'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.

[ClayPerrine]

Try these tests:


1. Disconnect the Yellow wire on the starter. Then turn the key to the start position. Does the fuel pump run when you do this?

2. Disconnect the big rubber hose between the air flow meter and the throttle body. Make sure the air flow meter is plugged in. Turn the key on. Open the air flow meter with your finger. Does the fuel pump run?


Clay

[RKramden]

Try these tests:


1. Disconnect the Yellow wire on the starter. Then turn the key to the start position. Does the fuel pump run when you do this?

2. Disconnect the big rubber hose between the air flow meter and the throttle body. Make sure the air flow meter is plugged in. Turn the key on. Open the air flow meter with your finger. Does the fuel pump run?


Clay

#1 pump will run in this scenario.
#2 I can turn the flapper from the top of the AFM with the cap off. The fuel pump will run.

[ClayPerrine]

Try these tests:


1. Disconnect the Yellow wire on the starter. Then turn the key to the start position. Does the fuel pump run when you do this?

2. Disconnect the big rubber hose between the air flow meter and the throttle body. Make sure the air flow meter is plugged in. Turn the key on. Open the air flow meter with your finger. Does the fuel pump run?


Clay

#1 pump will run in this scenario.
#2 I can turn the flapper from the top of the AFM with the cap off. The fuel pump will run.

Then the double relay is working as expected. Start by fixing the false air problem (the split hose between the throttle body and the AFM). If that doesn't fix it, then the AFM is probably bad.

[RKramden]

Try these tests:


1. Disconnect the Yellow wire on the starter. Then turn the key to the start position. Does the fuel pump run when you do this?

2. Disconnect the big rubber hose between the air flow meter and the throttle body. Make sure the air flow meter is plugged in. Turn the key on. Open the air flow meter with your finger. Does the fuel pump run?


Clay

#1 pump will run in this scenario.
#2 I can turn the flapper from the top of the AFM with the cap off. The fuel pump will run.

Then the double relay is working as expected. Start by fixing the false air problem (the split hose between the throttle body and the AFM). If that doesn't fix it, then the AFM is probably bad.

Clay, I am leaning towards the AFM as the issue as well, I will try another one once the new hose arrives. Do you have any idea why the car and pump will stay running with the AFM unplugged? Last night I got the RPMs up by slowly increasing the throttle. If I punched it, it would die.....this is all with the AFM unplugged!

[ClayPerrine]

Clay, I am leaning towards the AFM as the issue as well, I will try another one once the new hose arrives. Do you have any idea why the car and pump will stay running with the AFM unplugged? Last night I got the RPMs up by slowly increasing the throttle. If I punched it, it would die.....this is all with the AFM unplugged!

That is a sorta "limp mode" function. If the AFM dies, the L-Jet sees the ignition pulse that is over a certain RPM and will keep the engine running. Without a AFM signal, it will just barely run. Good for getting the car off the street into a parking lot, and not much more than that. It only knows how to make the car idle, nothing more.