just curious

 

It's accurate to 104K/Pa
Considering ambient air is 96-99ish K/Pa, not much.

 

Lemme see. If 97 kPa = 14.068 psi then 104 kPa = 15.083. So it can only handle 1.01 psi of boost.

Am I thinking right? If so, what does the ECM do when the kPa is higher than 104k. Does it go apesh!t, or does it just stop adding more fuel?

 

With the stock 1 bar MAP sensor the ECM does not see boost. If you replace the MAP sensor with a 2 bar unit it will handle boost. You must recalibrate all the tables with MAP axes too, and all the calculations that are based on MAP values.

 

Huh? How do you recalibrate the tables with the ???????

Sorry, I'm still trying to figure all this out.

 

I think that GM has three different MAP sensors. 1 bar, 2 bar and 3 bar. The 1 bar MAP is for non boost applications. It measures from 1 bar vaccum to atmospheric pressure. The 2 bar unit measures from 1 bar vaccum to 1 bar boost. The 3 bar unit measures from 1 bar vaccum to 2 bar boost. All these sensors has an output range of 0 to 5 Volts, so the ECM has no way of knowing that the sensor has been changed.

One example ...

When you replace the stock 1 bar sensor with a 2 bar sensor you change the scale of all the MAP values in the ECM. The 0 volt value will be 0 volt with the new sensor too. The old sensors 5 volt value (atmospheric) will be 2.5 volt with the new sensor. When you do this on an NA engine it will allways be on the left half of the tables. To compensate the ECM calibration to be 'the same' as before the switch you need to compress the VE and SPARK tables into half the space. You have to remove every second column of values. You must also multiply all calculations that uses MAP by 2. Now the engine should run the same as before the switch ... and you have a lot of unused cells in the right half of calibration tables. Those cells are for the boosted fuel and spark calibration.

 

OR,
Use the MAF input, remove the PCB on board ROM, and write your won code.

 

I'm not that cool yet

Thanks for the info JoBy. So if I changed around all the VE tables to handle the boost with a 2 bar MAP, I would essentially make 50 kPa = max atmospheric pressure, and anything beyond that would be boost, right? And I would do that by removing every other column in the VE table.

I thought the 7747 didn't recognize any VE values over 100?

 

You got it ...

about VE ... you are right, but the ECM does not have to know about it ... Use a bigger injector and lower the VE numbers. The absolute values will be wrong, just like the MAP values. I don't think that it is important. What is important is that the ECM delivers the right amount of fuel and spark timing ... even if it is fooled ... I would just replace the MAP sensor and tune the engine to run 'right' and not care so much about what the numbers are. This is what I am going to try to do anyway.

To get all the numbers right you probably have to use an ECM with software for boost.

 

Cool.

Grumpy...could you write code to make a 7747 compensate for boost? I've tried to get into source code editing but I have no idea what to do. I got the assembler and disassembler, but just couldn't get them to work. Even then, I would have to learn another language. I already have basic, javascript, fortran, HTML and other things floating around upstairs.

 

Could I?.
No,
That takes a team effort or one very sharp guy.

You have **just** change every reference to MAP, not just the VE tables, everthing. The AE correctio due to MAP, the baro lookup, and recalulation, and probably 50 other places.

Stuff like this takes months to do.

I had commented stuff, the prom, and the RAM all laid out, and spent months just putting the pieces together. And this was someone spending LOTS of time telling we which end of pencil to use. It will be the sweetest wine in the world when done, but, stuff like this takes a real commitment (or willingness to be committed)......

 

I see...yikes