Evening All- As some of you know i'm bringing my 928 back to life after a 4-5 year nap. I think most of my troubles are the result of a gummed up fuel system ( my fault ) I seem to remember reading that you could " jump " a relay to get the fuel pump to run w/o the engine running all in an effort to circulate fuel thru the system....hoping to clean up the lines a bit. Would it be the fuel pump relay........if so, what terminals do you jump. Just looking for some advice.

Geffen928

 

It would be the fuel pump relay; But are you sure you want what is in that tank, after the 4-5 year nap...to flow through your system?

N?

 

I've drained the tank, installed a new pump, filter and relay.....All with 10 gallons of the finest liquid petrorelum money can buy...even have 2 cans of thechron (sp?) in the mix.

 

Geffen;

You won't circulate the fuel by bridging the relay (pins 30 and 87), all you'll essentially do is flood the motor with gas. That is unless you pull all the injectors and catch the fuel in some form of container.

Personally, i've used Techron twice on two CIS (early) cars, both times I needed to tow them home. Buyer beware...

 

Why wont bridging the pump circulate fuel? What else can it do but run up to pressure at the regulator, and feed the excess back to the tank? If the air plate isnt moved, the injectors will never open, nothing will get into the engine........
jp 83 Euro S AT 50k, CIS in good shape.

 

Don't forget, on a cold engine, with the WUR bypassing a small amount of fuel, the injectors will see some fuel.

 

A cold WUR will lower control pressure to make it easier for the air plate to deflect, but AS LONG AS the air plate is NOT moved (or any attempt made to suck air past it), the distributor will NOT pass enough pressure to open the injectors (~55psi).

 

A lower control pressure doesn't make the airplate easier to move, it allows the control plunger to uncover it's slits at a greater percentage, thus bypassing fuel to the metering chamber. Don't forget that there is an upper and a lower chamber in the distributor and it is the pressurer differential that dictates how much fuel goes to the injector. I can open a injector with as little as 24psi, this was measured by the use of an air hose when I cleaned mine recently.
Kempf and I spent the whole weekend at SITM this year trying to diagnose my non-functional 83 Euro, we physically had injectors pulled and pumping fuel by bridging the relay.

 

Agree with Scott on not running the bypass for a long time. It may cause a CIS in unlnown condition to hydrolock-BTDT. I will add that when I tested a new injector it took almost 50 psi of pressure to activate.

My 931 had sat for 4 years when I bought it. Replacing the pump and filter was a given. I then removed ALL of the components attached to the fuel distributor and sprayed/cleaned with aerosal throttlebody cleaner. Don't use carb cleaner as some of them contain meth chloride which can harm the internal o rings. Also, don't use compressed air on the distributor components as this could also harm the o rings. Do the same cleaning to the WUR and the fuel lines between it and the distributor. This got the 931 driveable but the air fuel mixture needed adjustment about once a week for several months until all of the crud was out of the system.

Dennis