem occurs. You are familiar with the record capabilities of most scanners, but I have a Chrysler DRB3 for all of my vehicles, and those list both sensors with a "present" or "no" to show if their signals are showing up. Watch if one of those switches to "no" while you're driving, even if the engine does not stall right away. You could be getting a weak signal that the computer interprets as "something", so it keeps the ASD relay on, but it is too weak to accurately read the timing. Some engines, like on the Neon's, will be shut down by the computer when the timing of those sensors do not agree, as in a jumped timing belt, (cam and crank sync fault code), but I can tell you for sure, the ASD relay will still turn on or pulse on and off during cranking even though there is intermittent spark and no injector pulses.
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Wednesday, September 20th, 2017 AT 1:18 AM

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