No start .

[olympia57]

I'll try to keep this simple in light of the other live thread on starting problems .
S1 with Motronic 1 ( basic ) standard with no modifications .
Drove perfectly and after a long run last October I dusted it down and garaged it . battery disconnected , never started in that time .
Would not start when I went to awaken it after winter . It has never displayed any starting problems.
Have conducted numerous checks and issue is down to no spark.
Pump operation and delivery checked.
Main relay and fuel pump relay bench tested and all checks conducted on bases OK
Terminals bridged on both bases .
Coil votages and resistances checked OK.
Ref sensor checked and OK
Distributor cap and rotor arm checked , both of which are new , and OK .
Old Immobiliser surgically removed using correct wiring diagram for it and the car .
12V at each injector .
All earths checked and remade .
Starter motor wiring terminals checked and verified .
Spark plugs removed and checked , all OK

Checks later today will be to confirm coil is actually working and that the 12v supply to it is not dropping off when engine is cranking .
There is no transistorised ignition module in or around the coil and all wires run back through the main loom through the bulkhead and back to the ECU .
Is the trigger for the coil generated from the ECU ?

[olympia57]

OK now into open heart surgery .....

First failure I have found is this relay which is situated to the left above the ECU . It's a five pin as shown.
The coil is open circuit .
I have not identified it's purpose as yet and haven't got a spare to match it ....yet .
Can anyone identify it's purpose ?

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[Ralph in Socal]

I’m pretty sure that’s the main relay directly next to the ecu in S1 cars

Ralph

[olympia57]

I’m pretty sure that’s the main relay directly next to the ecu in S1 cars

Ralph

Thanks for the reply Ralph.
I'm thinking / hoping that too .
It may be the culprit .
Ron's posting one over but I'll see if I can pick one up locally too.

[RossDinan6]

You can temporarily install a jumper between 87 and 30. These are the contacts. If the relay is bad, you should run with the jumper. Just do not leave it there!

[olympia57]

You can temporarily install a jumper between 87 and 30. These are the contacts. If the relay is bad, you should run with the jumper. Just do not leave it there!

Thanks Ross already did this and there was still no spark.
Looking into it further this relay, Bosch 0332014112, is specifically for fuel injection systems and incorporates a diode to prevent back EMF getting to the ECU . It is used for the same function on numerous vehicles Jaguar, Landrover , Alfa etc ..it's cheap and available .
I'm quietly optimistic that it's non operation has cut power to the ECU and thus preventing the trigger pulse to the coil .
The real pita is that not one of the several wiring diagrams I have for my series one shows it . This could be because of the fitment of the Motronic system on the late series one instead of the earlier L jetronic . I'm quite familier with the L jet system and all the diagrams show it as fitted to my car .
The one good thing , I think , is that I've been smeared with the Motronic's DNA and know it a little better .

To be continued ....

[RossDinan6]

The thing is, if the contacts are connected weather by the ignition energizing the coil, or by being by passed by a jumper, it should start. You have another problem. Crank position sensor is a good place to look.

[Beaker]

Pretty sure that relay is in the engine bay beside the fuse box in my '81 635. A tap with a screwdriver has got me out of trouble with that a few times.

I would also suggest checking the crank sensor and its connection above the fuel rail. I could be wrong but I don't think you'll get fuel or spark without that.

[olympia57]

Pretty sure that relay is in the engine bay beside the fuse box in my '81 635. A tap with a screwdriver has got me out of trouble with that a few times.

I would also suggest checking the crank sensor and its connection above the fuel rail. I could be wrong but I don't think you'll get fuel or spark without that.

The main relay is , and is on mine too.
But , as of yet , I have found no reference to this relay on any of the several wiring diagrams I have for a series one car Motronic 1 equipped car . Your owners manual will most probably shows L jetronic schematic which is completely different .

The crank sensor you mention is called the reference sensor and sits adjacent to the speed sensor both of which terminate in a plug clipped onto the rearmost manifold steady bar . The grey plug base is the ref. sensor and it does have to be within tolerance to allow start.
Mine is .
Thanks for the suggestions .

[olympia57]

To conclude the thread .
The non start problem was caused by an open circuit speed sensor .
The ref, sensor was within spec at 960 ohms but the speed o/c but despite the belief that the speed sensor would only cause rough running on mine it prevented start.
The other issue found was a o/c coil on the main relay adjacent to the ecu under the dash above the glove box. This relay differs from S2 Motronic equipped cars .
I cannot explain why the car was driven into the garage 6 months ago in perfect driving condition , never started in that time and with the battery disconnected but when it came to start it again these two problems occured .
But we live in strange times ......
Thanks for all the help and I hope this helps others down the line .
Don