I finally got round to getting the injectors pop tested they have 150K on them so I was just making sure they were OK. The spray pattern was fine and none of them dribbled but the pop off pressure is supposed to be 260 bar and they were all just under 240 bar. Will this make them pop early and in effect increase timing? What difference will the 20 bar loss in pop off pressure actually make? So at what point is it adviseable to replace or rebuild the injectors? I was told it would cost me about $20 to get each injector sonic cleaned and have the pop pressure put back to 260 bar has anyone had this done and was it worth the effort? they quoted me silly money to totally rebuild them, about the same $$$ as some new DDP2s. This is for a commercial 6BT engine. Many thanks for any info.

Gaza

 

I've read that just having the inlet pressure to the injection pump too high will effect timing so it follows that too low pop off will do the same.
As far as percent of normal before it matters I don't know.

I had the injectors on one of my JD tractors adjusted back up to the recommended pop off but it was because some were quite different than the others. The JD tech told me it didn't matter much if the pop off pressure dropped some, most important was that they were the same.

 

I would have to agree with infidel, 'specially the last statement. I would think it would be more important to have them all the same then exactly at 260. Although there would have to be a limit to how far they sink to where you need to rebuild/replace.

 

The actual pressure having dropped around 10% is not a huge deal but it does have some effect. The higher the pressure, the more precise fuel control you get, the lower the egts, and the better your mileage. However, this effect is quite small. I would not worry too much about it for a while, then at some point get the injectors that you want.

The pressure is only part of the equation. As the injectors get older, the holes actually get larger and they flow more fuel but it is less precise. There are people who have gone over 500k on original injectors and what they find when they put a new set of stockers in is that they have significantly less power but also much better fuel economy.

 

That might explain why I can get 27lb of boost when the only fuel mod I have is to move the afc forward.

Gaza

 

I believe 1 bar is 14.7 psi at sea level so 20 bar should be 294 psi could make a difference no ?

 

Percentage wise (7.8%) 290 psi isn't much compared to a normal 3770 psi (260 bar)
How much difference it makes I don't know.

 

I would guess it would b about 7.8% difference.

 

Would my mileage increase by 7.8% if I replaced them with new OEM sticks?
Also when people say they got a 1-2mpg increase from say fitting DDP2s is that from old injectors to new DDPs? as thats not comparing apple to apples.

Gaza

 

There are two factors in mileage if you assume identical injector design. The first is pop-off pressure. The higher the pressure, the more precise the fueling. Pressure and fuel economy are not linearly related. In the example above, I doubt the mileage gain from changing the pop off pressure would be anywhere near 7.8%.

The other factor is the holes and how well they atomize fuel. DDP's website actually has a pretty good explanation of it. The bosch injectors are pretty good but have a rough edge which is where the ddp's do better. The cleaner the hole, the better atomization you will get.