'74 1.8L LJet/fuel pump, Fuel Pump not staying on Options

[RKramden]

This is my first time starting a topic, I don't know if I am even typing in the correct location, but I am having an issue with my '74 LJet and fuel pump. The pump starts with the ignition switch, Pump also runs when Air sensor arm is manually moved. However when starting, it seems that the air sensor is somehow cutting off the fuel pump circuit. The PO had bent the arm so it never opened, but I have bent it back to move as designed. If I disconnect the electrical plug to the Air Sensor, the car starts and runs fine......any thoughts? BTW I have replaced the dual relay, but that did not fix the problem.

[porschetub]

This is my first time starting a topic, I don't know if I am even typing in the correct location, but I am having an issue with my '74 LJet and fuel pump. The pump starts with the ignition switch, Pump also runs when Air sensor arm is manually moved. However when starting, it seems that the air sensor is somehow cutting off the fuel pump circuit. The PO had bent the arm so it never opened, but I have bent it back to move as designed. If I disconnect the electrical plug to the Air Sensor, the car starts and runs fine......any thoughts? BTW I have replaced the dual relay, but that did not fix the problem.

My understanding was that the pump only gets power from ignition switch and won't start until the AFM air gate moves off the cut off switch,this should happen when the engine is cranking before starting.
I think the switch is to stop the pump on throttle overrun,in the later L-jet version (bus) the ecu controls that function so they use a different AFM.
When you say the car runs when you disconnect the air sensor ?do you mean the AFM? if so I can't see how it would run with the plug off.
Whats the condition of the wiper board inside the AFM ?,if the wipers have bad contact it can cause the issue you have,can be cleaned or reset if tracks are worn.
Good luck.

[ClayPerrine]

[
My understanding was that the pump only gets power from ignition switch and won't start until the AFM air gate moves off the cut off switch,this should happen when the engine is cranking before starting.
I think the switch is to stop the pump on throttle overrun,in the later L-jet version (bus) the ecu controls that function so they use a different AFM.
When you say the car runs when you disconnect the air sensor ?do you mean the AFM? if so I can't see how it would run with the plug off.
Whats the condition of the wiper board inside the AFM ?,if the wipers have bad contact it can cause the issue you have,can be cleaned or reset if tracks are worn.
Good luck.

The fuel pump will run when cranking via the wire from the relay board to the double relay. There is not enough air flow during cranking to open the flap. Once it is running, the air going into the AFM causes the fuel pump contacts to close.

And, any air leak between the AFM and the throttle body will cause it not to run. The air bypasses the AFM, and goes directly into the throttle body. That keeps the AFM from opening enough to keep the engine running.


Definitely replace the big tube between the AFM and the throttle body. Then report back on how it runs.


FYI.. My wife has an L-Jet injected 914. I was trained by VW to work on the L-Jet systems in the 80s. And I have been keeping my wife's 914 alive for 34 years now.