Going to look at a fantastic 1973 911S tomorrow. Need a bit of advice.

[savagejayj]

WOW, the ivory paint with the white what looks like houndstooth seats is stunning, great choice, it really pops.

[Simonjjb]

My German Shepherd Xander is ready for a drive. He doesn't need seats. And he might get seats soon since the carpet has made its way over the Atlantic and I can pick it up tonight at the post office.

Back seats and parcel shelf have the original sound absorbing materials glued back down.

Attachment 499023

Love the car and the Pooch

[NorthernThrux]

Car has had a cold starting problem since I got it back from Robert Gross. Finally spent a few hours to check the cold start solenoid, the thermo-time switch and the relay that activates the solenoid. Found two issues, one of my own making. The leads on the thermo-time switch were switched. So the yellow wire was being switched to ground and the red/black wire was going to the heating element. I think this is my fault because I pulled those leads off while installing the hoses on the airbox and fan shroud and may have interchanged them.

But even after I figured that out, and I was getting 12V at the cold start solenoid, the solenoid would not click. This was a subtle issue. The solenoid relies on the fuel filter assembly being grounded as it is rubber mounted to the body. Added a ground wire (is there an official place to add it?) running to the electrical console right by the CDI unit. Voila! Instant starting now. Contemplating adding a momentary “on” switch by the driver’s side seat belt receptacle to ground pin 85 of the cold start system relay for those times when the engine needs enrichment but the thermo time switch says no sir, I’m still warm. I’ll give it a try the way Porsche intended first and see how it goes.

Grounding pin 85 allows the cold start relay to close when the starter motor is turning, and essentially parallels what the thermo time switch does. I like this solution compared to applying +12V directly to the solenoid because it leaves the whole system intact and just allows you to help goose the solenoid if the thermo time switch gets fooled. Or instead of a momentary “on” switch, I may get some kind of thermostat that grounds pin 85 when the intake plenums are relatively cool, even if the thermo-time switch says the engine is warm. Something like an adjustable electric fan thermostat to play with. Bit first I’ll go with the pedal to the floor warm start procedure in the manual.

[frederik]

This is interesting... I don't have perfect cold starts either and will check the system like you did. Is there a clear description of all the cold starting parts and how they're supposed to work somewhere?

My cold start currently goes like this: hand throttle fully up, turn key and leave it for a few seconds to prime the fuel pump, then press accelerator fully and engage the starter. After a second or 5 the engine catches, but not on all cylinders. I have to keep the accelerator pressed for a second or two until it suddenly starts firing on all cylinders. Then I release the accelerator and all is fine after that. How did your cold start go before?

With warm starts, I also have to "help" a little with the accelerator for a second or 5.

[sithot]

The 2.5ST that Gary Kempton (GK Restorations) took back to the original Björn Waldegård specs had a switch mounted on the shift coupling console. You reached between the seats to activate it. Worked like a charm.

[NorthernThrux]

This is interesting... I don't have perfect cold starts either and will check the system like you did. Is there a clear description of all the cold starting parts and how they're supposed to work somewhere?

My cold start currently goes like this: hand throttle fully up, turn key and leave it for a few seconds to prime the fuel pump, then press accelerator fully and engage the starter. After a second or 5 the engine catches, but not on all cylinders. I have to keep the accelerator pressed for a second or two until it suddenly starts firing on all cylinders. Then I release the accelerator and all is fine after that. How did your cold start go before?

With warm starts, I also have to "help" a little with the accelerator for a second or 5.

There is some description of the cold start system in the original Porsche shop manuals. And lots on the Bird and here. Just search "mfi cold start". It's how I learned. But briefly, Fuse 2 in the engine bay console supplies power to a normally open relay. When the starter cranks, a lead from the starter energizes the relay and sends the 12V from the aforementioned fuse to the cold start solenoid on top of the fuel filter assembly. That sends fuel to the mfi stacks through hoses and plastic tees in the base of those stacks. That fuel assembly needs to be grounded so the solenoid actually actuates. Now the trick is the other end of the coil for the relay goes to the thermo-time switch, which normally allows it too go to ground and hence activate the relay coil. But as the thermo-time switch warms up (either from the engine or the yellow wire from starter powered internal heating coil) it no longer goes to ground and hence the relay isn't activated. It's quite simple really.

The relay coil is only powered when the starter cranks, and the thermo-time switch is only internally heated when the starter cranks as well. It heats up fast, so after 5-7 seconds, the relay coil is no longer grounded via the thermo-time switch and you no longer get fuel flooding the intake manifolds. So if your car doesn't start after 7 s of cranking, you are out of luck as far as the fuel enrichment system goes.

My cold starting symptoms were having to crank incessantly (4 or 5 tries of 5 second each) with foot to the floor with the hand throttle raised. Then it would catch on a couple of cylinders and then with some more throttle pumping, it would go. You shouldn't have to touch the throttle pedal till the engine fires as per the owner's manual. Warm starting was fine. Just push the pedal to the floor and start, as per the manual. In all cases, I aways run the fuel pump for 5 seconds or so before cranking.l

[csbush]

The ground wire is a short brown wire with loop terminals on each end. One end goes to one of the three fuel filter assembly mounting bolts, and the other end goes to that body ground just a little forward of the mount.
My 70 S starts just fine with the solenoid, but is hard to start when it isn’t hooked up, so I know the importance. I have never needed anything else.

[NorthernThrux]

The ground wire is a short brown wire with loop terminals on each end. One end goes to one of the three fuel filter assembly mounting bolts, and the other end goes to that body ground just a little forward of the mount.
My 70 S starts just fine with the solenoid, but is hard to start when it isn’t hooked up, so I know the importance. I have never needed anything else.

OK, thanks for that. I got one end correct, the colour right (that's easy, all the grounds are brown!) and even the right terminals! I'll move the other end to the body ground this weekend.
And yep, it sure does make a difference. Starts like a modern car when that solenoid is working, not so much when it isn't.

[frederik]

Thanks for the description, this definitely helps. Your cold start sounds like mine but worse, so hopefully I’ll be able to find the problem on my car. Best of luck with finishing yours!

[edmayo]

Ravi, you correctly explained the workings of the start system, and when the engine doesn't start within 5 sec. or so turn ignition off for a few seconds, then crank starter again, the thermal switch will have cooled off and will operate again for a few seconds. This was done so that if engine doesn't start you don't flood the cylinders. If you want to see this, just remove grey wire from solenoid and hook to a grounded test light. Remove high tension lead from center of dist. cap and ground it. Now when you crank engine the test light will come on for a few seconds, stop cranking, wait a couple seconds and repeat, light should come on again for a couple seconds.