Spill Valve Timing / Pre CR Chips:
What is a spill valve?
It allows more or less fuel to pass through the injector pump. Effectively giving us electronic control over how much fuel is injected.
This technology is found on engines such as the 1HD-FTE, 1KZ-TE, ZD30 Di, 4JJ1 and many other pre common rail engines around the 2000-2005 era
Just as with our CR injector chips. A spill valve chip, will allow us to hold the valve open longer than the ecu is allowing, by supplying an earth source to the valve after the ecu has turned it off.
When people talk about spill valve timing, a lot of them confuse this with actual injection timing.
Spill valve timing relates to how long the valve is held open. The longer it is open for the more fuel that will be allowed to pass.
These types of pumps run an advance slide that is also controlled electronically. This is what moves the actual injection timing of the pump. Not the spill valve.
Only a chip that is able to modify the crank angle sensor, can adjust an engines injection timing. As far as I am aware Unichip are the only brand that can do this for every engine type and configuration.
Some engines, mainly older common rail and pre common rail vehicles can have substantial improvements to the power and economy by altering the injection timing. As time goes by the quality of the tune from factory in regards to injection timing is getting better and better, somewhat negating the need to have control over this aspect of the tune.