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Injector duty cycle prematurely reached ?

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Hi guys,

Im looking at a friends vw 1.8t high powered drag car at the moment which has a running fault

it has 1300cc injectors twin 044 pumps with a holley lift pump VP C16 race fuel and in my opinion is reaching a 100% injector duty cycle far to early ( around 550hp ) should be enough fuel for a 1000 hp when using the injector calculator built in to the Nira ECU,

The car has been previously run with more power with the same hardware with no problem at the track running high 9s.

all of a sudden it felt like the car went in to limp mode then power returned but hasn't run cleanly since under load

Things ive checked and noticed..

fuel pressure good and rising relative to boost

injectors scaled properly to ecu using the built in calculator in the Nira software

VE table all above 1 ? why is this ?

Will not run up to the rpm limit cleanly on a dyno run. around 6600 to 7500 hesitates and should run to 8500

Not running lean according to afr

Any ideas / fresh input would be great


Is this a return fuel system or returnless? If the entire VE table is above 1, some kind of base injector calculation is wrong (dead times, etc). What is up with the ignition system? Are you sure it's strong enough to light the mixture?

Hi Raymond

The ignition system is all good and new also was working great when on the dyno last week but ill run through the voltages and ground connections again

The fuel system has a return

Check for a clogged fuel filter, or other plumbing issue (collapsed suction hose, fitting with insufficient clearance, bad check valve), preventing proper flow.

What is your base fuel pressure? What brand of injectors? The more modern injectors can run at 4bar or more base pressure.

I seem to be having this exact same problem with a 2jz supra running ID2000s and a Haltech Elite 2500. I kept getting an error code for fuel injectors being past 90% duty cycle when I would have expected the injectors to be at about 50% DC. The interesting thing is that it also wont reach the rpm limit under full boost. All the obvious stuff checked out okay. Unfortunately I wont have a chance to get it back on the dyno again until March or April, so this will be bugging me all winter. I hope you get it figured out before me.

Do you have a pulsation damper in the system? Seeing so many build threads or posts on the facebook guild page where weird fuelling problems with large injectors on well over rated fuel systems dissappear when they fit a damper.

I've had odd duty cycle errors due to anomalous trigger signals, seems like something to look at since you're not able to rev.

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