Switch for lower Rev Limit
 

Is there a choice somewhere to use a switch (like TableSwitch) to choose a lower than standard Rev Limit?

I have not seen one, but sometimes I miss things.

MS3 Basic (Extra)

yep, aidan I think has it implemented on his car. "pit lane speed limiter" or something

Found This:

https://www.miataturbo.net/megasquir...et-mode-88019/

This is how I solved the "problem".

I don't have EGT, but EGT out of range can trigger CEL and therefore Limp Mode.

Using ADC13 (spare) with a voltage divider and switch to short part of it to ground, I can simulate a 0-1000 degree (0-5V) EGT. With say, 500 ohms and 2000 ohms, with the switch open, the signal will be 1V or 200 degrees. I have a limit set for EGT below 100 degrees. So when switch is closed, shorting the 500 ohms, EGT will be "0" degrees (2000 ohms across sensor 5V to Ground). With switch open, EGT goes to "200" degrees, and CEL turns on and Limp Mode is engaged.

I have EGT alarm set up to change nothing (don't add fuel), so car runs normally within Limp settings, but has no EBC, a low Rev Limit, and a low Boost Limit.

I have proven that the out of range EGT does indeed trigger Limp Mode.

I may use higher resistor values. I plan to match TPS full range resistance as a minimum.

However, I have one remaining issue. with 1.4.1 FW on MS3, Limp Mode is not operating correctly. EBC is indeed set to zero, and the Rev Limit works correctly; but, no Boost Cut. I have put in a question to MSEXTRA, but I kind of doubt they will do much with FW<1.5.

Moderators: Please change title to: "Valet Switch for Limp Mode"

pics of settings for my simulation (Open Input sits at about 900 degrees).


https://cimg3.ibsrv.net/gimg/www.mia...4ac5d7db9f.png

https://cimg4.ibsrv.net/gimg/www.mia...b0c2ba916e.png

https://cimg5.ibsrv.net/gimg/www.mia...c73085c7f1.png

Good stuff man, thanks for posting. It's amazing how any settings and options MS3 has to play with. It's pretty rare anyone else drives my car, but I've definitely flashed a no boost tune when dropping it off for tires before. Never know what 18 year old is going to want to take a joyride having never driven anything rwd or over 100hp. If that's a normal situation for you I could definitely see this being useful.

Thx. Well, I have the 3-pos switch that I wanted to use. I can still run lower boost cut with Table-switch, but it seems weird to have to give (2) inputs to accomplish all the things for "NONEOFIT": Boost Cut and Rev Limit reduction. This hunt was for a way to change rev limit and this will accomplish it.

This will give me None, Some, and All; without an actual tune change.

I don't often give car to strangers, but I will soon have grandchildren that will be old enough to drive, and I will likely let them.

I'm hoping I missed some strange setting that is preventing the boost limit to be changed in Limp Mode. I mean, really, any limp mode should include boost limit.

Raising this with a question for the EE's:

So I want to cheat ADC 13 to trigger limp mode via EGT as above.

Can I use a voltage divider from 12 V and a switch to supply it with either 0V or 2.5 V? Or do I need to tap into Sensor 5V instead of the easily available 12V? 12V would be from pin 1 of MS3X DB37.

Thinking 1/4 Watt resistors, Ground : 2500 Ohms : 10k Ohms : 12V.

Calling @Joe Perez

Sure. Just use a resistor divider. Vout = (Vin × R2) / (R1 + R2) where R2 is the lower resistor (connected to ground) and R1 is the upper resistor connected the 12V. Run the switch from vout to ground. A better solution is to use a 2.5Vzener in place of R2, which you can get from ebay. It will eliminate sensitivity to variations in the 12V.

With 1/4 resistors at say 12V nominal, you will want to keep it under 20mA (0.25W / 12V). I would design for less than 10mA for derating. Current through a resistor is calculated by V = IR, or in this case, V/I = R

As for the OP, what about table switching timing, with timing pulled at the high end?

Couple more details for the divider...

calculate the high side resistance (as well as the current limit resistance for a zener) with the voltage drop and target current.

(12V - 2.5V)/0.010A = 950 ohms
use 1Kohm (R1)
recalculate current
(12V -2.5V)/1000ohms = 0.0095A
now R2
(2.5V - 0V)/0.0095A = 263ohms

you can probably get away with less current, say ~2.5mA
so R1 = 4 x 1000ohms or 4kohms
R2 = 4 x 263ohms = 1.052kohms

your original values will give you 2.4V at 12V with ~1mA of current. Those values may work for you, but at that current level I would decouple it with a 0.1uF capacitor in parallel with R2

I like the Zener approach. Even though I don't need a very exact value, it does turn the unregulated 12V into a regulated 2.5.

Thanks, Ted75zcar.