define injector offset??
10-04-2007, 04:08 PM
#1
define injector offset?? Most sources say it is the time to open an injector.
So if it takes 1 msec to open, and I want a pulsewidth of 1.5, then the pcm really has to hold the injector open 2.5 msec's.
But, a couple of sources have phrased it a little differently.
As the difference between the opening lag and the closing lag.
(it takes longer to open the injector than it does to close it)
So if it takes 1 msec to open, and .25 msec to close, the offset is really .75 msec.
And if I want a pulsewidth of 1.5, then the computer should send a signal for 2.25 msec's, considering that the injector will stay open for another .25 msec after the signal drops.
So if it takes 1 msec to open, and I want a pulsewidth of 1.5, then the pcm really has to hold the injector open 2.5 msec's.
But, a couple of sources have phrased it a little differently.
As the difference between the opening lag and the closing lag.
(it takes longer to open the injector than it does to close it)
So if it takes 1 msec to open, and .25 msec to close, the offset is really .75 msec.
And if I want a pulsewidth of 1.5, then the computer should send a signal for 2.25 msec's, considering that the injector will stay open for another .25 msec after the signal drops.
10-04-2007, 09:54 PM
#3
I want to get a better offset table built for my 60 lb Mototron/Siemens injectors on a SD 2-bar tune for a turbo setup I'm currently running. The car has been down for the past two years and I just got it back on the road 5 days ago. Idle is hunting, smells rich (but could be varying), o2's aren't switching as fast as I'd like, hard warm start. Before I start changing everything else, I'd love to know the offsets are right since they're central to everything else around them.
This build was done a little over two years ago, and I blew the engine on the maiden voyage, one mile from home. So all the parts are basically new, and I never had the tune worked out on the initial build either, since I was just beginning the tune at that time.
All the stats on the net about the 60's say .055 offset, which sounds _very_ light to me.
The other two stats are 1.14 on time and .85 off time, which gives a difference of .29 which sounds more realistic but still light.
Also that .85 off time is based on 600 kpa, but is that the air pressure seen at the outside of the nozzle or the fuel pressure internally to the injector? Is the 600 kpa stat even relevant to a real world scenario? And can that off-time be scaled, if we know what it even is supposed to represent? I can't imagine it being for an injector in a 90 psi boost environment, so it's probably fuel pressure.
If so, then the injector probably closes slower at 60 psi, but how much slower...
It could be possible that the closing time would slow down to something within .055 of the opening time, I suppose.
It's enough aggravation to make me want to convert to a lo-z setup.
This build was done a little over two years ago, and I blew the engine on the maiden voyage, one mile from home. So all the parts are basically new, and I never had the tune worked out on the initial build either, since I was just beginning the tune at that time.
All the stats on the net about the 60's say .055 offset, which sounds _very_ light to me.
The other two stats are 1.14 on time and .85 off time, which gives a difference of .29 which sounds more realistic but still light.
Also that .85 off time is based on 600 kpa, but is that the air pressure seen at the outside of the nozzle or the fuel pressure internally to the injector? Is the 600 kpa stat even relevant to a real world scenario? And can that off-time be scaled, if we know what it even is supposed to represent? I can't imagine it being for an injector in a 90 psi boost environment, so it's probably fuel pressure.
If so, then the injector probably closes slower at 60 psi, but how much slower...
It could be possible that the closing time would slow down to something within .055 of the opening time, I suppose.
It's enough aggravation to make me want to convert to a lo-z setup.
10-04-2007, 10:02 PM
#4
p.s. these injectors won't close without fuel pressure. I had the engine running for minutes at a time, with no fuel pressure, managing the throttle application manually, until I realized my VE table was full of bad numbers on the initial load of the 2-bar tune.
Apparently manifold vacuum will draw fuel through the fuel system, if there is no pressure behind the injector to snap it closed. I learned this when I was unplugging the fuel pump to ensure I was clearing a flood condition.
Apparently manifold vacuum will draw fuel through the fuel system, if there is no pressure behind the injector to snap it closed. I learned this when I was unplugging the fuel pump to ensure I was clearing a flood condition.
