Crank, no spark. Maiden voyage cut short

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TimU
Posts: 280
Joined: Tue Dec 14, 2021 2:16 am
Location: Sydney

Crank, no spark. Maiden voyage cut short

Post by TimU »

Well, my maiden voyage to didn't quite work out as planned.
Car ran perfectly for ~200km, but cutout while driving - No spark at the coil.

Car was towed and is currently parked up at a local mate's house, pending next steps.
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Next steps:
- Source a new flywheel reference sensor to test.
- source a known good Motronic 059 DME ECU to test.
- inspect flywheel to check for reference lug.

1986 635csi, M30B34 motor.

Here's what I've done to test and troubleshoot.

What have I missed?

Symptoms:
- Car cranks strongly but doesn't fire.
- No spark from the coil main lead when arcing to the block.

Recently replaced components:
- both Flywheel reference sensors (new)
- Flywheel (2nd hand)
- Distributor & rotor (new)
- Oxygen sensor (new 4 Wire)

Tests and results:

Following this guide:
http://www.bigcoupe.com/phpBB2/viewtopi ... 08#p116308

Components needed to get spark to the engine:
Ignition Switch, OBC Relay, Main Relay, Coil, Reference Sensor, ECU

Main relay:
1. Jumper bypassed main relay (pin 30 to 87&87).
2. Pin 86 in the harness gets 0.6V with ignition on - Should this be 12v?

Fuel relay:
1. Jumper bypassed fuel relay (pin 30 to 87).
Can feel and hear fuel flowing through the lines.
Unable to test pressure at the roadside.

OBC Relay:
1. Jumper bypassed OBC Relay.
Jumpered 2 green wire pins of the white harness. White harness not plugged (with bypass wires). Green harness is still plugged in.
2. Unable to test voltage at the green pins at the roadside.

Coil:
1. Pulled main lead from distributor. No spark from the coil main lead when arcing to the block.

2. Replaced with known good coil and main lead.
No change to spark status.
(thanks @stewart and Duncan Falk and Dave Granger for your help last night!)

3. With ignition key on, Terminal 15 (+) has 13V.
I believe this confirms the ignition switch is good.

4. With key off, Resistance between T1 (-) & T15 (+) is within spec at 0.5 Ohms.

R between T15 and centre head within spec at 6000 ohms.

But voltage at the coil tower when cranking was only 13V, and it wasn't sparking when grounded to the block.
I would have expected a much higher voltage (like 1,200V)

Flywheel Speed & Reference sensors:
1. Both sensors are new Bosch cables replaced 4 months ago.
2. Unable to check Flywheel end at the road side.
3. AC voltage within spec (I think)
- Pull rubber boots back off the two sensor plugs.
- Pull the main relay & fuel pump relay to disable the FI system.
- Set voltmeter to AC volts
- Back probe the black and yellow wires while cranking with the sensors connected.

* Speed Sensor (Black Connector) -- 4.0v AC volts max at crank.
• Ref. Sensor (Grey Connector) ------ 0.2v AC volts max at crank. *Should this be 0.4?)

Flywheel:
Unable to check reference lug at the roadside.

DME ECU:
xx 059 purple label
Unable to test ECU at the roadside.

So that's where I'm at.
Any obvious misses or bad readings?

Next steps:
- Source 1 new reference sensor to test.
- source a known good 059 dme to test.
04/1986 635csi Euro spec
Australian Delivered, RHD
L.Tigre
Posts: 50
Joined: Fri Jul 22, 2022 3:53 pm
Location: Greenville SC

Re: Crank, no spark. Maiden voyage cut short

Post by L.Tigre »

Ouch. That photo with the tower makes me sad, and nervous.

I've not troubleshot this before so take my advice with two grains of salt. But I would suspect the relay. I don't think it's typical to see any correct electronic signal of 0.6V for anything active; that is more like a leakage / faulted value. I would investigate those more.

