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Crank no start, no spark at the coil (started checking at wires and worked my way back to the coil). Here's all the pertinent information:
BACKGROUND
-Guy states car just wouldn't start back up one evening. No warnings/other issues prior
-Battery is new, truck cranks strong and even
-No lights come on dash/interior at all, even though the truck responds and cranks.
-No power at OBD2 port.
-Customer did state lots of electrical work done about a month ago. New horn wired up, new ABS module, some other things I can't recall.
DIAGNOSTIC RESULTS
-No spark at the coil, 50 psi fuel pressure cranking
-Power at coil during cranking from ASD all the way back to the coil driver pin at PCM. Driver is switching / grounding other side during cranking (LED test light flickers -- brightly FIRST PULSE, then very faint/dim*)
-Signals present at PCM from Crank and Cam Sensors (scoped).
-5V reference from PCM is good
-Changed coil twice, still no spark.
I'm thinking that the PCM may be to blame. No other reason I can think of as to why all activity needed is present but still no spark from the coil. One thing I forgot to do is measure current ramp with scope. Is it possible for the driver to be cooked and producing weak current? Can a bad coil damage the driver on these trucks? Not an expert by any means so all advice is much appreciated. Thanks in advance!
If you suspect the driver, try scoping coil negative while cranking. Then you'll be able to see if the driver is pulling the coil all the way to ground the way it should, and also if the ASD relay is continuing to supply power throughout the entire cranking event.
Super late update for anyone looking, but the customer ended up junking the vehicle.
Apparently, a shop had gotten their hands on it a couple weeks prior to the issue and having me look at it. They had done lots of electrical or wiring work according to the customer. I advised he take it back to them, and he did, but they were no help. Ultimately, the customer ended up junking the truck.
In hindsight I recognize my diagnostic shortcomings. The missing interior/dash lights and no power to the OBD2 port suggested one or more main fuses were busted, and I identified at least two on a wiring diagram after the fact. These were probably interfering with CAN communication.
I was so tunnel visioned on the coil not sparking (but amazed that it still cranked and had all the necessary inputs) that I couldn't pull myself from under the hood for 5 seconds. Had I slowed down, I'm sure I would have found the busted fuse or wires, and been able to do some bypass testing and get it running. I have done some training and had more experience since then, so I'm confident that if I run into a similar situation I will approach it much more carefully.
Ken
The following user(s) said Thank You: Tyler, juergen.scholl
We genuinely appreciate the update. It's easy to be critical of yourself in this kind of situation. Some vehicles we come across have more issues at work than the owner is willing/able to fix.
The fact that you went out of your way to learn from this one puts you head and shoulders ahead of the majority of techs out there.
The following user(s) said Thank You: juergen.scholl
Topic Author
It's easy to be critical of yourself in this kind of situation. Some vehicles we come across have more issues at work than the owner is willing/able to fix.
