Hey all,

I hear constantly this story but what is the exact reason? is it more HC, CO or NOx?

I am doing research into exactly how I am going to pass emissions out here in AZ when they use a sniffer. Further, I have no cats.

Thanks,
Ben

 

durning the exhaust stroke the intake opens. as the exhaust is leaving the cylinder it creates a vacume drawing raw gas into the chamber and out the exhaust before the exhaust valve closes.

 

duration and overlap are the main emission killers.

 

This sounds correct.

So hear me out then: if we can program our PCM's to wait just a millisecond more before firing the injectors, we could potentially overcome this issue. Correct?

 

Problem with closed loop A/F ratio control is that the air that blows through the exhaust valve during valve overlap will fool the PCM (via the O2 sensors) into thinking the engine is running lean, whether it has fuel in it or not. As a result, the PCM pours in fuel the engine doesn't need, and it runs excessively rich, and you get excessive HC and CO.

I dont' think you can alter the injector timing in the stock PCM. I can with my MoTeC aftermarket ECU.... but never saw that capability in the stocker. Even it you could program the injection timing, you might not want to delay the start of injection. Most systems work on "end of event" programming, which fixes the desired end point of the injector pulse (when the intake flow stops), and calculates backwards from that point to determine when to start the pulse. In actuallity, at high duty cycles, the injector is firing against a closed valve a portion of the time, where it evaporates form the heat and waits for the valve to open and air to carry it into the cylinder. And that applies only to the 94-97 sequential injection. On the batch fire 93's, there is always fuel sitting on the intake valve, waiting for it to open.

 

Well, I am talking specifically about passing emissions only.

My intent would be to just program the PCM to go into WOT with any small throttle response. Once in PE mode, I can program it to actually take out fuel so I can run at 15:1 AFR or so. Essentially I won't be in closed loop anyway.

I am going to dig into the stock PCM because I have heard in fact you can modify the injector firing event.

 

You can program it lean at 15:1 (which isn't really very lean). But you still have open valves and fuel blowing through during overlap. Lean it out too much, and the NOx will go up.

 

I think your concern is going to more at idle for emissions than at partial throttle. Once your rpms increase, the overlap isn't going to mess up your o2's as much.
I've tried using the PE mode to lean the engine out before. Even in PE mode, the fuel trims adjusted for the o2's reading lean.