E34 M20B25 1988 manual transmission - cranks but wont start..

[Pavlos12]

Hello,
first I want to say I already read tons of threads with this problem, did "troubleshooting" with bentleys manual and I still cant find what is wrong.. Here is my story:

Two months ago:

After 3 weeks of parking I washed the car normally and next day I normally started the car. After 5 minutes I shifted reverse gear and I started to back the car out of the garden. When I reached hump of my gate, the car shutted down immediately. I was cranking up with uncovered fueltank and my dad was listening if the fuelpump is running - wasnt, so I get out the pump from the fueltank for testing and it worked, obviously.. (I wasnt know about that DME CPS etc. problems before..) This time I started googling what it can be, I tested relays if they switch and theirs continuity, everytghing ok. Next I measured CPS sensor resistance - OK, but someone tell me that even though it is fine, it can be defective.. Because of no time left I disconnect the battery. After 2 weeks I came back, connect the battery and THE CAR STARTS for 5 seconds (it was the best feel at the moment) but it again shutted down... I ordered new CPS from two brands and it didnt help, so I put back the original one. Next I tried buy new NGK spark plug wires with new spark sensor on in, because I hoped that is like camshaft sensor.. Didnt help. I found in bentleys manual that faulty DME can damage the coil. So i ordered new coil and it didnt help. The car doesn't want to start even for those five seconds.

I found just one thing which I don't know how to deal with.
On this forum I found thread for E30 525i. There is a troubleshooting and on one of the steps I cant met.

2) With the key on, verify that power is present at DME pin 27 and pin 18. Power to pin 18 is from the main relay and there should be power to the injectors and fuel pump relay. A power check means seeing a voltage within about a tenth of a volt of what you measure across the batter terminals"

My voltage on pin 27 is about 0,4 Volts less than battery has..

I tried contact local "E34 club" in my country, but nobody knows and nobody has same engine close to me to try switch DME's and other stuffs.
Mayme an animal damaged wires? Fuses in enginebay are ok, GNDs which I found I cleaned.. Please, any opinions?
Thank you for your time

[moroza]

Sounds like a fuel pump or something related. First, see if it's working at all; grab a coat hanger or some other metal object, and simply touch one end to the positive battery terminal under the hood, and the other to the top of the fuel pump fuse. Either disconnect the fuel send line to verify it's working, or have someone listen. If it is working, that leaves three possibilities: hardware (weak pump and/or a bad check valve or fuel pressure regulator), software (electronic problems resulting in the pump not being told to turn on), or something unrelated. The first possibility requires a fuel pressure tester; the second, wiring diagrams and a multimeter. If the pump isn't working when manually powered, that again leaves two possibilities: the pump is actually bad, or the wiring to it is. The spot in front of the right rear wheel where the pump power wire goes through the body is the most likely break point. To really be sure, remove the egg-shaped panel inside the trunk to access the pump, and give it 12V directly. Still doesn't work? Bad pump. Now it works? Bad wiring.

I'm not certain about the M20 ECU, but most other E34 don't power the fuel pump continuously while running, only when needed and for a few seconds when the key is ON. This is why the fuse has to be powered manually.

[Pavlos12]

I forgot to say - I jumped the fuel pump relay with piece of cable and fuelpump is running, so wiring to FP is OK, but the relay is not getting power/is not grounded via DME.
I have the car for 7 years and the fuelpump was running only with running engine and for all the time until the key off. Never before starting engine like other cars do for "pressurize" fuelsystem.
And no spark is here too. I took out sparkplug and put it on cylhead cover and no spark seen

[moroza]

In that case, it sounds like electric or electronic problems. The next thing I would check, then, are sensor resistance values at the big plug into the ECU, and overhaul (take apart, sand or file to shiny metal, reassemble, spray with battery contact sealer) all the relevant ground contacts on the body and engine block. I would also investigate and probably outright replace, regardless of appearance, the (two?) fusible links. If after all that it still won't spark or power the fuel pump, I'd suspect a bad ECU, and look for a known good spare to test with.

Is there by any chance an aftermarket alarm or immobilization system?

