Got some stuff done today on the car. Got the wiring harness cleaned up and the fans wired up. Started it up and tried to set the timing but the timing marks were jumping all over the place using fixed timing. Not sure if it was my timing light or what. Got all the sensors cals set. Also noticed that the MAT is now stuck at 70 and not doing anything. didnt respond to jumping the connector or anything. Here is the log for what it's worth...I caught a weird one (the 21 June log) as well that has some crazy spikes even though the car was just idling.
Dinked around with the bias resistor value based on some forum research with the GM IAT and changed it to 26.9k and it read high but was at least fluctuating and changing. I think it might be a resistor value? Would having the OE IAT wiring in place with the GM wiring in the options port mess with anything?
The bias resistor value is a set value of 2490, unless you opened the ECU and removed the bias resistor and soldered in a different one its 2490.
Your saying the mat sensor does not work, you first need to verify this. You can easily plug the sensor in and use a blowdryer or heat gun to see if there is temperature rise.
The sensor just acts like a resistor (thermistor) it changes ohm value as the temp changes so using different resistors to alter the input temp by jumping the pins is possible if you dont have a Jim stim to test with.
Since they just fixed the circuit I would check your wiring into pin 20.
Success! Got the MAT sensor to read. it was my wiring. Had to rewire the 5 V reference into the sensor like an actual smart person. I tried calibrating it per the OE GM sensor settings and it read -1, and then switched it to your recommended settings and it was ~86 (its 65 here and the car is cold) I ended up massaging the numbers to get it to read the correct ambient temperature. I think I need to look up the sensor brand's resistance settings. It's not an OEM GM part. Anyways, here's a cold start log. Mega rich at idle, and my wideband is taking forever to read correctly. It bounces around during warm up. Thanks for the help!!!!
guess i jumped the gun. partial success. the IAT now reads colder as it gets warmer in actuality. Think I need to also wire to ground. I'll give it a shot tomorrow...
Well this has been sitting on the back burner for a while since I'm still having issues with the IAT. the readings are very jumpy and incorrect. I am working with DIY on some more troubleshooting. I did, however, choose a new ground point for the main battery ground. I had it grounded to the head through the power steering bracket which I found out was aluminum, so not the best. I used the distributor hold down bolt/bracket instead and it idles much, much better.
I did make some changes to the fuel tables and warm up enrichment to remove some fuel since it was idling at 11.5/1. I have it sitting around 13.5-14 now, but its a little jumpy from what I'm assuming is my ham handed attempt at tuning things lol. I ran it 3 blocks up the street to put some gas in it staying out of boost and she runs like a top.
My question for you @a91what is, while im working on the IAT issue, are there other things i can touch up in the tune in the mean time to keep busy, or is the IAT issue a dead stop on that front?
Anyways, log of cold start attached. I let it warm up fully and grabbed a log of the idle there as well. She runs a bit warm, but I'm gonna swap the coolant out for some new stuff since I accidentally put the old coolant back in.