4th Gear Dyno switch - 3rd Gen '06 5.9 CTD

[noplugs]

So, lets say you have an 3rd Gen 5.9 CTD with an Automatic transmission and you want to dyno it. Well, you can but you have one problem. When you are on the dyno in 4th gear with the Torque Converter locked and you floor the skinny pedal,  the transmission downshifts to 3rd gear and skews your numbers. What that leaves you with is having to gauge how far down you have to hold the skinny to get the best numbers but not too far that it downshifts. Now, try to get consistent numbers doing THAT.

First, Im going to put up my warning. DO THIS MOD AT YOUR OWN RISK(This modification allows you manual control of your transmission while it is still being controlled by the ECM. Modifications can void your warranty and we make no guarantees or take any responsibility for any damage that may result.)

First, this modification is EXTREMELY simple. It is actually based on Cumminalongs Mystery Switch so I will be quite honest and tell you to go read that one and then come back here. There was no need to reinvent the mod so I'm just going to reference his (after all he gave me the idea).


Did you read it? Ok, : (You'll note I plagiarized a few diagrams from Cumminalong)

Parts list
Momentary lever switch
Wire
33 ohm resistor
Electrical tape

Like the  "Mystery Switch" what we will want to do for the 4th gear lock is ground Pin #6 "3-4 Solenoid Control" using a switch and a 33 ohm resistor.


Service Manual Diagram (Note we are using pin#6 for this modification)


Connector (closeup of the connector)


Here are 3rd/4th Gear (red) and Torque Converter (black) Taps. Once this is done, seal the connections with electrical tape.



Since I was doing both of these modifications, I decided to use two different types of switches. The push button for the Torque Converter lockup and the lever switch for the 4th gear lock. This way I can activate them by feel and not be confused as to which one does what.

Switches mounted in the cubby hole



Switch Mount Location. Here is the finished location out of the way so they cant accidentally be activated.



So how does this 4th gear lockup work. Essentially, by grounding this wire, you are activating the 4th gear solenoid and keeping the transmission is 4th gear. The ECM downshifts to 3rd gear by deactivating the solenoid so this mod bypasses that control and lets the current continue to flow.

To use this mod once you are on the dyno, get the truck up to 4th gear normally. Activate the switch and then let the engine/drivetrain slow down to 1500-1700 RPM. Once you are at the correct speed for a dyno run, keep holding the switch down WHILE you accelerate. Since the truck will not downshift, you can hold the skinny pedal to the floor and finish the run.

Now, we have not had a chance to test this on the dyno YET but in road testing it does keep the transmission from downshifting.  As soon as we can do a dyno run, we wil let you know what our final our results are.

As a side note, in testing, it left a nice smoke filled 4 lane highway...


(Credit goes to Cumminalong for putting this idea in my head and for some of the diagrams.)

[Cumminalong]

You da man, Rob!

I'll certainly be adding another switch in the cab now.