NEW INJECTORS what's the cleanest way to adjust constants?

[Turbo-VW-ABA-A2]

Running MS2 3.57 board 2.889 code

Engine: 2.0 T3 turbo 8 valve ABA VW about 200-220 crank hp

injectors: 30lb @ 4 bar pressure

I'm just about maxed out with these 30lbs units (even at 4 bar...) and seeing duty cycles in my logs approaching 102%.

Here are my questions:

1. Why would I see a duty cycle >100%? Do I have some problems with constant settings? Maybe opening time or req'd fuel is off?
2. I have purchased 42 lb injectors which are a better fit for my engine. What constants do I change to get these injectors working without being super rich. Is it just the required fuel that needs to be changed?

I'm very happy with my tune overall and have been keeping an eye on my A/F ratio when the duty cycle gets up there. I have not noticed an "open" injector condition, overly rich, or lean A/F at all even at high RPM's.

My required fuel is 10.0, using single squirt batch simultaneous.

help is much appreciated!

[Turbo-VW-ABA-A2]

o yeah and I'm running 15 psi boost and A/F reads 11.3-11.5:1 even high rpm conditions (6K max)

something tells me the duty cycle calculation is tricking my mind

[DonTZ125]

Ummm... I'm not fully up when it comes to feeding turbos, but it seems to me that if you're getting 11.3 on the WBO2 at WFO redline max boost, then a) your injectors aren't oversized, and b) something's weird about your DC!

[Turbo-VW-ABA-A2]

feeding a turbo motor as opposed to an NA motor isn't that much different. The BSFC is higher for a turbo motor and will result in the user requiring more fuel to output equivalent hp to an NA motor.

I agree with your comment though. I am not seeing any operating issues with my injectors, only that my duty Cycle calculation is a little strange beng over 100%

I'm going to take a closer look at my datalog to see where I am getting duty cycle >100%. I wonder if it's just a couple of VE cells that are overly rich and I am overlooking??? It could be AE activiating also. I don't think it is though.

I dunno... any other thoughts?

btw idle PW is about 2ms, max I have seen is about 22ms.

[Bernard Fife]

T-vw...,

The duty cycle values are calculated based on the combination of VE, req_fuel, opening time, etc. They are not measured duty cycle values (because this isn't measured). Values over 100% aren't physically possible, but they are 'calculated' values based on your injector flow rate and tuning parameters.

If you see values over 100%, and your engine is not running extremely rich (either from the VE table or accel enrichments), then this indicates that you do not have enough fuel flow to support your engine's power (by the amount the indicated duty cycle is over 100%). Note that duty cycle2 has no meaning if you are not using dual tables.

In your case, even though you are seeing more than 100%, it seems that your AFR is okay, so 100% actual duty cycle (i.e. max injector flow) is probably enough (but leaves no margin at all if anything changes in the airflow). It also means you are completely unable to tune there, because any changes you make won''t change the amount of fuel delivered (until you are are under 100%).

This is the duty cycle of injector driver #1 (and injector driver #2 if dual tables option is not selected). The duty cycle is the percentage of the time available that the injector is opening or squirting. Values over 100% are not physically possible, and indicate that the settings in MegaTune exceed the capabilities of the injectors (which may be too small).

This is here: http://www.megamanual.com/mt28.htm#f

In theory, you only need to change the req_fuel for your new injectors. But that depends on your opening time being very accurately specified. Errors in the opening time will show up most at low pulse widths (idle and cruise), so you may have to re-tune those a bit.

Lance.

[Turbo-VW-ABA-A2]

Lance,
thanks for the help in explaining the difference between calculated and actual values in MT. That's a great link. The hp figures for the engine do indicate i'm at the very limit (theoretical) of the exisitng red top 30lb/hr injectors. I have not messed a ton with tuning WOT VE numbers (I dug into the spark map first to find power) however, certainly I will be keeping an eye out on my A/F as the RPM's increase. Datalogs have shown steady a/f in the 11.3-11.5 range WOT even up to 6K rpm so that's a good sign.

I used the opening time suggestion of 1ms for the Bosch red tops. Whether it's wrong or right----you got me!

My VE values just about top off at 135 (according to the manual they should not exceed 130), so perhaps I need to turn my required fuel up?

In the end it's just a calculated value, so I guess it's really a matter of fine tuning the VE, req'd fuel and opening time to make sense of duty cycle??? I'm just not sure how much weight can be put on the duty cycle value......or I guess how much I should worry about it.

It makes sense to upgrade my injectors at this stage anyway, so I'll take that route to be on the safer side. As you mentioned I can assume an opening time of 1ms (same bosch type injector EV1 style, actually motorcraft injectors) for the new ones and just adjust req'd fuel.

thanks again for the help

-Paul

[Turbo-VW-ABA-A2]

UPDATE: This past weekend I was able to fit the 42lb/hr Lucas/Delphi units.

Changes I made to MegaTune: Required fuel was 10, now 7.5. Opening time was set at 1ms, I chose 1.1ms based on another users input on the forums. Also, I went with a 3 bar regulator as opposed to the 4 bar I was using with my 30lb injectors. Reasons here were lower pressure to improve pump life and lower chance of fuel leaks etc. Technically my fuel pump should draw less current, but have not confirmed.

Here are the (on the road) results:

1. Tuning high load areas of my map is easier (more resolutiuon). With my old injectors it appeared a small VE change meant huge chnges in A/F esp high load rpm. No longer the case.
2. My Duty Cycle calculation is about 73% max, much better than my 107% using the 30lb injectors.
3. Off idle response seems to be easily tuned via VE or accell enrich. I had trouble doing this before.
4. WOT used to go full rich (in the 10's A/F) when my injectors would max out, now the A/F is actually controlled to 11:5 or so all the way to redline. This should make more power, and save some fuel.
5. Was able to bleed the wastegate valve to achieve 1-2 more psi under full boost. Of course more injector means more boost available.

thanks everyone!