Questions on logging sensors, etc


No amount of evidence will ever persuade an idiot.
Dec 9, 2002
I have a few questions regarding 5v analog inputs for logging with XFI. First off I've been searching around for sensors and they seem to 2 types; expensive ($125+) and not expensive ($16+). I currently have the 2 that came with the Caspers XFI fuel and oil logging kit installed and they work fine. I also have a Bison 3.5 for the MAP. Now I would assume the more expensive ones are more reliable and accurate but I see people using the inexpensive ones often. The inexpensive ones seem to mostly 5v powered. Have they been reliable enough to use for less important AUX inputs? I am not a fan of messing with the 5v TPS wire to power them. Would it work to tap the 12v feed for EGR and run it through a 12v to 5v converter ( to power the 5v sensors? The sensors I would like to try to add are alky pressure and a few air temp sensors for intake experiments. Could that 5v feed 3 or 4 of those sensors? From what I've seen of the specs they only draw a few mA.
As far as logging the alky pressure, I haven't been able to find a brass -4an gauge port adapter, just one -4an aluminum and one in stainless steel. The mostly seem to -6an. Which adapter are people using?
If anyone has any pictures of sensor locations and neatly wiring them I'd love to see them. Thanks!
Now I would assume the more expensive ones are more reliable and accurate but I see people using the inexpensive ones often
I've found the $100+ ones Holley sells, have the same mfgr/pr #, etc, selling for your $16 price.
Some discussion on other boards about the absurd mark up.
I used the "less expensive" sensors, on my Dominator install. The Dominator has the ability to control 5VDC, so I never had the 12V issue.
I've not set up a FAST, for many yrs. So, I'm not familiar w/ their set up..
Ha, that's interesting. There is a 5v reference and a 5v aux ground with the XFI. I was considering a terminal block with easy access in the glove box, running an multi conductor cable from the AUX inputs and 5v ground/reference and running the wires back from the sensors to the block. There are enough wires running all around the engine compartment already.:rolleyes: Just trying to map out what would be an easy install and neatly wired, especially for the alky transducer. The others are just something I'ld like to fool around with for conversation sake (and performance if it shows so).
Any input on the gauge port?
I put the alky feed line up under the alt, as the 2 gallon fuel cell was there.
At the rear of the alt, I made an alum j block with sensor in it, and 2 an ports for the nozzle feeds.
I tried to find the pics, but have had no luck.
I'll look elsewhere....
You will likely will have to wire the temperature thermister with a pull up resister to the 5V and program the temp vs ohm curve. I am sure XFI has instructions for it. Even though it is messy, probably better off using the 5v from the xfi for the sensor power.
I just started researching air temp sensors. I've got to see how people are using a regular GM type air temp sensor and then logging it with a XFI (or any 5v signal).
Now I see the temp sensor measures resistance. No 5v signal back to log.
After some searching I found this on a website for a company called Autosport Labs. The sell logging devices called RaceCapture. They are recommending Wells SU107 temp sensor which is the typical GM style sensor. The call it a High Resistance ECU style sensor. They recommend a 2.2k pull up resistor shown in this illustration:
Air temp sensor with stepup resister.png

So that looks "simple" enough to do. The next issue would be figuring the gain and offest numbers. It suppose it would ok to use ambient air temp for the first values and then use something like a hair dryer for the second values. Does that sound like I'm on the right track?

I found another website with sensors called Low Dollar Motorsports. They have some reasonably priced sensors that look better than the typical Ebay ones. They happen to have what they call a turbo intake air temp sensor kit. This image is was with the other pictures of the sensor:

With this sensor, they give the resistance values to the temperature but I don't see how you could use them. I'm not real good at reading electrical schematics but I don't see a resister symbol. I see the 5v feed, signal out to ecm and ground. Can you explain schematic? Does this sensor not need a pull up resister?
If you have to calibrate the sensor your self, then you may want to try well iced water, will get you very close to 32F, and boiling water will get you very close to 212F.
The XFI may let you enter the pull up resistor ohm value, so you can select a reasonable resistor based on your needs. It does not have to be 2.2k ohm. It may also auto generate a table based on a few input values from a calibration table or that you determine through your own calibration.
The image from the low dollar motor sports web site shows an ECM with the pull up resistor as part of the ECM. Unless you have an input specifically configured for temperature, you will need the pull up resistor to use a standard 0-5v input.
The Innovate Logworks manual has some good info for sensor set up and calibration that may be useful for the XFI, if the XFI does not have documentation available. That is were I learned about setting up a temperature sensor. The XFI software will have to have the features available which I would be surprised if it did not.
It may also auto generate a table based on a few input values from a calibration table or that you determine through your own calibration.
Yes, I believe that is what happens. I guess it would scale it from 0v to 5v. They have a formula to get the Gain and Offset. This is the window to set up an Aux sensor.

The high and low limit will just change the color of the line on the graph to signify it's out of a good range.
I will look for that info in the Logworks Manual. Thank you for helping me to understand this.
After looking at the Lowdoller schematic closely, I noticed the 5v feed has a resister in it. Also there is a chart with F*, C* and K ohms at each temp from 22*F to 284*F. on the buy it page.
I downloaded the Logworks. They have a nifty Thermistorcalc that you can enter in info and it will calculate a temp/volts table depending on the load resister used. That table can be used to enter info for the XFI. :)