Digifant 1 Fuel Pump Relay Earth Signal Issue

Hi everyone,
This is my first post here, after reading a lot of very detailed chats about my current woes (details to follow).

First off I have to say - I do not own a GTI. I own a mk1 LT 31, running a factory Digifant 1 setup, of which there are less than 5 still on the roads (by my count!) I have a few years of history with this beast but I’m too attached to it now to give up. It also seems that there are many many more similarities between g60’s and the mk2 golf than there is with other LT’s so I’m asking here after not having much joy elsewhere despite a great community online for the mk1 LT.

So my problem is that there is currently no earth signal being sent to my fuel pump relay from the ecu. I can run earth to the relay from pin 3 of the ECU and run my pumps and ‘jump’ the relay to make the pumps runs but I cannot get the ecu to send earth.

I’ve checked my earths but what am I missing? Just had the ecu back after 2 new transistors being soldered on and still won’t work!

Look forward to hearing any opinions on this matter

 

I had a '79 LT, 2.0, so I've a bit of a soft spot for them too. Ex German fire service, turned it into a rally service barge.

What fuse box does it use?

 

Hi Tristan,

It’s a CE1 I think, with the 167 fuel pump relay and the 30 digifant relay. The rest is pretty standard and not ecu related.

sounds awesome! That would’ve been the 2.0 Porsche 924 petrol engine?

my LT is my baby, a lockdown project that has escalated into a huge overlander camper shell with roof extension and lots of bodywork, recon cylinder head, lift kit etc...I’m too far in to go back now !

 

Hi,
It did run like this - but no more. It will power the pumps but the engine will not start as it is. I’ve since sent the ECU away for ‘repair’, had it back, and now it won’t run.

I used to hear the ISV valve clicking open and closed with ignition on pre crank, but not got this any more either.

checking pin to pin at the moment, got the VW wiring diagrams and checked all the earth points, all good...not sure what I’m gonna find here but would like to know the loom is sound

 

okay, it’s got a relay 42 in slot one, and a 30 in slot 2. 167 is in slot 3

 

I

I shall upload a pic at lunchtime, working from home so can nip in and out. All the relays except the starter relay are in the fusebox (which is in the NS footwell) I’ve got a rusty psych under my fuse box and the remnants of a burnt spade terminal (used to be a minibus so there were extra electrics) but I’ve got rid of all excess now to work out why it won’t start

 

Yes the so called 924 engine, though i prefer to think of the Porsche having a van engine lol.

 

They’re clipped above the fuse box. The standard fusebox has a line of fuses underneath and one row for relays above; this houses the wiper relay, a relief relay and emergency light relay. I have pics on my phone but can’t upload as I don’t have a URL.

 

It’s definitely not the CE2, it’s basically the ce1 83-92 with 2 and 3 for the digifant relay and fuel pump relay respectively

 

Apologies if I’ve missed this, reading this on my phone, have you checked the ECU is getting power?

 

And ceramic type fuses though they are different locations. My fuel pump fuse is in slot 15 for example

Hi Nate,

I started digging around with this yesterday, actually.

does power come to the ecu through pin 1 ?

It’s a standard 25 pin harness. All other pins are identified through wiring diagram. Pin 1 is a red wire connecting via 2 connectors to 2 thicker and thinner red / black wires at the fusebox. Guessing that runs to ignition switch but ran out of testing time last night

 

Oh so this is Digifant 1? Yeah that tell the ECU the car is cranking as I remember, Its not needed though to make the ISV work and pump prime. Should just be ground on 13 and 19 and power on 14

 

That started it! I turned it off very quickly though. Does this mean there is a relay issue?

 

Thanks for pointing me in that direction. So as far as my wiring diagram says I am basically feeding the fuel pump relay 12v straight from the ignition switch when I do this. It previously had an issue with its earth at terminal 85 back to pin 3 on the ecu but I’ve repaired and checked the sh*t out of that wire pin to pin and it’s definitely working now lol.