Start up problem 72, MFI 911T
 

All,
I have a problem starting my 72 911 T with MFI, however, once started it runs great.

If I reactivate the cold start up valve connected to the top of the gas filter(just need to re connect the wire, would this make a big difference?

Is there another way that I can improve the starting process rather than re activating that start up valve, I have been told be a few people that it could be dangerous and is the start of the many a fire in the engine compartment.

Any info/advice would be appreciated.

Marc

Marc,

The conventional wisdom is to put a momentary-on spst switch in series with the wire to the cold-start solenoid, so that you can control when additional fuel is dumped into the base of the throttle bodies during cranking.

In my view, the 72 and later stacks are much safer because the fuel is squirted internally. Much better, in my opinion, than the brass tubes in the aircleaner for the 2,2, which if misaligned, can dribble fuel down the outside of the stacks.

Make sure the hoses and tee fittings are perfect with no cracks and no aftermarket bits, only the factory Porsche stuff, and I'd thinkyou would be OK.

John gave you good info. Nothing else to add. Without the cold start injector you will continue to have problems.

I use a can of go juice (ether) and one second spray through the grill. My wrench (Eisenbud-Denver MFI guru) disabled/dismantled my cold start as it was problem proned. YMMV

I wired my 70 E with a momentary switch but added a relay powered by the starter circuit so fuel can only be introduced when the starter is running, much like the original design.
I just felt this was a better, and maybe safer approach.

As to fires, I do not fully understand why this is a problem since I would think with the engine running it would either draw the fumes into the engine, or snuff it out from the turbulence.

The switch/relay was pretty simple. Provide the power (+12Vdc) to the coil from the starter circuit, which I believe was the yellow wire in my 70, and ground it through the dashboard mounted switch. The auxillary +12V for the solenoid also comes from the yellow wire, but is switched via the relay.

Hope this all makes sense!

Best,
Ron Young
1970 911E Targa
1973 Jag E type V12 OTS

Bill,
STOP

Using ether that way is inviting a BIG explosion and winding up with the deck lid wrapped around your face. Serious bodily injury! All it takes in one little spark from your plug wires and KA BOOM.

Please pay attention and apply some common sense. We want to see you stay alive.

Best,
Grady

Mark,

Sorry to get distracted. I had visions of Bill launched in a sub-orbital trajectory, tail flames and all.


I would run a very small hose (even smaller than the factory hose) from the cold start solenoid valve (on top of the fuel filter console) to a suitable container outside on the ground. Using a jumper wire from the fuse panel to the solenoid, confirm it turns on the fuel flow when activated. When deactivated the flow should stop immediately. It also should not slowly drip. – no runs, no drips, no errors.

With the solenoid wire connected and the ignition disconnected, have someone crank the engine when cold. Observe the flow. Depending on the temperature you may only get a short flow. The warmer and the longer you have been cranking, the shorter the flow.

If the solenoid fails to operate when everything is cold, inspect the wiring for that circuit. Look at the connections at the thermo-time switch located on the crankcase breather cover. Check to see that the cold start relay functions properly (on the electrics relay panel.) The circuit goes through both 14-pin connectors. I‘ll draw up a current flow diagram tomorrow.

The next thing I would do is inspect the condition of the left heat exchanger and the hoses leading from the heat exchanger to the thermostat. It is critically important for hot air to get to the thermostat to turn it off. Now, disassemble and clean the thermostat. It is important to get the bi-metal discs in the proper position. Checkhere If the thermostat is set properly and turns off fast, an engine will start when pretty cool without the cold start solenoid. In genuinely cold weather it is necessary.

