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Pressure in stock ECU may not change smoke?

Diesel Tuning Fundamentals

Discussion and questions related to the course Diesel Tuning Fundamentals


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My stock ecu, use fuel quantity just as reference to be converted in Main duration ºCranck, so if I decrease pressure this dont change the actual main duration, it just inject less fuel and also less smoke right? Otherwise if ask more pressure fuel mass increase and probably more smoke

To cut a long story short most ECU will calculate milligram/stroke and a injector flow table with a milligram/stroke and fuel rail pressure reading will give a injector on time as a result.

So going up in fuel rail pressure could give a shorter injector on time.

As for smoke. Your running a diesel and just forget about AFR please in general as it’s can be so misleading. A diesel is all about timing from start to finish combustion.

Lets say you run full power with the air mass needed to run your engine without smoke. Your going to lower your fuel rail pressure and the ECU calculates the extra injector duration needed the inject the same milligram/stroke. After lowering your fuel pressure you now got smoke but why as air mass did not change???? Thing is your end of injection is now to far retarded as end of combustion now takes place @ a later stage also creating a load more EGT as well and engine efficiency is down as well and as a result not all diesel fuel will burn efficient creating some smoke in the presses. As for making power we try to injector fuel as hard and short as possible running fuel rail pressure to the max trying to build big but very stabile injectors and that not easy I can tell you.

I understand this point

But my car is Audi A3 8P 2.0TDI 170cv with Siemens PPD ECU

As the damos file show me:

Driver wish: X-RPM \ Y-Pedal % \ Z-Torque

Smoke: X-RPM \ Y- MAP \ Z-Torque

Torque to IQ: X-RPM \ Y- Torque \ Z-IQ

IQ Limiter: X-RPM \ Y- (20-35) ??? \ Z-IQ

SOI: X-RPM \ Y-Toque \ Z-SOI

Duration (Injection pulse): X-RPM \ Y-IQ \ Z- ºCRK

Pressure: X- (0-700) ??? Y- (0 and 1) ??? - Z- mbar X and Y with same IQ factor dont give me good scale

Pressure correction on temp: X -RPM \ Y- Temp ºC \ Z - %

Boost Request and N75 maps: X-RPM \ Y-Torque \ Z- mbar for Boost and % for N75

So I dont find any IQ to Pressure.. This case I think is IQ to Duration only

Tuning aftermarket ECU you know all maps.. You cant find nice damos for Siemens PPD around web same as find for BOSH

Attached Files

PD or PDE as we call these pump injector are a different story. I would not toy about with fuel feed pressure on them as there is a possibility of injector damage as they work a bit with a pressure balance but OK. Feed pressure to low and you will get vapour in the pump chamber and to hi fuel pressure possible damage to injector, rocker arm and cylinder head on some model VAG TDI engines as the cylhead starts flexing due to hi force on the injector and injector O ring no longer sealing getting diesel in you engine oils as a result.

On these injector it’s all about pump cam profile and plunger travel speed sets fuel injection pressure to some point but there is also fuel spill from the pump chamber to limit fuel pressure so these injectors are more complicated than you think. Fitting a bigger nozzle will give more fuel delivery but big chance in deviation in fuel metering stroke between injectors and possible poor low power performance as fuel injection quality will suffer due to bigger nozzle holes with less nozzle velocity/bigger diesel droplets.

So all you have to play with is start of injection and injector duration.

I know this injectores and this ecu not easy, and its not all people tune this ECU but I saw people with 300hp+ with sotck injetores, as you see I'm runing max 27 SOI and around 50 duration, and also run without smoke at 1.9bars tubro boost, so for 300hp I guess its not only duration and soi that they change.. to feed 2.5bars boost with GTB2260vk

Before give more duration I tink better see how much cam profile duration and also when it start pressure the injector

We have done a 2,5L 5 cyl TDI at about 400Hp and this ones runs 52 crank degrees injector duration but need 370 to 350Kpa air inlet pressure. It run 270Hp on the stock injector running 200Kpa boost so well in line with your set-up.

At 320Kpa inlet pressure it dos not smoke injecting the same fuel mass but problem is EGT goes up due to diesel not burning fast giving a delay in end of combustion and as prove if needing more boost we get about 10Hp more with the same timing fuel setting but why is this? The injector we use on this engine have bigger nozzle holes so fuel deliver quality is less needing more end of compression temp and a bit more oxygen to burn diesel a lot faster. As a PD fuel system is camshaft activated your unable to injector fuel without cam lift so unable to advance start of injection so on a PD fuel system your limited on what you can do.

Yes I would have a look if there is some more duration/lift on the pump cam but chance is your running out of duration very soon. Non of our DP ECU setting show more than 52 degrees duration. The way to go forward is making a cam with shorter duration and faster lift but I do not think a VAG cylinder head can handle this stress as there will be a load more force on many parts. But yes I like to DP over the newer E5 commonrail as they get stuck @ 280Hp.

That makes sense, so the diference PD to CR is that CR dosent use cam profile to pressure de injector?

Some logs, Max EOI 25.9 at 3750rpm with 49.7Deg and 23.8 SOI get more deg at higger rpm and also more SOI 26.5 but give less EOI

Not tested yet, but will try max EOI 30 at harcut 4750rpm this point give me max 56deg

If at higger rpms you have more injection delay it will not really do 56deg right?

Looking @ a load of maps it looks like these injectors get a lot of fuel spill from the pump chamber @ about 3000Rpm onwards. The hard thing is it’s very hard to test these injector for flow rate as build as the cambox for testing has a lift profile that lift more gentle to eliminate more testing error and fuel delivery deviation by the test equipment it self. Fuel temperature is one of the testing criteria as well indicating that tolerances are very important as well.

So in all it’s hard to say what the real fuel per stroke will be but looks what your adding on duration is about the same as you have to advance @ the same time ending up with about the same for end of injection but still able to maintain same power from max torque onward up to about 4700Rpm so fuel mass/stroke must be getting less as torque is dropping and smoke limit dos not kick in so here you have it I think. One other thing could be less fuel entering the pump chamber in time when RPM goes up explaining needing to go more advance on begin injection so you need to compress what ever is in the pump chamber on diesel and vapour so fuel feed pressure could help a bit there as well. So in all a lot of things that affect fuel delivery and I use my own build aftermarket diesel ECU so making fast changes is not a problem to find power/torque but some of the mapping just looks odd compared to a CR fuel system. PD injectors will be trail and error.

Most stuff we run and test are semi truck and industrial engines with PD injectors and these are more stabile in the fuel delivery over RPM so more predictive on fuel calculations and power delivery but harder to test due to massive power output.

Forgot to mention Bosch is using a thing called BIP on PD injectors. The ECU know when the pump valve is closed by reading data from the injector coil so it compensates for injector delay.

So I tested [email protected] and [email protected] about 54deg @4750rpms, now came more litle smoke and huge power gains and EGT set limit to 900ºC but never reach that limit yet :)

1.960bar boost with GT1756 based on stock GT1749vc next step is 4bar sensor to alow more boost

Also not using stock head, that one crancked in every cylinder and you can also see some parts wihout aluminium because old tunners removed EGT limit

Now using AMC head with litle homemade porting :D