Oh dear. What a old topic.
These pumps are very mysterious. Pumps them selfs are not limited but but duration is limited. That means that you can bypass stock nozzle limits by changing bigger nozzles. So lets say most of the pumps
are "limited" to 52-54mg/stroke. That is just calculated duration value from IQ measuring solenoid. Every ms that solenoid is open means some mg of fuel. So lets say you get 200hp with 54mg/str and you switch to nozzles that are about 30% bigger. So with that same amount of duration you get 30% more fuel to cylinder in same time. In real life it is not that simple, but in matter of simplifying it is. Therefore you may expect 260hp with supporting mods. That sounds simple. Well it is and at the same it's not. This is the thing that grinds my gear very badly. With VCDS you are able to read your solenoid status, it works mostly between 20-80% value. With 80% value solenoid is reached it's maximum duration, so not that much power gain there after that. Thats how I've seen it. Like you said - it's like theres nobody who exactly know how these pumps work. I'm reaching 80% value with my current nozzles on 4800rpm with 39mg/str and 3800rpm with 43mg/str. 39mg/str is the maximum IQ for stock 150hp engine - so that is very confusing to me. My conclusion is that with really big nozzles filling "chamber" pressure drops and you need more duration from IQ solenoid to keep it up. I really don't know how it really works but this is some conclusion I have made.
So now you ask how come I'm having such a big power with these "+66%" nozzles. Of course there may be that the nozzles I'm having are bigger than they claimed. Other thing is that I've made some mechanincal changes to to vp44. As starter I believe AKN has smallest pump elements of all 2.5tdi engines. I've but bigger 3-plunger high pressure AKE elements to pump and adopted it on pump bench.
You are not able to do much with test bench - it passes or fails. You just need to input pump values you need to calibrate, so with bigger pump head pumps IQ was set very low and thats why I'm having
some rough idle. It's the same thing you have with vp37, that when you set basic IQ level as low you get you are able to have more fuel with same amount maximum IQ. I'm not that good with explaining but let me give some example. So lets say you have pump that has basic IQ 6mg/str and maximum IQ on revs 50mg/str, so there is actually 44mg/str increase in fueling. Then you have pump IQ set to 1mg/str and same 50mg/str you actually get 49mg/str fuel increase and thats 5mg more - more power. If you get my point?
Mainly there are not known options to remove pump ecu limits because the pump ROM is burned after successful pump test on the pump bench. Once it is burned - it stays there. Unless you erase it and burn again. Pumps itself are capable of big power for sure - see 800-1000hp cummins engines with vp44. Problem is how have full access and control over the pump.
Aaand what comes my current setup, it is working very nice. Even with the nozzles that are bit low quality and therefore bit too smokey for my taste. I'm pretty sure car has over 350hp after last mods and has less smoke than earlier with same ecu. I'm on the right direction.
I took one acceleration video few days ago with my "high fuel ecu":
Hoping to get better results on this season standing mile events.
