280Z EFI Temperature Sensor vs. Resistance Chart

[Captain Obvious]

Here's a chart that I whipped up showing the resistance vs. temperature function for the temperature sensors for the 280Z EFI system. There are a couple values in the manuals at a few temperatures, but this fills in the gaps. Note that Bosch used the same sensor curve for both the air and water temp sensors, so this chart applies to both water and air:

And for those of you who care about the theory, this chart was created using the Stienhart-Hart Equation with coefficients derived from data points in the manual. Stienhart-Hart:

I did the chart in Degrees F because that's what I use, but if anyone wants this in Degrees C, let me know.

[siteunseen]

175F would be around 300 Ohms for my CTS?  I would like to replace my adjustable knob potentiometer  with a more fixed style like the small screwdriver style that Fastwoman has.  Seems like she set her's at 257 for her car.  Maybe I should find a 0 to 500?

Thanks. 

Maybe it was 275?  I'll have to find that thread now.  

[Captain Obvious]

Maybe just a little above 300 Ohms at 175F. I'm seeing 325ish. Keep in mind though that there is a pretty wide tolerance band allowed for those sensors though.

The FSM says it should be between 290 and 360 Ohms at 176F and the center of that range is 325. Essentially they're saying "325 Ohms +/- 11%".

[EuroDat]

Thanks Captain. I can use that formula to map the temp on my spitronics when I get back and have some time to work on it. Like your attention to details.

[Captain Obvious]

Thanks Chas. Glad to help.

My 77 has been running great, but we has a couple days of colder weather and I was out driving in nighttime temps that were lower than anything the car has seen in a year maybe? In those colder temps the car still runs great, but I think it runs a little rich. With that in mind, I made that chart because I wanted to take a closer look at the readings from my temperature senders. I was thinking that maybe one of my senders (primarily the air temp) had drifted out of spec and was causing a little richer mixture.

Good news? The resistances from my senders look fine.
Bad news? The resistances from my senders look fine.

It seems like the whole system is working as intended, and it was either designed that way, or maybe over the years there has been some "gain drift" on the enrichment contribution from the ATS.

I know I'm chasing minutia and most owners would be more than satisfied with the current performance, but like you, I have to tinker. Can't help it.  

[Zed Head]

I have an adjustable FPR and an adjustable "tweak" on my coolant temperature sensor circuit and I find that I can't get a great air-fuel mix across the full range of activity.  I can tune it for part-throttle mid-range, clean-smelling exhaust at throttle lift, but I get a small miss at full throttle.  If I add fuel the full throttle response is great but I get a little bt of gassy smell cruising around town, coming to the lights.  The newer, like 80's to 90's EFI systems with O2 sensors and lower RPM fuel cut might solve that.  Back in the 70's when all cars stank, 90 percent had carbs, and people couldn't smell them through their cigarette smoke ruined noses anyway, these 280Z EFI systems were probably considered super-clean.  

Forgot to say that I also have non-spec. injectors so not comparable directly to the stock system.  But I've been trying to get the perfect tune forever.  Very difficult.

Edited September 11, 2016 by Zed Head