chips, injectors and duty cycles

[bastianshaw]

Hi im wondering about the mark d 19lb chip; what does a chip burned for bigger injectors do exactly? my rookie guess is adjust the duty cycle? But now that I think about it, it seems that would be a function of the hardware. whats the deal?

[jlevie]

A chip tuned for larger than stock injectors has maps that call for less injector on time to compensate for the greater flow rate of the injectors.

[bastianshaw]

ok so it just lowers the duty cycle back closer to stock right?
what is the benefit of this?

[jlevie]

On an otherwise stock engine, the only benefit that I know of from changing the injectors is better atomization of fuel from the later injector designs. The stock injectors have enough head room to achieve 12.5-13:1 AFR with a proper chip, which is as good as it gets with respect to power.

[LJ851]

There is no benefit to larger injectors unless your engine needs more fuel than your current injectors can supply. Basically, you want the smallest injector that will flow enough fuel for your engine at 85-90% duty cycle maximum.

[bastianshaw]

no guys i was talking SPECIFICALLY about the duty cycle...what is the benefit to having a larger injector fire w a duty cycle closer to stock?

why mot just chnge the maps w he chip and let the motronic figure out the duty cycle?

think about running any chip burned for stock injectors, but then you swap in 19's the motronic fixes it...it seems redundant to burn a chip for them; unless im missing something, hence the query.

[LJ851]

no guys i was talking SPECIFICALLY about the duty cycle...what is the benefit to having a larger injector fire w a duty cycle closer to stock?

why mot just chnge the maps w he chip and let the motronic figure out the duty cycle?

think about running any chip burned for stock injectors, but then you swap in 19's the motronic fixes it...it seems redundant to burn a chip for them; unless im missing something, hence the query.

Motronic doesnt affect full throttle. The fixed tune in the chip dictates that, hence the need to match the chip and injectors.

The pros and cons of injector sizing are this: Too small and the duty cycle goes too high and can overheat and damage the injector. If it's way too small you will run lean and lose power.

Too large and the idle and low speed drivability suffer along with fuel economy because the duty cycle is so short the injector cant atomize the fuel well.

[bastianshaw]

ok but 19lber have proven to work fine in all aspects w the stock chip

its not like you NEED a 19lb burn to make them work

[jlevie]

Actually you do need a tune matched to the injector flow rate. The DME is adaptive, using data from the O2 sensor, and can to some degree compensate for more or less flow through the injectors. But that adaptation is limited. I would guess that most folks who say that you can change injectors without a matched tune haven't spent time on a dyno and don't really know what is going on with the mixture.

[bastianshaw]

Actually you do need a tune matched to the injector flow rate. The DME is adaptive, using data from the O2 sensor, and can to some degree compensate for more or less flow through the injectors. But that adaptation is limited. I would guess that most folks who say that you can change injectors without a matched tune haven't spent time on a dyno and don't really know what is going on with the mixture.

Thats odd because after installing 19lbers in my gfs car w stock ecu, it runs way better.

It seems to me the ecu is adaptive enough to use those injectors, so maybe its just a marketing gimmek from some of the chip tuners

[LJ851]

Maybe your gf's car has a worn out afm or vacuum leaks. Running "way better" does not mean anything, what are your before and after afr's?

The full throttle map on the chip is not adaptive in any way. It will never "learn" anything and does not know how big your injectors are. Changing injector size changes your afr at WOT, no gimmicks necessary.

[brody]

The O2 sensor once in closed loop will trim fuel accordingly. It's not perfect but it can handle 19# injectors. It cant compensate for col start, cranking fuel or WOT. You know an octagon also can be used like a wheel.

[bastianshaw]

running better means something to me maybe not to you.

no idea on afr as I dont dyno my girls car lol

so yo are saying at WOT w a stock chip and bigger injectors what will occur? the duty cycle will be the same as on stock injectors= a rich condition?

[jlevie]

I have data that suggests that learned adaptation is applied to all fuel maps. From an engineering standpoint it would make sense for the DME to do so. Learned adaptation is programmed into the DME to account for manufacturing variations and normal wear and tear. It would make little sense to apply that only to part throttle maps. But the larger question here is whether the minimum allowed fuel trim is sufficient to account for the increased flow of 19lb injectors. To find that out you have to run the car on a dyno and get A/F ratio data in part and full throttle operation.

I know for a fact that the stock 14lb injectors can, with proper tuning, result in 12.8-13:1 AFR over the entire operating range of an M20B25. That is race car rich and the engine makes the most power with that AFR. But that is too rich for the street where the engine spends a lot of time at lower engine speeds and lighter loads. The only disadvantage of the stock injectors is that don't atomize fuel as well as four pintle injectors.

[brody]

Motronic 1.3 is barely adaptive. Every time you come back to idle adaptation clears and starts again. If idle is not being triggered properly you run into problems with how the car runs. Motronic 1.3 is adaptive at in closed loop only when the ECU is getting O2 data. Moronic 3 and up can be considered "adaptive" more so than 1.3

When you say you can get a car to run 12.5 to 13.1 across all conditions what ate you doing to achieve this? If motronic was truly adaptive, it would pull back to 14.7:1 for idle and part throttle since that is what it is programmed to target at idle and PT which shows its barely adaptive.