1969 911S cold start enrichment problem

[lopena]

Hi guys:

My car is a bone-stock ‘69S with all original MFI components intact.

I’m currently chasing a very difficult cold start situation and have discovered that the fuel enrichment solenoid atop the fuel filter console is not spraying supplemental fuel into the air cleaner assembly, even during very chilly weather.

I took off the solenoid and it tested fine when connected to 12V.

I then hooked a test lamp to the gray/red wire going to the solenoid and discovered that no current flowed through the wire when I cranked the engine while it was stone cold (38 degrees F).

So, my problem is an electrical one, upstream of the solenoid…it is not being energized.

Where should I next look? The so-called thermo-time switch atop the engine breather *looks* okay but how do I test it to be sure?

Does the Slow Acting Relay have anything to do with the functioning of enrichment solenoid on the fuel filter?

Anything else I should look at?

As always, I appreciate all of your help!

Alan
N.J.

[Frankr]

Get rid of that crap and get a simple mechanical choke system. Works every time. You have total control.

[edmayo]

There is one fuse (three panel fuse block) two relays, one delay switch and two thermal switches. All can be tested with ohm meter and test light in order. I can try to create a list for you and overall explanation. Or you can do what Frank says, just have to be careful to not flood engine.

[gled49]

My experience with 69 MFI is that the 2 thermo switches that drive the 2 cold start systems have to low of temps at +10* & -10*. I would abandon the air filter “P” circuit and concentrate on the starting solenoid on the injection pump. Use the late model 60* thermo switch after isolating that system, and diagnose the circuit. On my outlaw car with a 69 injection pump I use a cold start button to energize the pumps cold start solenoid, it works all the time.

[lopena]

Thanks, everyone!

I agree that I can avoid all of these cold start problems by ditching the complicated (and sometimes dangerous) fuel enrichment solenoid but that’s not my aim here. I’m looking to get my car to function properly as it was originally designed. I consider this challenge to be fun and is a reason I bought an MFI car instead of a CIS.

That being said, I will continue to investigate why my solenoid is not getting power. The fuse is good, so it must be one of the relays, thermal switches or delay switch.

Ed: if you have the time, can you tell me how to test the thermal switches…we’ll start with those.

Once again, many thanks to all of you!

Alan

[lopena]

My experience with 69 MFI is that the 2 thermo switches that drive the 2 cold start systems have to low of temps at +10* & -10*. I would abandon the air filter “P” circuit and concentrate on the starting solenoid on the injection pump. Use the late model 60* thermo switch after isolating that system, and diagnose the circuit. On my outlaw car with a 69 injection pump I use a cold start button to energize the pumps cold start solenoid, it works all the time.

gled49:

I want to make sure I understand what you’re saying. Are you saying that the fuel enrichment solenoid atop the fuel console will not operate until the ambient temperature falls to 10 degrees Fahrenheit?

Alan

[Frankr]

There is one fuse (three panel fuse block) two relays, one delay switch and two thermal switches. All can be tested with ohm meter and test light in order. I can try to create a list for you and overall explanation. Or you can do what Frank says, just have to be careful to not flood engine.

I only did that once. It does require a gentle touch.

[gled49]

From memory: The yellow wires going to the thermo time switches are activated by the starter system. They ground thru the switch body. The other wire on the time switch grounds the P circuit or pump solenoid I think thru a relay to activate cold start by grounding the circuits. It’s called a time switch because after a few seconds of cranking, the thermo time switch heats up because of the now hot yellow wires and interrupts the ground connection of the other wire. If the car doesn’t start, you need to let the car sit so the time switch will cool and re-connect. If my cars don’t start on the first attempt, I just keep cranking till it starts. Obviously the system is very sensitive to heat. If you still have the 10* time switches your done maybe before you even start. All CIS cars have the 60* thermo time switches which is all that’s available now. Now you have to confirm that the rest the rest of the system works, relays, wiring etc. I’m not around my 69 specific wiring diagrams to help any further. You should test cold start solenoid to see if it works with 12 volts. It’s the upper of the 2 solenoids. Again I would abandon the P circuit in favor of cold start solenoid.

[lopena]

gled49:

I’m trying to understand your last post. Please forgive my lack of in-depth knowledge and experience.

Questions:
1) what does “10*” mean? Ten degrees Celsius? Ten degrees Fahrenheit?
2) what is the “P circuit”? What is the “pump solenoid”? Is that the solenoid atop the fuel console?
3) the “cold start solenoid” that you refer to is on the MFI pump…correct?

Many thanks for your patience!
Alan

[gled49]

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