WEEBEDNA

I've only owned my 81 928 for a couple of weeks now. I'm in the process of replacing the fuel tank and while doing, I noticed that someone ran a wire (not stock thats for sure) directly from the fuel pump to an empty spot on the fuse block (below the fuses where the relays connect). I'm not sure yet if there is supposed to be a relay at that position on the block or if its just an empty spot.
In any case, I'm not sure why this was done. Seems like this wouldn't be safe. I do have manuals and plan on researching but any insight would be appreciated.

Landseer

Sounds like you have the insight.
An owner explanation might would be more beneficial.

123quattro

What you really need to do is verify if that wire is running the fuel pump, or a relay controlling the fuel pump. You don't want to run a pump with switched ignition because it won't turn off in the event of a crash.

beentherebaby

The primary reason a relay is used with electric fuel pumps is to reduce the switching current across the ignition switch which can typically be 10-15 amps. for an electric fuel pump. In the case of ECM cars it also allows for fuel pump pressure cycling before starting the engine. A relay won't shut off the fuel pump in a crash unless the power that activates the relay is removed - same as if you wired direct to the pump via the ignition switch.

Landseer

Probably would be a worthwile safety precaution to wire-in an impact switch as, on my Jeep.

This particular owner probably was trying to avoid buying a $60 fuel pump relay, else, didn't know what he was doing, needed to fix a car with a bad relay, so he bypassed it. Original wiring might still be intact and useable

Dennis Wilson

When I bought my 78 5 speed there was a fused jumper installed between the 15 and 87 relay posts. Since all work since 1991 had been performed by Porsche dealers (even oil changes based upon the invoices), it is apparent that one of their mechanics performed this modification. This setup worked fine EXCEPT for the safety function, as discussed above, was bypassed.

Dennis

James Bailey

The correct relay shuts off the fuel pump if the engine stops running. Good in a crash but also if you are working on the car or just listening to the radio a hard wired fuel pump keeps running if any injector leaks you might fill a cylinder with fuel ! liquid gasoline does not compress so if you hit the key and the engine fires...when it gets to the cylinder full of fuel it can hydrolock which can bend connecting rods or lift the cylinder head ...bad things !

Larry Velk

One reason to install a jumper is to bypass a female socket which is heat fatigued. If this is all you do all the functions remain intact. I have a fuel pump socket bypassed on one of our XR4Ti's as the German metal used in the female sockets goes completely limp if heated by any excess resistance. If our board sockets get limp a bypass, properly done, can "repair" a bad connection and still work as normal as far as protections and function. This doesn't look easy on a 928 - it wasn't too hard on a Merkur as the 'always live' side was an easy access by bending a relay prong. You can get to the back of our relay boards, but this isn't true of all cars. On a 928 I'd just try to fix the female socket.

Dennis Wilson

Jim,

Agreed. I'm amazed the dealers mechanic would set it up this way. Prior to the dealer maintenance starting in 1992, all previous recorded repairs were performed by 928 International, who we all know wouldn't perform that modification.

Dennis

WEEBEDNA

Thanks everyone for the info. I'll chase down the correct wire for power to the fuel pump and see what happens. I just ordered a new relay ($23) just in case the old relay is the issue.

Landseer

Where did you order?
We bought (I think same) for 59 two weeks ago.

Alan

Different years have different fuel pump relays late model S4/GTs have a regular Bosch SPST relay, early years integrate the pre-prime pulse & engine running interlocks and are typically much more expensive. make sure you get the right one...

Alan

riviera455

Same thing has been done by some po on my car, a non factory wire running to the fuelpump without relais.
pump works as soon as egnition is on.
i dont listnen to the radio , and disconnect that wire if i work on the cars elektrical stuff
i think it worked for years like that, the last po i know off has two left hands, he didnt work on the car himselve;

in a crash it can be dangerous, but i am not planning to hit a tree,,i drive slow and safe