Potentiometer in place of engine temp sender to ECU?

[CODE4]

My friend with a '79 280Z performed this:

He bought a Autometer A/F gauge (the LED one with lean, stoich, and rich indicators). Now, for most people knowing their mixture is not helpful if they do not know how to adjust it IF it is running too lean/rich. What he did was wire a Potentiometer in place of the coolant temp. sender in his water neck so he can manually adjust the coolant temp as far as the ECU is concerned. I thought it was a pretty cool idea and that I want to do the same with my DSM. Their are two coolant sender units threaded into the water neck on my 99 RS, one is for the gauge, the other is for the ECU.

Chiltons manual says the sender has the following resistances: @77 deg F -9-11 kilo Ohms, and @212 deg F 0.6-0.8 kilo Ohms. Grab a pot. covering those ranges and you can force the ECU to run the mixture lean, rich or anywhere in between =]

It is a cool mod in my opinion and when I perform it I will post pics.

[kjewer1]

Its not going to work The ECU in a DSM couldnt give a shit what your coolant temps are as far as the mixture goes, except to turn the "choke" on and off. No variability. Now, this will work if you put it on the baro pressure signal line, but let me advise against it. Its a big time hack mod. Works fine on some cars, but on a turbo DSM its not worth the chance, and there are better options out there.

If you do go against my advice and try this, please, for the love of God, dont use an O2 sensor voltage guage ("blinky guage" or otherwise). Datalog the damn car. Its very easy to induce knock with a SLIGHT change in baro pressure. The AF guages will not show you this. I could go on for hours why the voltage of the stock O2 sensor is damn near completely useless on DSMs, but I'll spare everyone. Maybe another novel for another day. So be safe, use a logger.

[95_GSX]

kevin you missed something in his post, he said that he had a 99 RS. so would it really be a loss???

[CODE4]

I have since read more and talked to some people that are knowledgeable with the DSM ECU, and have heard that modifying the resistance in place of the ECT is damn near useless except for cold start and WOT, even then I do not feel like fiddling with a knob to tune it. I have been referred to Apexi AFC if I want to mess around with mixtures.

Thank you though 95_GSX for the imput.

The reason why I think it works so well on my friends 280Z is because it has maybe a fraction as many sensors and such going to the ECU so it relies more on his than on DSMs.

[kjewer1]

Originally Posted by 95_GSX

kevin you missed something in his post, he said that he had a 99 RS. so would it really be a loss???

I guess I did miss that. I would have given the same repsonse, just with less detail. I'm not sure if the NT cars use a baro signal, in fact I beleive they are map sensor quiped, so they dont have all of the air metering sensors the turbo cars have. At any rate, an AFC type thing and logger are still the only "right" way to do it. The trick mentioned does work on some cars, and its almost always older cars. Its still risky and the gains are minimal though.