I need to add some code to my PCM to adjust the base injector flowrate for manifold vacuum. I have some ideas as to what it should look like, but it would be nice to see what GM did. Do any of the commonly used ECMs have this feature? I know most just use a vacuum ref. regulator at the fuel rail. Mine is vacuum referenced, but its installed remotely, so it would take a decent ammount of vacuum hose to reach it. Not sure how fast it can respond with all that added hose length.

 

The LS1 PCMs are set up that way. The FPR is in either the fuel filter or pickup/pump assembly (in the tank). Runs constant pressure to the rail. It has been a while, but IIRC GM used an injector constant table that was based on manifold vacuum.

I've looked around the HDD for more info on this but can't find anything.

RBob.

 

I have a modified version for PCM $85,
I download it from the net but do not
remember from where or who post it the
first time.

W/T1500

 

Is TGO still messed up for downloading files through IE?

I just downloaded the above attachment, and it doesn't seem to be any sort of proper file for use with a program. There's no file type extension.

 

It's work ok with Firefox

W/T1500

 

To my knowledge, most or all GMs are set up that way now. My newer GM has just a single fuel line out to the fuel rail. The people who are privy to the LS1 code aren't giving away too much info on how the logic works internally. I think I may have seen a table posted at one point, but that's it.

I have seen the $85 code for the vac. regulator. I had something similar in my custom code for the $0D. One thing about this, though, is that the injectors are directly exposed to the manifold vacuum, so the actual flowrate can potentially change quite quickly. With the vac regulator routine, your mainly trying to match the response of the regulator, so the logic will likely not need to be as sophisticated.

The fuel code in these runs real time with the engine, so the PCM can do the calculations for each individual cylinder. The best control stratagy would likely be to have a table that modulates the base injector flowrate based on a filtered manifold vacuum term. To control the response, I will likely need some logic to handle the filtering based on the throttle input, engine speed, whether or not the car is idling, etc. I think it can be made to work better than a standard vacuum regulated FPR, and the response should be fast. But, it cant be too fast, or it can set up a feedback loop under certain conditions.

 

Maybe your over thinking it. The filtered MAP compensation table for the main control amount and then use AE/DE for the transitions until the filter catches up. Might be easier and just as effective than trying to cover all aspects of possible fuel control. Just a thought.

 

Does the LT1 have an injector offset function? I read somewhere it does and thats how you can compensate for the rich lean variance between front and rear cylinders which is common with LT1 intake manifolds. Is that something similar to what your looking for? I dont know if its based on vacuum or not tho

 

Actually, these use whats called a transient air mass for the transient fuel calcs. Basically, there is a matrix of transient airmass terms for all the inputs that are used during transients to try and predict what the upcoming airmass for the current cylinder in the firing order will be.

I definitely dont want to make something thats complicated and impossible to tune. But, I also dont want to lean on other parts of the fuel logic to correct for response or inaccuracies. Just have to find the right balance in the middle somewhere. Im leaning toward code that will have several filter coefficients, based on the conditions. Probably would want to have the code be able to tell when the vacuum is stable/unstable, and changing quickly so the appropriate ammount of filtering can be selected.

 

This PCM has that as well. Its a bit different in that its to compensate for low speed fueling imbalances in the intake. Basically the fuel can be trimmed for each injector during certain conditions.

 

Well, heres what I settled on. Standard blanket filtering the manifold vacuum seemed like a bad idea as any filtering thats enough to be meaningful will result in phase lag during transients, which could cause feedback and engine surging during certain conditions. Seems like either no filtering or non-linear filtering for the vacuum would be best. Basically I use the unfiltered change in manifold vacuum to construct a derivative vacuum term and an integrated change in vacuum term to use for looking up a non-linear filtering term for the manifold vacuum. Basically, the derivative term tells whats happening over the short term, while the integrated rate of change tells which direction the manifold vacuum is heading overall. I figure this gives a good indicator of what the manifold vacuum is doing. Large changes in derivative with little integrated change in manifold = noise and more filtering while large change in derivative along with large integrated change in manifold vacuum = change in engine load and little filtering. Other values will have filtering somewhere in between. Seem like a reasonable stratagy?