I measured from the connector at the AFM plug back to the GM AIT, and the results were consistent with what I got directly at the GM AIT.

By the yellow wire, I assume you mean the harness at the megasquirt? I'll pull up the carpet and scope that out next.

Thanks,
Jim

orange. yellow is coolant.

So I dug into the harness at the megasquirt, and found a crufty wire on the car side of the harness that connects to the orange megasquirt harness. I carved out the bad section of wire and re-crimped. The car ran fine until it got hot, then again spiked to 435 IAT.

I jumped out and checked resistance at the GM IAT, and it read .888k ohms. So that feels about right for a cool day, and certainly doesn't look like 435 degrees.

The problem is clearly thermal - when cool, the car starts and runs fine. It takes more than 20 minutes for the fault to occur.

I also noticed I had a reset in one of the logs. I'm still scratching my head on this one.

Prior to installing the megasquirt, I had a Bipes that was crimped into the harness. I'm wondering if I should go through and carve out any of the places where the Bipes was connected.

Any other ideas?

Thanks,
Jim

Related question:

When this happens, is there a way to prevent the megasquirt pulling all my fuel off when the IAT reads 435 degrees?

its really weird that's happening to you, as if the connection comes loose, it goes to a fail safe mode where it just defaults to 70°F iirc. this makes me think it's providing a signal but at an extra range...hell the MSI shouldn't even be giving you a value higher than 255°

temp wire fixed, AFR still hosed.
 

Update on this problem:

The harness on the car side was intact. On the Megasquirt side, I found that orange wire had been borked by the strain relief barrel in the db25 connector. I cut out the bad section of the orange wire, reconnected it with a butt connector and now I have reasonable temps.

However, I have a new problem. At idle, AFR's are crazy lean (so lean that I didn't try to drive it).

I've attached a quick log of the car at idle. Any idea what's going on here?

Thanks for your thoughts!!

What kind of wideband is it? My earlier statement is still true here. These readings are false. You would not be able to idle at 18:1.

If an LC-1, when's the last time you did a free air calibration?

AEM Uego, new o2 sensor.

I think I will double check the ground on the o2.