max Inj duty cycle

[lotus23C]

Hi
I have just done a log on a pretty standard Audi 1.8T and was surprised that the duty cycle on high rpm went over 100%, to 122.9%, but it didn't lean out.


I have 3 questions
I thought100% was that, maximum, am I reading 122.9% correctly?
How is it that an OEM setup is maxed out on a standard engine, with, realisticly very little turbo boost - is this common?
Anyone know what bigger junkyard injectors will fit into an AEB 1.8T?
thanks

[billr]

Yes, you are reading 122.9% correctly, but keep in mind that number is what the MS is trying to command the injectors to do. Obviously, "all the time" (100%) is the most an injector can be open. If it isn't showing lean, there are many other factors that could be involved. As always...


Yes, it makes no sense for an OEM to use injectors with a lot of extra flow. That would increase those pesky dead-time and voltage-comp problems we discuss here often, and (most) OEMs are trying to keep in compliance with emissions and CAFE regs that we can even ignore.

Am I reading the screen-shot correctly, MAP is getting up to 184 kPa? That is hardly "very little" boost, if this was an NA engine in OEM config. If OEM was already boosted, then what was max boost and rpm for that? Increasing rpm from OEM max also impacts the available max injector DC.

[lotus23C]

Yea, thanks Bill. Engine was always boosted. I was just surprised there wasn't much in the way of headroom with the injectors. Yes, it shows 184kpa, but that's all gone after 5500rpm -ish and it's down to 133kpa, or 5psi of boost, soon after. Glad I didn't wind up the boost duty to get more, as I hadn't noticed the injector duty problem.

[jacky4566]

You're AFR is around 11:1 which is probably richer than the stock ecu would run. Best guess would be closer to 12.5-13 for a stock turbo engine. So your asking for more fuel than the original design.

The easy win here is to bump up your fuel pressure but that might not be enough or lock the injectors. Is the fuel pressure rising with boost appropriately?

[whittlebeast]

Are you running a rising rate fuel pressure regulator?

[lotus23C]

Thankyou gentalmen. No, I am using the OEM reg. which, I have just found out is 3 bar and the injectors are 210cc at that pressure, which isn't much. (My 4age has 265cc injectors ) I haven't checked the actual fuel pressure but am picking up an adjustable FPR (1:1 rate) and intend to go up to 4.5 - 5bar. Some chip tuners fit an OEM 5 bar reg. on their K04 upgrade tunes and leave the injectors, so it must work.

[Rick Finsta]

Plot MAPxRPM/100 versus Duty Cycle on a scatter plot. If your injectors aren't delivering a linear amount of fuel relative to the commanded pulse width, you'll see it as an upwards hook at the top right of what should be a nice straight line. Easy way to see if you're running out of fuel and need more pressure differential across the injectors or more volumetric flow to the rails.

[prof315]

Just so you know ... all of the 180Hp model 1.8Ts have 315cc injectors

[Nath88]

Would the theoretical maximum effective injector pulsewidth be the engine cycle time minus the injector dead time? So as RPM goes up (or more squirts), the safe injector duty cycle decreases?

[whittlebeast]

Would the theoretical maximum effective injector pulsewidth be the engine cycle time minus the injector dead time? So as RPM goes up (or more squirts), the safe injector duty cycle decreases?

You are on the right track. See http://www.msextra.com/forums/viewtopic ... 34&t=60224 for more info.

[Nath88]

Ahhh yes that makes more sense. I guess once that pulsewidth is exceeded the injectors will follow a non-linear curve until full open. This may be an issue for my 10,000rpm 2 stroke. Probably skew the VE table a bit from actual.

[billr]

I think that the injectors just stay "full open" once the DC hits 100%. It's not really a "non-linearity" of the flow, it flat-lines at max.

Yeah, the VE table (and much else) becomes rather meaningless once 100% DC is exceeded.

[Nath88]

Yes that is true, I was thinking there will be a non-linear region between where the injector has time to fully close, and where it doesn't try to close at all (100% duty). Where the injector partially closes, then reopens.
For example, if the injector takes 2ms to open, 1ms to close, (1ms dead time, 3ms minimum injector cycle time) and there is 6ms between injection events, the maximum linear duty cycle is 50%. On my 410cc/min injector that should be about 205cc/min of flow. Between 50% and 100% duty cycle there will still be an increase from 205cc/min to 410cc/min flow, but it won't be linear because the injector isn't fully closing. I still think it's best to avoid this area. :/

[whittlebeast]

On a 2 stroke, each injector has one spray event for every rotation of the crank shaft. So twice as many of everything compared to the 4 strokes. My 800 cc, 7500 RPM, 130 hp, 2 cylinder, two stroke ran a pair of 800 cc injectors.

At 10000 RPM, one rotation of the motor happens every .006 sec. If the injector needs .003 sec rest time and you loose .001 sec with dead time, all fueling has to be done in .002 sec. Things get ugly fast on 2 strokes.

Andy

[lotus23C]

Just so you know ... all of the 180Hp model 1.8Ts have 315cc injectors

OK, thanks, but do they fit straight in?

[prof315]

Just so you know ... all of the 180Hp model 1.8Ts have 315cc injectors

OK, thanks, but do they fit straight in?

Yes. Slightly different design but ALL 1.8T injectors fit all 1.8Ts.

[lotus23C]

Just so you know ... all of the 180Hp model 1.8Ts have 315cc injectors

OK, thanks, but do they fit straight in?

Yes. Slightly different design but ALL 1.8T injectors fit all 1.8Ts.

Thanks again for this, thou, I have read info that conflicts with this, mine are EV1 injectors, I'm assuming EV6 injectors will drop in and EV12s won't?

Thanks

[prof315]

So here's the deal as I have observed concerning VW/Audi 1.8T engines and their injectors.......

All of them are "short body"
All of them use an EV1 connector
All have plastic bodies
Some ( AEBs mainly) have a long metal "nose" these are the smallest one in terms of flow rate and are meant to be used with a 4 Bar FPR