And I assume this parallel rheostat would go to ground somewhere between the ECU and the series trim pot? Doing so would make the lean adjustment over ride the enrichment adjustment.

Now, on to the ECT trim. Would I use the same size pot for this? And is it safe to assume that increasing the resistance in a series set up would show the ECU a cooler temp?

Thanks again for your help here.

Sam

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With the additional pot to lean the IAT (simulate higher intake air temp) you will need to place one lead to ground and the other to the sensor wire, ahead of your other pot, so that it doesn't have that bias in it. Nothing bad would happen if you did, but you may get confusing results.

The impedance of this additional pot will have to be quite high, because you will want to be able to turn it 'off' so it's not influencing the other pot/sensor combo. 'Off' means set to it's highest resistance since there isn't really an off. Looking at the table for the GM sensors, 25K ohms = 0 degrees F. Assuming you were above 0, a 25k pot would essentially be off since it would be higher resistance than your actual temperature sensor, so the current would flow through the sensor, not the pot. With a 25K pot wired this way, your IAT would never indicate lower than 0 degrees. BTW, -40F is 100,700 Ohms.

Handy reference table:



I think you could easily get away with a 10k to 20k pot for that depending on how cold you get. I imagine underhood air does not stay at zero for long.

This is how it would work - as you turn the knob to lower the resistance, at a certain point current will stop flowing through the sensor to ground, and start flowing through your pot to ground. You have the ability then to reduce the resistance to 0 as you continue turning the pot, as it will eventually go to no resistance at all. That would simulate a very high air temperature, over 200 degrees. I'm not sure how high a temperature MS looks at but that should be high enough for your purposes.

Then, for the second part of your question, a 5k pot wired in series with your CLT sensor ought to do the trick. Looking at the table, it can fool the MS into thinking the water temp is about 65F or so at max which should be plenty cool for a good WUE shot.

Here is an extremely crude Paint drawing of the setup:



You will be like the Wizard of Oz behind the curtain, turning all these knobs Somebody smarter than me could figure a way to richen/lean with one knob. I'm looking into it...

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It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

You could richen/lean with one pot AND a switch to go between series and parallel wiring... Two pots is easier to think about on the fly, though.

Lou

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Home of Slant6-powered fun machines since 1988

Thanks again gunpilot. This kind of info and discussion. moves my "stupid border" just a little. That's where the smart stops and the stupid starts.

The 5k pot I have wired in there now changes the temp reading by about 40 degrees. When it is 81, the laptop display shows 41. That is enough to make it about 1.5 points richer.

I have done a lot of thinking about the MS EFI system, and have figured out where my real ignorance lies. I should start a thread about that, and hopefully move my "stupid border" a little again.

Sam

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The coolant & air temp sensors are NTC (neg temp coefficient)- as temps goes up, resistance goes down. One wire from sensor is grounded, the other is a 5V reference thru a dropping resistor & is monitored by the computer. So at very cold temps (hi resistance) voltage is close to 5V. As things heat up, resis goes down, & the 5V is pulled down closer to 0V. Many ECT read about .4 to .6V at normal operating temp.

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63 Valiant Wagon
225 - 4 bbl

That is a good general information. Thanks. My"stupid border" has been moved further.

Sam

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Just asking, as I am not sure...
How would this work on the water temp sensor, compared to the iat sensor?

I believe the water temp sensor has a bigger effect on things than the intake air one?

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I have no idea what I am talking about.

With the coolant sensor (CLT) you can trigger the warmup enrichment, which you have settings for in the tuning software. So you can turn the temperature back to a level where you have told the software what percent above the table you want enrichment, or, actually, leaning, if that's how it's set.

With the intake air, you are affecting the settings that are already coded in the firmware. With the CLT, you are able to set the level via the tuning software. I wouldn't see using it other than temporarily, like on startup.

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It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

This thread has collected enough data and ideas to print out and archive.

I have been in over my head with house renovation the last couple of weeks, so have not finished up with a nice panel, and all four pots: 2@ IAT and ECT.

I'm on my lunch break now, so have a few moments to browse the Forum here.

Sam

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I tried a 25k ohm pot to fool the IAT and send less fuel. I think it may be too high value. The top half of the rotation does very little, and then about half way down it starts to crash lean, and the adjust-ability is too coarse. It is hard to get it dialed in. ONe thing I did discover is that this particular engine does not like to go leaner than 16:1 on the road. You can feel a noticeable drop off in smoothness and power. I may look for a 15K. Radio shack does not stock this item in their stores. I will have to look elsewhere.

Sam

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