Wiring for Fuel Pump Relay

[p911sc]

I am helping a friend with a 1984 928S L Jetronic and am having a power supply problem to the fuel pump. The fuel pump relay has 5 pins, numbered 30, 87, 31, 15, and 31b. I've found that port 30 in the relay panel has a 12V power supply,port 87 provides power thru the fuse to the fuel pump. I have done a continuity test and found that pin 87 connects to the fuel pump. I have jumped pins 30 and 87, and have been able to get power to the fuel pump. But I do not have power to the control side of the relay. Does anyone know where the power for the control side of the relay comes from and what the other pins in the relay connect to?

Thanks in advance
Rick

[Landseer]

We can trace thru them with you, but it might be better to skip all that and solve your no-start problem directly.

Can you say more about the situation?

[p911sc]

Thanks Landseer.

Right now there appears to be numerous problems on the fuel side and I am trying to get a sense for the overall damage. The car has not run in 6 or so years.

The fuel pump is bad. After jumpering terminals 30 and 87 in the relay panel, we have 12V across fuel pump but its not running. I would guess that this could be a burned out pump or excessive lacquer buildup from fuel sitting in it??

In addition, the power to the relay seems wrong?? The power side of the relay (Pin 30) is receiving 12 V which seems correct. The control side of the relay is receiving 1.3 V, which doesn't seem right, unless it is receiving voltage which is first passing thru a variable resistor like the airflow sensor???

Fuel pump relay does not appear to work either. Removed the relay and tried to jump the control side (with 12V battery) to close contacts 30 and 87. No luck.
Rick

[Landseer]

There's a sort of regimen for reviving one that's down.
I generally don't try to start them without going thru the process, or most of it.

Basically, I've found from experience that I can isolate down to "control voltage" on the Fuel Pump relay.
But I can't ever isolate it and solve it. It doesn't stay solved. So I've learned to reframe the issue as "electrical reliability" and attack it all. Saves sanity and many tow truck calls and lessens marital risk. (I've got a friend who's skipped these steps and is suffering. His wife has walked home twice now)


Lots of things will bring the fuel relay down for safety. I think even big air leaks can cause the air inlet door not to open, disallowing fuel pump, for instance.

Before you go further, try the 3way jumper of the AFM/injection relay --- make a male spade ended wire, 3 ends, and link 30 to 87 to 87. Then measure for control voltage at the fuel pump as you have been. 31 is ground, 31b is a switched ground, btw. That relay (you can see it shown on the 928 Specialists website diagram) is a critical relay that often goes bad. I always replace this on a rescue car. But then, pull the jumper out and start attacking the whole thing correctly.


Fuel supply --- If you don't take precautions, a new pump will jam. BTDT. Basically change the tank outlet strainer, feed hose, pump and filter. Feed hose comes off to drain tank. 17mm nut of the strainer is carefully removed from tank (hard to get onto this / sometimes tank female spins in the plastic which is bad) and you clean the tank. If the pump is newer and hasn;t been burned out, sometimes they can be removed and leads reversed, with a little brake clean or WD 40 to free them. Then, not reliable though.



Electrical. Gotta clean the critical grounds. No choice here. And, remove the CE fuse panel for polishing, alll new fuses(must be european/vw as BUSS fuses and chinese cheapies are a fraction too long and won't seat) and some new relays. I always replace the fuel pump relay (about $60 and AFM/injection relay $30) as these are mission critical. And replace all 24 relays with 53 relays. Look for melted wires that rob power via cross circuits on back of panel. Inspect all the color coded, labled plugs for melted or deteriorated wires. These will be critical indicators because if melted there, they will be melted throughout their respective circuits. Deal with those later.

At this point I might remove the Z plug (black, center of panel) and replace with the proper panel jumper to bypass alarm, which will keep the car from starting and interrupt the fuel pump relay power.

Panel grounds are crucial, there are two sets of them just above the panel. Solid brass / polish them, like the panel.

