changing injectors..

[nissan200sx.dk]

When i adjust for bigger injectors, should i chance the master or just %..

[smelly]

Here is the answer I received when I asked this question. I went from 17lb injectors to 72lb injectors.

"72lb is about 4 times more fuel than 17lb so if you have only changed the injectors then you want only about a quarter (25%) of the original pulse width. Also be aware in the Vi-pec the 'master fuel trim' is an adder, not a multiplier like most ecu's, so if you put a value of 50% into the 'master fuel trim' field that will actually add 50% to the current pulse width which give you 1.5 times more fuel (i.e 150%).

So, you are best set the 'master fuel trim' back to 0% and instead use the 'master fuel' setting - change this to about a quarter of its original value (i.e if it is currently 10ms, change it to 2.5ms)

i.e 17/72 = 0.236 = 23.6%. So to inject the same amount of fuel with the new injector you will need approx 24% of the original pulse width."

Hope that helps.

[Simon]

Start by adjusting the master. The trim can then be used if needed as a fine adjustment.

If your doing a full tune the master fuel will be enough and the trim can stay at 0. Tuning will take care of the rest.