Digifant 1 Fuel Pump Relay Earth Signal Issue

If you're jumping the ECU relay then you're just supply power the ECU. The ECU is then working as it should and activating the fuel pump and running the engine.

So that means you've got an issue with the wire coming from your ignition switch, or the relay itself. Should be able to run it as long as you like with the jump wire in, the relay is always on with the ignition when its working corretly

 

Yes, I think so. The jump is giving the power to the relay and in turn the fuel pump relay ; which before was not grounding, oddly. I will trace the ignition wire tomorrow and see if there is some issue there but I am so so happy to hear it running again!

 

Yes, the ecu control relay 30. Actually, I think it kept the fuel pumps running longer than usual. It’s very strange as before sending the ecu away I tested everything and the issue was that the fuel pump relay terminal 85 was not receiving ground from the ecu terminal 3, and now with the new transistors which are just internal ground switches

 

Sorry pressed enter too soon...now with the repair it was an issue at the ecu relay, and the devices powered through this not responding. Previously my ISV (used as reference as its audible) would always click with ignition; now it won’t unless the relay is jumped. I’ll check the power supply from the ignition switch tomorrow and hopefully find something wrong there...thanks for your replies, been a great help!!

 

So update after this mornings investigation.

jumping the ecu power relay from terminal 30 to 87 gives power to the ecu. The ISV clicks WITHOUT turning the ignition on. If I turn the ignition on, pumps prime and I can fire it up and run it.

Runs at a fast idle for a few mins. But if I blip the throttle, it stays open and revs at about 2k rpm for a minute or two then dies down to a really low lumpy idle. The ISV when I turn off the ignition STAYS OFF even though battery connected and relay still jumped.

I have 12v with ignition going to terminal 30 at ECU relay 30, and continuity between terminal 87 and pin 14 on the ECU connector. I have earth at the ECU relay to the earth star behind the fusebox, and on the black earth wire that serves both the fuel pump relay and the ECU relay.

I’m stuck for what to do now, I don’t know why the ecu relay isn’t powering the ecu, I have the original and a new one which I’ve both tried and the same issue remains with no power to ecu unless I jump the ecu relay.

I had hoped to get this out for a drive today looks like it is going to take more head scratching though. Any suggestions of what to check next?

 

Thanks for the reply, yeah seems to be looking up, my money is on the ecu relay. I’ve got switched positive and the ground wire is good, so looks like my 2 relays are deaded. I did open up the original and see a bit of burnout on the board inside. I’m off to the breakers tomorrow to see what they’ve got for me, will order a new one if it fires up. Many thanks for your help

 

So I opened the relay up and sure enough found a burned out track. Got a new one and a spare in the post.

I wanted to run it to temp and set ignition timing and see if I could get it on the road again. So, bypassed the relay to do this, set timing, and put in a new o2 sensor Id been saving for when it was dry enough to lie on the floor.

Starts and runs beautifully, but cut out on the test drive when turning around to come back. Took me 10 mins to get it started again! The starter seemed to be cranking faster than it should be, it’s a swapped out one as my original is getting repaired, so maybe some issues here, but it might point towards the ignition switch? I had this issue before when I first put it all back together but the engine was running like balls then and it runs fine now. After cutting out, i got it home, switched it off, and it started right back up again. I gave the starter a few whacks when I broke down but didn’t seem to do much...

I’ve ordered a Febi ignition switch to try as it’s only £14, any suggestions on what else could cause this? Really hoping I don’t have one of those Digifant cut out nightmares I’ve read about and have to pull the whole loom out...

 

Thanks for your reply again!

I’ve been under and checked all the starter wiring, had to slightly shorten and put a new ring connector on the 6mm red cable going to alternator as it was a bit split at the insulation right at the end.

I repeated the same test drive yesterday this time without letting it warm up; I made it back this time but it was stuttering when I parked it and as I looked back at my exhaust I saw a puff of black smoke. I checked the plugs and they were wet so I concluded it had flooded itself in just 10 mins or so of driving, hence the hard start. Not great, got some fresh oil to go in before I go anywhere.

