Cruise control mod for fixed throttle position

[Zerfstead]

Here is an idea I would like to try.
I drive a 2006 Scion xA with auto trans and a factory cruise control. When the cruise is engaged, the speed varies + and - 2 mph while going over a freeway overpass and makes (I think) too aggressive and output. I have been watching the TPS number on the ScanG II. I think I can add a switch to open the power to the servo motor in the cruise module and the result would fix the throttle position at the set value. Then I have a speed control that operates in the normal cruise mode and in throttle set mode.
On a long trip, set the cruise at 50mph and then switch to fixed mode to lock the throttle position. The SGII should show changes in grade and wind conditions.

[SVOboy]

That sounds like a good idea if you can do it! Cruise driving with load control,

[Zerfstead]

OK... I couldn't stand it. I added a switch to interrupt the voltage to the cruise control motor and it works just fine.
Here is what I've done.
Engage the cruise normally
Select the TPS (throttle position sensor) display on the Scangauge II.
I use the following guage displays.
MPG MPH
GPH TPS
When the speed and TPS stabilized, I toggled the new switch shutting off voltage to the cruise control drive motor. This locks the throttle position but allows me to disengage the cruise control or turn it off in the normal way.
Now the engine output is fixed. This allows me to evaluate my road conditions better. Or gives me a baseline for wind or grade or other variables. Since the TPS is now fixed I can change the Scanguage II TPS display to monitor another variable. WHAT A DEAL!

[GasSavers_Red]

Nice find, as soon as my allergies quiet down I'm going to see if something similar can be done on the Jeep

[rvanengen]

How much work do you think it would be to develop a CC to not only hold the throttle position, but to monitor speed within a set range (selectable by the driver)?

This would ensure that the car would not go above an absolute set speed (ticket avoidance), but also to not allow it to go below a set minimum speed (avoid being too much of a blockage to traffic flow).

[VetteOwner]

nice i just reinstalled cruise control on my chevette. i must say i love it so much. mine is prolly as old as the car yet still works. it has a hard time in the wind cuz ifa big gust comes along it slows the car real fast and the cruise control guns the engine to get it back up to speed...ive turned down the sensitivity and it seem sto help alot. i think while im driving when it lets off to slow up a bit it engine brakes too much(cruse control on a 4 speed manual) so it presses the throttle a bit and you get a slight lurch. but if its on the slightest hill it stays steady(going up or down). i dunno if anyones old enoguh here to remember installing these ort what. (its old enough to show how to hook up the vaccum servo to a vega...). it does work and all functions work according ly just fine tuning it seems to be a bit of a pain

[cfg83]

Zerfstead -

Thanks for the mod. I will research if I can apply the same to my car. Can you post a picture or two of where you spliced into the servoe motor power?

CarloSW2

[Zerfstead]

I removed the cruise control cover and the circuit board to see the drive motor. The drive motor is on one side and the magnetic engager is on the other side.

I drilled a 0.188 hole in the rear of the housing near the top and ran the (2) wires through and sealed the hole with 5 minute epoxy. If you use silicone (RTV), use the sensor safe type to eliminate the possibility of circuit board corrosion from the fumes.

Be sure to seal the firewall where the wires go through.

I cut the red wire to the motor and attached the red lead from the circuit board to an 18 gage red wire. This red wire is power and it is soldered to the toggle switch pole.
The wire from the motor is red and an 18 ga wire (I chose orange) is attached. This orange wire from the motor is soldered to the togle switch other pole. I used a double pole mini switch and used both contacts to increase the amp capacity of the switch. (not necessary)

I removed a switch blank, there are extra places for switches on the left side of the steering wheel... the panel that has the mirror controls, and drilled a hole, mounted the switch and snapped the switch blank back in place.
My logic is when the switch is in the down position (ON) the motor is connected normally. When the switch is in the up position (OPEN) the motor is frozen in place.

[VetteOwner]

better hope you can be somewhere where u can set it on level ground

[Zerfstead]

You are right about using a throttle lock in hilly areas. Here in Houston the only hills are the overpasses!
The question of normal cruise control vs throttle lock for improving FE may yet to be determined, but locking the TPS as a fixed value allows you to monitor other variables.