[Pavlos12]

That car had some "alarms".. 7 years ago I found big messy wiring under steering wheel, but it was disabled before, there was unconneted unknown cables so i put them out. But I have in my plan to check it again, maybe i missed a wire and now he is grounding something.

Ok Im gonna find and clean all the groundings and find the fusible link. Thank you, I will reply next weekend

[Pavlos12]

Hello.
I found one fusible link (80amps) and its ok
The cable is added to battery positive and go into interior.
All the grounds have good continuity between battery negative and whole engine Block, ecu body, chasis etc..


Wiring under steering wheel was edited by unknown person for and alarm, but it was cut of. It worked before but I put it into "original" condition.

Did not help, still no spark and fuel.

Is ecu same for m20b25 e30 and e34?
Thank you

[KitTheRam]

I think the post above may answer this but check if there are any relevant comments in my recent thread.

https://www.bimmerforums.com/forum/s...getting-a-live

[Pavlos12]

Thank you for you thread.
But my problem looks like bad crankshaft sensor but sensor is ok. The car had an aftermarket alarm connected to some original wires but I cut it away 7 years ago and it did not fail.. Today i checked the rest of cutted wires and didnt see anything suspect, but i think i saw only green big wire, purple maybe not?
And the car is just cranking, i think ecu Dont ground the relays. :/

[KitTheRam]

The fuel pump wire is green and purple or violet as BMW like to call it (GN/VI). See the diagram of the circuit below, however my car is an 1995 M50 engined one so that maybe why it’s different?

0929A418-3F60-4D1B-B7BB-E057BF6D5DDB.jpeg 4870A1B6-002E-47AE-9B8F-08A29E8A7F36.jpeg

[moroza]

To clarify a previous suggestion, I recommend testing the big ECU plug for power, ground, and sensor resistance values. A sensor may test ok at its (smaller) plug, but a break in the wiring harness between it and the ECU would result in the same symptoms as a broken sensor.

I don't know for certain if the E30 ECU is the same, but I bet the E30 subforum knows the answer.

[Pavlos12]

I found some ECUs on ebay and some france parts website with the same numbers as mine ECU has and they says E30/E34. It sounds believably..

With the plug I did this test:

Disconnect the battery and the DME cable. Then:

1) Disconnect the coil negative and check continuity from that connector to
DME pin 1. Also verify that from DME pin 1 to ground is an open circuit.

2) Check the resistance across DME 47 & 48, which should be 500-560
ohms. If the CPS is dismounted, the resistance can be seen to change
from about 500 to 540-560 when a ferrous object is brought to the face of the
sensor. Neither pin should be grounded.

3) Check for continuity from DME 36 to main relay 85 and from DME 3 to fuel
pump relay 85.

Reconnect the coil, remount the CPS (air gap should be 0.040"), plug the
relays back in, reconnect the DME, and connect the battery. Then do the
following checks:

1) With the key off, verify that power is present at DME pin 18 and main relay
86 & 30.

2) With the key on, verify that power is present at DME pin 27 and pin
18. Power to pin 18 is from the main relay and there should be power to the
injectors and fuel pump relay.

3) With the key on, verify that no voltage is present at the DME grounds (2,
14, 19, 24).

4) Verify that power is present at the coil positive and at fuel pump relay
pin 30. Those get switched power from the ignition switch via C101.

and everything in the plug is correct.

- - - Updated - - -

To KitTheRam: I Will check that cable better, I think I was looking for something else.

[Pavlos12]

But I remember that something was unclear to me..

Reconnect the coil, remount the CPS (air gap should be 0.040"), plug the
relays back in, reconnect the DME, and connect the battery. Then do the
following checks:

How can I check it when the plug is on DME? I remember that I disconnect it again and check it unplugged, and every measuring I did on the plug, not on the DME, thats right, right?
Step

3) With the key on, verify that no voltage is present at the DME grounds (2,
14, 19, 24).

I measured only the no voltage, I will try measure continuity to the grounds

[KitTheRam]

Cool, best of luck, sure you’ll sort it one way or the other!

[Pavlos12]

Hello, how have you been?

I didnt figure out anything new so i decided buy another dme with the same manufacturing numbers.

My question is will I need a programmer to launch it? Its 1988 year and it shouldnt have ews.

Thank you so much