Can you compare to the IAT reading before you start the car for the first time in the morning? I'm curious because when I first started using the GM sensor, I had very good match to IAT, but lately I noticed that the GM sensor was starting to read as much as 4F higher before I started the car in the morning. Seems like the sensor has drifted a little. I'm working on a revised scaling table. I'll send it to you if your GM sensor is reading high as well.

 

Will do tomorrow morning and will let you know!

 

well both sensors should age at the same rate... and that should be pretty slow I would imagine.

mine is in and ready for the ECU to be patched - hopefully the one I did last night will "just work" ...

 

ok got my results from this morning.

Raw 2byte ADC was 657, MAF IAT was 15degs

so 5*657/1024 = 3.21volts
3.21v = 16.5degs.

Is that about right? Not sure why there is a difference between MAT and IAT??

 

So MAT is about 3F higher than IAT. That's close to what I'm seeing. I'll post up a revised scaling table soon.

 

I am actually using the scaling from http://www.bmotorsports.com/shop/pro...roducts_id/400

and then using the voltage divider formula "5*($Ohms/(2250+$Ohms))" to convert ohms -> volts

ps - Iam just doing the XML update now, will shoot you and email - I am redoing the turbo section..

 

ps how certain are you on the 2250 ohm internal ECU resistance?

 

Yep, that's what I did.

I measured it indirectly, so it could be a little high or low. My latest scaling table is based on an ECU internal resistance of about 2425 ohms. I tweaked the ECU internal resistance value until the GM sensor matched the IAT sensor after sitting overnight. Temp in the garage in the morning is about 55-60F (close to the temp when joedr checked). I need to test it at a few other temps before I know that rescaling based on ECU internal resistance is the solution. It might be that the actual sensor resistance vs temp values need to be changed.

 

hrmm yes, but I think its more likely the 2250 is slighltly off.

Ummm I have some pictures of the ECU board - let me see if I can see any resistors on it Probably a 1-million shot but hopefully it will work....

 

I will check in the morning for the values again.

The car has been off for the last couple hours and both IATs are showing 95 F (engine off).

 

Can we just unplug the sensor then measure the resistance across the pigtail to work out the ECU resistance?

ie, either pigtail (the one that works) to +5volt? that should give us the resistance of the ECU resistor?

 

Huuum! After a few mins.... the AIT was showing 96.8 and MAT stayed at 95 F.

Just attached a 10-15 min trip log of AIT and MAT... that was done earlier today with temp around 80 degrees.

 

The voltage read by the ECU is the voltage across the temp sensor, so putting a probe on the wiring from the temp sensor to the ECU will not measure a resistance. Best thing to do would be to meaure the resistance across the temp sensor, plug it into the ECU wiring, turn the key to ON, and then measure the voltage across the sensor. The internal resistance can be calculated from that info.

 

Hrmm I guess it would be too hard to find the +5v signal anyways.

 

The difference this morning was still 1.8 F between the two. The coolant temp was also set at 77 F.

This was after a few mins with the key on.

See here....