1978 – 1984 US L-Jetronic 928s fuel pump relay

This fuel pump relay is P/N 928.615.113.01 (available superseded P/N: 928.615.113.03).

 

The transistor Ignition Unit RPM output signal 15 connects to central electric fuse panel O7 which connects to Fuel Pump relay terminal 31b.  This signal is also used by the tachometer display in all model years to US 1984 L-Jetronic  and model year 1978 – 1979 Air Conditioning Compressor Relay.  

The fuel pump relay will not turn on (switch closes) until the engine RPM reaches cranking speed (~50 RPM).  When the relay turns on the circuit from the 30 (12V connected directly to the battery) to the 87 that connects to the + terminal of the fuel pump and the fuel system is pressurized.  If the engine stalls due to any reason, the fuel pump will turn off.  This is a safety measure.  



The connections to the fuel pump relay P/N 928.615.113.01 are:
15 = ignition switch turned on
30 = direct connection to battery, always battery voltage
31 = ground
31b = engine RPM signal
87 = switched output, circuit to fuel pump + terminal

Standard relays do not have an RPM signal input or logic to control relay “turn-on/off” based on RPM.  I suggest replacing fuel pump relay if it has never been replaced or the replacement history is unknown.   This relay currently is available to purchase, however at some time the production could be discontinued.  Even though the relay is available, only Porsche dealerships or focused part vendors stock them so it may take days for a replacement part to be delivered.

Note, the Euro/ROW 1984 Porsche 928 uses the LH Jetronic and EZF Spark system.  Different relays are used in that model.

Hello Kai,

I’ll answer directly to your questions below:

I'm working on a late 79/80 928. It doesn't have the spider fuel distributor. It just has a front pressure regulator and two rear regulators. Someone took almost all the relays out of the fuse block.

>> This is a US version 928 with L-Jetronic Fuel Injection.  The L-Jetronic injection was used in model years 1980 - 1984 for US, Japan and Canada.  This system wasn't used for ROW/European markets.  See the relay chart below:

 

But I had a couple relays that worked (Not for FI system used the 30-87 jumper. I got the car running. At first no NOID, but I repaired that. As soon as I got noid she fired on an ether shot. Then after that it ran on it's own.

>> Good job!  The L-Jetronic sytem requires two special relays (a standard relay CANNOT be used), therefore they need to be purchased an installed:Fuel injection (AKA Airflow) Relay Part Number:  928.615.119.00Fuel Pump Relay Part Number: 928.615.113.01 … this relay receives an RPM signal from the TSZ spark box and only turns on with engine cranking RPM or greater. 

It's carrying 40lbs of fuel pressure but the pump stays running all the time. And there's a hissing sound near back of engine. I got new injector seals to install today, old ones were a cracked up.

>> The proper fuel pressure (relay socket jumpered 30 to 87, engine not running) is 2.5 bar (plus-minus 0.2 bar) which translates to 33.6 to 39.1.  So 40 psi is OK but on the high-end of the range.  If the fuel pump  is always running that is likely due to the wrong relay being installed.

We opened all injector wiring pigtails up and found several broken wire sheathing at the terminals. So we isolated them. When doing the seals today, we'll test all the injectors for squirt/flow.

>> Good, these are low impedance injectors (later models from Euro 1984 and US 1985 to 1985 are high impedance, make sure they’re proper).

I'm working on this baby for a friend, who's not wanting to put any money into it until he figures out if it's a good candidate for a resto. He also offered to sell it to me because I think he's not really in the restoration mindset. He's typically a guy who buys and sells kind of low end used cars and this one is going to take some time and money to get going. Beautiful body condition, not a dent or a spot of rust, interior is a total wash. Just shot to hell...engine and Trans appear to be good 97000 miles with 150lbs of compression on all cylinders. Build date 10/79.

>> Porsche often started building for the next model year in September of the prior year.  In this case it is a model year 1980.  When properly cared for, the engines will run well over 250,000 miles. 

I think he needs to buy the correct relays to start with.

>> You are correct, custom Porsche 928 relays are required.

If it were mine. It would get the engine pulled and freshed up and a new wiring harness. But that's just my thinking. The old one is brittle in the engine compartment everywhere. Especially the FI harness. The relays are pricey and a few hundred dollars to replace all the missing ones. What do you think?

>> I do not know what the Porsche collector market is where you are located.  In general, all Porsches have greatly increased in value.  The 928 is beginning to be more recognized as an important part of Porsche’s history.  It is a great driving car.  Restoration can be expensive as replacement parts can be quite expensive.  However, it may be more economical to deal with a company that has used parts (like 928 International ( www.928intl.com ) that may be needed. There were only about 60,000 Porsche 928s built between 1978 – 1995, so they are a rare model.  Personally I’d like to see everyone restored and brought back to their past glory.

I've got it running. It just won't idle very well. Dies and restarts. The exhaust is very dark. And there's that fuel hissing sound. Sounds like the pump stays running and builds up too much pressure or there's a restriction back to the tank. Maybe a bad FP regulator?

>> It sounds like you've made great progress.  The dark exhaust may be caused by too rich of an air/fuel ratio which can be adjusted at the airflow meter.  The hissing could be a vacuum leak.  It is hard for me to diagnose from a distance.  I hope this 928 will be brought back to life!

Good luck, tell us how the restoration proceeds.

If I helped save a Porsche 928, I'm very pleased!