Good luck -
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smtguy
Posts: 159
Joined: Sat Apr 29, 2017 3:38 pm
Location: Southern California

Re: Crank, no spark. Maiden voyage cut short

Post by smtguy »

I think I would start with the Main and Fuel pump relays. Both can leave you stranded -
Good luck!
1983 Bronzit 633CSi 5 speed
2004 Audi TT Quattro 6 speed

Scott
TimU
Posts: 280
Joined: Tue Dec 14, 2021 2:16 am
Location: Sydney

Re: Crank, no spark. Maiden voyage cut short

Post by TimU »

L.Tigre wrote: Sun Sep 25, 2022 2:53 am Ouch. That photo with the tower makes me sad, and nervous.
Having decent roadside assistance membership is great peace of mind.
My NRMA membership gives me 25km free towing in any metro area, and unlimited towing from remote country areas to the nearest NRMA service centre.
L.Tigre wrote: Sun Sep 25, 2022 2:53 am I've not troubleshot this before so take my advice with two grains of salt. But I would suspect the relay. I don't think it's typical to see any correct electronic signal of 0.6V for anything active; that is more like a leakage / faulted value. I would investigate those more.
Yes, you're right, however I don't think this is causing my "no start" fault.

Looking at the ETM (page 1360-0), Main Relay socket PIN 86 should be receiving 12V when the following conditions are true:
- 12V battery is functional and feeding power to the ignition switch input (hot at all times)
- Ignition switch at Run or Start positions
- On-board Computer Code Relay is closed (Normally Closed)

However, BOTH the OBC and Ignition Switch is bypassed when using a 3-pin jumper wire in the Main Relay socket (pins 30 to 87+87), effectively "hotwiring" the Main Relay harness to an ACTIVE state. Pin 30 is fed directly from the battery.

Jumping pins 30 to 87+87 on the Main Relay then energizes:
87 pin 1)
- Motronic Unit (ignition power input trigger)
- Electronic Transmission Control Unit (ignition power input trigger)
- Idle Speed Actuator (ICV)
87 pin 2)
- Fuel Injector (+) power (then the Motronic unit controls the negative (-) pulses to each injector)
- Fuel Pump Relay trigger
04/1986 635csi Euro spec
Australian Delivered, RHD
TimU
Posts: 280
Joined: Tue Dec 14, 2021 2:16 am
Location: Sydney

Re: Crank, no spark. Maiden voyage cut short

Post by TimU »

smtguy wrote: Mon Sep 26, 2022 1:27 am I think I would start with the Main and Fuel pump relays. Both can leave you stranded -
Good luck!
Yes, thanks, I have done that already
04/1986 635csi Euro spec
Australian Delivered, RHD
L.Tigre
Posts: 50
Joined: Fri Jul 22, 2022 3:53 pm
Location: Greenville SC

Re: Crank, no spark. Maiden voyage cut short

Post by L.Tigre »

You have progressed beyond my meager powers to assist. But, when you isolate and fix it, please post so I can see what it was. Because it's all coming for all of us, sooner or later...

good luck out there-
TimU
Posts: 280
Joined: Tue Dec 14, 2021 2:16 am
Location: Sydney

Re: Crank, no spark. Maiden voyage cut short

Post by TimU »

-
L.Tigre wrote: Wed Sep 28, 2022 2:27 am You have progressed beyond my meager powers to assist. But, when you isolate and fix it, please post so I can see what it was. Because it's all coming for all of us, sooner or later...
good luck out there-
Thanks, will do.

I'm pretty sure I've isolated it down to one of the 3 things below:
1) Crankshaft Position Sensor (Grey plug) could be faulty or dislodged.
2) Motronic 059 DME ECU may have failed, preventing spark triggers to the coil
3) (worst case) flywheel reference lug may have broken off.

I have sourced a spare DME and CPS and will try them in the car this weekend.
04/1986 635csi Euro spec
Australian Delivered, RHD
Pod
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Re: Crank, no spark. Maiden voyage cut short

Post by Pod »

When troubleshooting, I always start with a known-good ECU as its the easiest thing to swap over! Good luck.
TimU
Posts: 280
Joined: Tue Dec 14, 2021 2:16 am
Location: Sydney

Re: Crank, no spark. Maiden voyage cut short

Post by TimU »

Good news!
My no spark fault that left me stranded last weekend has been fixed.

I replaced the ECU and she fired up straight away.
Drove 200km home without missing a beat.

