A handy fuel pump relay tweak

[S2central.net]

Ignore the previous message - it has been replaced by 4D0-951-253 which appears on LOADS of applications. Audi sticker price (out of date) is below £20 so its worth a punt and/or a spare as you say.

[BrianSmith_S2]

Ignore the previous message - it has been replaced by 4D0-951-253 which appears on LOADS of applications. Audi sticker price (out of date) is below £20 so its worth a punt and/or a spare as you say.

Ive just re checked the voltage seen at the blue/black MAF wire and earth ( i couldnt wait till tomorrow, the suspense was killing me after a glass (or 2) of wine )

Im now seeing 8.5V with ignition on. I never turned her over, its getting too late now.

By the way ive kept the battery on a charger every evening for a few hours so she should be near full, and the dash voltmeter was indicating 12V when i was seeing 8.5V at the MAF

[S2central.net]

Theres some used ones on eBay too e.g 280562921661 for little money from fairly fresh Passats and the like - note the '372' label but its identical function to our '208'

[S2central.net]

@brian - somethings not right there - do that again with 208 relay removed... then open another bottle !!!!!!

[BrianSmith_S2]

Theres some used ones on eBay too e.g 280562921661 for little money from fairly fresh Passats and the like - note the '372' label but its identical function to our '208'

Yep, i will try and source one from G&S tomorrow and post availability and price It probably isnt a relay issue but it wont hurt to have a spare in the toolbox.

This voltage issue at the MAF is confusing me now, i hope with the added daylight over the weekend i will be able to get in and look at the immo wiring under the dash.

[BrianSmith_S2]

@brian - somethings not right there - do that again with 208 relay removed... then open another bottle !!!!!!

Just did as you suggested (must be the born in Belfast in me ) and with the relay removed im now getting 9.54V at the blue/black MAF wire with ignition on.

Hows that possible? does it indicate the ECU is f****d?

[S2central.net]

Don't panic yet - might just be an undiscovered wiring anomolie on the schematics - or maybe the alarm installer did something weird.

Either way... 9.5V is an odd value that makes me think there is something more sinister going on with regards the loom.

Is your MAF black/blue wire protected by Fuse 28 ?

[S2central.net]

Turns out.......

The schematic is WRONG - very wrong.

Been out at mine (July '93) and discovered that the fuel pump relay only activates the fuel pump and lambda probe heating.

The MAF, ISV, EVAP, WGFV and the INJECTORS are all activated when ignition is ON - protected by Fuse 32... I need to write this up in detail and annotate the schematics.

I have an ABY IMMO loom here that I will also check over the weekend - be interesting to see if it is the same.

[BrianSmith_S2]

Turns out.......

The schematic is WRONG - very wrong.

Been out at mine (July '93) and discovered that the fuel pump relay only activates the fuel pump and lambda probe heating.

The MAF, ISV, EVAP, WGFV and the INJECTORS are all activated when ignition is ON - protected by Fuse 32... I need to write this up in detail and annotate the schematics.

I have an ABY IMMO loom here that I will also check over the weekend - be interesting to see if it is the same.

Yep, im looking forward to the weekend, be nice to actually see clearly what im doing during daylight hours when im checking out the immo wiring. This crawling all over the car, in the dark evenings after work is not good

[S2central.net]

FYI - this is cheapest source of new relays I could find in UK - http://www.volkswaparts.co.uk/4D0951...lPumpRelay.htm - 8 quid new !

Probably a pattern part as opposed to VAG original but thats big deal if the quality is OK.

Just got to unravel the wiring mystery now - I remember buzzing out the IMMO loom a long time ago and it checked out perfectly with regards fuses and relay terminals. Wondering if the early ABY cars had the 87a terminal on the CEP and therefore used something else... but that doesn't make sense as 87a is clearly shown on 3B schematics too... You just cant trust those German electricians - maybe its their little joke

[S2central.net]

I have in my hands a CEP dated October 1990 and that includes the 87a terminal so that is as it should be.

Also checked my IMMO loom again and it's wired as per schematic with those green/black wires from 87a to fuses 24 and 28.

I hope not to have to lift up the CEP on my car for a look at ABY electrical spaghetti.

[S2central.net]

I got some way to unravelling this one, but its so damn cold out there my fingers and brain are freezing over. I lifted the CEP enough to see that it looks like terminal 87a is used as I expected but it still doesn't make sense as the FP relay isn't driving this wire. I cannot be 100% sure as I don't want to pull the entire panel up today. I looked at an old UR schematic that shows that 87a terminal is driven by the FP relay so I am scratching my head here.

There is so much cabling up there I cannot see clearly, but I have discovered this green/black wiring is used in factory anti-theft circuit. If I pop that relay out then power is lost not just to ECU, but injectors, MAF, ISV etc - just when ignition is on.

I can kill the 12V feed to ISV etc by also pulling S32, S27 or S24 (should just be S24 according to diagram)

Then I can kill the MAF 12V supply by pulling S32 or S27 (should be S28 according to diagram). I have no idea why I haven't discovered this before now so apologies while I try to reverse engineer some sanity from all the confusion.

Typically - I had a non-immo ABY loom in my hands just a week ago that I could use for much more detailed investigation on the bench - under a roof. I had to deliver that to someone locally but maybe I can look at it for and hour and get to the bottom of this as its pretty much undocumented.

Your badness with seeing 9 odd volts at the MAF black/blue etc tells me you should swap something out on the anti-theft circuit - you are losing way too many volts through it or something. I'll send you something privately on that Brian.

[BrianSmith_S2]

I got some way to unravelling this one, but its so damn cold out there my fingers and brain are freezing over. I lifted the CEP enough to see that it looks like terminal 87a is used as I expected but it still doesn't make sense as the FP relay isn't driving this wire. I cannot be 100% sure as I don't want to pull the entire panel up today. I looked at an old UR schematic that shows that 87a terminal is driven by the FP relay so I am scratching my head here.

There is so much cabling up there I cannot see clearly, but I have discovered this green/black wiring is used in factory anti-theft circuit. If I pop that relay out then power is lost not just to ECU, but injectors, MAF, ISV etc - just when ignition is on.

I can kill the 12V feed to ISV etc by also pulling S32, S27 or S24 (should just be S24 according to diagram)

Then I can kill the MAF 12V supply by pulling S32 or S27 (should be S28 according to diagram). I have no idea why I haven't discovered this before now so apologies while I try to reverse engineer some sanity from all the confusion.

Typically - I had a non-immo ABY loom in my hands just a week ago that I could use for much more detailed investigation on the bench - under a roof. I had to deliver that to someone locally but maybe I can look at it for and hour and get to the bottom of this as its pretty much undocumented.

Your badness with seeing 9 odd volts at the MAF black/blue etc tells me you should swap something out on the anti-theft circuit - you are losing way too many volts through it or something. I'll send you something privately on that Brian.

Thanks Paul, Im just heading out now to look over some more of the wiring loom under the dash before it gets too dark

[S2central.net]

Sending you an email

[BrianSmith_S2]

[QUOTE=BrianSmith_S2;523477]Yep, i will try and source one from G&S tomorrow and post availability and price It probably isnt a relay issue but it wont hurt to have a spare in the toolbox.

QUOTE]

I went to G&S today but they dont sell the fuel pump relay