280z Air Intake Temp Sensor Readings

[NC280z]

Good evening everyone,

 

     I've been tracking down an issue with my Z running slightly lean, and found that the intake air temp sensor is reading around 750 ohms less than it should for any given temp, which means it reads around 18~20 degrees hotter than the actual air temp. I know that sensors are prone to drifting with age, and was curious if anyone here has found replacements for these sensors or if everyone just resorts to using a potentiometer instead. I had the AFM rebuilt a few years back, but it looks like they only replace the carbon trace pad and not the AIT sensor. I appreciate any help you all can offer.

 

 

 

 

 

 

[datzenmike]

Replace the air temp sensor? Nissan 22631-N1400


You can also adjust the air fuel ratio with the AFM...

 

 

[NC280z]

Thanks for the part number! I've already adjusted the AFM spring tension, but it won't compensate for the temperature difference in a consistent manner. Basically, adjusting the spring tension made it quite rich at idle, and between 15~16.5 AFR under light to medium acceleration. If I adjust the spring tension any more it'll be terrible at idle. I'll need to replace the sensor or chuck a resistor in there to make up for the drift. Thanks again for the part number!

[datzenmike]

At idle the throttle is closed and the AFM doesn't measure the air coming in. Isn't the idle governed by the throttle position switch?

[NC280z]

The AFM does measure air coming in at idle, but only the small amount that doesn't go through the passage for the Idle Bypass in the AFM. The throttle position switch enriches the mixture at idle, but the AFM plays a small part (namely, the air temp sensor).

 

I've done some math on the sensor readings, which are skimpy in the Fuel Injection Bible. I'll post those ranges below. What else is interesting to note, is that the company US Sensor manufactures NTC thermistors (air temp sensors) for varying applications, and a few match the ranges for our IAT sensors. They also have some that offer increased/decreased resistances for normal operating temperature ranges, so instead of using a potentiometer or resistor and increasing by a specific amount, you could run one of these sensors in place of the stocker and increase the fuel amount across the entire operating range in a more linear and consistent manner. Just a thought. Anyways, here are the measurements for a stock IAT in F'.

 

50', 3250-4150 ohms

68', 2250-2750 ohms

86', 1552-1815 ohms

104', 1071-1197 ohms

122', 740-940 ohms

176', 290-360 ohms

[NC280z]

Datzenmike, I believe you are right about adjusting the AFM. The AIT sensor was a slight issue, but after watching the video it occurred to me that all of the gas stations in the Stafford VA area have 10-15% ethanol in pump gas. This would explain why I'm slightly lean, and it doesn't help that my wideband is calibrated for gas and not ethanol mixed fuels. I had adjusted my AFM slightly, since my rebuild bumped compression from 8.3:1 to 9.6:1, but I never took ethanol fuels into consideration since my home in North Carolina had plenty of pure gas available.

 

Thanks for posting that video, and I hope the readings and sensor replacement(s) I posted help my fellow Datsun'ers, as Nissan no longer offers replacement intake temp sensors.