Injector Values

[bigmatt]

My 05 1.9CDTi (120) Vec C is mis-firing. A mate at work put the op-com on it on Friday to read the values of the injectors - Number 2 was constantly at +5, the others varied.

What are the optimal readings that they should be at? I have searched all over the web and various forums so was wondering if anyone knows what they should be. I think I will be replacing each one, but want to know which ones to replace so if anyone has the values they should be at when the op-com is on that would be great!

Cheers

Matt

[the-wizard]

My 05 1.9CDTi (120) Vec C is mis-firing. A mate at work put the op-com on it on Friday to read the values of the injectors - Number 2 was constantly at +5, the others varied.

What are the optimal readings that they should be at? I have searched all over the web and various forums so was wondering if anyone knows what they should be. I think I will be replacing each one, but want to know which ones to replace so if anyone has the values they should be at when the op-com is on that would be great!

Cheers

Matt

Think there supposed to be within -3/+3 but not 100% sure as thats for the 150 ps, remove injector plugs & spray with elec contact spray to see if there's any difference.

[DieselWig]

I've never understood this. How does the ECU know to inject different amounts from each injector during the life of the injector? I know that injectors are tested at a test facility prior to fitting to an engine and can have fuelling corrections programmed into the ECU based on the injectors performance as new, but once installed, how does the ECU recognise individual injector performance? I can understand that various sensors can inform the ECU of different conditions, such as intake pressure, pedal position, temperatures etc., but what tells the ECU to instruct the injectors to deliver more/less fuel on an individual injector/cylinder basis?
I know I've asked similar questions before and have been told that knock sensors can see this, but I didn't think the 1.9cdti had knock sensors - could be wrong.
Any info would be great.

[jonnyaykroyd]

I've never understood this. How does the ECU know to inject different amounts from each injector during the life of the injector? I know that injectors are tested at a test facility prior to fitting to an engine and can have fuelling corrections programmed into the ECU based on the injectors performance as new, but once installed, how does the ECU recognise individual injector performance? I can understand that various sensors can inform the ECU of different conditions, such as intake pressure, pedal position, temperatures etc., but what tells the ECU to instruct the injectors to deliver more/less fuel on an individual injector/cylinder basis?
I know I've asked similar questions before and have been told that knock sensors can see this, but I didn't think the 1.9cdti had knock sensors - could be wrong.
Any info would be great.

I think the crank angle/position sensor is fast enough for the computer to measure the acceleration of the crank with each combustion stroke. If say cylinder 1 has less acceleration than the others it will add more fuel to injector 1 to compensate.

[DieselWig]

Maybe the camshaft sensor then? If it has sufficient resolution to detect speed change during a revolution (which maybe it has to have for injection start of injection timing), then this would make sense. Can anyone confirm this is what happens?

[jonnyaykroyd]

I would have thought crank angle would be higher resolution than cam because there are 720 degrees of rotation to every 4 stroke compared to only 360 degrees at the cam?

Piston acceleration is one possibility however I also found this info in dieselclass.com.

http://dieselclass.com/Fuels%20Files/Common%20Rail%20High%20Pressure%20Fuel%20Injection %209-2010.pdf

"Zero Fuel Mass Calibration (ZFC)
Just as mechanical manufacturing tolerance for injectors requires changes to injector
energizing time, injector wear also changes injector operating characteristics. Injector
deterioration contributes to increased emissions calling for a re-calibration of the stored
correction factors which compensate for unique operational behavior. Without a strategy
to recalibrate an injector, a vehicle could pass out of compliance with emission standards
and emission system durability requirements. The process of recalibrating injectors
during service is called Zero Fuel Mass Calibration (ZFC)
One common technique for accomplishing ZFC correction occurs during vehicle
deceleration. Calibration occurs when the engine is driven only by the vehicles kinetic
energy and no fuel is injected into the cylinders. Fuel rail pressure is adjusted to a
specific value. With no movement of the throttle position sensor from idle position and
the engine in an over run condition, the ECM will begin to increase energization time to a
single injector. When a measurable engine speed increase is detected, the ideal energizing
time stored in the ECM based on initial calibration codes is compared to the actual time
to produce the engine speed change. Mathematical comparisons made between the two
values result in a change to stored correction factors. Each time the conditions for ZFC
are met, another injector is recalibrated."

However if with Op-com or a scanner the ECU can be seen adjusting the injector correction factors at idle then it can't be ZFC and must be based on piston acceleration.

[jonnyaykroyd]

Some more good info (basically a 2 part article on common rail system):

http://www.autospeed.com/cms/A_108104/article.html
http://www.autospeed.com/cms/article.html?&A=108105

The latter (part 2) describes "smooth running control" which is basically the adjustment of individual injector quantity using engine speed. Crank sensor provides the speed and cam sensor tells the ECU where the engine is at in the firing order (so it knows which injector to adjust).

[DieselWig]

Great info, thanks jonnyaykroyd - and yes, you're 100% correct, crankshaft sensor would make more sense for detecting speed variability - I wasn't thinking straight.

If this is indeed true of the 1.9cdti, then maybe bigmatt's #2 injector is playing up - not that I doubted the-wizard, just that I wasn't sure how the ECU could know. Sorry for hijacking your thread bigmatt

[bigmatt]

Hi,

I managed to get my Op Com and below are the values at 850prm approx and 2000rpm approx

It would appear No 2 is stuffed - what about the others they look constant!

Value2.jpg

Value1.jpg

Cheers

[jonnyaykroyd]

It's interesting how number 2 hardly varies at all with the change in load/rpm, whereas the others vary 0.3-0.5mg/stroke.

Maybe 5mg/stroke is max correction that can be applied.

On the basis that it's trying to add more fuel (and lack of fuel is the cause of your misfire) i'd be looking at checking 1) Injector wiring continuity - could be a high resistance fault, or 2) try a DIY injector purge/clean: http://www.youtube.com/watch?v=DuTTb_acdxs

With the clean you basically run the engine off the cleaner (which is something like 60% diesel). To do this you have to loop the fuel out line from the fuel filter straight back to the fuel tank via the fuel return line so the lift pump in the tank can still run and you don't spray diesel everywhere.

I can't understand how 3 out of the four injectors look in perfectly serviceable condition (based on the correction factors you've got) but number 2 is bad. Definitely triple check your wiring. I don't know if this can happen on the Z19DT but on the Z19DTH the injector wiring terminals within the plastic connectors fail - i have a video on youtube showing this: http://www.youtube.com/watch?v=xyhkW0lXoDg

Is you're missfiring constant? or intermittent?