Injector opening time measurement using Injector Test Mode

Philip Lochner · Post by **Philip Lochner** » Mon Jan 07, 2008 4:54 am

Injector opening time can be measured using injector test mode
Injecor opening time as function of voltage can be measured using injector test mode - or can it?

Both these parameters are very important when tuning an engine.

Some time ago I wanted to do a "before cleaning" and "after cleaning" comparison and lifted the injector rail on a Rover V8 I was working on.

I wanted to check the spray patterns and their RELATIVE fuel delivery when it occurred to me that I could check their opening times by starting with a very small PW and increasing the PW until I started seeing the slightest amount of fuel appearing (in the form of drops) at the nozzle tips. This is how I found that the opening times on these injectors varied from 1.25ms up to 1.55ms (all with same Bosch part no) with most being around 1.4ms.

I also tried to measure the opening time as function of voltage but the adjustable power supply I was using did not have enouh juice to supply the current the car was drawing but with a sufficiently powerful adjustable power supply it should be possible to measure opening time as a function of voltage as well.

The reason I ask "or can it?" at the top is: What is the definition of "the injector is now open" as I'm sure the pintle takes time to lift off its seat until it hits the stop and during this time fuel is flowing in increasing amounts...

AR 67202 · Post by **AR 67202** » Mon Jan 07, 2008 6:14 am

the time from the start of the opening till fully open is negligible, and imo independant of voltage.

The movement of the pintle is so small, i think we can disregard the amount of fuel that might pass during movement.

Post by **efahl** » Mon Jan 07, 2008 7:33 am

http://www.not2fast.com/efi/injector_in ... #openclose

Click on the colorful diagram on the left...

Abbreviated version: mechanical opening time < ~100 usec.

Vicoor · Post by **Vicoor** » Mon Jan 07, 2008 6:00 pm

I don't know about injector test mode, But injector opening time can be measured with an oscilloscope. the best way is to measure current and there is a tell tale "hump" in the wave form that indicates opening and closing. I spent some time trying to gather info onlin about this and the effect of using low impedance injectors with resistors. One very well done article stated that using resistors caused a larger variance in injector open time. I found just the opposite.

I used nippondenso injectors from an '86 Toyota supra. these are 2.8ohms and I used a 10ohm resistor to limit current.

I've attached images showing first with a resistor:

and then without a resistor:

As you can see by the hump the injector close time was almost double without a resistor which would have severely hampered fuel control. I can't wait to get my megasquirt up and running so that I can test this with PWM current limiting.