Correct operation of fuel pump relay

I'm having real trouble with the fuel pump and the associated electrics… What is the correct operation of the fuel pump relay when you turn the key?

When I turn the key to the point just before the engine turns over, the fuel pump relay clicks on and off. The voltage on the fuel pump jumps from 0 to around 12 and back again, in time with the clicking. This happens whether the fuel pump is connected or not.

When I turn the key all the way to start the engine, the voltage on the fuel pump drops to a consistent 8 or 9v, so the relay is definitely closed at this point, and I guess the drop in voltage is due to the load on the battery while turning the engine over.

After 3 or 4 attempts at starting I thought I'd examine the fuel pump, and it was almost too hot to touch. I tried with a spare fuel pump and found the same problem.

What is going on???  :?

Rich

Just in case anyone has similar trouble to me with this, I've solved this through trial and error.

Firstly, the fuel pump relay "clicking" on and off is correct - this allows the fuel pump to prime the system prior to starting the car. The pump will run continuously once the engine has started.

Secondly, my fuel pump was broken, so the excessive heat was due to it not being able to turn over when the current from the relay flowed through it. If you experience this, buy a new pump!

HTH

Rich

I've just replaced my relay with a new one from gsf. Old one never used to prime when turning the ignition on but the new one does… Is a 1600 GTI rather than an 1800. :dontknow:

McScrew, was your car cutting out after about 6 miles?
I'm having similar problems.
I am beggining to think it may be bad contacts in the fuse box as when it cuts out, i give the relay a wiggle and my car starts again.
This kind of suggests the relay is ok, doesn't it?  :dontknow:

Anyone know how difficult it is to change the fuse box?
How much one would be?  :dontknow:

Cheers
Cam80

cam80 said

McScrew, was your car cutting out after about 6 miles?
I'm having similar problems.
I am beggining to think it may be bad contacts in the fuse box as when it cuts out, i give the relay a wiggle and my car starts again.
This kind of suggests the relay is ok, doesn't it?  :dontknow:

Anyone know how difficult it is to change the fuse box?
How much one would be?  :dontknow:

Cheers
Cam80

The last time my car drove 6 miles was about 10 years ago! It's been off the road ever since  

Your problem does sound electrical, especially if waggling the relay around cures it. I'd start by replacing the fuel pump relay, and see if that cures it - they're ?20 from GSF, or a bit more from VW.

You could then try the fusebox if that doesn't fix it - they're ?76 new from GSF - so it may be worth taking it apart to see if you can see where the problem lies - do make sure you label everything if you do that though!

HTH

Rich

Cheers Rich'

I'll give the relay a try first, may try and get one at a scrappy 1st for about a pound though, :shhh:    i take it early mk2 gti's and audi 80/90's use the same relay? :dontknow:

Cheers,

Craig

I'm not sure if other Audis or Mk2s do use the same relay - I've certainly not heard of them being used before - although it would make sense.

It's worth asking in the wanted section in case someone's got one spare, or if you're coming to Gaydon for the Mk1 Annual Meet-up, there's bound to be someone who'll sell you one. Failing that you may have to just buy one  :?

It'll be worth it in the end though  :wink:

Rich