spark plug firing WITHOUT engine turning over
TECH Fanatic
Joined: Feb 2015
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The coils will only fire with a pulsed control signal from the PCM. Either the PCM is freaking out or it is seeing a pulsed/trigger signal on the crank sensor input to trigger coils. Time to bust out a meter to see what's going on. Using AC mode to see pulsed/triggered signal can be helpful (when you don't have a scope). Getting comm working at PCM is going to be needed to use HPtuners. Since the PCM had comm when checked on the desktop you may have another module on comm/can bus that is causing the comm issue. Disconnecting the other modules or try pulling fuse that supplies the module to diagnose/isolate problem module.
Thread Starter
Teching In
Joined: Feb 2008
Posts: 23
Likes: 1
The coils will only fire with a pulsed control signal from the PCM. Either the PCM is freaking out or it is seeing a pulsed/trigger signal on the crank sensor input to trigger coils. Time to bust out a meter to see what's going on. Using AC mode to see pulsed/triggered signal can be helpful (when you don't have a scope). Getting comm working at PCM is going to be needed to use HPtuners. Since the PCM had comm when checked on the desktop you may have another module on comm/can bus that is causing the comm issue. Disconnecting the other modules or try pulling fuse that supplies the module to diagnose/isolate problem module.
Thread Starter
Teching In
Joined: Feb 2008
Posts: 23
Likes: 1
Well, traced all wires, found a bad ground, fixed it and that solved my OBD port issue as well as most other issues. got it all back together and upon cranking it backfires through the exhaust. Swapped coil packs to other side, same issue. Put a scanner on and it gives me a Crank position sensor circuit error. P0335 So, as I traced these wires already I am hoping for a defective Sensor. It is a new sensor and i understand it must be learned, but not sure how it can learn it if it isnt running.
Teching In
Joined: Jul 2020
Posts: 28
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Bad grounds can do weird things for sure!
if you crank the engine, does the rpm register on the scanner?
Do you have the correct crank sensor for the engine? (Grey or black)
Crank sensor relearn should be done after replacement, but will still start and run well, seems to help missfire detection
Lastly, is it plugged in? Done that before, especially when trying to diagnose harness issues and forget to plug it in as its sometimes the most difficult to plug in
if you crank the engine, does the rpm register on the scanner?
Do you have the correct crank sensor for the engine? (Grey or black)
Crank sensor relearn should be done after replacement, but will still start and run well, seems to help missfire detection
Lastly, is it plugged in? Done that before, especially when trying to diagnose harness issues and forget to plug it in as its sometimes the most difficult to plug in
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Teching In
Joined: Feb 2008
Posts: 23
Likes: 1
Bad grounds can do weird things for sure!
if you crank the engine, does the rpm register on the scanner?
Do you have the correct crank sensor for the engine? (Grey or black)
Crank sensor relearn should be done after replacement, but will still start and run well, seems to help missfire detection
Lastly, is it plugged in? Done that before, especially when trying to diagnose harness issues and forget to plug it in as its sometimes the most difficult to plug in
if you crank the engine, does the rpm register on the scanner?
Do you have the correct crank sensor for the engine? (Grey or black)
Crank sensor relearn should be done after replacement, but will still start and run well, seems to help missfire detection
Lastly, is it plugged in? Done that before, especially when trying to diagnose harness issues and forget to plug it in as its sometimes the most difficult to plug in
Thread Starter
Teching In
Joined: Feb 2008
Posts: 23
Likes: 1