914 won't start - no power to fuel pump

[Snowdoggie]

My 914 won't start. The starter cranks but I don't hear the fuel pump clicking so it looks like I am getting no power to the fuel pump. I don't hear anything from the back either. Nothing but the starter cranking. Not getting fuel.

[Snowdoggie]

I already checked the fuel pump relay. Switched it out with another relay. That didn't fix it.

Its a fairly new fuel pump.

[Snowdoggie]

There doesn't seem to be power the the fuel injection either. I hear nothing back there.

[Nostril Cheese]

Check that you actually have 12V to the fuel pump. The pump should operate for a second or two before cranking.

What year and model is it? 1.7, 1.8 or 2.0? There's a couple things that can prevent the fuel pump from operating depending on the model.

[Snowdoggie]

Originally Posted by nostril cheese

check that you actually have 12v to the fuel pump. The pump should operate for a second or two before cranking.

What year and model is it? 1.7, 1.8 or 2.0? There's a couple things that can prevent the fuel pump from operating depending on the model.

1975 1.8.

[Dave at Pelican Parts]

The 1.8, stock, uses L-jetronic fuel injection. It does not use the relays on the relay board to power the FI or to power the fuel pup. Instead, it uses the "double relay" that hangs off the battery tray. Check that you are getting power to the correct terminals of the relay when the key is on, and also when you are cranking the starter.

The L-jet fuel pump runs when either the starter is cranking, or when the flap in the air flow meter is opened. You can turn the key to "on" and push on the flap in the meter and listen for the fuel pump. The pump in 75+ cars is up in front underneath the fuel tank, so you may not have been listening in the correct place.

You can find more about L-jet in non-Porsche web sites, as lots of other cars (including late VW Buses) used L-jet. Bosch L-Jetronic Fuel Injection Manual is one place with info. Google can help you find others.

--DD

[Snowdoggie]

Originally Posted by Dave at Pelican Parts

The 1.8, stock, uses L-jetronic fuel injection. It does not use the relays on the relay board to power the FI or to power the fuel pup. Instead, it uses the "double relay" that hangs off the battery tray. Check that you are getting power to the correct terminals of the relay when the key is on, and also when you are cranking the starter.

The L-jet fuel pump runs when either the starter is cranking, or when the flap in the air flow meter is opened. You can turn the key to "on" and push on the flap in the meter and listen for the fuel pump. The pump in 75+ cars is up in front underneath the fuel tank, so you may not have been listening in the correct place.

You can find more about L-jet in non-Porsche web sites, as lots of other cars (including late VW Buses) used L-jet. Bosch L-Jetronic Fuel Injection Manual is one place with info. Google can help you find others.

--DD

Thanks. I will check the relays under the battery tray. I just put a new tray in and something there might have been moved around. That makes sense. I don't hear the fuel pump from the front.

[mark 74 carrera]

Dave,

I have what I believe is a stock set up on a 1974 914 1.8 with L-jetronic. I have no power at the fuel pump. Relays on driver's side panel in engine bay are working and getting power.

Are the two relays you mentioned above that are under the battery tray between the engine bay relays and the fuel pump? In other words do you think those two relays are the culprit for no power at the fuel pump?

I am new to the 914 and electrical stuff in general but I want to track this problem down myself, well at least with some help.

Thanks, Mark

[mark 74 carrera]

Dave,

The relay under the battery that is most aft or toward the rear is not getting power. The front one is. I'm going to try and track this harness using the wiring diagrams.

Mark

[Dave at Pelican Parts]

As I said, the dual relay is what provides power to the FI "brain" (ECU) and to the pump. The power to the brain should be on when the key is on, I think, but the power to the pump should only be on when the starter is cranking or when the flap in the air flow meter is open. So check by pushing the flap open with the key on.

--DD

[mark 74 carrera]

Dave,

When I open flap on the air flow meter, there is no power to fuel pump. When I open the flap, I can hear the forward fuel injection relay click, but the rear "fuel pump and ignition" side relay does not click hence no power to the fuel pump.

Are these two relays connected to each other or just sitting next to each other? When I removed the relay cover, it looks like the soldering is intermixed between the two relays.

Do you think it's the relay and I should replace it?

Mark

[Dave at Pelican Parts]

There are two relay mechanisms, with the connections interconnected, in the one plastic housing. It is possible for one to fail and the other not to. The relay is represented by the dashed-line box in the following diagram: http://www.pelicanparts.com/914/parts/Electrical/914_electric_74_AFC-B.jpg

A is from the battery, N(15) is from the coil (+) terminal, T(12/12) is to the pump, 86a is from the starter circuit (by way of the relay board), 85 is ground, 86b powers the ECU and the fuel injectors, 86a and 86b are the "air flow meter flap is open" signal, and 88c powers the Aux Air Regulator.

If you have easy access to a second dual relay, swapping them could be an easy diagnostic step. If not, you can still use a multimeter to check that the proper signals are there. When N(15) gets powered, make sure that 88a and 88b also have +12V. If that is the case, jump power to 86b or open the air flow meter flap, and check for +12V on 88d and 88d. If you have power on 88d and the pump still doesn't run, check for continuity between the pump's power connection and 88d, and check that the pump has a good ground connection.

If you are getting ground on 85, and +12V on N(12) and 86b, and the pump still doesn't run, the relay is most likely bad.

--DD

[mark 74 carrera]

Dave,

Thanks for the help. I have ordered a new relay and a refurbished fuel pump. When I wired the fuel pump directly to the battery, nothing happened. I was going to change out the rubber fuel lines down below anyway for safety reasons. I thought they were going to break off in my hand.

I read somewhere on a Pelican thread about the 74 seat belt relay. I went to check it and found that one of the PO had soldered a bridge between the two large yellow wires. Of course, that would have been too simple. Parts should be here by this weekend and I will try to get it started again.

Mark

[mark 74 carrera]

Dave,

Thanks again for your help. I replaced both the fuel pump and the relay we discussed. After everything was hooked up, I could hear the fuel pump when I open up the air flow flap. After about 5 minutes (I did add some gas to the tank) the car started up and ran pretty smooth when revved. It idles low and rough.

So, I turn it off and then I see a growing pool of gas under the drivers side engine area. It turns out that the two rubber lines that run from the fuel rail? to the injector are really old and they are both leaking. I will replace all four tomorrow and all furl lines eventually.

Mark

[Dave at Pelican Parts]

Replace all of them before you drive the car. Fuel spraying + hot engine parts == fire. FIRE BAD!!

--DD

[FDeLange]

This thread is encouraging... have had my 1975 914 1.8 sitting in my garage for years too frustrated at troubleshooting and brick walls. Similar situation, turn key, hear click, however I dont hear the pump kick in before I attempt to start. I know the pump works because I have run a wire direct from the battery to the pump. Where is the second relay and the air flow flap typically located? I found the relay under the battery.

[Dave at Pelican Parts]

The relay under the battery is 2 relays in one housing.

The air flow meter is attached to the side of the air filter box. It's the thing with a quarter-circle bump-out on the side of it, and an electrical plug with five wires (I think) plugged into it.

--DD

[porschetub]

Originally Posted by Dave at Pelican Parts

The relay under the battery is 2 relays in one housing.

The air flow meter is attached to the side of the air filter box. It's the thing with a quarter-circle bump-out on the side of it, and an electrical plug with five wires (I think) plugged into it.

--DD

Top marks Dave you really know these cars,you have helped a lot of people on here including myself,I have worked on cars since age 12 and you learn a lot over the years.....but every car is differant.
The 1.8 system is certainly less fussy but still important to have good connections and wires in the FI loom.