Jack_the_Diesel_Killer
May 16th, 2009, 04:24 AM
Hello Everyone
Complete noob to Efilive though I do have engine tuning experience. I did search the forums before posting so I hope that everyone will have a little patience if I am asking the obvious.
Downloaded the software and have been going through the tables trying to make sense of it all. While there is a ton of stuff there, once you figure out the way GM does things it is pretty straight forward.
The question is this - How is commanded/desired fuel pressure converted into a signal that the pump can understand?
The obvious answer is table B1010, but I don't think so, at least it can't work without some questionable math assumptions. I'll lay out my reasoning below and try not to bore everyone to death.
The inlet metering valve on the pump is pulse width modulated. Varying duty cycles produce different fuel flow rates. Parameters B1008 and B1009 show that this is in fact the case. The problem comes in when trying to convert flow to pressure. Table B1010 deals with flow, not pressure. Given rpm we can easily convert mm3/stroke to mm3/sec. Still doesn't tell us pressure. Since rail pressure is the difference between the rate at which fuel is going in as opposed to fuel going out - to the injectors - the only way that table B1010 can be used to command a specific pressure is if they assume that any given injector PW ( tables B0720 and B0721 ) will create a given pressure, all other variables being constant.
This method can work but it has some serious shortcomings. Minor variations in individual injectors would have an exaggerated effect on fuel pressure. More importantly from our hot rodding point of view is the fact that any changes to B0720 or B0721 will result in the wrong fuel pressure being delivered to the rail. In other words, if you increase any of the PWs in those tables you will receive a significantly lower fuel pressure than that commanded. I realize that there are closed loop algorithms in the ECU that will correct for this but they will take time. Rapid throttle movements may result in delivered fuel pressure never matching commanded fuel pressure.
Which brings me to my next question. Is it possible that there is another table that Efilive is not seeing? Since we know that the ECU software does use Duty Cycle could there be a table that has inputs, for example, of mm3 and rpm, and an output of Duty Cycle? If this supposed table were available it would be a lot cleaner and controllable method of dealing with non standard injectors, etc.
This is fascinating stuff. The amount of work that the Efilive guys have done is incredible.
Hopefully some of the more experienced members here will jump in. I could be completely wrong, maybe there is something that I am not seeing. Either way this is really fun stuff and I would like to learn.
Complete noob to Efilive though I do have engine tuning experience. I did search the forums before posting so I hope that everyone will have a little patience if I am asking the obvious.
Downloaded the software and have been going through the tables trying to make sense of it all. While there is a ton of stuff there, once you figure out the way GM does things it is pretty straight forward.
The question is this - How is commanded/desired fuel pressure converted into a signal that the pump can understand?
The obvious answer is table B1010, but I don't think so, at least it can't work without some questionable math assumptions. I'll lay out my reasoning below and try not to bore everyone to death.
The inlet metering valve on the pump is pulse width modulated. Varying duty cycles produce different fuel flow rates. Parameters B1008 and B1009 show that this is in fact the case. The problem comes in when trying to convert flow to pressure. Table B1010 deals with flow, not pressure. Given rpm we can easily convert mm3/stroke to mm3/sec. Still doesn't tell us pressure. Since rail pressure is the difference between the rate at which fuel is going in as opposed to fuel going out - to the injectors - the only way that table B1010 can be used to command a specific pressure is if they assume that any given injector PW ( tables B0720 and B0721 ) will create a given pressure, all other variables being constant.
This method can work but it has some serious shortcomings. Minor variations in individual injectors would have an exaggerated effect on fuel pressure. More importantly from our hot rodding point of view is the fact that any changes to B0720 or B0721 will result in the wrong fuel pressure being delivered to the rail. In other words, if you increase any of the PWs in those tables you will receive a significantly lower fuel pressure than that commanded. I realize that there are closed loop algorithms in the ECU that will correct for this but they will take time. Rapid throttle movements may result in delivered fuel pressure never matching commanded fuel pressure.
Which brings me to my next question. Is it possible that there is another table that Efilive is not seeing? Since we know that the ECU software does use Duty Cycle could there be a table that has inputs, for example, of mm3 and rpm, and an output of Duty Cycle? If this supposed table were available it would be a lot cleaner and controllable method of dealing with non standard injectors, etc.
This is fascinating stuff. The amount of work that the Efilive guys have done is incredible.
Hopefully some of the more experienced members here will jump in. I could be completely wrong, maybe there is something that I am not seeing. Either way this is really fun stuff and I would like to learn.