no rpm signal

Backstory - I have a LM7 5.3 gen3 swapped into a BMW. Car would start and idle for me enough to drive in and out of my garage. I sold my house and had to bring the car to my parents house, this was beginning of January. I drove the car onto the trailer, and backed it off the trailer, no issues. I tried to move it a couple weeks later and I couldn't get it to start up. I started diagnosing now the weather is warmer and am stuck.

The issue I'm having is a crank no start, I didn't have injector pulse which pointed me to rpm signal and discovered I'm not getting an rpm reading.
What ive done so far:
checked for rpm reading with vcm as well as a tech 2 scanner - not registering an rpm on either
ohm tested wiring from ecm to crank sensor - good
replaced crank sensor - no change
verified all grounds to the ecm are connected and good
all 12v constant to ecm is present at all times
all switched 12v to ecm is present in run and also while cranking
have dtcs for throttle position sensor, egr (not connected)


Questions: does this setup get its rpm signal from the crank sensor or does it rely on the cam sensor? or does it need both signals?
Battery voltage stays around 12.4-12.6v with key on but has been dropping to 10.6v during cranking, is that too low and causing issues with the sensors reading?

i did set VATS to none and performed a write entire. Attached is the current file and recent log when i was cranking it over the other day.

Attachment 118750Attachment 118751

Attachment 118753

You have good ~12v at CKP pin C?

Good ground at pin B?

If you put a jumper wire in C and another wire in A, and quickly tap them together, does the scanner RPM PID show some sort of activity?

Plug in the sensor you removed (or remove the one already installed, just trying to save time). Monitor scanner RPM while passing something ferrous (screwdriver) back and forth across the face of the sensor. Get anything?

Scanner rpm is from crank sensor. PCM tach output is from cam sensor.

Quote:

---

Originally Posted by blindsquirrel

Attachment 118753



You have good ~12v at CKP pin C?

Good ground at pin B?

If you put a jumper wire in C and another wire in A, and quickly tap them together, does the scanner RPM PID show some sort of activity?

Plug in the sensor you removed (or remove the one already installed, just trying to save time). Monitor scanner RPM while passing something ferrous (screwdriver) back and forth across the face of the sensor. Get anything?

---

Thank you

No 12v at C , good ground at B

Checked for 12v on pin 2 at the ecm and didn't have anything . I disconnected that lead at the ecm and manually applied 12v and the car starts up now . Is there an input I overlooked that supplies voltage here? Or possibly a bad ecm?

Quote:

---

Originally Posted by mccarthy69

verified all grounds to the ecm are connected and good
all 12v constant to ecm is present at all times
all switched 12v to ecm is present in run and also while cranking

---

How did you check these? What pinout/diagrams are you referencing to make sure it's all correct?

Attachment 118791
Attachment 118792

I have Mitchell diagrams I got through identifix ill try to attach them here
it shows hot at all times pin 20 and pin 57
hot in run/start pin 19
pin 1 and pin 40 ground(same for both connectors)

The pinouts for the crank sensor match up to the diagram you attached

I used a multimeter to check the voltage, had someone crank the engine to verify it wasn't dropping out during cranking

Hot in run/start: 19 and 75

And, they come from different fuses, so power at one isn't affecting chances of there being power at the other.

Attachment 118796

I double check in the morning , thanks

Quote:

---

Originally Posted by blindsquirrel

Hot in run/start: 19 and 75

And, they come from different fuses, so power at one isn't affecting chances of there being power at the other.

---

Checked today both are getting battery voltage in run/start

Going to try and bring this thread back if not ill try to repost it. Here goes
Engine – 5.3l v8 gen 3
Trans – t56
Car – 97 bmw 3 series
Ecm – 411
Cable throttle
Issue – crank no start – no rpm signal – crankshaft sensor not getting 12v reference
*CAR USED TO RUN - car started and ran without issue until I moved it from one house to another, drove on the trailer and drove off, has not wanted to start since*
Basic checks – per my wiring diagrams:
Blue 20 and 57 B+ hot at all times – confirmed
Blue 19 and 75 B+ ignition run/start – confirmed
Blue 1 and 40 ground – confirmed
Red 1 and 40 ground – confirmed
All 3 wires to crankshaft sensor ohm out fine
I do not get 12v at blue pin 2 in run or start (crank sensor 12v reference)
I’ve double and triple checks these readings with an assistant to turn to crank to verify I’m not dropping voltage while cranking.
If I disconnect blue pin 2 at the pcm (still connected to crank sensor) and manually apply 12v to it the car will start and run.
Tune was write entire after Vats disable – since the car will sit and idle with the above test I think that shows proof that vats is not enabled.
Tried another pcm – no change
I used a snapon multimeter to perform the electrical checks, I was a tech for 10 years I know my way around electrical issues but I’m at a loss here. I feel like I may be overlooking something or could be an issue in programming.

