fuel injection failure

[kingspoint]

I have a 1983 Porsche 928s , ran perfect for years , has been garaged for a while was not running , recently I got back to the car would not start at all, cranks but does not run, I placed fuel in the system manually and it started instantaneously ran for a few seconds shut down, I tracked the relays for both fuel and L Jetronic replaced them both with factory originals , still no start, I replaced the L Jetronic control unit and rechecked , still no start , adding fuel at air intake starts car immediately and it will idle as if fine tuned until gas is consumed , then shut off . I checked injectors for pulse and have none , the injectors light up with ignition on but when cranking they do not blink at all , I checked under the vehicle and located a broken wire to the oxygen sensor , but do not think this would interrupt the fuel injection system . any ideas of what could be wrong , I think I covered all aspects of fuel system and ignition system, ignition system does prove out as car will immediately start with fuel added manually . Could the distributor pick up wire be a cause for failure , it appears the distributor has spark to the plugs but no signal to the injectors ?? anyone have any ideas ??

[stepson]

The fuel injection relay (928.615.119.01)is on the top row and the 4th relay from the right. No other relay number will work. Please check the position and the part number of the relay that you replaced into your car.

The fuel pump relay (928.615.113.01) is on the bottom row and directly next to the large double headlight relay. Please also check the position and part number of that relay as well. Again, no other relay number will work.

If IIRC, the O2 sensor is on the same circuit as the fuel pump. If that O2 wire shorted, it could have blown the fuel pump fuse (#13) in which case, there would be no fuel pressure and no fuel to inject.

[kingspoint]

fuel pump is operational , fuel pump relay was replaced , will verify position on relay location , fuel was verified at both fuel rails . and return to tank . power is present at injectors , they do light up with ignition on , but when cranking no change is observed while cranking, (light should be flickering) light stays on bright no change during cranking operations . Note: fuel pump was replaced and is new and operational .can hear pump when ignition is switched On .

[kingspoint]

will replace O2 sensor rewire and recheck for operation, was wondering if there is any company that can verify integrity of L Jetronic unit control , I have 3 most recent came out of a running 928s

[stepson]

Originally Posted by kingspoint

fuel pump is operational , fuel pump relay was replaced , will verify position on relay location , fuel was verified at both fuel rails . and return to tank . power is present at injectors , they do light up with ignition on , but when cranking no change is observed while cranking, (light should be flickering) light stays on bright no change during cranking operations . Note: fuel pump was replaced and is new and operational .can hear pump when ignition is switched On .

Outstanding!
Okay, so the noid is not noiding. Check and clean the injector grounds on the passenger cam cover as well as the Ljet computer ground above the passenger footwell. You have power to the injectors apparently, but not the needed ground to make the circuit for the injectors.

[kingspoint]

will clean all grounds ,thanks for the input will update after it is done , if you can think of any other possibilities , give me a shout , I will go thru all grounds on fuel system and ignition sys .

[stepson]

Originally Posted by kingspoint

will replace O2 sensor rewire and recheck for operation, was wondering if there is any company that can verify integrity of L Jetronic unit control , I have 3 most recent came out of a running 928s

L-Jet computers are pretty robust. The easiest test would be to ask a buddy to put your computer in his previously running car. If his car starts and runs, it's not the computer.
Testing a computer in your car could damage a previously good computer due to something in your car being bad.

[JK McDonald]

Hey Kingspoint - The small internal Distributor Pick-Up Coil (Green Wire - Out) provides a Pulsed (Square Wave) Signal to 4 components needed for a L-Jet 928.

1 - Fuel Injection Computer Connector -
2 - Ignition Unit -
3 - Fuel Pump Control Relay -
4 - Tachometer -

As the Fuel Injection Computer receives the pulsed signal from the Distributor (In on Pin # 1) - the ECU sends out timed Ground Signals to the 8 injectors - Triggering them in pairs.

With the Spark Plugs firing - then the Green Wire is correctly sending the Pulsed Square Wave from the Distributor to the Ignition Unit. With the Fuel Pump Relay supplying +12 volt power to the fuel pump and the Fuel Pump is running - then the Distributor pulse is reaching the Fuel Pump Relay. With +B 12 volt power to the Injectors then all that is missing is their Ground Signals.

Perhaps the Distributor Pulse is NOT reaching Pin # 1 of the Fuel Injection Computer.

Good Luck Michael

[JK McDonald]

Hey Kingspoint - Have you had the opportunity to further troubleshoot your Fuel Injection problem? If you're lucky the lack of a ground to your injectors will simply be from a corroded Grd terminal connected to the passenger side valve cover or the Grd terminals just above your Fuse/Relay panel as Stepson suggested.

Keep Us Posted - Michael

[Danglerb]

Sounds like a green wire issue, but I've also seen a car with all 8 injectors frozen, noid would show that though.

[stepson]

Originally Posted by Danglerb

Sounds like a green wire issue, but I've also seen a car with all 8 injectors frozen, noid would show that though.

Will it?

Noid shows an electric signal. If the electric signal is present, but the injectors are frozen/gummed up, etc, won't it still show that signal?

It seems as though the signal could occur without a drop of fuel getting through the injector.

Or am I wrong about that?

[Danglerb]

If the noid blinks, but the injector doesn't click, bad injector.

Green wire is like bad CPS on later models, no signal to injectors.

[stepson]

Originally Posted by Danglerb

If the noid blinks, but the injector doesn't click, bad injector.

Green wire is like bad CPS on later models, no signal to injectors.

I don't have any green wire cars on purpose, but I thought the green wire issues would cause a "no spark" situation. You are saying that it can cause a "no fuel" problem as well? In the first post, the OP says he can feed it fuel manually and it will run.

I learn something new every day about these cars.

[Danglerb]

Manually adding fuel is almost a joke to me regarding the 928, it used to be so common in forsale ads, and tells you almost nothing about the depth of the problem.

One time it worked for me, my smog guy was an old school mechanic working out of a gas station. I got the bright idea to run my 85 Euro as close to out of the old gas in the tank and then put in a few gallons of fresh just before the test. I drove it until it sputtered, put in some fresh gas, but had a car ahead of me getting the test, so parked and turned it off. Would not start, at all , period, running down the battery etc.

Smog guy comes over with a booster pack and can of ether, and I'm like, are you sure, and he says yeah. Starts and dies. He says let me keep giving it some ether to let it run for a about a minute, and that did the trick.