I ran a fuel pressure test at the bleed nipple / testing point on the FPR. Got 3.1 bar idle, 3.6 bar with vac line removed, and no loss in holding pressure after 20 mins. The FPR on my LT is pn 037133035A. The vw LT workshop manual states 2.5 bar and 3.0 bar as the idle and idle without vac line test results respectively. The chap I bought the FPR from says they were all set at 3.0 bar however so it may have been an un necessary purchase, but at least I’ve got a spare now. I wasn’t certain if a supposed 0.6 bar above spec would cause a flooded engine stall, but I did have the fuel rail off and in storage whilst I replaced the head so I feared it may have gummed up. I’m going to try your machine oil trick I read in another thread; any type in particular?

Without having time to test further during the working week, I threw a couple of parts at it (CTS, O2) but these didn’t stop rich running. At least they’re serviced and originals boxed away for emergencies. But, I had a good look around the engine bay last night and discovered what may be the actual culprit. The Packard 3 pin connector for the throttle valve potentiometer will not connect fully. It has its retaining clip in place but without this it basically falls off upwards (!?) and won’t seat causing erratic fuelling. Am I right in reading that between this and the hall sender the injector opening duration times are principally controlled? If so, I hope I’ve found the problem, and I’m off to rebuild the connector and have ordered an aftermarket Topran TVP in case this connector issue has burned a trace on the original somewhere. Does this sound like I may be heading in the right direction at last? ‍♂️ Otherwise it is timed and serviced all correctly and raring to go with less than 100 miles on a recon cylinder head

 

Back again, thanks for your help this far! So I’ve put a new connector on the TPS and it has helped with the cut off, it falls back down to idle normally now after a blip.

Did the test as described, as well as a visual check and no change so swapped the FPR and I do now have the right pressure. But it’s still getting to 80 degrees then starting the same business, blasting black smoke out and eventually cutting out if I leave it.

I took all the spark plugs out and cleaned them as they were black with dry soot and did a compression test on each cylinder whist I was there, everything totally to new spec.

I’m wondering how this is still happening and why it is temp related - I’ve checked the common ground signal on all my Digi senders (hall sender, cts, co2, and throttle) and they’re all good. I’m wondering if there is some issue with the o2 sensor signal? I’d checked it but now I’m wondering if I need to double check it all. I don’t know why it only does this when it’s warm, any ideas?

I did investigate my air intake and find a piece of newspaper blocking one of the main fresh air ducts ‍♂️ That’s gone now and I’ve reset basic settings but hasn’t taught the ecu anything new about not riching the mix up...

 

That’s a great write up, I’ve had a look at that before, will go through it all again.

CTS is brand new VW part, and unfortunately I did try to run it to temp with the o2 disconnected and it did exactly the same.

Will hopefully get it running nicely this week...I reset the basic settings / ignition timing without the pcv valve removed previously so maybe that makes a difference having only clean air being measured

 

Okay cheers, yes that makes sense, I did follow the basic setting procedure, ie run to 80 degrees, pull CTS connector, rev 3 times, check ignition timing to 6 degrees BTDC, adjust idle screw (didn’t need to do this) but didn’t check the co2 as have no means to do so. Have done this every time I’ve unplugged or plugged in a sensor and the ignition timing was okay.

Think the only thing I haven’t checked is the warm air flap on the clean air intake.

 

Yeah, it’s saying 2.5k rpm in the manual for me. And timing is spot on, fuel system all working well, as well as no issue with sensors or wiring. The only sensor I haven’t tested is the co potentiometer / map sensor. I’m starting to think that I have an ignition issue / weak spark and will have to go back and check all the basics there, I’ve an aftermarket coil on that looks ancient and as I haven’t checked any of that since before the ecu swap I haven’t been able to determine if it would run better with the old Bosch one back on. Thanks for your advice, massively appreciated especially at first when it was the relay issue, I’ve been reading up a lot on Digifant and it’s only my second car / van so it’s been a learning curve...still love it though. Thanks again