Wideband into EGR TEMP input question

[ohmegamike]

One for the ECU gurus... I want to eliminate the pull up resistor on my ECUs egr temp input. I've been following traces and flow thrus on my ecu till my eyes hurt! Anybody here know where the pull up resistor is located? Hope it's not built into one of the vertical ceramic ICs!... Thanks! -Mike-

 

[ohmegamike]

The ecu pin 15 signal goes into IC101 pin 5 and there's a resistor silk screened on the ceramic substrate. It's a single resistor going right up to the 5 volt line on IC101, and it's probably the pull up, but if I cut/scrape the conductive material off that IC and it's not the right resistor, then I've got problems!

 

If you REALLY want to get rid of it, you can bypass IC110 for the EGR voltage. I figured it out sometime back, but found out later that a MAP sensor's output voltage isn't affected by the bias, so I never really advertised it:
remove jumpers J101 and J105, and connect a small jumper between pins 5 and 7 of IC102's empty pins. If you trace everything out, you'll see what I mean. On JDM boards, pin #15 doesn't go through IC110, but goes to IC102 instead. So, you can eliminate the 2 jumpers that take it through IC110, and then just jumper it in and out of IC102 (I count IC102's pins starting from the side with the gap: 1,gap, 2,3,4,5,6,7,etc). I don't know whether its necessary or not, but I also soldered a 100K pull-down resistor to the jumper on IC102, to pull it slightly to ground.

 

[ohmegamike]

Well yea, I really wanna get rid of it! Why not have a good open input to play with??? I'll check it out! Thanks for the info! -Mike-

 

[ohmegamike]

Thanks again Keydiver. I've got it working nicely now. I had to do some experimenting with the scaling on my LM-1 wideband, but it's reading correct now. I'll also add that the input is very accurate as a voltmeter up to about 4.7-4.8v when I checked it with an HP Power Supply. If anybody else is interested in connecting a LM-1 or another WBO2 and reading/logging the A/F ratio with MMCd, here's some info on the input scaling.

Volts input ECU pin 15 - A/F Displayed on MMCd
0v - 7.9
0.5v - 9.3
1.0v - 10.7
1.5v - 12.2
2.0v - 13.5
2.5v - 14.9
3.0v - 16.3
3.5v - 17.8
4.0v - 19.1
4.5v - 20.6
5.0v - 21.9

Hope this info can be useful to others here...

Mike