> Hello
> Does anybody out there know the pressure and flow specs of the CIS fuel injection fuel pump vs the early 1980-84 electronic fuel injection pumps. I have put an 83 USA spec motor in a 79 car and am running the old CIS fuel pump. The engine starts but dies almost immediately like it has run out of fuel. Ether makes it run longer so I know it is fuel related. Thanks in advance.

According to the FSM :
 For AFC fuel injection '80-83 Pump delivery rate: at least 1150 cc/30sec. Pressure (engine stopped fuel pump bridged):2.5 +/- 0.2 bar For CIS 78-79 Pump delivery rate: at least 1120/30 sec. with one pump, at least 1360/30 sec. with 2 pump System pressure 5.2-5.8 bar Sounds as if you need to change pressure regulators or even pumps. Quit spraying that ether in there.. bad...bad :-)
Jim V
Try jumping the fuel pump - the ignition switch in the crank position powers the pump then the injection brain takes over when the engine is running --crash the car so that the engine stops and the pump is turned off or leave the ignition switch on while installing a radio and the pump stays off because the engine is not running. Otherwise the fuel pump could flood the engine and hydraulic the motor .

Jim Bailey
928 International

Hi All,
Specs: 1981 5-sp, stock L-Jet

I just got the VDO rail-mounted FPG installed and checked things out... (Jeannie took care of me after a shipping mishap. Thanks Jeannie!)

* With the fuel pump relay jumpered and running, the fuel pressure is reading about 36-37psi....... Normal * When the jumper is removed and fuel pump stops, the pressure immediately falls to approx. 15 psi. Within 5 minutes, the pressure drops to 5 psi. I'm guessing the check valve is kaput. Anybody out there seen this before and have other areas to look?

Thanks in advance,
'81 5-sp 121k

The Bosch bible states that, for efi systems like the L-Jet, pressure in the system should not have fallen below 1 bar (14.5 psi) after 20 minutes. Interestingly, the Porsche tech specs book (for the US '80, but should be identical to yours) does not list any figures for a post-shutdown leak test, unlike for the K-Jet systems.

The Bosch book advises to check all fuel line connections for leaks, and make sure that the cold start valve and injectors are not leaking. Then (quoting): "Test the fuel pump check valve by running the engine and then shutting it off. Immediately clamp shut the fuel supply line from the fuel pump. If the pressure drops below specification, then the pressure regulator is faulty. If the pressure is now within specification, then the fuel pump check valve is faulty."

Good hunting!

Glenn E



A Porsche 928S4 fuel pressure reading should be like this: (starting MY. 89):

Pressure reading 3,3 +/- 0,2 bar at idle with vacuum connection on the pressure regulator.

Pressure reading 3,8 +/- 0,2 bar at engine not running, pump on and vacuum connection at pressure regulator (Relay bridged 87-30).
-Switch off fuel pump: Pressure at gauge should be 3,8 +/- 0,2 bar)
-Maximum pressure drop with hot engine: 0,5 bar in 30 min.

Regards, James