O2 voltage not reading correctly

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brplut40
MS/Extra Newbie
Posts: 9
Joined: Sun Apr 06, 2014 7:12 pm

O2 voltage not reading correctly

Post by brplut40 »

I have an innovate MTX-L O2 sensor with a MS1/Extra (running 029y4 firmware). The yellow wire from the O2 sensor is connected to the O2 input on the MS1. The MS1 project is configured to use the Innovate LC1, MTX-L, PLX 0-5v 10-20:1 AFR. The ground for the O2 sensor and the meqsquirt are the same, the engine block. On the MS1 with a multi-meter clamped to the ground and testing the O2 input, I get 5v. The O2 digital guage shows 22.4. On the MS1 vref I have 4.98, so there is not a large voltage difference. When I look at the O2 voltage in tunerstudio it is showing 3.9v. The AFR guage in tunerstudio is showing around 17.9 even though the actual guage shows 22.4. Does anyone know why on the MS1 board I am getting 5V but the software is only seeing 3.9V? Without the MS1 reading the AFR right, I cannot tune the car.
Matt Cramer
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Re: O2 voltage not reading correctly

Post by Matt Cramer »

What volts do you get on U1 pin 28? Check if there's something in the ECU pulling it down.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
brplut40
MS/Extra Newbie
Posts: 9
Joined: Sun Apr 06, 2014 7:12 pm

Re: O2 voltage not reading correctly

Post by brplut40 »

U1 pin 28 has 11.6v which is the same as the battery voltage. A little low, but I wouldn't think it would cause the variation with the O2 reading.
Matt Cramer
Super MS/Extra'er
Posts: 17499
Joined: Thu Apr 16, 2009 8:08 pm

Re: O2 voltage not reading correctly

Post by Matt Cramer »

I need you to check the voltage on pin 28 of the 40 pin CPU socket, not the DB37 connector.

If you've got 11 volts on the CPU socket, you've got real problems.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
brplut40
MS/Extra Newbie
Posts: 9
Joined: Sun Apr 06, 2014 7:12 pm

Re: O2 voltage not reading correctly

Post by brplut40 »

It is at .36 volts.
Matt Cramer
Super MS/Extra'er
Posts: 17499
Joined: Thu Apr 16, 2009 8:08 pm

Re: O2 voltage not reading correctly

Post by Matt Cramer »

In that case, something on the board IS pulling it down. Try cleaning the board to make sure there's no flux on it.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
brplut40
MS/Extra Newbie
Posts: 9
Joined: Sun Apr 06, 2014 7:12 pm

Re: O2 voltage not reading correctly

Post by brplut40 »

what should the voltage be so I know if it is cleaned and working properly?
Matt Cramer
Super MS/Extra'er
Posts: 17499
Joined: Thu Apr 16, 2009 8:08 pm

Re: O2 voltage not reading correctly

Post by Matt Cramer »

The same voltage that's coming in on the O2 sensor input on the DB37.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
brplut40
MS/Extra Newbie
Posts: 9
Joined: Sun Apr 06, 2014 7:12 pm

Re: O2 voltage not reading correctly

Post by brplut40 »

Everything on the board looked ok. I am not a EE, so I am not sure exactly what to look for, but there were no points that were touching or over soldered. Anything else that I should look for or test?
brplut40
MS/Extra Newbie
Posts: 9
Joined: Sun Apr 06, 2014 7:12 pm

Re: O2 voltage not reading correctly

Post by brplut40 »

I did a little more testing on the board and here is what I have found. The voltage entering R29 and R1 is 5.00v. the voltage out of R1 is 3.888v This is where the voltage drop is happening. I am not sure why though. When the car off I measured the resistance of the R1 resistor and it is right at spec at 1k ohms. The resistance of the R29 resistor measured at 558k ohms which seems out of spec, but I am not sure how the rest of the circuit would effect this measurement.

Here is the diagram that details the circuit for this board. http://www.bgsoflex.com/v22/megasquirt_ShemV2.2.pdf

Any other ideas or things to look at?
Matt Cramer
Super MS/Extra'er
Posts: 17499
Joined: Thu Apr 16, 2009 8:08 pm

Re: O2 voltage not reading correctly

Post by Matt Cramer »

Have you tried giving the board a good cleaning with rubbing alcohol or acetone?
Matt Cramer -1966 Dodge Dart slant six running on MS3X
brplut40
MS/Extra Newbie
Posts: 9
Joined: Sun Apr 06, 2014 7:12 pm

Re: O2 voltage not reading correctly

Post by brplut40 »

We have found the solution. Because I am running a wide band O2, the D11 diode is not needed.

http://www.msefi.com/viewtopic.php?f=38&t=3160
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