Electrical Issue, 75 1.8 L-jet Options

[Grump]

I had to completely install all wiring in my roller since it was stripped for color change. The engine ran fine when pulled from donor. Was going to start it up yesterday but decided to test wiring first. Good thing since when I turn the key to the on position the fuel pump comes on. Not supposed to until it's in the cranking position. This is the same FI harness that was in the donor. I checked my wiring of the fuse panel, gauges, and switches and almost 100% certain they are correct. I even took all fuses out and has no effect. I did swap dual relay, fuel pump relay, voltage regulator board, and power supply relay. I spent 2 days trying to track this problem down, but am at a loss. I hope someone here can provide some help. Thanks... Bill

[914itis]

Calling Timothy_nd28
He is the ljet resident expert. He will be here shortly .

[timothy_nd28]

Any pics of this restoration?
You are correct, the fuel pump should not turn on by merely turning the key to the "on" position. Do you own a multi meter? If you were to pull the air flow meter connector off, does the fuel pump still activate when you turn the key to "on"?

[Grump]

Any pics of this restoration?
You are correct, the fuel pump should not turn on by merely turning the key to the "on" position. Do you own a multi meter? If you were to pull the air flow meter connector off, does the fuel pump still activate when you turn the key to "on"?

timothy was instrumental in getting the 1.8 running 2 months ago. When disconnecting the AFM, the pump does not come on. I replaced the ignition switch just to eliminate that as a problem. I disassembled all the wiring on the donor just to make notes, draw sketches and take photos to eliminate the guess work. Checked all my grounds and connections. I messed up somewhere but a re-check several times doesn't reveal any mistake. Electrical problems, as all who has had them can attest to, are a real pain. I do have a multi-meter and use if often. When I disconnected the AFM I put the meter on the fuel pump leads because I couldn't hear it even if it did run, which it didn't.

[ClayPerrine]

There are two things that make a fuel pump run on the L-Jet system.

1. The air flow meter.
2. The cranking circuit.

The air flow meter turns on the fuel pump by energizing one of the coils in the double relay. There is a second coil in the same relay that is energized by the start circuit.

Check the engine harness connection to the relay board. There should be a short yellow wire with a female spade connector on it. Make sure that spade is connected to the right rear connector of the 4 pin connector block on the left rear of the relay board. If it is connected to one of the other connectors, it can cause the pump to run anytime the key is on.

FYI.... you do not need any relays on the relay board for the L-Jet system to work.

[timothy_nd28]

I think you identified the problem. With the AFM connector pulled, the fuel pump stops (with ignition switch to on). It's possible that the AFM's flap isn't springing back to the zero position, which is causing the fuel pump contacts to remain engaged.
Reinstall the AFM's connector, turn the ignition switch to on. The fuel pump will be on (your original problem). Now, remove the AFM's black plastic cover.


Look at the red arrow. Are these 2 contacts touching each other?

[Grump]

I think you identified the problem. With the AFM connector pulled, the fuel pump stops (with ignition switch to on). It's possible that the AFM's flap isn't springing back to the zero position, which is causing the fuel pump contacts to remain engaged.
Reinstall the AFM's connector, turn the ignition switch to on. The fuel pump will be on (your original problem). Now, remove the AFM's black plastic cover.


Look at the red arrow. Are these 2 contacts touching each other?

Hello. Just looked. Contacts are not touching.

[Grump]

I think you identified the problem. With the AFM connector pulled, the fuel pump stops (with ignition switch to on). It's possible that the AFM's flap isn't springing back to the zero position, which is causing the fuel pump contacts to remain engaged.
Reinstall the AFM's connector, turn the ignition switch to on. The fuel pump will be on (your original problem). Now, remove the AFM's black plastic cover.


Look at the red arrow. Are these 2 contacts touching each other?

Hello. Just looked. Contacts are not touching.

I keep thinking it's something in the ignition circuit. The only new item since it ran last is it's a different 12 pin connector.

[timothy_nd28]

Odd, you did say that when you pulled the AFM connector off, the fuel pump does quit? Pull the springy metal contact back slightly, increase the air gap. Is the pump still on when you manually pull it?

[Grump]

Odd, you did say that when you pulled the AFM connector off, the fuel pump does quit? Pull the springy metal contact back slightly, increase the air gap. Is the pump still on when you manually pull it?

Still runs. Sounds like it springs back to a metal stop. Contacts are open.

[timothy_nd28]

With your multimeter, and the AFM connector pulled, measure the resistance between pin 36 and 39 on the AFM

[Cap'n Krusty]

I could be wrong, but I believe the FP is activated through the FP relay when the AFM flap moves off the stop. I KNOW there are more than one version of the double relay, and they DO NOT interchange. The VW unit is different from the Porsche one. Check the part numbers.

The Cap'n

[Grump]

I could be wrong, but I believe the FP is activated through the FP relay when the AFM flap moves off the stop. I KNOW there are more than one version of the double relay, and they DO NOT interchange. The VW unit is different from the Porsche one. Check the part numbers.

The Cap'n

I put back on all the items that were on the last time she ran. If it worked then, it should work now, unless the squirrels gnawed on it.

[timothy_nd28]

The dual relay is a pretty neat circuit. As Clay stated, this relay turns on the fuel pump when you turn the ignition key to the start position. As you release the key, (hopefully engine running) the voltage from the ignition switch is dropped, but the AFM contacts take over and keeps the dual relay energized, thus keeping the fuel pump engaged. It's a neat handoff between the AFM and the ignition switch.

You have an odd problem. When the key is just to the "on" position, your dual relay is being energized (it shouldn't be). We quickly isolated the issue by removing the connector to the air flow meter. With this connector removed, the fuel pump stops. This tells me that the AFM is somehow providing continuity between pins 36 and 39 on the AFM. Or pin 36 is getting 12volts somehow.

[Grump]

The dual relay is a pretty neat circuit. As Clay stated, this relay turns on the fuel pump when you turn the ignition key to the start position. As you release the key, (hopefully engine running) the voltage from the ignition switch is dropped, but the AFM contacts take over and keeps the dual relay energized, thus keeping the fuel pump engaged. It's a neat handoff between the AFM and the ignition switch.

You have an odd problem. When the key is just to the "on" position, your dual relay is being energized (it shouldn't be). We quickly isolated the issue by removing the connector to the air flow meter. With this connector removed, the fuel pump stops. This tells me that the AFM is somehow providing continuity between pins 36 and 39 on the AFM. Or pin 36 is getting 12volts somehow.

Seems I can't find the pin number location diagram. I can't remember where I seen it.

[timothy_nd28]

[r_towle]

Sorry, but that is a totally stupid way to number anything.....
It has 7 pins..geez.

Have you though about a possible short circuit inside the wiring harness?

I might suggest that you follow the power from the pump, back to the source.
You may find it.

[timothy_nd28]

If it was a short in the harness, the pump would stay on if the connector was attached or detached from the AFM. Since pulling the connector off the AFM kills the pump, the short has to be inside the AFM. Well, that's where my moneys at (IMG:style_emoticons/default/biggrin.gif)

[Grump]

If it was a short in the harness, the pump would stay on if the connector was attached or detached from the AFM. Since pulling the connector off the AFM kills the pump, the short has to be inside the AFM. Well, that's where my moneys at (IMG:style_emoticons/default/biggrin.gif)

No reading at all between 36 and 39. No voltage either. With the AFM cable detached and I turn the key on I hear a relay on the board click. Can't tell which one.

[timothy_nd28]

You are measuring at the pins on the AFM?