Inspecting the old ECU back at home, I discovered two blown resistors.
They were definitely not like this when I inspected and reflowed the solder joints a few months ago.

I'll resolder the joints back together, and keep it as a spare if it works.

I'm a very happy boy! 😁
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04/1986 635csi Euro spec
Australian Delivered, RHD
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Sbeaud
Posts: 279
Joined: Fri Jan 04, 2019 9:38 pm
Location: Okahumpka, Florida USA

Re: Crank, no spark. Maiden voyage cut short

Post by Sbeaud »

Great to hear you're back on the road Tim. I admire your electrical trouble shooting skill.

Scott
1988 M6
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Ralph in Socal
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Re: Crank, no spark. Maiden voyage cut short

Post by Ralph in Socal »

Resistors overheating is a sign that it's component is not functioning properly. Same effect as the fan resistors. Unfortunately trying to figure what is controlled by those Resistors is not part of my abilities. Try to trace which pinout on the connector those lead to and it will help you diagnose. Hopefully before it affects your replacement ecu. Well done getting back to running and finding that fault. Good luck

Ralph
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
81 633 csi (retired)
TimU
Posts: 280
Joined: Tue Dec 14, 2021 2:16 am
Location: Sydney

Re: Crank, no spark. Maiden voyage cut short

Post by TimU »

Unfortunately simply soldering the resistors back to the board did not allow the ECU to work.

Tracing the PCB lines, it appears these resistors are for the power transistor connected to the spark circuit.

I'll need to do some research on how to test the transistor function. Maybe it can be replaced :-k
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04/1986 635csi Euro spec
Australian Delivered, RHD
L.Tigre
Posts: 50
Joined: Fri Jul 22, 2022 3:53 pm
Location: Greenville SC

Re: Crank, no spark. Maiden voyage cut short

Post by L.Tigre »

Congrats and well-done, I am glad to see the troubleshooting documented even if it’s at the edge of what I can follow.

I do know that a given component will sometimes fail “randomly” and that is due to just minor quality variations in the part itself, which appear after long exposure to thermal cycling and mechanical stresses. So there is sone chance that you never find a root cause other than “resistor faulted.” Which I guess would be a welcome outcome.
KneeGrowNetwork
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Joined: Tue Nov 08, 2022 6:53 pm
Location: Atlanta

Re: Crank, no spark. Maiden voyage cut short

Post by KneeGrowNetwork »

TimU wrote: Sat Oct 01, 2022 10:39 am Good news!
My no spark fault that left me stranded last weekend has been fixed.

I replaced the ECU and she fired up straight away.
Drove 200km home without missing a beat.

Inspecting the old ECU back at home, I discovered two blown resistors.
They were definitely not like this when I inspected and reflowed the solder joints a few months ago.

I'll resolder the joints back together, and keep it as a spare if it works.

I'm a very happy boy! 😁

Where did you get the Ecu from?
TimU
Posts: 280
Joined: Tue Dec 14, 2021 2:16 am
Location: Sydney

Re: Crank, no spark. Maiden voyage cut short

Post by TimU »

KneeGrowNetwork wrote: Wed Nov 30, 2022 11:01 am Where did you get the Ecu from?
Local BMW spare parts breaker.
04/1986 635csi Euro spec
Australian Delivered, RHD
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Slownrusty
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Location: Houston, TX

Re: Crank, no spark. Maiden voyage cut short

Post by Slownrusty »

Congrats Tim.

A bit late to comment on your thread, but the first thing that came to mind was the ECU, which you figured out and glad that you were able to source a spare (that is VERY lucky!).

Seems like these ECUS as they are nearing 40-years old are leaving quite a few owners stranded.
TimU
Posts: 280
Joined: Tue Dec 14, 2021 2:16 am
Location: Sydney

Re: Crank, no spark. Maiden voyage cut short

Post by TimU »

I also managed to pick up another 059 DME ECU from a local guy on FB marketplace.
I took a gamble on his untested unit for $100 and it works fine.
I've reflowed the solder on all the power transistor and resistor joints now, and have put it on my shelf as a future spare.

If they start to get too expensive, I would probably just spend the money on a conversion to a modern stand-alone ECU.
04/1986 635csi Euro spec
Australian Delivered, RHD
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