Fuel Console Solenoid and Air Box Fuel Circuit

[chris belyea]

Hi,

I have a ’70 911E that I’m putting the MFI back on to the motor. I’m hoping fire it up for the first time this weekend but wanted to make sure I understand how the fuel from the solenoid to the air box works. I’m not sure if this is part of the cold start circuit or not but I had the engine and MFI rebuilt off site by someone and I’ve found a used fuel console. I bench tested the solenoid at the top of the console and I here a click so I believe it is working. Now I’d like to test it in the car before putting fuel through the system. Can someone describe what should happen so I can check to see if the sequence is working? I’m assuming if I turn on the ignition, the solenoid should open and allow fuel to pass into the air box squirting fuel into the velocity stack. But I don’t know for how long and if there should be a certain pressure at the outlet of the solenoid. Perhaps all I need to check is that fuel is passing through the system.

Hopefully I’ve described accurately what I’m looking for. Any insight into what should happen on a MFI system upon startup will be welcomed.

Thanks

Chris

[NorthernThrux]

See this post and a few that follow, including Ed's clarification. https://www.early911sregistry.org/fo...=1#post1028872

Ravi

[edmayo]

Be sure you have the fuel lines hooked up correctly. Read Arne's post from when he went thru this. On a first start like yours it helps to do a manual activation of the cold start circuit by powering the solenoid with a temporary jumper wire for a few seconds at a time to get the system filled up.

[Richy]

The cold start solenoid will not switch on unless the key is in the start position to activate the starter solenoid . The thermal time delay switch and the cold start relay and fuse also have to be working , but at least you know the cold start solenoid works . The thermal time delay switch will activate the solenoid for only few seconds .

[Arne]

Be sure you have the fuel lines hooked up correctly. Read Arne's post from when he went thru this. On a first start like yours it helps to do a manual activation of the cold start circuit by powering the solenoid with a temporary jumper wire for a few seconds at a time to get the system filled up.

Yes, wrong fuel line hookup is easy to do, given that some early diagrams from Porsche were wrong. Figuring this out was a major pain.

[chris belyea]

Thanks for the reminder. I remember seeing something on this a while ago but I had to go back out and check to see if I hooked them up correctly. I think I've got them correct.

On an unrelated note. I noticed that the rear engine seal hits the MFI belt and pulley. This is the seal that has 2 flaps. I thought one flap sealed the top of the engine tin and the other sealed the bottom. Do I need cut the seal or have I installed something incorrectly here?

Chris

[gled49]

The upper lip of the seal is cut out for belt clearance on MFI cars. It’s about an 8” cutout.

[chris belyea]

So an update....I made all the connections and before connecting the fuel pump I put a test light on the solenoid and I'm not receiving power when I start the car. I'm not sure I have the correct wire connected. When I bought the car, MFI was long gone and some of the wire had been cut. The only wire I saw near the fuel console was a brown wire with white bands on it. I know the wiring diagram says it grey with white but I don't know what the brown wire is for. So if I'm missing the grey wire, is there something I can tie into or do I need to take the 14 pin connector apart an find the wire?

Also, the check valve inside the solenoid assembly leaks. Is there a way to rebuild these? New ones are just under $1000!

Thanks

Chris

[edmayo]

To your first point, the test light wire goes on the wire, not the solenoid, power comes to the solenoid, not the other way around. To your second point the brown/white may be a ground for the license lights. When some one has butchered the wiring all bets are off. The gray white wire comes from a relay on the relay board,,,,is that relay even there? Where is the solenoid check valve leaking to? If you are seeing the fuel on top of the fuel filter housing it may just be the seal between the solenoid and the filter housing. There is no way to rebuild them,,,swap meets and the internet is your friend.

[NorthernThrux]

The relay Ed is talking about switches power from Fuse 2 in the console to the solenoid. The solenoid/filter body needs to be grounded for the circuit to be completed. The relay itself has power to its coil come from the starter circuit. The other side of the coil is grounded through the thermo-time switch (which should show continuity to ground on an engine that hasn’t been cranked in the past 10 seconds). So check for all the voltages and grounds at this relay first (including making sure you have the relay!).

There is a fuel filter and cold start unit on ebay at the moment. Needs to be cleaned up for sure, and no idea if it works. Just happened to notice it today while looking for some dash knee pads.

Ravi