Club G40 Forum

Technical => Electrical => Topic started by: Fifress on January 26, 2017, 04:10:55 pm

Title: In-car CO POT adjustment.
Post by: Fifress on January 26, 2017, 04:10:55 pm
I remember reading about how you could set up a potentiometer to adjust from the driver's seat. Can't find where I read it or if it was some thread on here.
I ordered the parts, 2k potentiometer dial, a 3.5 digit ohm displlay and a step down piece 12v to 5v for the 3.5 digit display.
The plan was to set it up, bypassing the CO pot to be able to adjust it using the display (dial has values on it, but the display looks nicer).
But I know the CO pot has a temp sensor also....

My question is this, to wire the potentiometer, I would have to tap into the 1 & 3 terminals, is this correct?
2 is for the IAT?, only one wire required?

The need to adjust Co is due to mods and tune
Title: Re: In-car CO POT adjustment.
Post by: hayesey on January 30, 2017, 05:18:38 pm
I have no idea why you are wanting to do this (just adjust the CO pot under the engine bay and then leave it alone).  What is the point of adjusting this in the car?

But anyway, the co-pot and temp sensor share a common earth so the temp sensor still needs this earth which is pin 2 if I remember correctly, the FAQ section has some wiring diagrams in it and what pin is what.
Title: Re: In-car CO POT adjustment.
Post by: Fifress on February 02, 2017, 10:57:50 am
I'm not 100% sure about my CO pot, sometimes it feels like its burning rich.
This way I could adjust it effortlessly whenever any modifications are done and keep an eye on its resistance values...

Just wondering if anyone had done this, i'm sure I read it somewhere (not with the digital display)
Title: Re: In-car CO POT adjustment.
Post by: G40supercharged on February 05, 2017, 09:10:00 pm
A resistance meter puts out a current and then measures the resulting voltage across the resistance. This means that you will not be able to measure the CO pot resistance with the car running. The signal from the resistance meter will affect the reading that the ECU sees (the ECU is already trying to do the same thing as the meter). I'm not sure what type of meter you have got (the Ebay ones are usually just voltmeters) but I would avoid connecting it with the engine running. If it is a resistance meter then it is fine to use with the engine off and the CO pot connector removed to check the CO pot reistance. It would be OK to put a digital voltage meter onto pin 1 of the CO pot to monitor the voltage signal that the ECU is seeing while the engine is running. 

I may be wrong, but I think that the CO trim pot signal is probably only used by the ECU around idle so you will not be able to compensate for major fuelling issues by adjusting it. However, to replace the CO pot with your external control you would need to cut the wire for pin 1 to the CO pot then connect the variable part of your potentiometer to the cut wire on the ECU side. Connect a fixed end of the potentiometer to earth such as terminal 3 of the CO pot. This will replace the internal part of the CO pot with your external potentiometer (the CO pot internal is actually wired up as a 2 terminal variable resistance rather than a 3 terminal pot).

Hope that makes sense!
Title: Re: In-car CO POT adjustment.
Post by: Fifress on February 14, 2017, 09:48:46 am
That is great information, didn't know about ohm reader sending out voltage!
I know its only around idle fuel trim...thought it would be usefull to see how it was doing.

Makes a lot of sense :)