Tell me about the 1973 MFI cold enrichment system please....

[jsoderbe]

Hi Guys,

So I have some problems to get my cold enrichment system to work on my 1973 911 T Targa. I have looked through this site and I think I have gotten to understand the function; meaning the Termo Time Switch, the relay, the solenoid.

What I dont understand is how the voltage should be distributed. The problem is that I have exactly 0.00 V at the cold start solenoid and that is not enough to open it. I am guessing it should have 12 V, right?

I have measured all the wires at the relay. The yellow wire from the starter have power (measured to 10 V while cranking), and the other side of the termo time switch, meaning the red/black wire have slightly less, maybe 8 V while cranking. The white/red 12 V to the relay have constant 12 V. The ONLY wire that doesnt have power seems to be the grey/white to the solenoid!!

I have tried two different relays, both tested by using it as a horn relay. That might not test the relay fully, though....

The relay:



The relay panel:



So, anyone that have an idea where to look for problems?


Regards,

Johan

[HawgRyder]

A relay is just a device that removes the current rquirement of a set of points/switch/or sensor.
Think of the relay as a booster for current.
The trigger to the relay is what you are looking for...probably a temperature sensor in your case.
The sensor cannot handle the load of whatever is downstream...so they put a relay in to do the job.
The cold enrichment system is either time...or heat controlled.
If it is heat...look for one attached to the block or intakes.
If it is timed...it could be anywhere...and is probably a bi-metalic leaf type switch (the leaf bends as the coil around the leaf heats it up and contacts the point).
Hope this helps.
Bob

[Hellafunctional]

Is the thermostat/hose in good working order?

[jsoderbe]

Yes, if you mean the enrichment in the MFI pump? Thermostat is nice and clean, and the hose is new.

If you mean the thermo time switch I dont know....


Johan

[Porboynz]

Sounds like you are on the right track checking the relay (OK) and measuring the voltages around the thermo time switch. My understanding is that the thermo switch operates under about 14C so maybe its too warm where you are? This device must have a bi metallic operated contact in it that passes current <14C while you are cranking the engine. I presume the current passing through it also heats it so it shuts off after a few seconds cranking to avoid totally flooding the engine. Therefore you can test your relay and cold start solenoid by shorting the thermo switch contacts with a jumper and getting a helper to crank the engine while you measure voltages and or observe fuel squirting into the stacks. A common issue is the fuel filter assembly is rubber mounted so if you do not run an earth to it the solenoid never operates.

[jsoderbe]

Thanks, excellent advice! I did not know about the 14 degree celsius, so itis definately to warm in my garage (22 dregrees). I will pull it outide and measure. Also very helpful with the grounding, since I cant recall having a ground wire.

Regards,

Johan

[dicklague]

Years ago I installed a push button on my dash and used it to trigger the solenoid on top of the fuel filter. Now I have a manual cold start system. Works great.