Cranks but it will not start after driving across a bumpy train crossing

Tiny
HARLEYMAN6684
  • MEMBER
  • 1997 DODGE CARAVAN
  • 3.3L
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 130,000 MILES
The van ran fine never a problem. I drove across a rough train crossing with a bump van cut off has not run since. Two mechanic and $500.00 in parts and labor and they still do not know the problem. Replaced the crankshaft sensor, coil, TCM, two relays and still no spark or fuel.
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Friday, December 16th, 2016 AT 10:46 AM

8 Replies

Tiny
CARADIODOC
  • EXPERT
Was any testing done or did they just throw random parts at the problem? What led someone to replace the transmission computer? Has anyone read and recorded the diagnostic fault codes? Do you know how to do that yourself?
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Friday, December 16th, 2016 AT 11:56 AM
Tiny
HARLEYMAN6684
  • MEMBER
Yes test were run no codes, my brother changed the tcm one of his friends told him that was the problem. I am a para of 33 years was a mechanic for many years in the 60 till 84 when I got shot and paralyzed. The battery was disconnected before I could run a obd scan. Both mechanics are good hooked up a computer show cranksensor bad but when it was replaced still no fire or fuel in cylinders but fuel rails are pressurized. I am thinking the automatic fuel shutoff. One mechanic said the PCM checked out fine the other mechanic say the PCM is bad. I don't think it is the computer because it has always cranked first try never missed while driving, accelerated quickly no warning lights nothing.
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Friday, December 16th, 2016 AT 8:20 PM
Tiny
CARADIODOC
  • EXPERT
First lets clear up a few things. You might have a separate fuel pump relay, but if you do, it is turned on at the same time as the automatic shutdown, (ASD) relay. Those relay(s) will turn on for one second when you turn on the ignition switch. THAT is why you will have fuel pressure, and that proves the relays are working, the Engine Computer has control of them, and their fused circuits are good. You might hear the hum of the fuel pump too.

The Engine Computer turns those relays on again when it sees engine rotation, (cranking or running), and it knows that by receiving signals from the crankshaft position sensor and the camshaft position sensor. The next important tidbit is the air gap for the crank sensor is critical. If you installed a new sensor, it either had a thick paper spacer on the end to set that gap, or it had a thin plastic rib molded onto the end. Some aftermarket sensors use that plastic rib. OEM parts use the paper spacer. As soon as the engine is cranked, that spacer slides off and is done doing its thing. If you remove, then reinstall it, you must stick a new spacer onto the end of it. If you don't, it will usually go in too far and be broken by the ring on the flex plate. If you reinstall a sensor with the plastic rib, you're supposed to cut that rib off, then use a paper spacer. That's because the rib gets worn down over time and will not properly set the gap a second time.

Once the signals are received from those two sensors, the Engine Computer turns the ASD relay on, (and the fuel pump relay, when there is a separate one). The ASD relay sends current to the ignition coil pack, injectors, oxygen sensor heaters, alternator field, and possibly the fuel pump.

The easiest way to tell if the ASD relay is being turned on is to measure the voltage at any of those items. The switched 12 volt wire will be the same color at the coil pack and every injector. For most models that is the dark green / orange wire. A test light works best for this because digital meters don't respond fast enough. You should see the light turn on for one second when you turn on the ignition switch, then it will go off. What is important is if it turns on again during cranking. If it does not, the signal is missing from one of those sensors.

If you're lucky, you'll get a diagnostic fault code for the sensor with the missing signal, but they often don't set just from cranking the engine. Then you'll need a scanner to view live data. Both sensors will be listed with some type of indication showing if the signals are there. I have a Chrysler DRB3 scanner for my vehicles. That lists each sensor with a "No" or "Present". Aftermarket scanners should provide the same information.
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Sunday, December 18th, 2016 AT 1:59 PM
Tiny
HARLEYMAN6684
  • MEMBER
I will contact the two mechanics tomorrow and find out what each one did, both have NAPA service centers so I am sure what parts were replaced came from NAPA. Thanks for your help.
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Sunday, December 18th, 2016 AT 3:21 PM
Tiny
HARLEYMAN6684
  • MEMBER
They are closed until after Christmas will post more then. Thank You for your help and I hope you and family have a very Merry Christmas
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Wednesday, December 21st, 2016 AT 6:08 PM
Tiny
KEN
  • ADMIN
Merry Christmas!
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Saturday, December 24th, 2016 AT 2:07 PM
Tiny
HARLEYMAN6684
  • MEMBER
Turned out to be the crankshaft wires were shorting out. The dodge dealership figured it out after the first and second mechanics changed the pcm twice ect.
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Thursday, February 23rd, 2017 AT 5:47 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. For future reference, when the 5.0-volt feed to the crank and cam sensors, which originates in the Engine Computer, is grounded, the computer shuts that supply down to protect it. Shorting the wires to ground or together will not damage the computer. Once a supply is shut down, you have to repair the short, then turn the ignition switch off and back on to reset it.

Happy to hear it's solved.
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+1
Thursday, February 23rd, 2017 AT 7:10 PM

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