Hi there,
last weekend my car (´89 convertible; V12, Marelli) passed out on the Autobahn. It was a hot summer day, but I was just cruising with 70mph for around 30 minutes when the engine went off. Once stopped I tried to crank, but as there was no quivering with the speedometer I thought either the CPS or the flywheel sensor went bad. So we towed the car home...
This weekend I thought of an easy repair. At the end I found having no sparks at both coils and no clue what to check further. What did I do already?
- I checked CPS and flywheel sensor - the both looked correct from its seat
- I measured the resistance: 710-760 Ohm - was quite well
- I swapped the CPS and the flywheel sensor with some spare parts from a donor car (these had 7xx Ohms as well)
- I checked Pin 13 of the ignition ECU for 12V - okay
- I checked the 12V at the coils and at both amplifiers - okay
- I checked GND at the ignition ECU Pin 12 and at the amplifiers - okay
- I checked ignition ECU between pin 1 and 2 and between 3 and 16 - both 7xx Ohms (CPS and flywheel sensor go here)
- I swapped the ignition ECU from a donor car
- I grounded the engine block additionally to the body (a spare bolt at the firewall)
- charged the battery

The starter turns the engine well, but no spark on either coild against engine block.
What do I overlook?

 

check the Marelli ECU under the left side ( in a RHD car ) front footwell side panel , could be a loose main connector etc ?

main ECU is in the trunk right side over the right wheel arch ,

BB

 

Hi BB,
I checked the injection ECU for loose plug or wire damage and replaced the ignition ECU (Marelli) in the footwell side already.
Tom

 

Pin 18 of the injection ECU is a coax that runs to pin 24 of the ignition ECU. Make sure that wire has continuity, and that it is not shorted to ground. That contains the signal from the ignition ECU to the injection ECU that tells the injection the engine RPM. If that wire is shorted or open, it might prevent the ignition ECU from operating.
Have you made sure that none of the ignition signal wires are shorted to ground?
Have you checked the ignition coolant temp sensor? If it's open, the ignition ECU might not work, but not sure.

 

Not sure what "okay" means here.

The amplifiers should open/close a ground path to the coils.....like the breaker points in an old fashioned points-ignition car. Right? If I'm correct then your test light, when to applied to either coil's "-" post, would flicker as the engine was cranked.

Also, in the back of my mind I have a notion, quite possibly incorrect, that the Marelli ECU won't function if the Coolant Temp Sensor is open. The CTS for ignition, not fuel injection. Perhaps worth a check?

Cheers
DD

 

Thank you very much!
These are points I will check. Maybe Tuesday as we are at the proms tonight.
Yes, the amplifiers are the drain gates to GND. I simply checked the 12V provided by the "white" wires to have them Vcc providede. I did not check for the drain pulses of their pin1 to the coils (12V is standing here, coming from the coils though).
Will check GND shortening, CTS and pin18 cross line soon.
Tom

 

I was reading through this thread, got to the bottom, and the SITE offered up a PAST THREAD (yours) that was presenting a similar issue... Could it be that the problem you are having now is a FIRST COUSIN of the issue in 2021?

 

Hi Jay,
I feared you remembering my old thread and asking me this... and I thougt the same yesterday.
But. I always had spark last year. The spark plugs just fouled very quickly. I found a couple of maybe reasons for that, but the problem never fully disappeared. So the car run quite reliable since this. And started alway right away.
I have no spark at all today. Directly at the coils.
If someone draws a line, I am happy.
But first let me get into a suit - will do the tests tomorrow.
Tom

 

Had a couple of hours to proceed my search today.
Seems to turn out being a "white wire problem".
I tried the above suggestions:
- pin 18 of the fuel ECU to pin 24 of the ignition ECU is fine, zero ohms, no shortage to GND
- no shortage or 12V at the crankshaft and flywheel position sensors cabling
- but... open circuit for the temperature sensor... I found that both pins went out of the green plug at the sensor. I corrected this.
Still no spark.
Probably I pulled the pins off myself when testing the sensor some days ago. I pulled on the wire instead pulling the plug...

But... the 12V ignition feed:
I have 12V at coils and AMPs.
I have astonishingly... just around 11.5V at the ignition ECU plug pin25. I did not bother about that before - I thought that might come from endless cranking.
Thus I open the white wire 10cm away from the ECU plug and tested while cranking - just 0.5V. Still 12V at the coils.
Okay, now it´s clear, why there is no spark... at least an approach to solve it.
Once I repaired the "white wire" around where the 12V goes away from the loom to the coils - I assume it must be somewhere between here and the firewall.

 

Yes, classical "white wire problem".
Ignition feed 12V is provided by a thicker white wire within the ignition loom coming from the firewall going to around the place, where the smaller wires go off the loom to both coils. At this place the thicker white wire distributes 12V to a) 2 thin wires going the AMPs in front where the cooler ist, b) two thin wires going to the coils unad c) a little thinner wire than the feed itself going parallel backwards with the thick white wire to the firewall where the thinner ones provides 12V to the ignition ECU.
See pic attached.

The latter wire going back to the ECU was loose in the a), b), c) junction. Once connected the machine started right away.