I'm hitting 80% DC at 4600 RPM's and climbs to the 110 range around 6300 RPM's. According to a select few individuals, my car is not making enough horsepower to max out my stock injectors. So my question is can something else be causing them to max out? I have a new fuel pump, filter, and regulator.

 

110% DTC isn't possible. What are you using to datalog?

 

It kinda depends on the definition of Duty Cycle some schools compare the engine RPM (milliseconds per cycle) and the IPW . If the IPW is greater than the firing cycle time then the DC will be over 100%. Others talk about the DC as a straight percentage between 0 and 100% activation. It will depend on your scan tool. ref.. Here is one definition.. http://www.stealth316.com/2-calc-idc.htm that can go above 100% and here is a different one http://docinjector.com/info1.htm that is 0-100%. TTS DataMaster uses the first type of calculation EG: an RPM of 6300 and IPW= 20.95 = DC of 110% .

 

I think its possible. I have stock injectors and mods in sig and im at 86% duty cycle. Any more than bolt ons and id be moving to 30lb injectors. Eric L

 

you can max out your injectors with just a cam/heads combo. you need bigger injectors.

 

I am using TTS Datmaster.

 

The commanded DTC may be 110%, but the actual is only 100%. The open/close point simply over lap and the injector never closes.

I'm not personally familiar with the XFI280 cam, but it wouldn't surprise me if you are indeed maxing out your injectors.

What are your fuel trims and O2 voltages when you get to 100% and up?

 

Fuel trim cell 15, LTerm and STerm are at 128, and O2 are in the 900's.

 

DataMaster uses the correct formula to calculate the DC, dividing the calculated pulse width (BPW) by the time available for 2 crank revolutions. But the DataMaster logs I've evaluated all seem to indicate a higher DC than I would expect. Maybe it reads the BPW wrong.

In any case, why not just go for larger injectors. There is no downside to reasonably oversized injectors.

 

I guess I'm going with the majority and saving up for larger injectors. Would 36's be too big?

 

Like injuneer said there is no downside to reasonably oversized injectors. You can't go to big as long as the car is tuned for them. Get 36, 42 or whatever. If you plan to do more mods in the future get the 42's. It won't hurt anything.

 

mdenz3, I like your definitions of 'commanded' and 'actual' it's easier to understand. It's almost saying at 110% DC the PCM wants 10% more than the injector can put out. (That's if you can trust DataMaster's DC calculation , Fred's post # 9)

 

Mystery Bird:
About the > 100% duty cycle ... you're at high RPMs (6300), you're shifting and probably came off the gas pedal for a few milliseconds BUT the engine RPMs would have increased a few hundred RPM which would shorten the time available for injector "on" time and the air flow (MAF signal) probably stayed the same or even slightly increased because it measures what was an accelerating stream but because of inertia the air column takes a few milliseconds to respond to the momentarily smaller demand. The same for automatics at the shift points ... the small RPM over-run between shifts means the duty cycle calculation has a smaller window for the same (or larger) injector on time which is calculated using RPM and grams of air passing through the MAF at THAT instant. But, 80% at 4600 RPM still says larger injectors are needed.