ZG862

I've reached a critical point in my restoration.
The car has a brand new battery and the immobiliser has been removed.
I've done the mechanical checks, removed the DME relay and the engine cranks with the starter very nicely.
DME back in, fuel in (having been drained to zero and engine bay filter replaced) - but no hint of a start after much cranking (with pauses to cool the starter).

Head scratching has started with "I have no central warning lights at all. That can't be right." Much gazing at the wiring diagrams has followed (made much easier by Alan Moore's 928 Electrics Wiring Diagram Primer) and I've:

• Found the fuse for the central warning informer (No.18, 7.5A) It's good.
• Re-seated the connections to the CWI (which was moved around a bit during immobiliser removal)
• Seen that I do have most lighting circuits - the sidelights indicator comes on as expected. (I also have power windows, sunroof, door locks, interior lights - Circuit 30 stuff?)
• Found that I don't have indicators or hazards (though I've not checked the flasher unit at D1 yet).

It occurs to me that this stuff should be on at key position 2 and I should be hearing sounds from the fuel pump - which I am not. Maybe Circuit 15 (the ignition circuit) is not being energised? Not sure of the best way to check.

There is probably something really basic that I'm missing and my excitement about getting a start has turned into brain fog; Please can you help?

Z

newsboy

Have you checked that you have fuel and spark? Tested the main (under seat) DME with a multi meter to see if your flywheel sensor is good?

ZG862

Thanks Steven.

To test that the flywheel sensor is good, am I just looking for a voltage across pins 8 and 31 once per engine revolution? How do you get on these pins when the engine is cranking?
I'm assuming with no fuel pump sounds at key position 2 I will have no fuel. My issue is determining why I might have no fuel pump...

No_snivelling

You say fuel was drained to zero. Did you bleed fuel all the way back to the engine compartment by opening a connection there?
The lines from the pump to the injectors is a long haul and would contain a large volume of fuel. If lines are dry, I would think it would take an awful lot of engine cranking to get fuel to the injectors. Unless I am missing something obvious.

ZG862

Thanks @No_snivelling .
I have indeed done an awful lot of engine cranking (and it's more likely me missing something obvious). I syphoned fuel from the tank, then drained it at the fuel pump, then drained more at the engine bay fuel filter. I didn't drain the fuel rails but would Imagine that IF there was flow into the injectors then this would be long gone.

The thing that is on my mind is that there is going to be no fuel going anywhere if there is no power to the fuel pump, and my 1st thought was that the lack of any warning lights might be telling me that there is no power in circuit 15 (the bus that goes live when the key is switched to the ignition position - position 2 in the handbook).
If this does go live - which seems inevitable since its the mechanical switch, this energises the 1st solenoid in the DME relay. However, as far as my limited circuit diagram reading skills show me, the DME relay will only send current to the fuel pump if the DME control unit itself switches the 2nd solenoid in the DME on pin 3 (Black/white) to ground - which if it does I should be able to see at fuse 34.

Off to test whether this is a load of made up twaddle.

Z
PS/ The warning lights thing may be a separate issue. Everything there seems to be powered off 15E - and I can't work out how this gets energised.

ZG862

Progress.

On a hunch I disconnected the cruise control stalk plug at the steering column. I now have warning lights.
I also have power at the DME relay fuse, but I don't seem to have power to the fuel pump (although I need more hands to be 100% sure on this point).

In other news, the Blaupunkt Symphony seems to be powering up - although the cassette tape in it won't eject. I won't know if it still works until I finish reinstalling speakers. There should be a prize for anyone who can guess what is on the tape...

Z

willmip

Is the fuel pump definitely not receiving power and not just borked?

orange911

Not sure of the Bosch fuel pumps, but I knew of a fuel pump on a boat go bad after running out of fuel and running the starter too much. Unlikely here, but check power at the fuel pump with ignition on. Also, spray a little starter fluid in air cleaner with the filter removed to confirm you have spark.

Another diagnostic tool I recommend is the Focus 9 DME relay: https://www.ftech9.com/new-products/993-ssr. It identifies if the DME is sending power to the fuel pump, but make sure you opt for the diagnostic upgrade with the lights.

ZG862

Borked? As in broken? Conceivably, although pretty much everything else has fired up despite the years. I've stuck the trickle charger on overnight and I'll see if I can find the elusive fuel pump voltage tomorrow.

I have a rear light unit out for lens replacement; that couldn't cause this could it? Grasping at straws here...

ZG862

Thanks for the tips, @orange911 . Looks like I need to go shopping tomorrow too...

willmip

This might help

https://rennlist.com/forums/964-foru...what-pins.html

ZG862

Very helpful indeed.

ZG862

I'm such an idiot. I couldn't work out why basic continuity tests between the DME relay contacts and endpoints weren't working. In frustration, I removed the central electric panel and tested just that. Still no joy. So I carefully disassembled all 7 layers of the CE panel to find which pieces of copper MUST be broken. Well of course they weren't broken - I was plugging the DME relay into the R52 socket, not R41 where it is supposed to be. What a twit! Everything carefully reassembled I thought I'd go straight back to cranking - which wasn't the smartest move either as my battery is complaining and wants a full charge. Back to some more structured testing and it seems that I can get 12V at the fuel pump fuse and even get it to run by bypassing the relay (connect 3,5, and 7 as per WillMip's link) - but I'm not sure that the sound that it is making is quite right. Would it automatically prime from the new fuel in the tank? Could there be air in there?
Incidentally, before I did all this, I cracked the right hand fuel rail connection - which spilled fuel. Old or new, I can't be sure but I took it as a good sign. I have OK oil pressure whilst cranking. It occasionally spike up. Again, a positive sign.

Once the battery is charged again, I'll have another go once I have some starter fluid - although I think I should pursue the fuel pump irregularities first. I wonder if I could have disturbed the electrical connection when I drained it? Think I should disconnect the battery before playing under the access panel (assuming that is where the connector is. I don't recall, and it may well be remote so I'd better read up first).

Let's assume that I get to good fuel flow. With the DME relay bypassed (I have a spare too, but it's1 less thing to worry about), should I expect to get a start EVEN IF the crank position sensor is dodgy?

Thanks for all the help so far chaps!

Z

systemsc

Read here under No-Start; https://www.systemsc.com/diagnostic.htm

ZG862

Thanks Loren. Some of these basic tests are a challenge with my simple multi-meter, but the sequence and test objectives are very helpful. I'm finally beginning to understand the structure of the Porsche wiring diagrams so it's all starting to make a little more sense. It reinforces the view that if I can't hear the fuel pump running when it should be, there's no point in going further.