Hi !

Does anyone know how the ECU computes the fuel needed to inject into the engine ? Is it RPM-wise or boost-wise ? I.e. - inject X amount of fuel at 6000RPM or is it inject Y amount of fuel at 12psi ?

Will the car run very rich if I get stage3 M2 ECU and only add DP, CB, Efini Y-pipe and modify my intake to the car (IC being stock atm) or will the ECU actually see that I'm not running full boost and will adopt to that ?

Please don't move this to ECU section, as it's pretty much dead

Thanks,
Tadej

 

Anyone ?

 

I believe it's off RPM it uses the injectory duty cycle. If it was off boost, the ECU could already compensate for higher boost levels.

As far as the injector duty cycle, it doen't add X amount of fuel, I believe it sets the injector duty cycle to XX%. This is why simply adding larger injectors is a bad thing without the proper fuel managment (since 850's running at 80% duty is a LOT different than 1200's running at 80%).

No, the ECU will just run a little richer than normal. It's not a huge problem, it might hurt your gas mileage and rob you of a little performance. Nothing you'll probably ever notice. From what I understand, M2 ECU's are very conservative so you shouldn't have a problem.

 

I am not as educated on ECU's as some on here, but here is the basic concept.

The ECU uses a fuel "map" that looks like a spreadsheet. RPM is on one axis, and boost on the other. The amount of fuel (or injector duty cycle) is based on the RPM of the engine and the boost that the map sensor is seeing. The duty cycle that is in the cell corresponding to the RPM and Boost at any given moment is what will be sent to the injectors. There are many other "variables" that are factored in (water temp, air temp, etc.), but you get the basic idea.

So, if you do not have the mods to match an upgraded ecu, you will run rich all the way across the board.

Hope this help.

Jeff

 

The ECU uses both RPM and boost to determine the amount of fuel to inject, among other things (these are the two major factors). It's essentially a 2D matrix as Jeff says, plus additional corrections for air/water temp, etc.

Based on the inputs, the ECU opens the injectors a specific amount of time. The ECU doesn't select a "duty cycle", the duty cycle is simply a calculated value (total time the injectors are on per rev vs. total time available per rev).

If you use a reprogrammed ECU that is well tuned for a set of mods, and you have fewer mods, you would normally lose some performance compared to a stock ECU or an ECU with a correct program. A stage III would have a lot more fuel added and probably a fair amount of timing retarded, both of which would slow you down. It is best to use an ECU tuned for your mods but one that is tuned for MORE mods is usually okay to use, aside from the possible slight performance hit. These are generalities and obviously there are always exceptions.

Wade

 

Well, don't you think I would run around 13psi with DP, MP, CB, Efini Y-pipe and modified intake ? This is what the ECU in question is tuned for (13psi, but with IC and without Y-pipe)

 

Wade is definately one of the ones I was talking about. He knows more about these ECU's than most all of us on here. Definately one to listen to.

"Just ask, and they will come"

Jeff

 

You learn something everyday on these forums...we almost everyday.

 

Don't read too much into these statements about the reprogrammed ECUs being tuned for a specific set of mods. The programming is actually pretty general. While you can tune these ECUs on a dyno for a specific setup, I don't know anyone who does that regularly. I think that ECU is probably appropriate for your mods. It can handle a bit more, so it may be a bit rich, but it shouldn't be drastically over-rich.

jds

 

Thanks guys for clearing it up

 

how does spark timing factor in here? is it basically another map based on the rpm and boost axis?

 

Exactly. Both the leading and trailing ignition are controlled by seperate maps or matricies based on RPM and Boost. These are tweaked along with fuel in a reprogrammed ECU.

Jeff

 

anyone know of any write-ups on how to ignition timing on say a PFC?

Obviously you just use a wideband to determine whether fuel needs to be added or subtracted, but what do you use for ignition advance/retard?