Cold Satrt Fuel Solenoid 1970 911E

rick2443 · 07-09-2009, 07:43 AM

Hi, first question here, thanks for looking: my 1970 911E has no lead on the cold start solenoid on the fuel filter and consequently doesn't start well when cold, I attached a lead to the connector, touch the other end to the fuse, put a shot of fuel in and she starts instantly, but how is this supposed to be wired, I know there is a relay on the electronic panel, any ideas? thanks, Rick.

356RS · 356RS's Garage

Rick, there is a thermo-switch on the engine that is in the closed position when the engine is cold. 12 volts runs through the thermo-switch from the starter solenoid when you are in the start position on the ignition switch up to the small fuel solenoid on top of your fuel filter housing and opens the solenoid and lets the fuel run into the small jets in the air filter housing. When the engine is warm, the thermo-switch opens and stops the 12 volts from completing the circuit. Hope this helps.

dlague · 07-09-2009, 08:47 AM

on my 1973 with MFI I wired the solenoid to a push button switch on the dash. I push it in for a couiple of seconds as I crank the engine to start.

That way I know when it goes on and off. I know many here with MFI have done this modification. Sort of like manual choke or a "tickler" on a motorcycle float bowl.

rick2443 · 07-09-2009, 09:05 AM

thanks Mark and Dick, hey Mark, is that thermal switch on the driver's side, low, at the rear of the ngine, made of ceramic? thanks, Rick.

356RS · 356RS's Garage

Rick, the temp switch is located on the engine breather cover, top of the engine case, flywheel end.

rick2443 · 07-09-2009, 11:42 AM

Thanks again Mark, I just got the car 2 weeks ago, so far it's great, a few minor issues, may have a few more questions later. If there is no longer existing wireing can I rout one as you say from the starter solenoid to the switch to the solenoid valve with an in-line fuse? or what was the original wireing? thanks, Rick.

356RS · 356RS's Garage

Rick, first tell me whats missing. Do you still have the "start enrichment" relay on the engine compartment relay console? It's the round black one closest to the 3 side mounted fuses. See if the yellow wire & the red/blk wires are on the thermo-switch, and the gray/wht wire & brown wire for the fuel solenoid on top of the fuel filter are all still there. If they are then you can check the circuit and get it back to original and working right.

rick2443 · 07-09-2009, 02:44 PM

Hi Mark, yes the relay is there, I'll check for the wires at the thermal switch tonight, but ther are no wires going to the solenoid, nor can I find any in the area. Do the gray/wht wire & brown wires come from the relay? I'll report back tomorrow, thanks, Rick.

rick2443 · 07-10-2009, 06:58 AM

Hi Mark, I couldn't find the thermo switcjh, I undid the clips and took the top half off the the breather and felt around at the back but couldn't find anyththing but the fuel lines into the breather, then I checked by feeling the lower half and didn't feel anything, am I in the rigth area? I thought I'd find the switch even if the wires aren't there.

356RS · 356RS's Garage

Rick, the thermo-switch is located on the cover of the oil breather which is bolted to the top of the engine case, in the center next to the MFI pump and just above the flywheel area. The cover will have a large hose going to the oil tank, a small hose going to the MFI pump and will also have the thermo-switch screwed into the left side of that breather cover. Remover your air filter assembly and you will find it.

356RS · 356RS's Garage

Rick, this is what you are looking for. I should have posted this yesterday.

rick2443 · 07-13-2009, 05:43 PM

Hi Mark, that was a big help, thanks alot, I thought you meant the intake breather cover, I found the thermo switch and the wires are attached and head straight into the harness, I presume it goes to the relay Now all I need is a connection to the solenoid? Does that sound right?

356RS · 356RS's Garage

David, You should already have a wire (yellow) that comes from the starter solenoid and goes through the 14 pin connector and ends up at the relay. That is #86 on the relay. From the relay #87 (gray w/white) then goes to the cold start solenoid on top of the fuel filter. So how this all works is: When the starter is engaged, 12 volts is present on the yellow wire that goes to the thermo-switch. If the switch is cold the contacts are closed and then the red w/blk (which is ground in the switch) then goes down to the relay at #85, closes the relay and then 12 volts leaves the relay at pin #87 (gray w/white) wire on to the cold start solenoid. If you have all the wires it should be fairly easy to check all the components.

matt demaria · 07-14-2009, 02:29 PM

I believe that in the middle 70's that there was a TSB regarding disconnecting this particular cold start circuitry. It produced too many engine fires.
The early MFI's had the pissers mounted in the metal air cleaner cover. The later ones had the pissers in the stacks. The problem was when the system got old or out of tune there were backfires up the intake stacks. The combination of dumping gas in the middle of a backfire would start the meltdown of the stacks and proceed from there.

rick2443 · 07-14-2009, 02:37 PM

That's great Mark, what about the middle fuse at the back, I thought that was part of this circuit. Rick.

356RS · 356RS's Garage

Yes, sorry about that. The #2 fuse powers the transistorized speed switch and the auxiliary starting relay. Matt is right about the poor design of this. Always carry a fire extinguisher.

rick2443 · 07-15-2009, 04:50 PM

hey Mark, one more question, does the grey/white go directly to the solenoid? Is the #2 fuse in the circuit from the solenoid/thermo switch? thanks again, Rick.

356RS · 356RS's Garage

Rick, The gray/wht wire first comes from the aux starting relay through the relay panels 14 pin wiring harness, to the engine, ( there is about 11 wires coming out of the wiring harness) and out to the fuel start solenoid. The #2 fuse is the 12 volt power source for both the stop switch relay and the aux starting relay.

rick2443 · 07-23-2009, 03:32 PM

thanks for all your help, it's now wired up correctly and working good, I think your advise about hooking it up to an independent switch is a good idea though, and I think it would work better and be safer, I'm going to do that for my next project, but now I have an even more serius problem with my clutch, i'll post a new message on that, any help or suggestions you guys might have would be greatly appreciated, thanks, Rick.

dlague · 07-23-2009, 09:36 PM

I have had mine hooked up to the independent switch for 11 years now and it works flawlessly. As you said I am politive when it is spraying fuel in there. The solenoid is noisy enough that you can hear it click. I turn on the key.....build up a little fuel pressure with the pump and touch the push button once or twice and crank the engine. Starts very easily and quickly and I am sure the cold start is off once it starts.

Dick