1986 eta NO Start (CPS Voltage??)

[thechad76437]

Trying to get my E30 on the road again. It was initially parked because I couldn't figure out what was going on.

1986 325e All stock

Found 2 bad fuel pumps, so I converted to a single high pressure in tank pump.
Once I had fuel, I just knew it would start.... no dice. I had no spark now either.

I went through all the Bentley manual's ignition diagnostics.
Installed New spark Plugs (someone had platinums in it)
Coil checks good.
No Ground signal coming from DME to fire the coil. (Checked with test light)
Found 1 blown fuse, (interior lighting etc)
Replaced fuse, checked all relays (good)
Unplugged both engine speed and pulse sensors, and both checked good with Ohm meter. (plugs are very brittle on sensor side and started cracking apart) Plugged back in, and checked for Ground signal at coil. We have a flashing test light now!!!

The old girls starts up, though rough. I was thinking that a couple of injectors were stuck, because after letting it run for a few minutes, getting it up to temperature, and giving it some RPM off and on, everything cleared up for the most part. I took it for a quick spin up the road and back, and all seemed good. I shut it off, so I could tie up some loose ends and put little stuff back together in the fuel pump area. Start it up again, to move it into the shop. Now its firing on about 3 cylinders sounds like. Run out of time.

Come back that night, and won't start at all. Sounds like 1 cylinder is firing way late through exhaust or something. Loud ticking once per engine revolution.(estimate) Throw hands up and go to bed.

Current Status:
Back to having no gound signal to fire the coil. Although the loud ticking when cranking has stopped also.
Double checking Crank sensors. Both ohm out within spec.

Decided to check voltage coming to these sensors. One of the plugs, I get 5v on the first pin, a few mV on middle pin and ground on 3rd pin. (seems right) The second plug however, I have 1.5v on first pin, 1.5v on middle pin, and ground on 3rd pin.
I expected both of these to see 5v, considering RealOEM lists the same part# for both sensors. I do not have continuity between any of the 3 pins on either plug, and only the 3rd pin checks continuous to ground. Voltage was checked with key on. Continuity between pins checked with key off.
I do have 2 new sensors on the way, but trying to further troubleshoot in the mean time.

Question:
Does anyone know for sure what voltage each of these is supposed to have coming from the DME? I would like to know for sure they both are supposed to have 5v with key on, before I go removing a harness, to hunt for a bad wire.

Thanks!

[thechad76437]

I have gone through all of the wiring harness diagnostic for the plug going to the Motronic module. Everything checks out according to the Bentley manual.

I did find 2 questionable pins though.
--Pin #1 is not referenced in the Bentley diagnostic checks, but it has 12v with key on.
--Pin #35 is supposed to have 12v with key on (which it does) however when testing with a test light, it gives a dim light compared to the other 12v power pins coming in.

Pins #8 and #27 go to the Engine speed sensor. I used jumpers to power up the Motronic and check voltage on these pins. #8 has 1.8v and #27 has 1.4v. This does not seem right to me. I would expect one of them to have 5v and the other to check near 0. Maybe a few mV.

So I'm thinking I may have a bad computer. I went ahead and popped the covers off the Motronic, but couldn't get either of the boards loose to see the components mounted on them.
The numbers on the Motronic are 0 261 200 027 with (078) towards the right side of label.

Questions:
Can anyone shed some light on Pin #1 having 12v? Why wouldn't it be referenced in the Bentley?
Why would pin #35 have lower current, thus a dim light when checked with test light?
Can anyone verify that the engine speed sensor circuit is supposed to have 5v going to the sensor?
What's the trick to get the boards out of the Motronic to look for visibly damaged components on the boards?

I know I'm a "noobie", but any feedback would be appreciated. There is not much info out there that I could find on the ETA Motronic wiring or computers.

[ForcedFirebird]

The loud ticking when cranking makes me suspect the reference pin on the flywheel may have come dislodged - wouldn't be the first. The eta has two CPS's, one uses the flywheel starter ring gear to tell the ECU engine speed, then the other one uses a single pin sticking out of the edge of the flywheel to tell the ECU when the engine is at TDC (much like the missing teeth do for the later Motronic). If either of those signals are absent the car will not start as the fuel pump won't come on until the ECU sees engine rotation and won't spark since it has no idea what cylinder it's on, however, if the reference sensor (single pin) is missing a signal as the car is running, it will stay running.

Take the CPS out of the bell housing (want to say it's the rear one) and rotate the engine while looking through the hole for the CPS. If the pin is missing you can use a long drill bit/tap and thread in a 6mmx1.0 allen key bolt to replace the pin.

[thechad76437]

The loud ticking when cranking makes me suspect the reference pin on the flywheel may have come dislodged - wouldn't be the first. The eta has two CPS's, one uses the flywheel starter ring gear to tell the ECU engine speed, then the other one uses a single pin sticking out of the edge of the flywheel to tell the ECU when the engine is at TDC (much like the missing teeth do for the later Motronic). If either of those signals are absent the car will not start as the fuel pump won't come on until the ECU sees engine rotation and won't spark since it has no idea what cylinder it's on, however, if the reference sensor (single pin) is missing a signal as the car is running, it will stay running.

Take the CPS out of the bell housing (want to say it's the rear one) and rotate the engine while looking through the hole for the CPS. If the pin is missing you can use a long drill bit/tap and thread in a 6mmx1.0 allen key bolt to replace the pin.

Thank you sir for the input! I was kinda curious what size it was going to be, if the pin HAS come out.
I was planning on checking that pin when I replace the sensors. They should be here tomorrow, so hopefully I can cross that off the list in a day or two.
I guess once that is all straight away, I will know if its the DME or not. I did get the boards "unfolded" out of the Motronic Unit. I could not find anything that was obviously burnt or anything. Not really any corrosion either, but who knows on that front. I started trying to trace out the engine speed sensor circuit, but was going cross eyed after about 30min looking.
If the pin is present, and sensors don't change anything, I'll guess I'll try a used DME of ebay or something. At least these early boxes are cheap!!