Sequential Injection Oddity

[belize1334]

I pulled these figs off the DS-Map board for your viewing pleasure and also because the last one confused me a bit.






So, what has me confused is this "during heavy acceleration there is a batch fire every 10ms on top of sequential fire." In the diagram in the last image the batch fire appears to be timed to occur between successive sequential firings...but that's inconsistent with the "every 10ms" since the time between sequential firing is rpm dependent (20ms*6000/rpm). So, since the batch fire occurs four times over a full cycle in the figure, either the batch fire always occurs between successive sequential firings, or that figure is only valid at 3000rpm. If the latter is true, and it does occur every 10ms, then my question is, why? Why inject extra fuel in such a way that it only affects every other (or every third...depending on rpm) combustion event? And it only says that extra fuel is injected. How much fuel goes into these "extra" batch fires anyway? Is this where all of the increased fuel comes from under load or is it just a small fraction?

 

[belize1334]

Nobody except me thinks this is odd? Really?

 

[curtis]

I didn't take time to read and go through each one but it probably has something to do with detonation and this being a production turbo based car. 70% of the fuel used in a combustion engine is used just to cool the piston not to make power. I know it sounds odd but think of a brush fire. You pour out 5 gallons on a bunch of brush and damn there's a mushroom cloud when the energy is released. Most of use that with 10 or 15 passes down the track. Maybe this was the designers way of an extra safety margin if not they could have some serious recall problems with melted pistons which would cost millions. Yea the gas drinking mpg under WOT is effected but we're paying for the extra fuel not them, I've never noticed a city, highway and race mpg on the window sticker. /ubbthreads/images/graemlins/grin.gif My buddy did have a built vette back in the mid 90's, it had a computer to watch fuel economy, with the traction control off and foot planted we saw down in the 2 mpg range on a few long passes and this was with a 450 to 500 hp car.

 

[cspetros]

I remember reading someplace that the stock programming is such that fuel is actually dumped at WOT to prevent the engine from detonating. The ECU goes "Open Loop" at WOT, ignoring the o2 sensor, etc. This goes for both the Turbo and N/T cars, if I remember correctly. I wish I could recall where I read that... I also think I remember that it happens above 4000 RPM, also, even when it's not WOT. I was thinking this was related when I first read your post. Now that Curtis has replied, I feel more certain.

UPDATE: I read it on this page: 4g63 ECU Primer

To actually quote the page:


Quote:
Just as an aside, the ECU designers went one better than this in the cooling department. While under high loads, the ECU actually fires all four injectors in between the normal firing times. This extra fuel has no chance of being burned in the engine (at least until the valves open), but helps to keep things cool.



I found this primer to be extremely informative on the base level operations of an unmodified ECU. I think it should be posted as a Sticky or something.

 

[belize1334]

It's exactly that "fires all four injectors between the normal firing times" that I'm talking about. Except that, if the manual is correct and it happens at 10ms intervals, then this is not consistently timed between the events which are only rarely separated by exactly 10ms.

 

[cspetros]

Maybe it counts 10ms and then triggers batch injection, regardless of being consistent?

Quote:
How much fuel goes into these "extra" batch fires anyway?



In that pic it says the "amount" of fuel is dependent on the degree of acceleration. All you would need to find is the injector duty cycle when this is happening. Maybe, the duty cycle across all 4 is THE SAME as that for an individual injector during the same period of acceleration. I bet one of the ECU dissection gurus on the board here can probably tell us about this.

It's interesting that all of this information (along with a lot more useful info) was left out of the Mitsubishi version of the factory manual, but is included in the DSM version. /ubbthreads/images/graemlins/dunno.gif