'77 Carrera 3 no fuel issue

[awdbandito]

I have a '77 Carrera 3 that was running flawlessly and I returned from a 200 mile trip on Sunday. I went to start it this morning and it turns over but never fires. I verified spark, and pulled a fuel line from the filter. I am getting no fuel. When the ignition is keyed on, I get 12V at the fuel pump fuse, but I haven't gone anywhere from there. I don't have a lot of time over the next couple days, but thought I would post to see if somebody could give me info on this circuit.

Does the red fuel pump relay energize, then feed through the fuse, or is the fused line feeding the red relay?

When I get time I'll check voltage at the pump itself.

Thanks,

[awdbandito]

Anybody?

Does the fuel pump fuse feed the relay, or does the relay energize and feed the fuse?

[ossiblue]

Try this:
http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_82SC_Part1-2.jpg

It's the electrical diagram for an 82SC, but I believe the set up is similar. Looks like fuse 16 feeds the relay.

If I remember correctly though, you won't get voltage to the relay unless the air flow sensor contact is engaged--this prevents the fuel pump from operating when the engine in not turning over so just turning on the ignition switch and trying to measure voltage at the fuel pump or terminal 30 on the relay will give a false reading of no voltage.

I'm not familiar with your year and model car, so the above is only an educated guess based on the diagram. Others will soon reply with direct experience, however. Keep us posted on your findings.

[boyt911sc]

Originally Posted by ossiblue

Try this:
http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_82SC_Part1-2.jpg

It's the electrical diagram for an 82SC, but I believe the set up is similar. Looks like fuse 16 feeds the relay.

If I remember correctly though, you won't get voltage to the relay unless the air flow sensor contact is engaged--this prevents the fuel pump from operating when the engine in not turning over so just turning on the ignition switch and trying to measure voltage at the fuel pump or terminal 30 on the relay will give a false reading of no voltage.

I'm not familiar with your year and model car, so the above is only an educated guess based on the diagram. Others will soon reply with direct experience, however. Keep us posted on your findings.

LJ,

When the ignition switch is @ RUN position (not start), the fuel pump relay gets power @ terminal #87a (please refer to your wiring diagram). The coil is energized and the normally closed (NC) 87a-30 is switched to 87-30. The fuel pump will not run at this point because the FP is now directly connected to #87 (energized only @ START).

When you lift the air sensor plate (ignition switch @ RUN), the FP relay coil is de-energized and switching back to NC (87a-30) condition. Thus the FP run. The FP is at 87a-30 connection when it is running except for a very brief moment during start (87-30). Once the engine starts to run (air sensor plate moves up), the 87-30 status will switch to 87a-30.

You need to install a fuel injection pressure gauge to determine the condition of the pump. Or measure the flow rate per minute. HTH.

Tony

[VinceQN]

having the same problem...help!

[MBEngineering]

HI awdbandito and VinceQN

a wiring diagram for you education purpose only,






this diagram has the fuel pump at the rear?? and I am sure the Carrera 3 is at the front, it then should have the feed and the earth in the front, under the fuse box on a double connector to the pump, just check the fuel pump relay has not come out of it's socket in the fuse board under the front??

regards mike

[André 3.0]

Carrera 3.0 site : http://www.911carrera3.co.uk/

Carrera 3.0 forum: http://www.impactbumpers.com/forum/index.php?showforum=48

Regards André

[awdbandito]

My problem ended up being a fuse had rocked loose. I had the wrong fuse box diagram and was checking voltages at the wrong place. Once I figured that out it was easy.