relay to pump

[Cymru1]

Just need to check / need confirmation.

From the fuel relay to the actual pump the loom is a straight run (I.e no other fuses / relays / connectors) in the way. need to trace a fault. May be useful info before i start ripping things too bits.

Had a look at the wiring diagrams and it seems a complete run/wire.

I know there's a hundred posts about the FPR and read all of them. Now im convinced its a post relay issue.


Problem: relay works, has power, activates on crank. No juice coming to pump.
Crank and cam sensors new and confident about these.
Pump did work whilst bridging the relay, but now does not. But still works and starts fine when directly powered.


many thanks.

[newsh]

Could be a bad contact in an aftermarket alarm / immobiliser

Or inside the Fusebox / relay panel

[UrS4boy]

The diagram below is for an AAN so the fuse numbers are different than a 3B or ABY but the principle is the same: The ECU energizes the J17 fuel pump relay by taking it to ground via ECU pin T55/3 (if the ECU is happy with the G4, G28 and G40 signals). This opens up power to the fuel pump fuse (S17 for an AAN) via J17 relay pin 87F. From there to the G6 fuel it is a straight shot. At least *WITHOUT* an immobilizer in the picture.

[Cymru1]

Well. Couldn't find anything wrong on initial search for this problem. Ran fine for a few days then failed the other morning. Had no option but to run the fuel pump direct from the battery to get me to work!

What a difference!!

Perfect idle when cold and hot. Smooth at junctions coming off engine braking and convinced it had more get up and go.

Now reverted back to factory wiring to continue the search for the issue.

[UrS4boy]

How to "Turbo Charge" your Fuel Pump: DIY instructions for adding a battery-to-fuel p

Well. Couldn't find anything wrong on initial search for this problem. Ran fine for a few days then failed the other morning. Had no option but to run the fuel pump direct from the battery to get me to work!

Very dangerous. If you had been in a serious accident, the fuel pump would continue to run, potentially pumping fuel into a fire (or a spark) = crispy critters (and not the breakfast cereal).

What you might want to consider is adding a fused relay between the battery and the fuel pump that is triggered by the OE Fuel pump relay but supplies voltage directly from the battery to the fuel pump. I have a write-up from 2004 for this for the C4s but you can adapt it to the B3/B4 situation:

How to "Turbo Charge" your Fuel Pump: DIY instructions for adding a battery-to-fuel pump relay

http://forums.quattroworld.com/s4s6/msgs/24327.phtml

[Mikes2]

It doesn't go from the relay to the pump.

It goes from fuse 13 to the pump

[UrS4boy]

It doesn't go from the relay to the pump. It goes from fuse 13 to the pump

Sure. For an UrS4/S6 it is Fuse 17. Point is is IF you bypass the Fuel pump relay, you are losing a safety feature that de-energizes the FP relay anytime the RPMs drop to less than 13 RPM, i.e. the engine is stopped in a nasty front-ender. Your way, the fuel pump would still be running.

[Mikes2]

We are talking about an s2 here I thought (judging by his avatar)

So the relvant diagrams for an ABY are

track 20

http://s2-audi.co.uk/workshop/schema..._aby/page3.png

and track 42 on this one

http://s2-audi.co.uk/workshop/schema..._aby/page5.png

[UrS4boy]

Principle is the same. Fuel pump is fed from the J17 FP relay via a fuse only when the ECU detects that the engine is rotating at more than 13 RPM. This is true during a starting attempt as well as during an abrupt halt in engine rotation, e.g. frontal vehicle accident.

We are talking about an s2 here I thought (judging by his avatar)

So the relvant diagrams for an ABY are

track 20



and track 42 on this one

[LHD_Kid]

Dave, I've been looking at your guide to translate to my coupe - colours of the wires are identical both for the power and the trigger wires.

Thing is, I don't really understand the connections in your write up. It says to cut the 2 thick wires which is the positive and ground to the pump. This I understand. However, it says in big capital letters do not cut the 2 thin trigger wires. It doesn't mention anything about connecting into them, T-ing into them or anything.

Could you possibly just describe or draw me a quick picture to describe where each of the connections go, plug to pump, leave unconnected and insulate, to ground, to the battery, to the relay etc?

Sorry, I'm sure your original description is spot on, but I just can't follow it...!

[UrS4boy]

Thing is, I don't really understand the connections in your write up. It says to cut the 2 thick wires which is the positive and ground to the pump. This I understand. However, it says in big capital letters do not cut the 2 thin trigger wires. It doesn't mention anything about connecting into them, T-ing into them or anything.

"11. Now the first "scary" part, boys and girls (insert Count Floyd howl here). You are going to cut the yellow striped green wire and the thicker brown wire, about 2.5" back from the plug. Do it, do it now. DO NOT CUT THE THIN PURPLE OR BROWN WIRES!!"

That is because those two thin wires are for the fuel gauge sender. They stay untouched.

[LHD_Kid]

"11. Now the first "scary" part, boys and girls (insert Count Floyd howl here). You are going to cut the yellow striped green wire and the thicker brown wire, about 2.5" back from the plug. Do it, do it now. DO NOT CUT THE THIN PURPLE OR BROWN WIRES!!"

That is because those two thin wires are for the fuel gauge sender. They stay untouched.

Ok... Mr. Thickie here...!

So. The 2 wires I cut, basically the pump side ground direct to battery, and positive to battery via the relay and an inline fuse with the original wires just cut being used as the trigger......