Electrical Guru Question

[content22207_2]

For my automatic transmission carb conversions I previously have made a bracket that holds the auto trans full throttle kickdown microswitch. I just assumed that the microswitch must ground a signal from the auto trans governor at full throttle, much like the kickdown lever on a hydraulic valve body transmission.

Looking at the wiring diagram, it appears I may have been wrong. Full throttle kickdown microswitch grounds a signal from the Lambda ECU, but I see no connection between the Lambda ECU and the auto trans governor.

Question: Is the Lambda ECU indeed completely divorced from the auto trans governor?

These little microswitch brackets are a PITA to make, so I'd much rather not make them if they are redundant for non K-Jetters.

Bill Robertson
#5939

[kings1527]

Paging Dave McKeen

[content22207_2]

Wiring diagram in the sometimes error prone Workshop Manual shows no connection. I need to know if there's a connection not shown.

Bill Robertson
#5939

[Elvis]

Lambda has nothing to do with the automatic

[content22207_2]

Thanks for the confirmation. It will save me a lot of time and effort not to make those brackets.

Bill Robertson
#5939

[Jonathan]

There are two throttle spool microswitches on the automatic.

One with the flap and one without.

The lower one, with the flap, is common on both autos and manuals, and is the fuel enrichment related microswitch. It is the one related to the Lambda ECU. It has a LG (green) only wire on it with the black ground.

The upper microswitch, on auto trans cars only, has no flap, and is the kickdown microswitch. This is the one related to the shift computer governor and the one which will tell yours auto trans to go down a gear when you have it floored. The wiring for this switch is LGG (which means green and light green and to see the subtle difference, look for the wire with more than one shade of green) plus a black ground wire. It is limited though to the speed you're going and at what RPM the engine is at. It is the "passing" gear more or less, when you pull out and hammer it to go around someone.

You can swap the connectors for either of the two switches. In the event one of the two fails, or stays closed, you likely want the good one to be on the kickdown (trans computer) related one. You can live without the fuel enrichment one at all, considering how rarely most drivers floor it. If the fuel enrichment one is stuck closed, it will bypass the lambda ECU portion. If the kickdown one is stuck closed, it will keep the trans in the lower gear for longer. You can also live without either and completely unplug them if you can't confirm they work.

[content22207_2]

Apparently I'll need to make those brackets after all.

I did not realize there were two microswitches.

I've never had an automatic -- just 5 speeds. Those only have one microswitch. I use one of those to test fit the brackets (previously mounted to the outside of the bracket, since moved to the inside -- that's what takes so long to cut, but it is a more polished installation):

40728 40729

I stand corrected.

And will start cutting brackets this afternoon.

Bill Robertson
#5939

[content22207_2]

Bracket with the switch mounted on the inside:

40730

Bill Robertson
#5939

[Jonathan]

Here's a picture of a few of those things on the automatic.

40731

You can partially see the two microswitches stacked on top of each other there. And the double white electrical connectors above the W pipe for each of those switches.

Bill, you may already be aware, or it may not factor in to what you are doing with your carb kits, but there is also a secondary extension of the throttle cable that continues on after snaking around the spool and goes down the passenger side of the transmission to meet up with the bell crank contraption mounted on the side of the shift computer set-up. It also affects how the auto trans changes gears. Not specifically fuel related, but just thought I'd mention it.

[Ron]

You can swap the connectors for either of the two switches. In the event one of the two fails, or stays closed, you likely want the good one to be on the kickdown (trans computer) related one. You can live without the fuel enrichment one at all, considering how rarely most drivers floor it. If the fuel enrichment one is stuck closed, it will bypass the lambda ECU portion. If the kickdown one is stuck closed, it will keep the trans in the lower gear for longer. You can also live without either and completely unplug them if you can't confirm they work.$.02

FWIW- The Throttle Enrichment Micro Switch is tied to the Thermal Throttle Enrichment 'Sensor'. Either can ground the circuit, so it wouldn't be a good idea to use it for the transmission kickdown....

[content22207_2]

Bill, you may already be aware, or it may not factor in to what you are doing with your carb kits, but there is also a secondary extension of the throttle cable that continues on after snaking around the spool and goes down the passenger side of the transmission to meet up with the bell crank contraption mounted on the side of the shift computer set-up. It also affects how the auto trans changes gears. Not specifically fuel related, but just thought I'd mention it.