Best,
Grady

Thanks all for your advice, I have the wire disconnected right now but will reconnect and try wiring it up via the starter, this way it will operate only when the starter is running.
Great Advice!!
MarcSmileWavy

One last thing, the colour of the relay in the rear fuse box area should black right?
Thanks
Marc

Mark, I used black, but my E is not concours so it really didn't matter.
Best wishes,
Ron

To check to see if the cold start valve worked, I disconnected the brown/white wire to it and I connected another wire directly to power. It made a strong click sound which I assume indicated it opened. I replugged in the original power wire (brown/white), restarted the car, no strong click sound. Does this mean that the cold start valve did not get power when starting or that it just got less power, opened less and therefore did not make the click sound.
I wanted to make sure that the power wire to the valve was actually powered when starting the engine. I disconnected the wire, connected a volt meter to it, and viewed the volt meter when I turn the ignition on and turned the engine, the volts went from zero to about 6.5 Volts and then back to zero about 2 to 4 seconds later. I did this several times and started the engine. Is this supposed to happan or am I not getting enough volts to the valve for it to open? Do more volts to the valve open it more and thus I assume the volts going to the valve depend on the temperature of outside and the engine. ( ie microswitch)
Any info is appreciated. Just trying to understood how it all supposed to work.
Marc

Marc,

Check the relay socket for corrosion.

1. Middle fuse of the three-fuse block [circled device #80] provides power to the black [circled device #52] Cold-Start Relay, terminal #30.

2. From ignition switch terminal #50, Yellow wire to solenoid ... provides 'Start' +12 Volt signal to relay coil terminal #86.

3. If temperature at oval breather cover is below 113°F ... Thermo-Time Switch [circled device #14] terminal 'W' provides switched ground signal to relay coil terminal #85.

4. Cold Start Solenoid [circled device #12] signal at Gray/White wire is provided by terminal #87 of the Cold-Start Relay.

5. Ground at relay/regulator/CDI panel is provided by bare steel spot left unpainted for forward mounting stud, and there is usually a brown ground wire under one of the bolts for the CDI unit or the fuel filter console. I usually run a braided ground strap from the fender stud [after removal of electrical panel and thorough cleaning] to the upper bolt for the CDI unit and over to the fuel filter console mounting nut -- at the aluminum mount, not the stamped steel mount.

http://forums.pelicanparts.com/uploa...1131144739.jpg

Warren, thanks for the the explanation, really helps with understanding how the system works.

Since I plugged the wire back into the cold start solnoid valve the engine seems to start faster, for about a day and half it starts from cold within 2 to 3 turns. Usually it took quite a few turns, I must have sped up the rebuild time for my starter trying to get the thing going from cold. I hope this keeps up.

One last question, when I grounded the cold start solnoid (isolated it first) and connected it to +12v, it made a very loud easily distinguishable click. This does not happan when I plugged it back into its +12 V supply wire, ie when i start the car, is the clicking sound a distinguishing sound that indicates that it the valve opened or does the valve open different amounts depending on the outside temperature or engine temperature.? A smaller amount less of a click, etc.

This would at least tell me if the thing is actually working or if its only my imagination.

Thanks again, your info has gone a long way for me.

Marc

Marc,

There is a ground wire from one of the two large bolts that attach the fuel filter console to the mounting bracket. The other end of the wire is at the ground stud on the body just forward (and sorta behind) of the fuel filter. It is possible that wire is missing or defective and the cold start solenoid isn’t at proper ground. (The mounting bracket is rubber mounted through the body panel with the other side of the three mounts in the fender area.)

Nothing in this system should measure 6.5V. That indicates to me that there is/are bad/poor/corroded connection(s) somewhere. Follow Warren’s good advice.

Best,
Grady

Marc,

The cold start solenoid is a binary device ... open or closed, and should be getting at least 10.0 Volts for proper operation!

As Grady indicated, a grounding problem may be the reason for you seeing only 6.5 Volts.

I suggest removing the entire electrical panel so the ground location on the inner fender and on the panel itself can be cleaned thoroughly with household cleansers: ZUD or Barkeeper's Friend ... mild oxalic acid cleaner that is very good at cleaning rust. Remove and clean the filter console and bracket. Install new ground strap to electrical panel and filter mount.

Test cold-start valve with engine 14-pin connector removed, so starter won't activate. If it is still an unacceptable Voltage, try cleaning both sets of 14-pin connectors with a toothbrush and 91% isopropyl alcohol -- air dryed. The 14-pin connector terminals are silver-plated brass ... so don't use a wire brush or abrasives.