CAN bus and Common rail injection timing

[haggalin]

Hi

My knowledge so far is that diesel vehicles with electrically controlled common rail use measurements such as: engine load, air temperature, engine temperature, rail pressure etc. to calculate the amount of fuel witch is to be injected to the cylinder (i think with common rail there are about 5 seperate injections in each stroke). I imagine that the injectors are just connected with two wires which open up when an electrical current is applied. The amount of fuel is therefor controlled by a control signal from the ECU. Then, by adjusting the pulse width of that signal would change the opening time of the injectors and amount of fuel injected.

My question is: is there anyway of knowing the opening time of the injectors before the ECU sends the control signal? I know that the ECU calibrates the timing before the injection process starts so maybe by sending a request message on the CAN bus or through OBD i could access that kind of information. I was thinking that there would maybe be some kind of PID code i could send out to get that kind of information from the ECU. Does anyone have a thought on how to do this?

 

[MikeHalloran]

I can't think of a reason why that information would be present on the CAN bus, so I'm guessing you can't get it except by hacking the ECU, or direct measurement.

Which brings up a point. You can't 'premeasure' the injection cycle for a given cylinder event, but you can measure the cycle with external instrumentation, and use the collected information to adjust the _next_ cylinder's cycle, if that's what you're contemplating.



Mike Halloran
Pembroke Pines, FL, USA

 

[haggalin]

Thanks for the reply MikeHalloran

The plan is to make this an automatic process where the fuel injection is always 50% or 80% of the amount of fuel injected requested by the ECU.

The ideas for a method are maybe by taking a statistical analysis (similar to MikeHalloran's suggestion) of the timing vs. RPM (or something else), bluffing the measurements (with electrical circuits) which the ECU uses to calculate the injection timing or getting the timing information from the ECU before the process takes place (most preferable choice).

You think the amount of fuel injected can be changed so drastically by modifying the measurement signal without the ECU going into some kind of panic mode.

 

[MikeHalloran]

ECUs for gasoline engines are now so smart that they can infer the health/ presence/ absence of a given sensor, using what they learn from other sensors, or from the system's behavior.

Diesel ECUs are probably not all that far behind. I would not be surprised if the ECU detected your machinations within seconds.

Of course, the same people don't program every ECU, so what you learn on one, may not apply to any others.

I'm not suggesting that you give up. But be aware that your market window may be closing, as ECUs become smarter and more paranoid about their surroundings, and it becomes progressively more difficult (or illegal) to fool them.





Mike Halloran
Pembroke Pines, FL, USA

 

[BrianPetersen]

The correct course of action is to access the code (mapping) inside the ECU, and simply reprogram it to do what you would like. If it is a Bosch EDC17 controller, I think just about all of the common applications have been modified by tuners by now, and the ones that haven't, soon will.

Most people aren't out to *reduce* the amount of power delivery, though. What is it that you are trying to accomplish at the end of the day?

One thing you should be made aware of, is that current diesel vehicles with particulate filters and de-NOx catalysts have multiple sets of operating maps. At any given speed/load setting, it could be operating in any of the following modes which all have different calibrations: Normal operation, oxidation catalyst warm-up mode, passive DPF regeneration mode, active DPF regeneration mode, de-NOx regeneration mode, de-H2S regeneration mode, and probably more. Some of these may be specific to the VW common-rail for North America, but the DPF handling situation is across the board nowadays.

External tampering with injector delivery signals to any meaningful extent WILL be detected by the diagnostic systems. Re-mapping of the ECU, if not done properly to address every possible operating mode, could give trouble with this, too. If the code that is handling the emission equipment expects stoichiometric operation to regenerate the de-NOx catalyst with a certain fuel delivery and EGR rate, and you arbitrarily reprogram it to deliver less fuel, something isn't going to be happy.

 

[TrackRat]

I'm not sure what the OP is looking to accomplish but a lot of so called "tuners" are using interceptor boxes to alter the signal vs. remapping the engines particularly on Turbo apps. This allows easy removal of said interceptor for warranty purposes. As a result several car makers have enabled NVRAM tracking software in the ECU and owner warranties are being voided for documented ECU mods/over-boost operation.

 

[dgallup]

I'm not aware of any injection system that has smart injectors reporting back opening/closing times. Usually the dead time is mapped into the ECU as a function of voltage and pressure. The ECU just adds the dead time to the required duration of injection to get the pulse width for the drive signal. The dead time must be very low on these common rail diesel injectors that can inject 5 times per combustion event.

The only exception I'm aware of was the Ficht system used by the defunct OMC company. That injector's fuel delivery varied so much and was so non-linear they programed in the delivery curve for each injector. Service injectors were actually the best of the best and all fell within a narrow band so the technician could reset the ECU to a default curve if an injector was replaced.

There are lots of black boxes in the aftermarket that intercept the ECU pulse injector and send their own with varying effectiveness. I agree it is much better to just reprogram the ECU lookup tables. You can always set them back to stock if you need warranty service.

 

[TrackRat]

OP-

FWIW Bosch Engineering Group offers aftermarket performance Diesel ECUs if you are interested. These might achieve the disired goal?

http://www.bosch-motorsport.com/content/language2/html/3690.htm