Gti Fuel Pump Relay & associated wiring diagrams.

I've had my Cabbie about 6 weeks or so ('93 Gti Sportline) and it has been fine up until a few days ago when I had trouble starting it. Sometimes it wouldn't fire up but if I left it for a few minutes it usually started straight up. Once running it was usually fine but last night it died on me on the way back from a booze trip to the supermarket! I had suspected the Cobra alarm/immobiliser was at fault as sometimes it refused to arm or disarm until the remote button had been pressed numerous times, coupled with a strange reaction to the boot light switch and knackered remotes plus it's age I decided to remove it completely. I had planned on replacing with a more modern system. Anyway, today I stripped out the dash (second time in a week, last Monday I replaced the glovebox which had cracked around the hinges.) and removed all traces of the alarm, soldered back up the interrupted wires and heatshrinked them. I then tried to start the car, which it did straight away, but after a minute or so I heard a sort of buzz/ticking from the relays and then the car stopped. I minute or so later it fired back up again and I was able to check the relays, I indentified what I believe is the fuel pump relay and opened it for inspection. Once replaced I was able to hold the contact closed and could hear the pump prime.

My questions are should the pump prime itself briefly when the ignition is switched on like in a K-jetronic Escort or does it only run when cranked?

What activates the fuel pump relay, is it fed purely from the ignition switch or is there a speed sensing relay that operates it in turn?

Is my relay knackered?

Where can I find a suitable wiring diagram, I have a Haynes Golf manual no726 but I don't think the diagrams correspond to the late loom?

I have tried to search but it's all been a bit vague so any help is welcome!

some kjet vws will prime on the ignition, some wont. it makes no odds either way the main thing is that the pump runs while its cranking on the ignition. the brown haynes has your wiring diagrams, but you have to look further on in the revision section as the later fusebox diagrams wernt in the original edition of the haynes as they wernt invented yet

if you look in my sig at the jetta89.pdf that shows a pre-90 mk2 diagram which is mostly the same as yours, though obv not 100%.

to check for a relay issue swap a #53 relay into the fuel pump relay socket, this will make the pump come on with the ignition which isnt safe but it will let you rule in/out the pump relay

Thanks Rubber, I ended up ordering a new relay from GSF. It now primes when switched on. I've been running around all week without any problems whatsoever so assume it was just the relay. The next step is to check the current draw from the fuel pumps and replace if neccessary.

I've just ordered one of the Bentley Publishing manual's which I hope will cover my model in more detail.

I'll try that 53 relay swap as a matter of interest tbh!

ah cool, sounds like you're all sorted then

my theory on the prime is on some cars when you switch on the ignition you get a single spark from the coil, though im not sure exactly what causes this. this spark in theory would send a rev pulse to the fusebox which would in turn make the pump relay switch briefly

Right, I've not had much use out of my cabby for the last year or so, just over 100 miles between mot's but have started trying to use it again, with limited success.

Fuel pump electrics is the problem again so need to try to understand what's going on, pump has started to fail to prime again periodically, when this happens it usually fails to start so it obviously doesn't run when cranking either. Usually a quick fiddle with the pump sorted it but yesterday I had a nightmare trying to get it to run. Even with the cover off the relay, closing the contacts manually failed to get the pump running. At this point I started to check other relays that clicked when priming the pump, found that the one next to it which I believe is the Load Reduction relay had some corrosion on its main pins into the fusebox, cleaning these up seemed to solve the issue, fuel pump now primed?

I've tried to follow the diagrams I have but can't for the life of me follow them to any conclusion as they're so disjointed.

i saw one suggestion that was to remove the relay wiring from the fusebox and have the relay loose, is this likely to help?

Whats the the wiring relationship between the fuel pump relay and the load reduction relay, is it possible this was the problem? Can't find a diagram that shows ant hung useful tbh?

there isnt (shouldnt be!!) a relation between load reduction and fuel relay, they're totally different circuits. however it isnt next to the fuel relay, are you talkign about the relay in slot 1? if so thats the difgifant ecu relay so would well be the reason no priming is heard if its gone duff!  try swapping it for another 53 relay see if that helps, it is triggered by fuse 17 so check thats ok and contact points are clean

if your car is runnign digifant then it should always prime the fuel pump with ignition on, I was assumed it was kjet but since its a 93 i shouldnt have

as i say, check jetta89.pdf in my sig. this covers all the circuit tracks inside the fusebox and for the ecu wiring its on page 3

Mine is defo not Digifant, it's K Jetronic! The diagram 13.2 on page 13-28 of the Bentley book seems to represent my fusebox, fuel pump relay is in position 2, load reduction in 8 which is next to 2.

