Trying to diagnose a short

[jwakil]

The only fuse in the engine bay of my 81 930 is this red one that keeps blowing. I知 not able to get power to my AAR valve and I知 noticing limited turbo boost but not sure these are related. Does anyone know what all components this fuse supplies (or the wiring) so I can try to trace the short.

[DaytonaCoupe66]

Rear Fuse Box Diagram

https://rennlist.com/forums/911-turbo-930-forum/318548-930-engine-compartment-fuses-and-relays.html

These comments may help with figuring out the fuse panel but unfortunately the diagram doesn't hit directly on that top fuse. I didn't read through all of the threads - out the door.

Good luck!

[T77911S]

pwr is from FP rly2 to the WUR then the AAR
check for pwr at the WUR.

make sure both FP's are running.
you can remove the connector on the top rear of the AFM to run the pumps with key on and engine off. then remove both rlys and then put one in at a time to listen for the pump.

the over boost is a ground for the FP rlys that opens with too much pressure to turn off pumps.

now the power for the over boost rly (yel rly) may come from that fuse.
just remove the yel rly and see if the fuse blows.

[jwakil]

Originally Posted by T77911S

pwr is from FP rly2 to the WUR then the AAR
check for pwr at the WUR.

make sure both FP's are running.
you can remove the connector on the top rear of the AFM to run the pumps with key on and engine off. then remove both rlys and then put one in at a time to listen for the pump.

the over boost is a ground for the FP rlys that opens with too much pressure to turn off pumps.

now the power for the over boost rly (yel rly) may come from that fuse.
just remove the yel rly and see if the fuse blows.

Looks like my rear fuel pump (#2) is not even running. Based on the diagrams I think the fuse in question is for some electrical feature unrelated to the engine which I never bother with, like rear defroster or wiper, but my AAR and fuel pump power loss are related to each other and my main concern. I値l start looking at the fuel pump and WUR wires.

[T77911S]

[T77911S]

says power to "N" is from fuse box 1.

could just be a rly. if the pump is not running.


i split mine off.
i separated the 2 rlys and put them on 2 fuses.
i was able to remove the wire at pin 85 of rly 2 and run it to a spare fuse. (i dont have fog lights).

[jwakil]

Originally Posted by T77911S

says power to "N" is from fuse box 1.

could just be a rly. if the pump is not running.


i split mine off.
i separated the 2 rlys and put them on 2 fuses.
i was able to remove the wire at pin 85 of rly 2 and run it to a spare fuse. (i dont have fog lights).

I tried a new relay for pump 2 and didn稚 help. Basically something is happening between the relay and fuel pump 2 which is impacting the downstream AAR and WUR as well (btw these are not N). I checked the pump connections (it痴 in the left wheel area, right?) and they looked fine. But need to check the inputs and outputs at the relay,

[T77911S]

from the diagram (mine is very hard to see) it looks like there is a connector going to the FP where the wire splits off to goto the WUR. i would start there.
dont know where that connector is though.

[jwakil]

It turned out to be the relay to the rear fuel pump. That fixed the high idle and low power/boost issues, and makes sense since the output of that relay also feeds the WUR and AAR