No spark, no fuel

Tiny
THADRIAN86
  • MEMBER
  • 3 POSTS
Happy New Year and thank you for the reply! Okay, so we dug back in today and found a semi loose connection on pin 23 on the PCM. However, we also found only one of the 3 PCM's after we remade this connection secure would fire up the ASD and fuel system relay, so now we have fuel. However, we verified nothing is going to the coil. And nothing is going to the injectors. We have not verified crank or cam shaft position sensors yet. The ASD relay does not turn on for only a second it stays on now when the key is in the run position. Same with the fuel pump. I'm not sure if this is normal. So far I am thinking there is a short with something to the PCM or something communicating to the distributor and the injectors. Also we jumped 12vdc to the coil while cranking to see if we would get spark from the plug wires and still nothing but the coil was under load.
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)
Tiny
GONZO1234
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  • 15 POSTS
How do I check that if the pcm if its sending ground
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)
Tiny
THADRIAN86
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  • 3 POSTS
Shoot also 0 codes came up with that technique. Possibly because of the PCM swaps.
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)
Tiny
MEGHOLD
  • MEMBER
  • 2 POSTS
  • 1998 DODGE RAM
1998 Dodge Ram V8 All Wheel Drive Manual

Ive tried the wires and put in a new coil but my truck still doesnt have any spark! Please help!
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
Have you checked the crank sensor?
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
An led testlite should be safe for your computer. They don't recommend a 12 volt test lite on computer circuits. Touch one end of testlite to voltage the other end to the computer ground at the asd relay, engine cranking, the lite should be on. If the lite goes out, your losing voltage or ground.

You could use a jumper wire on the load side of asd relay, just for testing, that should run voltage to everything the relay controls. See if it will start?

In the diagram I posted, is the asd relay, the load side of relay has the line with the arrowhead on it. When the relay is energized, that line with the arrowhead moves to the other terminal for voltage. I'm not sure I explained that very well? If you don't understand what I've posted, don't try it.
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)
Tiny
CARADIODOC
  • MECHANIC
  • 33,864 POSTS
Fault codes get erased when the computer is unplugged. That removes the memory 12 volts.

The easiest approach now is to find a scanner to look at live data related to the Engine Computer, (PCM). Specifically, it will list the crankshaft position sensor and the camshaft position sensor as "No" with the ignition switch on, meaning no signals are being generated by them. Next, we want to see both of them switch solidly to "Present" when you crank the engine. Those two signals are what it takes for the computer to turn the ASD relay on again. These sensors are listed under the "Sensor Data" drop-down menu.

Under the "Inputs / Outputs" menu, the ASD relay will be listed showing its state, or "Request" as "on" or "off". It is supposed to be "on" for the first second, but you may not catch that because the scanner stops communicating when the ignition switch is off. What we're interested in is it should be "off" with the ignition switch on until you start cranking the engine, then it should switch to "on". Any other results are not acceptable.

We can try to do this without a scanner, but it can be rather cumbersome. Don't waste your time trying to run a 12-volt wire to the ignition coil. The results are meaningless and possibly even confusing. Those signal pulses from the cam and crank sensors that tell the computer to turn the ASD relay on are the same pulses that tell it when to fire an injector and an ignition coil. If the computer isn't turning the ASD relay on, it won't be firing the coil either, even if you do put 12 volts to it.

The place where you can add confusion is less than about one percent of crank / no-starts are caused by problems in the ignition system, less than one percent are caused by problems with the injector wiring, and perhaps as much as three percent are caused by fuel pump or fuel delivery problems. All of those are problems in the individual systems. By far a good 95 percent of these no-starts are caused by a problem related to the two sensors or the computer, and they affect all three of those systems at the same time. Fix one cause and all three systems will be working again. There are some newer engines that can be tricked into getting spark from the ignition coil, but that is neither a solution nor a valid clue. That is what I mean by "confusing the issue".

Next, I'd like you to go back to the tests you did in regard to the ASD relay. You listed multiple observations that can't agree. Monitor the voltage on the dark green / orange wire at the ignition coil or any injector. That must have 0 volts when the engine is not rotating. If you find something, unplug the crankshaft position sensors. I read once where one was generating noisy signals that tricked the computer into turning the ASD relay on at the wrong time.

Assuming you do find 0 volts, now see if it switches to 12 volts when you crank the engine. If it does, the circuit is working. If you do not find 12 volts, stop, turn the ignition switch off, then back on and verify there's 12 volts there for one second. If there is not, fuse 6, a 30-amp in the under-hood fuse box is blown. That's shown at the top of the first diagram. Or the relay is not being turned on. Pull the ASD relay out of its socket, then check for 12 volts on two of the terminals in that socket. Terminal 30 should have it all the time. Terminal 86 should have it when the ignition switch is in the "run" position.

I'm going to type up more wondrous information at home tonight and work on these diagrams for you. Let me know what you find up to this point.
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)
Tiny
MEGHOLD
  • MEMBER
  • 2 POSTS
No I havent. Would no spark have to do with the fuel pump?
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)
Tiny
GONZO1234
  • MEMBER
  • 15 POSTS
I have removed the fuse and choked or power and ground and it has both
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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No, however, have you checked fuel pump pressure?
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)
Tiny
JDL
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Then, I don't know why your losing at the coil? Goodluck.
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)
Tiny
GONZO1234
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Oh thanks
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)
Tiny
JDL
  • MECHANIC
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I hope you get it going your way.
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Sunday, December 13th, 2020 AT 10:01 AM (Merged)

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