97 Ram V8 Not Starting?

[MuleShack]

Have a 97 3/4 ton Ram with the V8 360.

Truck wouldn't start last week, so i changed the plugs and the wires and then put a new coil in.

It still wouldn't start, so i pulled a plug to see if i got spark...no spark.

I pulled the wire of the top of the coil and put a meter on it. When it turns over, i get a burst of power from the coil and then it drops off to nothing.

I figure this has to be a sensor causing this. Does anyone know which sensor might control this process? and where it might be located?

I do have a fix it manual, but that doesn't tell me how to diagnose the problem...so i could find it if someone had this issue before.

Thanks

[Jeremy airjer W]

What kind of "Meter" did you put on it.

Use a spark plug at the very minimum. Make sure it is grounded around the threaded area. If you still do not have consistent spark off the coil wire than I would suspect a possible crank sensor. Typically these will ground out the 9 volt reference voltage to not only itself but several other sensors. I believe the wire color is orange if you back probe it near the crank sensor connector turn the key to on there should be 9 volts. If there is no voltage turn off the key. Unplug the crank sensor check for voltage on the vehicle side of the harness while somebody turns on the key if the 9 volts returns than the crank sensor is grounded and likely your culprit.

[MuleShack]

I used a volt meter and put the pos terminal on the output on the coil and the black on the frame. I had it set at 50 volts and it bounced a little, so i set it to 10 volts and it surged to 8 or 9 volts and then dropped to nothing.

I had tested the spark on the plug by removing front right plug and putting it back in wire and grounding threads to manifold and no spark. that is what brought me back to testing the coil for output, because the distributor was just replaced under a year ago.

I just had the truck running about a week ago, as it started on the 2nd turn over and it was running for about 1/2 hour.

[Jeremy airjer W]

So you tested for power to the coil at the two wire connector or where the coil wire that goes to the distributor plugs in?

If you checked at the connector there will be 8-9 volts when you turn the key on. As soon as the ASD relay disengages (couple of seconds later) there will be no power until the key is cycled again or until you crank over the vehicle. It should be present for the entire time you are cranking over the engine. A couple of seconds after you stop cranking it will go away.

I'll be stopping by work within the next hour or so. I'll get a wiring diagram just to make sure I am on the right page!!

[MuleShack]

The issue is the voltage drops off after a quick spike and then goes to nothing while the vehichle is still turning over.

I could be cranking for 15 seconds, but the spike is immediate and then drops to zero for the remainder of the 15 seconds.

probably the sendor you mentioned earlier.

Steve

[Jeremy airjer W]

Everything I mentioned Above would be correct except for the wire colors. The power to the coil is supplied by the ASD relay which also powers the injectors and O2 heaters. The wire color is Dark green w/ an oronge tracer. This wire should have 12 volts (battery voltage) with the key on for a couple of seconds or any time the engine is cranking over or running.

If you do not see the 12 volts than we need to find out if the ASD relay is functioning or whether or not it is being energized by the PCM. The easiest thing to try is Swapping the relay with another. Make sure they are the same. If that doesn't work than you need to check for power and ground where that relay goes.

Two of the terminals should have power with the key on. One should be grouned all the time (this would be the one that supplies the power to the coil/injectors. the other one should be grounded with the key on for a couple of seconds or any time the engine is cranking or running.

The crank sensor wire is violet with a white tracer. This is a five volt reference not a 9 volt. Still test the same.

[MuleShack]

Thanks for the time Airjer,

i bought a code tester. I got 4 vehichles and on these older ones it seems like once a year something electrical goes out. by the time i pay for a tow and diagnostics it coveres the cost of this unit.

It gave me a P0320 code which i belive is the sensor under the distributor?

I'll see how this goes.

Thanks again.

Steve

[Jeremy airjer W]

With this code it could be either or according to step two of the flow chart. The code will set if no crank signal is detected, cam siganl is present with no crank signal, or no cam signal with crank signal present.

[MuleShack]

I got the part and going to try to get it put in Tuesday night.

Hopefully it is the cure.

[MuleShack]

Replaced the sensor under distributor and now the scanner shows no codes "Passed" but i have no spark yet.

I think that means my computer is shot?

[Jeremy airjer W]

It probably won't show a code if the codes where just cleared.

I really think you need to take a look at the crank sensor. At the very least check for power while its plugged in and you could even check for a/c voltage at the signal wire. I haven't run into to many pickup coils (the part in the distributor) on the new dodges. I have run into the crank sensors more frequently, thats why I was trying to point you in that direction.

The last thing I/we ever think to replace is the PCM. That doesn't happen unless it gets scrutinized by myself. Checking power, grounds, pins, confirming the loss off the failure at the PCM, and making sure all the wiring affected has continuity and is not shorted to a ground.

They are not cheap also! It may not be a bad idea to just spend the money for the tow and diag! Its much cheaper than a computer.

I had another thought you said you replaced the distibutor a while back. While you where replacing the senor did you check to see if the distributor shaft was turning while you where cranking?

Good Luck!!

[MuleShack]

I caved and had it towed to the dealer....

One last question.

If they do diagnose as PCM, dealer wants over 400 beans and NAPA only wants 200.

Is there any difference between the two and why would the price be so much difference?

[Jeremy airjer W]

Is the dealer including the install and flashing for $400. If they are I would say that is fair. The vehicle may or may not run with the napa PCM. Either way it will likely have to be flashed and there will be a charge for that if it doesn't run then there is another tow to the dealer after you install.

Most if not all of the computers we replace (which doesn't happen often) come directly from the manufacturer.

[MuleShack]

those prices were parts only....

They have not called back yet with a diagnosis.

[Shack]

I would bet the house on a crank sensor. It should be down by fly wheel harmonic balancer.

I would think $400 would be just for the unit it self. Flashing, install, tax and shop supplies would be on top of that.

I would look at used if it was PCM. It is rare they go (I have seen 10 or more crank sensors to one pcm)..

I know with newer 2.7L, if cam sensor fails or shorts, just unplug it and it will go into limp mode and at least start the eng., it will run funny, but start.

Sorry so late, I figure you had it sewed up.

[Shack]

I would go with a deal PCM, before an after market PCM. It will come down to the Warranty, but a used one could be a fraction of the price. I think Warranty on PCM is 8/80,000. You could ask about factory assistance if truck has less than 100,000 miles on it. PCM and cat converter are covered by a Federal emissions warranty. A big shot in the dark, but worth the ask if it is a PCM.

Good luck!

[MuleShack]

It turns out it was the crankshaft sensor.

Not a job i wanted to do anyway....as they said it took them 2 1/2 hours it wasn't a fun job...and 400 beans later it is running.

FYI

End of story.

[Jeremy airjer W]

There not that bad, once you get about five extensions, six swivels, three ratchets, a hand full of wrenches, and two adapter sockets! Then you have to figure out the right combination of the said parts. Make sure to have a couple of band-aids and a knuckle bandage ready also!

Glad its running!!