M44 DME issue

[Georgio01]

Hi All

i am currently experiencing a issue with my M44. After overhauling the engine i discovered that there was no spark.

What i checked so far:
1. I tested the Crank Position Sensor due to me knowing that it would cause no spark if its defective. The CPS tested OK!!!
2. I tested the lead from the DME to the CPS. I found that one pin has 5v. This is normal. However the other two pins are both GROUNDED. THIS IS NOT NORMAL. One pin should be ground and the other pin should be +12V.
3. I then used crocodile clips and supplied my own GROUND and +12V from the battery supply while maintaining the signal supply from the DME. VOILA!!!! i now had spark.

This all told me that the issue is on the cabling from the DME to the CPS connector.

4. I then removed the DME and then the ground issue went away which basically means that there is no short to ground on the cable specifically.

This now means that the issue is on the DME. When i opened the DME i did find some corrosion but really nothing to write home about. Do any of you guys maybe have experience with issues like this ? Anybody willing to share some information

Thanks guys
G

[Georgio01]

I have traced the pinouts from the connector of the CPS to the DME. ON the DME they are marked as PINS: 20, 28 and 78.

Then i traced the problem PINS, 20 and 28 to the main board of the DME and observed that indeed they are connected which makes sense why both were testing for ground. So that means this is indeed not a issue and the DME is not shorted out.

I then observed that when i put a earth cable directly to pin 20 i get spark. After multiple tests and consulting Bentlys i saw that PIN 28 is connected to the shield of the cable and the shield is a earth. i then disconnected the shield and the car started first time no issues. this meaning that somewhere theres a ground issue on the car. i dont know where yet but ill find it.

[Biolite]

Wow, a lot of tracing. Good sleuthing, man!