Hi all

I was doing some reading and found that a lot of folks have been adding a potentiometer in line with the temp sensor so the efi doesnt keep leaning out the mixture according to temperature.

I was reading that the efi runs the most stable with the car at 175 which means keeping the resistor reading at around 300 ohms.  If I were to add that and set the 1k resistor to about half, wouldn't that mean it is constantly richening the sensor's reading by 500 ohms?  What I'm getting at is my car will run at around 185 idling but 170 on the highway.  If I'm looking for the engine to be reading a constant 175, the potentiometer trick would just tell the computer it is constantly running cooler regardless of rpm and wouldn't really do what I'm looking for, correct?

The best writeup I found at AtlanticZ here.

 

Any ideas?

-chase

Edited March 31, 20231 yr by chaseincats
Added additional info

My '77 ran horribly up until about 2,500 RPM. I jerked and bucked between running good and bad, popped through the throttle blade too but above that certain RPM range it ran great. I read and read until I was overwhelmed by possibilities of what it could be. I decided to take a chance and went to Radio Shack and got the volume knob for a stereo. $5 dollars and some speaker wire I have plenty of now I have the potentiometer in the passenger's floor board so I can fine tune while driving.

From what I gathered in all that reading was the ECU would get out of spec over time and the pot addition brought it back to life. It worked great for me and now I have a new something to distract me while driving. 

Page 3 is the good stuff out of the whole thread...

Mine has had a potentiometer for 20 years or so.  I was organizing the garage today and I came across a hard copy of the instructions on how to install and tune it.  I am pretty sure I printed it on a dot matrix printer.  🙂

Mine sits right on top of the intake and I haven't had to adjust it since first dialing it in.

4 minutes ago, Jeff G 78 said:

Mine has had a potentiometer for 20 years or so.  I was organizing the garage today and I came across a hard copy of the instructions on how to install and tune it.  I am pretty sure I printed it on a dot matrix printer.  🙂

Mine sits right on top of the intake and I haven't had to adjust it since first dialing it in.

Could you take a couple pictures of the installation instructions?

Here's what I went by. It's really easy and even easier to remove if it doesn't help.

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html 

This can only be used to richen the mixture not lean it out though since it’s adding resistance to the temp sensor, correct?

If it's already lean as mine was just consider without the pot switch you're at -10????? whatever. So I add the potentiometer and can make it 0 or dial it all the way back and lean it out to -10. Go full the other way and I can fatten it up so much it barely idles.

So to quote some politician it's all relative to what it is today as to what it can be tomorrow.

 

Trying to make sense of the dial up more fuel thinking.

Mine is about half way between 0 and 10 on the volume knob. That's back to normal running on my 280. Resistance is trying to cut my dog's toenails.

 

Why is this better than messing with the afm out of curiosity?

18 minutes ago, chaseincats said:

Why is this better than messing with the afm out of curiosity?

It's easy to f#@k up an AFM.

You beat me to the answer Steve.

Much easier to try the volume knob.

Better to try an unmolested AFM than mess with the current one.

I messed with mine when tuning it with an air fuel gauge but marked all the original positions so I could reset it when I try this...