[urq] Fuel system diagnostics , failed on the very first test . :)

[urq]

The '78 Fox had a recall done to remote the fuel pump relay from the fuse
box, I believe the same fix was applied to the urq.  I believe the designers
did not account for the fact that the fuel pump draws more and more current
as it ages ... in the case of the Fox; the recall was because the increased
current draw led to overheated wires in and around the fuse box, perhaps
even some electrical fires.  Funny thing is that I had found the problem
before the recall and had rewired the guts of the fuse box to provide a
better connection ... but I digress.  

I believe that your problems with excess voltage drop are due to the worn
pump ... I suspect a clogged screen has little to do with it.  My
recommendation would be to replace the pump and then retest the electrics.
Extended high current may have created some high resistance conditions at
the connectors.  On the US cars the only connector between the fusebox and
the pump is right at the battery box, which is a nearly ideal location to
insert an auxiliary fuel pump relay to resolve the issue permanently.  

Steve Buchholz

-----Original Message-----

Well , not quite the very first test , but close enough . 

The first test is to measure battery voltage . 
As I charged the battery overnight , it was at 12,80 V . 
Has to be 12,00 at least , according to the book . 
So that one passed . :) 

Then a remote control for the fuel pump is needed . 
That's easy . A length of 2,5mm² wire , to spades on one 
side , a switch on the other et voila ...VAG1348/3A replicated . 
Pull the fuelpump relay , plug the spades  in contacts 
87 and 30 and it should work . It does , sorta . 

Next test is to measure the voltage at the fuel pump terminals . 
I only have tension with the ign switched on . That's not supposed to be ! .

Terminal 30 on the relay  comes straight from the battery . 
Certainly needs further investigation . 

Anyway , with the ign switched on , I measure 11,7 Volt and 12,65 Battery
voltage . 
This already raised an eyebrow , as the meter represents no load . 
So where's the 0,9 volt gone to ? The acceptable limit is 0,5volt drop . 

With the pump wired in and running , voltage drops to 7,60V !  
The pump barely runs and makes a noise like a worn out bearing does .  

If I power the pump directly off the battery , the rpm increases
significantly 
and voltage remains steady at 12,60 V . That's the way it should be . 
The sound is now a healthy buzzing like any normal fuel pump does . 

Finally measured the current draw , directly off the battery to the pump . 
That is close to 10Amp . Wich is a bit high , the limit being 8,50A . 
Possably an indication of a clogged filter . 



Conclusion 
I need to cure the electrical problem first , and check the filters . 

This is gonna be fun , the pre filter is most likely 28years old . 
And as usual , it's NLA .  So I'll have to machine something off a
std available filter .


To be continued .... 


Pat 
 




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