diesel injectors 'within tolerance'?

[adhdan]

I took the injectors out my engine this week & cleaned & tested them (volvo AD41B) , 5 of them were opening between 3500-3550psi but one was down at 3400psi. The book says 3700psi. I took 1 injector to a diesel place to make sure my pressure tester was reading correctly & they said 3550psi was 'within tolerance' which got me wondering exactly what acceptable tolerance is for diesel injectors?

I ordered some 0.1mm shims & spent some time going through them measuring the shims they had (they all had 2 shims inside but different sizes from factory calibration) I added 0.1mm to each then tested again & exchanged shims from one injector to another to + or - the opening pressures until i had them all @3700psi (within 50psi of each other)


I used the slow-mo camera on my phone to capture the nozzle spray & record the pressure gauge to get accurate readings. It works very well as you can go frame by frame. My iphone was doing 240fps in slow-mo. I couldn't upload videos so I've added in some screen shots

slow-mo capture of the nozzle firing


the exact moment before the nozzle opened and the needle dropped



I haven't got injectors back in yet & i don't know if it will make any difference but they all still work after dismantling them each several times which i think still counts as a win

 

[Bilgediver]

As well as opening at the correct pressure do they snap shut as you operate the lever slowly and then crack again without any dribble in between, This is important and may not show problems if you only pump quickly A long slow pump stroke and they should crack reputedly and not continuously .

 

[adhdan]

As well as opening at the correct pressure do they snap shut as you operate the lever slowly and then crack again without any dribble in between, This is important and may not show problems if you only pump quickly A long slow pump stroke and they should crack reputedly and not continuously .

they would crack repeatedly like a machine gun rather then a single long spray. A few leaked a drop or 2 back from the fuel return but none wept from the nozzles that i could see. I pressured them to 3500 & counted to 10 while looking for drips.