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Tiny
DEAN HEPP
  • MEMBER
  • 1998 DODGE RAM
  • 5.2L
  • V8
  • 4WD
  • MANUAL
  • 200,000 MILES
No power to coil. Negative side has good ground.
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Saturday, August 3rd, 2019 AT 2:43 PM

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Tiny
CARADIODOC
  • EXPERT
You will have 12 volts to the positive ignition coil terminal, the smaller terminals on the back of the alternator, and the wire that is the same color at every injector, usually dark green / orange, only for one second after turning on the ignition switch, then again only when the engine is rotating, (cranking or running). That same circuit feeds the fuel pump or pump relay. If you're expecting to see 12 volts in that circuit just with the ignition switch on, that won't happen. This is a safety circuit used on all car brands in one form or another in case a fuel line gets ruptured in a crash. Removing the 12 volts stops the fuel pump from dumping raw fuel onto the ground where it would become a fire hazard.

This circuit gets the 12 volts switched on through the automatic shutdown, (ASD) relay, and that relay is turned on by the Engine Computer when it gets signal pulses from the crankshaft position sensor and the camshaft position sensor. The fastest way to tell if the ASD relay is turning on is to observe its state during cranking, with a scanner. If it is not turning on during cranking, look under "live data" at those two sensors to see if they're listed as "yes", "present", "no", or something like that. Chrysler's DRB3 scanner lists them as "No" or "Present". When one of those signals is missing, there's probably a 75 percent chance that sensor is defective, but first inspect the wiring and connector terminals for breaks and corrosion.

If you don't have access to a scanner, use a test light on the dark green / orange wire at any injector, (or the wire that is the same color at all those places), or either small terminal on the back of the alternator. You can use a digital voltmeter too, but most of them don't respond fast enough. A test light is faster and easier to interpret. You'll see the test light turn on for one second when you turn on the ignition switch. If that is missing, we have to look in a different area. What is important is if the test light turns back on during cranking. If it does not, suspect one of the two position sensors.

Also read the diagnostic fault codes, but be aware fault codes often do not set for these two sensors just from cranking the engine. They need more time to be detected, as in when a stalled engine is coasting to a stop. For that reason, do not assume the sensor circuits are okay just because there is no fault code related to them.

Chrysler made reading fault codes yourself much easier than any other manufacturer. Cycle the ignition switch from "off" to "run" three times within five seconds, leave it in "run", then watch the code numbers show up in the odometer display. You can go here to see the code definitions:

https://www.2carpros.com/trouble_codes/obd2/p0300

or I can interpret them for you.

Let me know what you find, then we'll figure out where to go next.
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Saturday, August 3rd, 2019 AT 9:12 PM
Tiny
DEAN HEPP
  • MEMBER
No code shows up, apparently relay works. How do I find crank and cam sensor connectors to check them and how do I replace them? Sorry I have been retired for 20+ years. I love your web site!
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Tuesday, August 6th, 2019 AT 11:40 AM
Tiny
CARADIODOC
  • EXPERT
The better approach is to use a scanner to view live data and see if both sensors are developing their signals. Each one will be listed with a "Yes" or "No", or something like that to show if their signal is showing up during cranking.

The crankshaft position sensor is in the transmission's bell housing, right behind the right cylinder head. It looks like the one in the first photo. No spacer or other special procedures are needed for setting the critical air gap. That is handled by the mounting bracket design.

The camshaft position sensor is a disc under the rotor in the distributor. It is also called the "distributor pick-up". That one probably has a slightly higher failure rate than the crank sensor.

Do I assume you mean the ASD relay is working because you saw the test light turn on for that initial one second, but not again during cranking?
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Tuesday, August 6th, 2019 AT 5:54 PM

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