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Re: [T3] FI fuel pump relay and 70 FI Auto update


On 5 Sep 2006 at 6:36, Big Al wrote:

> The thing is that I DON'T hear the fuel pump make it's little
> pressurizing spin when the key is turned.
> 
> I put a multimeter on the fuel pump plug and it get's 12V for a second
> (just long enough for the meter to read it) and then off.  I'm guessing
> that that's all the pump needs. So power is not the problem.  I did not
> do anything to the pump other than clean the outside of it and that did
> not include any imersion of the pump, merely exterior cleaning.

In normal operation the pump runs all the time, but it's controlled by the FI 
brain, which shuts it off if the engine isn't turning over. So what you've 
observed is normal.

> So, any hints on what I did to kill the pump?

Well, in the first place, I'm not a fan of tank sealants. I suspect that you'll 
soon be looking for an unsealed tank because the sealant has sealed up some 
internal passages which are going to be important to you. But none of this 
would keep your pump from spinning.

OTOH, if those passages are sealed, as I suspect, you'll now need a lot more 
than 2 gallons of gas before any will be able to reach the pump.

It's possible that while you were doing all this other work, the pump just 
dried out and now can't get itself started.

> Any suggestions on what might be done to save the pump?

First get the tank at least half full. You may want to pull the gas sender so 
you can see down inside the tank. Make sure that there is SOME gas in the 
central cup.

Jumper the relay, then go under the car and gently tap the pump motor body with 
a small hammer. Tap in various directions until you manage to shake it just 
right and release whatever got caught in there. Once it starts to run, try to 
run the car. 

> Do I need to prime it somehow? (and if so, how?)

You'll have to get gas into the central cup in order for gas to be able to get 
to the pump. The pump WILL spin when dry, but you don't want to do this for 
long, as that is hard on it.

> I read about putting a jumper to the fuel pump relay to spin the pump,
> but what I thought was the FI fuel pump relay under the back seat was
> actually the FI voltage supply relay.  So, where is the fuel pump
> relay?

The fuel pump relay is under the dash, against the firewall, up and left from 
the steering column. It is the same part as the main FI power relay. To jumper 
it, just use a clip lead to short between the two red wires. If you get a small 
spark that means that the pump shows continuity. If there's no spark then it's 
likely that the pump brushes aren't making good contact with the commutator. 
Either way, a little shock on the pump body will usually eventually correct 
this.

Don't overdo the hammer trick. The pump motor has 2 brittle ceramic magnets 
just inside the shell. If you break one of them, you'll be buying a new pump.

-- 
Jim Adney
jadney@vwtype3.org
Madison, WI 53711-3054
USA

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