1969 911S cold start enrichment problem

[lopena]

You might need a trained mechanic. I’ve been a mechanic 50 years. It’s complicated, I can’t simplify any more.

Nope…I’m going to fix this on my own.

Yes, the overall MFI system is complicated, but my particular issue isn’t rocket surgery. The little solenoid on top of the fuel console isn’t getting 12V in cold conditions. I’m going to get a wiring diagram and work my way upstream, one electrical component at a time, until I find the problem. Then I’ll report back to this Forum what I’ve found and how I fixed it so that others with the same problem in the future can benefit.

Wish me luck.

Alan
N.J.

[edmayo]

I'll try to help guide you on this as much as I can over the internet.

[Frankr]

You might need a trained mechanic. I’ve been a mechanic 50 years. It’s complicated, I can’t simplify any more.

The designer's prior project was the heater/fresh air/fan control panel.

[lopena]

I'll try to help guide you on this as much as I can over the internet.

Thanks, Ed…I deeply appreciate your help.

So, let’s talk about the thermo-time switch atop the engine breather. I believe that the one closer to the rear of the car controls the fuel console solenoid…correct?

How do I test the functionality of this switch?

[edmayo]

First you need a basic understanding of the system, it is the most complicated system they used, it got better and simpler with the 72-73 type which was the best. In 69 they used both pump enrichment and fuel spray for cold starts, but at different temperature ranges. Later systems used only fuel spray for low temp starts. Your system uses a solenoid on the pump to richen the rack, and for colder starts, a fuel spray device in the aircleaner. I don't start with the thermal switches, for one there were never any specs published for them that I've ever seen. I've established my own based on experience, but also have found they are rarely the problem. So I start with more basic tests. Go to the rear fuse box, turn on ignition, and see if you have power at both power wires, and check all fuses for continuity. Remove both round relays from the fuse panel and go to the front relay board and in turn plug in each relay to the horn circuit and see horn works with each one. While the relays are out use a test light to see if term. 30 of both relay sockets are getting power. With an ohm meter test both thermal switches to see if there is a ground circuit from the switch brass base to the engine case. With a test light test that the yellow wire to each thermal switch gets power when the starter is engaged. Run these basic tests and lets see what you have.

[72targa]

^^^^ Ed, your knowledge and ability to explain continue to amaze me. You are a great teacher!

[lopena]

Ed:

You’re a national treasure.

A good number of MFI cars are still on the road thanks to your expertise and willingness to share it.

As for the above tests, I will tackle those in the days ahead, but we’re in for a spate of nasty weather so it’ll probably take me 3 or 4 days to complete.

I’ll be in touch…

With much appreciation,
Alan
N.J.

[garycox]

Count this as another post in praise of Ed Mayo. He has helped me countless times, here and elsewhere, for over a decade we are all very fortunate to have him here. Thanks for all you do.

I also have a 1969 911S, spent a lot of time trying to understand and sort the MFI and cold start, hours of internet reading. Still, in a few short posts here I feel like I gained some knowledge and more understanding

Thanks to all that contribute

[lopena]

Okay, guys, I’m back.

To recap: I’m trying to cure a cold-start problem and I discovered that the fuel-squirting solenoid atop the fuel console wasn’t getting 12V when it was cold out (35 degrees F).

I performed the following tests, as prescribed by Dr. Mayo:

I checked that the little fuse box in the engine bay was getting 12V - check.
I examined the fuses and their connections for continuity - check.
I pulled the two round relays on the electrical panel and tested each one using the horn circuit - check.
I confirmed that the “30” terminals where those two relays plug in were getting 12V - check.
I confirmed that both thermo-time switches on the engine breather were getting 12V during cranking - check.

As an additional test, I applied 12V directly to the squirter solenoid while the fuel pump was running and gasoline did flow out of the line to the air cleaner.

So, I’m still mystified why the squirter solenoid isn’t getting 12V during cold weather. The “bad” news is that it’s very mild out now (unusual for New Jersey in January) so further testing may be futile until colder weather blows in.

Ed: is there anything else I should be looking at or testing?

Thanks for all of your help, as always!

Alan
N.J.

[edmayo]

You're not supposed to get air cleaner spray until 14 degrees. What you seem to be missing is energizing the enrichment solenoid (top solenoid on the pump) which IS to be energized on every start up to 114 degree crankcase temperature, determined by one of those thermal switches. Pull the wire off the top solenoid (should be gray) hook a test light to it and crank engine, if it doesn't light for a couple seconds it isn't getting a signal. That's at least part of the problem. It is controlled by a relay and time limit switch, one of the relays you've already tested. Temporarily hook a jumper from a hot fuse to the terminal on top solenoid and see if it clicks. Don't have time now, will write more later.