What's a 53 relay?

When I try to open the links on your sig it just takes me to a Google docs page, no docs showing though?

ah you mean below

you need to sign into google or gmail, plus use android or windows devices as apple products dont seem to work!  try this direct link anyway:
jetta89.pdf - Google Drive

once open you'll see the kjet relay uses circuit 15 for ignition trigger plus pin 5 for the rev counter signal from D/26.

The x-over relay uses a feed from ignition switch to power circuit X, which isnt used by the fuel relay so I cant see how jumping it would help

Many thanks for your help so far on this Jonny, I'm getting closer to a solution!

I've just been down to the car (its in storage) and lo-n-behold, pump wasn't priming & wouldn't start. I looked at the load reduction relay (henceforth known as the LRR!) tried with it removed and fiddled with it a bit. i was then able to get the pump to run, removed it and pump still ran. This lead me to believe it wasnt the relay but I was affecting something else when I removed/replaced it, so I investigated the fuses below and found Fuse #5 was all but falling apart. So there was no issue with the LRR, it was just that as i fiddled with it I disturbed the damaged fuel pump fuse at the same time. I found a spare 30amp fuse (i know it should be 15amp but that was all I had, will replace later) and now fuel pump can be run at will by closing the switch on the FPR!

What I would like to do now is replace the wiring from the output of the relay and run a seperate fuse bypassing the fusebox and going to the fuel pump as I suspect the fusebox itself is damaged as well as the busted fuse. I cant see the back of the fusebox, is it wired between the relay and fuse or is it done on busbars? What's the best way of curing this permanently?

your best bet is a new fusebox if your old one is knackered, it could have damage to other circuits rather than just the fuel one you just dont know! also try to figure out what damaged it in the first place and fix i.e. if a water leak sort it, look for dodgy wiring etc.

the wiring on this all goes via 4 main plugs on the fusebox, no busbars so you'll have to find the rev counter wire D/26 and tap into it, plus the fuel pump power E/14. live, earth and ignition live easy peasy. the fuel relay uses larger 9.53mm spade terminals so you'll need to source those. ideally find a VW relay holder in the scrappy, MK3 golf are ideal source for large spade relays as they use 2 of them for the ABS system.

You'll need proper uninsulated latched spades plus a good crimping tool to do this:
Auto Electrical Components, Parts and Accessories for Trade and DIY: Polevolt Ltd

So if it's all wires surely I can cut the current wires ging to both relay and fuse and re-terminate connectors on the end to go directly to the relay and then just add a an inline fuse where the old fuse would have been?

I may also add a second relay, I did this on my Escort RS turbo, added a second relay in parallel so current was halved through each one, worked a treat. As the pumps get older they draw more current than the old wiring can take.

you cant cut the rev counter wire as it obviously also feeds the rev counter, the fuel wire could be cut but make sure you also add the spade hanging off it that powers the engine electrics.

as i say ideally change the fusebox as it could have other damage, you shouldnt need to add a relay as the factory setup is capable. if your fuel pump is drawing too much power it will need replacing as its likely to pack in soon! have you checked the lifter pump is still working, this will cause main pump to strain and eventually die

Having had another look behind it seems all the wiring is on multi plugs so I assume it's fairly straightforward to replace the fusebox. I agree that's probably the best solution, I'll order one up.

How do I go about checking the lift pump? Tbh might just replace both anyway. I'd rather replace stuff before it fails as once the car starts to become unreliable I'll probably never use it!

if you take one of the wires off the main pump and jump the fuel relay, or prime it off the key you should hear it running

Lovely job, just looked in the Bentley book, I can access the lift pump without dropping the tank!

What are the best pumps to get, genuine Bosch hi-pressure pump and Lucas lift?

vdo did the lifter pump originally, but anything decent will do. id only use bosch or equivalent quality for the main, you can get pierburg versions which should be fine but the one I had wasnt the same thread for the non-return valve and since it didnt have one I couldnt use it! found its way into a rallye 20v though so it went to good use