I've learned to replace the battery ground strap with a new $7 round one from Advance Auto. The flat one corrodes beneath the plastic on the ends and won't pass enough voltage if it ever got wet.

Clean the positive little wires at battery, they feed the panel.

Then the fuel pump ground: its in a stack of grounds for 84, hidden beneath the back of the passenger inner quarter trim panel. Takes removing the rear glued seat and many fasteners to remove it, but some have luck reaching behind to clean, you will see a picture of this ground point in a link I'll attach.

Then, Mission Critical, the computer and sensor ground and injector/harness ground --- not where you'd expect. They are on the passenger cam cover. Look closely for them in the link-- one buried and hidden beneath the emissions air valve at the top of O in Porsche, the other more visible near the H. You must remove that valve and associated piping in /out to properly clean that ultra crucial ground point. (the link doesn't show the valve / its a Euro and doesn't have the USA emissions setup)

Clean also the engine to body strap beneath the car, passenger side.

Then the 14 pin connector is diassembled and cleaned, plus remove/clean the hot jump post and wires beneath (11mm). The 14 pin connector is notorious for having melted / shorted / degraded wires and shorts can have major effect on ability to start the car.

The sensor for cam/piston engine position, needed to drive electronics, is located in distributor. It has aged, fragile connectors at distrib and near that 14pin connector ( at the spark box on inner pass. fender) I wouldn't mess with it unless they are broken. If broken, though, you've found a critical source of no-run. This is called the "green wire" and costs about $120. (If the car has a brand new one from 6 years ago, but hasn't run, its possible it got one from a batch 6 to 8 years ago that was wired wrongly).

Usually these cars are down because some / all of above electrical was fading out. Gotta fix it all for reliability. I spent 3 backbreaking full days on the last electrical cleaning and charged the customer $1000 and he got a great deal.

heres a link to a grounds cleaning for an 84 Euro (has the later engine management system, different than yours, a crankposition sensor instead of green wire, and some additional grounds)
Look especially for the picture, deep in the link, of the rear quarter panel ground on the red car (fuel pump ground point) so you can decide if you can reach it without removing the q panel.

http://forums.pelicanparts.com/porsche-928-technical-forum/586148-ground-cleaning-16v-euro.html

[p911sc]

Landseer,
Thanks for the ideas. We will work thru your suggested process. BTW the photos on the link are really helpful.

We are in the sights of Hurricane Irene so will not have a chance to get to this until sometime next week and will take a while. I will be back with an update once we have made some progress. I would appreciate your staying with us on this, your help is much appreciated.
Rick

[rockerarm]

P911sc, regarding the troubleshooting of the fuel pump and circuit, remember that just because you apply power to the fuel pump, it still needs a path to ground. So prior to replacing the pump assure it has an adequate ground. You may want to use a dvom and on the ohms part of the meter see if the internals of the pump have an open circuit. I'm not sure where this pump is located but if you can sometimes tap on the pump and see if it responds.
Regarding the fuel pump relays wiring:
#30 is 12v all the time.
#87 is wire to fuel pump.
#15 is 12v with key on.
#31 is the ground.
#31b is the magic little terminal that keeps everyone safe. This terminal goes to the distributor, or point, side of ignition coil. It provides the "signal" to the fuel pump relay that the engine is running, or cranking over. This is the "built in" safety feature as the manufacturer did not want the fuel pump running with out the engine running. Worst case scenario would be a ruptured fuel line oe car wreck and the pump is pumping gas onto the motor. So basically 31b is the tach signal to the fuel pump relay. VW has used this type of relay since 1975, on its water cooled cars.
Got it. Hope this helps, Bill

[Alan in AZ]

And the purpose of the ignition (15) connection is to cause the fuel pumps to run for about a second when the ignition is first turned on to prime the fuel rails.

Some folks have jumped 15 - 87 - however the 15 wire is undersized for this since its just a signal trigger (so DONT DO THIS!).

Alan