I've got provision for that second cable. I call it the "shift point cable". As the throttle cable pulls towards the front of the car, that cable pulls towards the rear. I've been told by adjusting the cable you can adjust how many RPM's before the transmission shifts.

There also is a 3/16" vacuum hose to a modulator valve. Factory hose has a fantastically large OD, but ID is 3/16".

Bill Robertson
#5939

[Jonathan]

$.02

FWIW- The Throttle Enrichment Micro Switch is tied to the Thermal Throttle Enrichment 'Sensor'. Either can ground the circuit, so it wouldn't be a good idea to use it for the transmission kickdown....

Ooooh, good point, Ron. Thanks for mentioning.

I'll edit my suggestion to: if you can't confirm the switch is working, then unplug it :)

[Jonathan]

$.02

FWIW- The Throttle Enrichment Micro Switch is tied to the Thermal Throttle Enrichment 'Sensor'. Either can ground the circuit, so it wouldn't be a good idea to use it for the transmission kickdown....

Ummm, let me make one more edit to that thought...

Ron, I got thinking about this more and maybe I wasn't very clear on what I meant by interchanging the microswitches.


I had meant to interchange the two switches if you know you have one bad one (and one good one) but not the harness side of the wiring. The microswitches are the same, except one comes with the "flap" and one doesn't. All that flap does is give the nub on the end of the throttle spool something to bump into and then the backside of the flap pushes on the little plunger end that goes in and out and opens or closes the switch and circuit.

Leaving the switches in place, if you knew your kickdown one (the one on the top) was bad and the lower one was good, you would disconnect both switches and then reconnect only the good enrichment switch with the kickdown harness side. Then the kickdown circuit (the more important one) gets a good signal and the enrichment circuit does without.

As an analogy, it would be like know you have a bad driver's side window switch and a good passenger side window switch and then changing which harness connector underneath goes to the good switch, i.e. so the good switch lets you operate the driver's window and the passenger window does without?

Comprende?

[content22207_2]

It's been quite a few years since I've seen an automatic, but they are starting to come back to me now: Doesn't the automatic microswitch have a very wide paddle compared to a 5 speed? They work interchangeably with my brackets, but I seem to remember the automatic microswitch paddle being much wider.

I guess DMC did it that way because only one microswitch could be triggered by the throttle spool.

Bill Robertson
#5939

[DMCMW Dave]

It's been quite a few years since I've seen an automatic, but they are starting to come back to me now: Doesn't the automatic microswitch have a very wide paddle compared to a 5 speed? They work interchangeably with my brackets, but I seem to remember the automatic microswitch paddle being much wider.

I guess DMC did it that way because only one microswitch could be triggered by the throttle spool.

Bill Robertson
#5939

The throttle enrichment switch has the wide paddle, and an automatic simply adds a second switch for the trans kickdown. The switches are identical and the paddle can be moved. You obviously don't need the throttle enrichment switch for the conversion but the trans kickdown would be nice to have.

[content22207_2]

One step ahead of you: I've been providing this bracket for automatic conversions in the past:

40740

In place on a carb (microswitch is mounted to the backside -- you can see its wires sticking out):

40741

I was just trying to save myself some fabrication time and energy (bracket is custom cut and drilled). Obviously I will continue to make them.

Bill Robertson
#5939

[Ron]

Ummm, let me make one more edit to that thought...

Ron, I got thinking about this more and maybe I wasn't very clear on what I meant by interchanging the microswitches.


I had meant to interchange the two switches if you know you have one bad one (and one good one) but not the harness side of the wiring. The microswitches are the same, except one comes with the "flap" and one doesn't. All that flap does is give the nub on the end of the throttle spool something to bump into and then the backside of the flap pushes on the little plunger end that goes in and out and opens or closes the switch and circuit.

Leaving the switches in place, if you knew your kickdown one (the one on the top) was bad and the lower one was good, you would disconnect both switches and then reconnect only the good enrichment switch with the kickdown harness side. Then the kickdown circuit (the more important one) gets a good signal and the enrichment circuit does without.

As an analogy, it would be like know you have a bad driver's side window switch and a good passenger side window switch and then changing which harness connector underneath goes to the good switch, i.e. so the good switch lets you operate the driver's window and the passenger window does without?

Comprende?Si. I've been into several of them ;-)
I see what you meant...if you abandon the bad one rather than "swap", were are 100% together(ground is ground and a switch is a switch ;-)..I read too much into it.