Quote:

---

Originally Posted by mccarthy69

Going to try and bring this thread back if not ill try to repost it. Here goes
Engine ? 5.3l v8 gen 3
Trans ? t56
Car ? 97 bmw 3 series
Ecm ? 411
Cable throttle
Issue ? crank no start ? no rpm signal ? crankshaft sensor not getting 12v reference
*CAR USED TO RUN - car started and ran without issue until I moved it from one house to another, drove on the trailer and drove off, has not wanted to start since*
Basic checks ? per my wiring diagrams:
Blue 20 and 57 B+ hot at all times ? confirmed
Blue 19 and 75 B+ ignition run/start ? confirmed
Blue 1 and 40 ground ? confirmed
Red 1 and 40 ground ? confirmed
All 3 wires to crankshaft sensor ohm out fine
I do not get 12v at blue pin 2 in run or start (crank sensor 12v reference)
I?ve double and triple checks these readings with an assistant to turn to crank to verify I?m not dropping voltage while cranking.
If I disconnect blue pin 2 at the pcm (still connected to crank sensor) and manually apply 12v to it the car will start and run.
Tune was write entire after Vats disable ? since the car will sit and idle with the above test I think that shows proof that vats is not enabled.
Tried another pcm ? no change
I used a snapon multimeter to perform the electrical checks, I was a tech for 10 years I know my way around electrical issues but I?m at a loss here. I feel like I may be overlooking something or could be an issue in programming.

---

Did you ever get this figured out? I'm having the exact same issue. Thanks

I don't remember where I got the info from but somehow the cam and crank sensors are connected internaly in the ecm (run off the same drivers) , I think on their 12v ref signal but there's not diagrams to reflect this. Once I disconnected the cam sensor I had no more issues on the crank sensor side and the 12v reference stays there .

Quote:

---

Originally Posted by mccarthy69

I don't remember where I got the info from but somehow the cam and crank sensors are connected internaly in the ecm (run off the same drivers) , I think on their 12v ref signal but there's not diagrams to reflect this. Once I disconnected the cam sensor I had no more issues on the crank sensor side and the 12v reference stays there .

---

Hi mate,

I?m having the same issue with an LS1 in a Nissan patrol.

Car ran fine, stopped, found no 12v from ECU to the crank angle sensor after live data indicated no RPM signal. Applied 12v directly and it ran, but then it stopped again.

I now have no RPM signal again, but there?s still power at the crank angle sensor plug.

When you said you disconnected the cam angle sensor, did you do that electronically in the ECU, or just unplug it?

I tried unplugging mine and it didn?t make a difference.

Really struggling with this.

Car?s running a factory Holden commodore ecu with VATS removed and a tune for mafless and cam. I don?t have the tools to delete camshaft reference from the ecu if that?s what you had to do rather than unplugging it, but I?ll find a way if required.

I know this is a real thread dig, but if you happen to see this and can give me the info required to fix I?d be very appreciative.

Cheers!

Quote:

---

Originally Posted by Ls1patrol

Hi mate,

I?m having the same issue with an LS1 in a Nissan patrol.

Car ran fine, stopped, found no 12v from ECU to the crank angle sensor after live data indicated no RPM signal. Applied 12v directly and it ran, but then it stopped again.

I now have no RPM signal again, but there?s still power at the crank angle sensor plug.

When you said you disconnected the cam angle sensor, did you do that electronically in the ECU, or just unplug it?

I tried unplugging mine and it didn?t make a difference.

Really struggling with this.

Car?s running a factory Holden commodore ecu with VATS removed and a tune for mafless and cam. I don?t have the tools to delete camshaft reference from the ecu if that?s what you had to do rather than unplugging it, but I?ll find a way if required.

I know this is a real thread dig, but if you happen to see this and can give me the info required to fix I?d be very appreciative.

Cheers!

---

It's been a while but If I remember correctly I didnt disconnect the sensor plug at the sensor I unpinned the power lead to the camshaft sensor at the pcm as this was quicker to test the issue than pulling my cowl apart to get to the sensor. I may have also unpinned the ground and signal leads to the camshaft sensor also just to 100% isolate the sensor. Once I did that I got the 12v back at the crankshaft sensor and the car was able to start . The car is still a work in progress and I still haven't gotten to replacing the sensor itself to see if that was the issue or if one of the leads I disconnected got pinched and shorted the whole circuit out . Not sure if this information is the fix for yours but I hope it helps toward finding a solution

Thank you for the reply! I sent an email and even shot a text over to America after I found some of your for sale listings, lol. After seeing you hadn’t logged in for a long time I figured it might be impossible to get onto you via a thread.

I’ll check the PCM and disconnect that wire from the pin to the cam angle sensor. Thanks mate.