924Board.org

[Tigger937]

I'm currently experiencing a hot F2 fuel pump fuse on the auxillary fuse panel, ie., too hot to touch. I've been reading previous posts on the subject as well. In addition, I'm losing fuel pump relays (2 burned out so far). I originally suspected excessive current draw from the fuel pumps, so I measured and found the external pump at 8.2A and the in-tank pump at 1.6A with the car running. Battery voltage measured at the battery was 13.8V. I also measured 11.6A at the F2 holder. Some time ago, after suspecting excessive current draw from the fuel pumps, I replaced F2 with an 8A Euro fuse. It never blew. Even after measuring 11.6A at the holder, the 8A fuse does NOT blow!!! I replaced the Euro fuse with another 8A and it wouldn't blow either. Then I replaced with a GBC8A glass case fuse from NAPA and it blew after 5 seconds. Incidently, putting a normally called for 16A Euro fuse in gets too hot to the touch also. I inspected the entire auxillary fuse panel including the F2 holder and all the wires and connectors look good, no signs of overheating or corrosion. I am about to pull the main fuse and relay panel to inspect. My question, is there a problem with these Euro style fuses? Do the blow characteristics change with time as they age? Also, what is the normal current and voltage rating of the fuel pumps? The car is an '81 931 with 22K on the clock, so obviously it has been sitting a lot and I'm sure this is contributing to the problem.
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1981 931 (Concours)
1982 931 (Daily Driver)

"Think outside the box"

[Smoothie]

Other components on the same fuse are the AAV, WUR and frequency valve. You could check those wires for overheating and unplug them to see if that stops the fuse overheating or check the amp draw on each.
Also check/clean the grounds - mainly #2 at the back of the luggage compartment and #3 near the distributor (-though I don't recall if bad grounding can cause excessive current draw - actually I don't think so, but obviously grounds should be clean anyway, so it wouldn't be a complete waste of time).
Another possibility is that some other component/s were added to the same circuit sometime after it left the factory.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Tigger937]

I checked the ground near the distributor...........I presume your talking about the one that runs from the coil mount to the head............and it looked good..............voltage drop was minimal, approx. 60mV. Where exactly is the #2 at the rear of the luggage compartment?

Some other measurements of interest (car running, fuel pump relay bypassed):
Battery voltage=13.9V
Ext. Fuel Pump voltage=12.2V
In-Tank Fuel Pump voltage=12.1V
F2 voltage drop=60mV-130mV (it varies when moving fuse in holder)
Battery+ to F2+=630mV
Battery+ to F2-=720mV
Battery+ to Fuel Pump Relay Socket 30=400mV
Battery+ to Fuel Pump Relay Socket 87=412mV

What's interesting is the voltage drop across F2.........130mV max. With 11.6A measured at the F2 holder, that works out to 1.5W!! Consider the fact that a 1.2W instrument light gets too hot to touch also. Hmmmmmmm. Could it be the Euro holders and fuses are out of spec. now and therefore cannot handle the current in this circuit?? I beginning to wonder if enough margin was allowed for in the design from the factory. I don't like it when things electrical get hot.
_________________
1981 931 (Concours)
1982 931 (Daily Driver)

"Think outside the box"

[Smoothie]