Someone in the A4 forum was suggesting running 30# injectors on a 1.8T A4 without reprogramming the ECU.

I thought the ECU couldn't adjust for this kind of change.

If it does, how?
thanks<ul><li><a href="http://forums.audiworld.com/a4/msgs/1020935.phtml">a4 forum post</a></li></ul>

(Name the movie for bonus pts)
Mike can the ECU adapt to bigger injectors or no?

if its not ridiculously big, the ecu will adapt. but if its riduclously big, then of course it probably won't.

but really, whats the point? you are not maxed out on your fuel injectors unless you get bigger turbo.

The O2 sensors will adjust the fuel trim, but if it adjusts too much, it will set an error code

...because the 02S is out of the loop.

modes.

If the ECU is running consistently rich (or lean) at part throttle, it makes sense that it would also run rich (or lean) at WOT. So it might use the fuel trim for both modes, but only adjust it during part throttle. Of course, it might not....

Is it around 26%? TIA

you will probably run rich, wasting lots of fuel.

The story so far:

He installed them, it ran well for a time, then went into limp mode.

He's currently researching chips I think.<ul><li><a href="http://forums.audiworld.com/a4/msgs/1020572.phtml">thread</a></li></ul>

This is the range of adaptation I saw my ECU in the 2.8 go through when I had an air leak past the MAF spoofing the system (while running the PES "G1").

When it hits 25% you get a rich/lean check-engine code.

Seems like at WOT you are pretty much going to go rich if you try this. But I don't know.

- Z

I'm not sure. But back when I was watching the short and long term fuel trims all the time I noticed that the long term one was constant (as in not adapting) when the pedal was mashed. I think that's the loop going "open." But it seems reasonable that the trim value that was frozen at the time is still used.

still, in regard to the original post, I don't see what the bigger injectors alone a good for. Let's say the ECU adapts perfectly. 15% bigger flow and -15% pulse width trim. In the net, you get what? Nothing I think. More fuel and more AIR and then maybe more HP.

i think this is why most of those guys over on vortex get away with running boost controllers.

otherwise it would lean out @ WOT, right?

...because it stayed right at 16.32ms with the 310cc injectors even though I was getting short and long term trim #s in the 20s.

...and I came up with the increase in injector size based upon the 235cc injector size in old non DBW cars and 270cc injectors in more recent DBW cars.

Of greater importance than the wasted fuel is the wasted power. Too rich costs hp.

Mike O.

From what I understand injector dutycycle is a comparison of pulse width vs available pulse period, limited by ECU and/or rpm. How does Bosch injectors go static at 14.5ms?

I don't think it matters WHEN it goes static, just IF it goes static.

If you do the math, at 6000rpm, you have 100rps, since the cam turns half as slow, it's 50rps, or 20ms for one cam revolution.
The intake valves wont be open for more than half that time, so you're looking at a window of about 10ms to inject fuel.
Injectors have a turn-on and turn-off time, so they actually need to be on for longer than the valve duration: turn-on + 10ms + turn-off = 14.5ms (there's probably a slight overlap programmed in as well) Any longer, and the fuel just puddles behind the valves, not exactly an ideal air/fuel mixture.

Just an FYI, low-impedance injectors turn on/off quicker than high-impedance injecotrs.

I think the reason our cars can get away with the maxed out injectors is because the fuel pressure rises at a rate of 2.5 times the boost pressure, and not a 1:1 ratio like others. IIRC, Mike was the one that found out about the FPR specs.

What I don't get is what he meant by injectors going static at 14.5ms at any rpm(I am assuming that's what he's talking about). When they go static, they stay wide open and don't close so the time it takes it to open and close is irrelevant.

On our cars the injector can really only go static above a certain rpms. For nondbw the ECU limits available pulsewidth to 16.33ms and dbw up to my year is 23ms. So it can only go static above the point where the ECU limit meets rpm limit. My point was the injector itself has nothing to do with the pulse width limit but rather the ECU and rpm. Unless my understanding is wrong. Dutycycle = pulsewidth/pulseperiord. AFAIK injectors don't have a rated max pulse period.

Also I have raised question about the source of the FPR info before but it was never answered. According to the tuners I spoke to, our FPRs are not rising rate, they're constant pressure FPRs. So I don't know who's right and who's wrong here.

If you're interested take a look at this spread sheet. I did some calculations of the exact available pulse width for all rpm points. I also calulated the dutycycle.<ul><li><a href="http://www-ec.njit.edu/~dxd0835/Images/LOG-01-110-xxx-xxx.xls">http://www-ec.njit.edu/~dxd0835/Images/LOG-01-110-xxx-xxx.xls</a</li></ul>