injector consistancy and calibration

[JayMaechtlen]

In a recent thread, there was discussion of injector-to-injector variations in a continuous-flow system, and the suggestion that modern efi injectors might not be any better.
What about the possibilities of calibrating the 'brain' for an installed set of injectors? The system could be tested bu cutting out injectors or varying duty cycles to determine the response of each unit. This (matching procedure) should give better emissions, economy, and power.
Perhaps some of the OEMs do this already? The VW dealer dinged us at a major tuneup for "calibration"- was that a snake-oil ripoff, or something valid?




Jay Maechtlen

 

[patprimmer]

In my opinion, ballanceing fuel flow cyl to cyl or correcting for injector variations is only valid if you have even airflow from cyl to cyl, and so long as the injectors maintain the same relative flow differences through their operating range and through time.

The other alternative is individual Oxygen sensors per cylinder with individual fuel tuneing channels for these sensors. this then corrects for air and fuel flow variations, and for non uniform variations and for intermitent or time dependant variations, however, I wouldn't like to be the one trying to justify the cost of such a system

Regards
pat

 

[GregLocock]

Well, in the final analysis the injector to injector variation was so slight that no compensation is needed for that.

However, there are substantial variations between cylinders - wall temperature, air distribution, exhaust backpressure, scavenging/charging differences, etc etc.

I think an adaptive EEC calibration would be a good thing, and give the sensitivity of idle vibration to cyl-to-cyl variation, I bet somebody is working on it.



Cheers

Greg Locock

 

[dgallup]

Typical injector production tolerances are +/-3% static flow rate and +/-4.5% dynamic flow @ 2.5 ms. That is new. During the life of the injector they are typically allowed to vary an additional +/-3% static flow rate and +/-6% dynamic from the initial calibration. Guys like Russ Collins (RC Engineering) can sell you more accurately matched sets. It is best to run the injectors a while to break them in and then do the matching but this gets really expensive.

Good port fuel injection manifolds do an excellent job of balancing the air distribution between cylinders. TBI and carb manifolds can't do nearly as good a job because they have to try to evenly distribute air and fuel.

It is possible to balance the A/F of individual cylinders in 4 cylinder engines with a single O2 sensor. It requires a lot of sophisticated software though to filter the signal and come up with the correction factors. I've seen such a system running on a dyno.

As far as calibrating the ECU for each injector, the Ficht DI system (which helped drive OMC into bankrupcy) does this. These injectors are rather non-linear and can only be calibrated by mixing and matching parts. So they measure each injector, bar code it and then download the data into the ECU at engine build. To avoid a major service headache they keep all the best injectors wich fall closest to the nominal curve for service. When a service injector is installed they ground a pin or something on the ECU to tell it to use the default calibration.

 

[Jefnes]

'calibration' charge from the VW dealer...mmmm

I tune VW M2.9 and M5.9 Motronic 'powered' cars.
and there is no real calibration that the dealer
can do (tuning wise anyway). The newer ME Motronic ecus, with the non-cable
throttle, are even better (more ecu power).


These ecu's keep the engine in-tune pretty much by themselves, as long as all the sensors are functioning properly and you stay within the control limits, typically
+/- 25% change in fueling. Anyway, if anything is
out of whack you'll get a check engine light.

Jeffrey Atwood