69E MFI Electrical Issues

[BRC911]

Hi all.
I am trying to get some issues worked out on my 69 911E MFI. I am using the factory SL 33 wiring diagram.

First, were is the "Time Limit Switch" (TLS) and what does it look like. I checked everything in the engine bay and I cannot match it with the diagram. The yellow power wire from the starter that goes through the "Thermo Temp Switches" (TTS) and to the "TLS" has continuity with ground even with the "TTS" disconnected. Is the "TLS bad?

Second, how does the "Thermo Temp Switch "TTS" work? Does it let the yellow starter power pass to the red & red/blk wires? Is there continuity between the switch posts and ground? Does the Power wire effect the switching action or works entirely on temp?

This car has a "Slow Action Relay" on it. I cannot find it on the wiring diagram. It has only three wires to it. I thought it was the "TLS" but the wires do not match. What is the purpose of this relay?

I tested the "Micro Switch", "Starting Solenoid" and the two "Shut-off Solenoids" and they all work by testing only. I get no power/action from any of three solenoids or micro switch.

I have to guess that my "TLS" is bad along with both "TTS".

The car runs fine but of coarse it is hard to start. Any help would be greatly appreciated.

Thanks in advance, Jim

[Flieger]

There is a temperature sensor in the crankcase breather cover that sends a signal to the solenoid on the fuel filter console that tells the engine to squirt fuel into the cold start injection nozzles if the engine is cold. I think even the 69E has this. The 69E pump is unique in that it has two solenoids on the MFI pump rear cover. One is the starting solenoid which pushes the main rack full rich for starting. If there are no cold start nozzles in the plenum or stacks, then this is your cold start system.

The other solenoid is the shutoff solenoid. This one pushes the rack full closed, past idle setting. This allows the engine to loose revs faster for better throttle response and also stops fuel from going into the engine with closed throttle, which would cause backfiring on the overrun. The shutoff solenoid is activated by a 12V signal from the microswitch; activated when the throttle is closed. The microswitch only gets a 12V signal to switch when the RPM transducer on the engine bay electrical panel says that the engine is above 1500rpm. The RPM transducer hass a 12V DC input power wire, a signal wire from the distributor points (12V DC square wave), a ground wire, and has a 12V DC output wire to the microswitch.

A common problem is bad solder joints or broken wire legs on transistors in these old RPM transducers. If the RPM transducer is bad, or the car is off, there will be no signal to the microswitch so the microswitch cannot do anything, and neither can the solenoid. There will be no continuity across the switch if the microswitch is open (if the throttle lever is not touching the switch).

I think the terminology you have on your diagram is different from the colloquial terms used here on the board. Maybe my explaination can help clarify something.

[BRC911]

Thanks for the response.
I will test the Transducer for outgoing 12V when running.

There are two temp sending units in the crank case breather cover. Both have Starter cranking 12v. When cold, is there power to the red & red/ blk wire that activate the relays? The red/black wire goes to the "Time Limit Switch" first then to the relay. I cannot find this switch to test it.

What about the "slow action relay" What is it and what does it do?

Thanks again.
Jim

[Flieger]

I am not familiar with those terms, one or two are probably something I have called by another name.

The transducer will only send 12V when the engine is above 1500rpm.

[BRC911]

Thanks again!!
I will do a thorough test of these key components again. The relay board there is quite different from mine. I will post a picture tomorrow. The 69E board does not have the square multi pin connectors.

Cheers, Jim

[Flieger]

If you can take some photos and point to the temperature probes and solenoids and relays you can see on the engine and are wondering about, that would be good. We could then link them to your diagram.

I am waiting for Grady Clay to provide the definitave answer here. He could set you straight in two minutes.

[BRC911]

OK.
So after another day of testing and replacing parts I got the entire MFI system to work. I had to replace both "Thermo temp Switches", "Micro Switch" and the "RPM Transducer".
I found that the Thermo switches once activated by the 12V power that they are grounded and that activated the relays. I initially thought the 12v power went through the switches.
The "Time Limit Switch" and the "Slow Acting Relay" are the same unit.

A couple of pictures of the Relay Board and the two Thermo Temp Switches


Thank you so much for all the help.
Jim

[Flieger]

Glad your car is up and running again.