Sequential injection - n00b question

[SkyUK]

I've seen a number of posts about advanced ECUs that offer sequential injection for the S6. What is Sequential Injection?

I know the crank runs a 2x120degrees and that at each 120 rise one pot is on squeeze and the other on blow. Does the standard ecu inject juice into both pots at this point or is it something else?

The reason I ask is that one of the 3rd party cats in my new custom exhaust system has exploded down the pipe and the designers/fabricators are blaming it on a backfire, and I'm trying to understand if a backfire is actually quite normal for a S6 engine. TIA

[nawarne]

I believe I'm correct in saying that the standard MBE ecu that was used by the factory was a 'carry-over' from the AJP V8 which, like the Rover V8, used a batch injection system. Thus, on both V8's each bank is injected according to the cylinder on 'ignition'....so yes, all cylinders on that bank receive fuel, which probably promoted the pops and bangs so beloved of us TVR owners.

The MBE ecu was also used on the Speed6 - likewise injecting batch-wise (but to 3 cylinders, instead of 4) hence the split of 123 and 456 cylinders. Sequential injection aims to inject only to the cylinder that is firing..I believe you can still programme these modern ecu's to slightly overfuel and give you pops and bangs on the overrun. I guess sequential injection should give you better economy when at optimal set up.
Nick

[Richie C]

The fuel isn't going to get into the cylinder until the intake valves open.

[Walford]

nawarne said:

I guess sequential injection should give you better economy when at optimal set up.
Nick

very little effect on economy, big reduction in emissions at low TP

just what every TVR owners has dreamt of, bring on euro 7,

[SkyUK]

Thanks for the info. I'm still a little confused... Does it batch inject every 120 degrees of crank rotation even though the inlet valve only opens every 720 degrees?

[Richie C]

http://www.carsdirect.com/used-car-buying/how-a-se...

[Mr Jenks]

SkyUK said:

Thanks for the info. I'm still a little confused... Does it batch inject every 120 degrees of crank rotation even though the inlet valve only opens every 720 degrees?

It injects just before the inlet valve is opened. There is no batch injection, each injector is wired and fired individually.

[Walford]

SkyUK said:

Thanks for the info. I'm still a little confused... Does it batch inject every 120 degrees of crank rotation even though the inlet valve only opens every 720 degrees?

stock TVR MBE does not run a cam sensor, so has to inject half the fuel every crank rev this could be in one pulse or more

[spitfire4v8]

Mr Jenks said:

SkyUK said:

Thanks for the info. I'm still a little confused... Does it batch inject every 120 degrees of crank rotation even though the inlet valve only opens every 720 degrees?

It injects just before the inlet valve is opened. There is no batch injection, each injector is wired and fired individually.

I'm not sure that's true. the injector may well fire before the valve opens, but only if the pulse width exceeds the valve open time. I think it's common to set the injection end point relative to the airflow in the port, ie set the injection end point just before the air stops flowing into the chamber, then widen the pulse width of the injector forward from that point as load increases. This means that at low loads you're injecting when the inlet valve is open but more importantly when air is passing into the combustion chamber, the two aren't necessarily the same thing especially if racey cams are used. If you're after good emissions you need all the fuel to stay in the airstream so injecting before the valve opens is a no-no as the air is still and fuel will drop out onto the inlet runners. At high loads you have no choice but to have some of the injection event occuring when the valve is shut just to get enough fuel in there (unless you're running high pressures and large injectors or a duel injector per port system?).
comments?