Merc PCM555 vs GM MEFI4B ECU
01-13-2006, 09:37 AM
#11
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Re: Merc PCM555 vs GM MEFI4B ECU
By the way guys, Volvo Penta may be changing the ECM they use for one that will be programed for sequential injection.
I suspect the difference in the 420HP rating is do to the crappy cast iron exhaust that VP still has on their engines. I here that may also be changing...
I suspect the difference in the 420HP rating is do to the crappy cast iron exhaust that VP still has on their engines. I here that may also be changing...
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Patrick
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01-13-2006, 04:13 PM
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Re: Merc PCM555 vs GM MEFI4B ECU
Originally Posted by Rage
Dave,
Thanks for the explaination.
I suspect I am missing something major here, not unusual. My layman's undestanding of a V8 IC engine is that there are eight individual power strokes none of which happen simultaneouisly to any other ie. 12345678 firing order. If four injectors fire simultaneously(??) every engine revolution (again I assume at the appropriate time for each individual cylinders power stroke) that would seem to mean that each cylinder gets three additional shots of fuel before the appropriate time for its power stroke. Where did I go wrong here?
I assume that the IAC is the fuel injector?
The amount of movement of the IAC stepper motor armature I assume determines the amount of fuel that will be delivered when the injecter fires or is the armature movement itself in fact the firing of the injector? Does this armature movement effect the time the injector is open and flowing fuel when signaled to fire or other? My understanding of the PCM555 is that it adjusts fuel per shot by the 'pulse width' or time the ECU electronically holds the injector open and flowing fuel.
It sounds like two different types of injectors each of which would not work with both ECU's. Again where did I go wrong here because no one has ever mentioned having to change injectors when switching between these two ECU's?
Thanks Dave.
Thanks for the explaination.
I suspect I am missing something major here, not unusual. My layman's undestanding of a V8 IC engine is that there are eight individual power strokes none of which happen simultaneouisly to any other ie. 12345678 firing order. If four injectors fire simultaneously(??) every engine revolution (again I assume at the appropriate time for each individual cylinders power stroke) that would seem to mean that each cylinder gets three additional shots of fuel before the appropriate time for its power stroke. Where did I go wrong here?
I assume that the IAC is the fuel injector?
The amount of movement of the IAC stepper motor armature I assume determines the amount of fuel that will be delivered when the injecter fires or is the armature movement itself in fact the firing of the injector? Does this armature movement effect the time the injector is open and flowing fuel when signaled to fire or other? My understanding of the PCM555 is that it adjusts fuel per shot by the 'pulse width' or time the ECU electronically holds the injector open and flowing fuel.
It sounds like two different types of injectors each of which would not work with both ECU's. Again where did I go wrong here because no one has ever mentioned having to change injectors when switching between these two ECU's?
Thanks Dave.
01-14-2006, 10:08 AM
#13
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Re: Merc PCM555 vs GM MEFI4B ECU
Originally Posted by articfriends
Batch fire injection Pulses all eight injectors once in pairs of four every 2 revolutions of the motor or you could say it alternately fires 4 injectors at the same time every other rpm,its simple but the fuel shot isn't matched to the 4 pistons being at their ideal position in comparison to tdc so sequential port injection makes slightly more power and has more ability to individually supply each cylinder as needed,Smitty
So depending on which of the four cylinders in a batch, an injector will fire on the..
1.) compression stroke for some and power stroke after for some?
2.) only on the power stroke?
3.) only on the compression stroke?
01-14-2006, 05:56 PM
#14
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Re: Merc PCM555 vs GM MEFI4B ECU
Here is some info that explains things, a little clearer maybe.. I copied it from the site that I have been building an ECU to run my fuel injection with. It is called Megasquirt, hoping it gives me a better handle on things than the Cutler I have been using for several years..
Hope this helps..
"Then there are three common modes of injection timing:
batch - all injectors fire at once, but not timed to any specific cylinder event,
bank - ½ the injectors fire at once, then the other ½, and so on, but not timed to any specific cylinder event,
sequential - each injector fires at a specific point in the 4-stroke cycle for each cylinder (i.e., 8 independent timing events)
Throttle body injected cars are usually batch or bank fire, simply because of the geometry. Most port injection set-ups before the mid-1990s were bank fire as well (including GM Tuned Port Injection for the 305/350).
Sequential injection requires:
at least as many injectors as you have cylinders, with one dedicated to each cylinder (i.e., not a 4 injector TBI on a 4 cylinder).
as many injector drivers as you have cylinders,
and also requires a camshaft position sensor (a crank sensor is not adequate for a 4-stroke cycle engine).
However, sequential injection does not necessarily mean you are injecting into an open intake valve all the time. The intake valve is only open less than 30% of the time in a typical 4 stroke engine. Once you are trying to produce more than about 25% of maximum HP your injectors are firing for longer than the intake valves are open. If your maximum HP is correctly calibrated to a safe 80% duty cycle, your injectors are injecting well over 50% of the time on closed valves."
Hope this helps..
"Then there are three common modes of injection timing:
batch - all injectors fire at once, but not timed to any specific cylinder event,
bank - ½ the injectors fire at once, then the other ½, and so on, but not timed to any specific cylinder event,
sequential - each injector fires at a specific point in the 4-stroke cycle for each cylinder (i.e., 8 independent timing events)
Throttle body injected cars are usually batch or bank fire, simply because of the geometry. Most port injection set-ups before the mid-1990s were bank fire as well (including GM Tuned Port Injection for the 305/350).
Sequential injection requires:
at least as many injectors as you have cylinders, with one dedicated to each cylinder (i.e., not a 4 injector TBI on a 4 cylinder).
as many injector drivers as you have cylinders,
and also requires a camshaft position sensor (a crank sensor is not adequate for a 4-stroke cycle engine).
However, sequential injection does not necessarily mean you are injecting into an open intake valve all the time. The intake valve is only open less than 30% of the time in a typical 4 stroke engine. Once you are trying to produce more than about 25% of maximum HP your injectors are firing for longer than the intake valves are open. If your maximum HP is correctly calibrated to a safe 80% duty cycle, your injectors are injecting well over 50% of the time on closed valves."
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