Tuning a non-adjustable FMU
11-19-2003, 12:06 PM
#1
1.5 BAR
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Join Date: Jun 2003
Posts: 1,408
Tuning a non-adjustable FMU
here's my crackhead Idea...
the fmu get's it's "signal" from a vaccum source on the intake manifold, and it boosts fuel pressure a certain degree for how ever much boost/vacuum it sees.
so if you ran a tee from the wastegate actuator into a mbc into another tee with some crazy checkvalve setup, so that the fmu reads vaccum from the intake manifold and then reads boost directly from the turbo.
you'd be getting more psi than the engine is actually seeing because of the intercooler.
So the fmu is putting more fuel into the engine than is needed, so you can "dial" back the amount of boost it sees with the mbc and the vaccum will stay the same because the checkvalve configuration would offset that.
the fmu get's it's "signal" from a vaccum source on the intake manifold, and it boosts fuel pressure a certain degree for how ever much boost/vacuum it sees.
so if you ran a tee from the wastegate actuator into a mbc into another tee with some crazy checkvalve setup, so that the fmu reads vaccum from the intake manifold and then reads boost directly from the turbo.
you'd be getting more psi than the engine is actually seeing because of the intercooler.
So the fmu is putting more fuel into the engine than is needed, so you can "dial" back the amount of boost it sees with the mbc and the vaccum will stay the same because the checkvalve configuration would offset that.
11-20-2003, 07:04 AM
#4
1.5 BAR
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Join Date: Jun 2003
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Re:Tuning a non-adjustable FMU
yeah, I'm gonna try it whenever I get my setup pieced together and running, the question is, which disc should I use? 8,10,12? I guess it should be a 12 just to be on the safe side... thought it shouldn't matter.
11-20-2003, 08:26 AM
#7
1.5 BAR
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Join Date: Jun 2003
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Re:Tuning a non-adjustable FMU
after thinking about it some more, I figure since MOST people are seeing rich conditions anyway from the intake manifold pressure, it would be kind of pointless to go to all that trouble and plumb it to the wastegate actuator...
so I came up with this...
the BLUE line is for the vacuum source, and has a checkvalve setup similar to the map sensor setup, so that the fmu only gets vacuum from that line, and then when boost i present it shuts off..
The RED line is for the boost/mbc that the fmu gets. when boost is present, the mbc meters off a little bit and the fmu senses less psi, therefore less fuel and the ratio can be leaned out. the other line is plugged by the checkvalve setup, and even if that setup should fail, then you'll just go back to running rich.
does this look/sound correct?
I'm kind of worried that there MIGHT be a point in between the checkvalve closing and the mbc allowing boost through when there is boost present, and I'm not sure how this is going to affect the ratio... because there might be boost present in the manifold but the checkvalve and mbc are both closed, this would only be a short amount of time if the mbc is adjusted properly, so I guess that would be the tuning point to listen for.... any suggestions?
so I came up with this...
the BLUE line is for the vacuum source, and has a checkvalve setup similar to the map sensor setup, so that the fmu only gets vacuum from that line, and then when boost i present it shuts off..
The RED line is for the boost/mbc that the fmu gets. when boost is present, the mbc meters off a little bit and the fmu senses less psi, therefore less fuel and the ratio can be leaned out. the other line is plugged by the checkvalve setup, and even if that setup should fail, then you'll just go back to running rich.
does this look/sound correct?
I'm kind of worried that there MIGHT be a point in between the checkvalve closing and the mbc allowing boost through when there is boost present, and I'm not sure how this is going to affect the ratio... because there might be boost present in the manifold but the checkvalve and mbc are both closed, this would only be a short amount of time if the mbc is adjusted properly, so I guess that would be the tuning point to listen for.... any suggestions?
11-20-2003, 08:50 AM
#8
1.5 BAR
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Join Date: Jun 2003
Posts: 1,408
Re:Tuning a non-adjustable FMU
okay I figured a mbc controller wouldn't work, atleast the way I thought of a mbc, I think the work by not allowing the wastegate to see ANY boost until they open? which would eat hairy ***** for furl management. so I came up with this...
it's basically the same as a mbc controller, only the spring/ball bearing is adjusted totally loose, so all boost can get past it whenever it wants, the only reason it's there is to shut off when vaccum in present and the vacuum flows through the other checkvalved line.
So the boost comes up to the ball bear and immediately pushes it out of the way, and from there it either goes off to the fmu or a certain amount is bled off with a ball valve or something. you adjust how lean you want to go by opening /closing the ballvalve a certain amount.
The next question I have is, if you have a bleed setup that bleeds say 1.3 psi at 2 psi... will it bleed 1.3 psi at say 6-7 psi, or will it bleed more like 4 psi at that level? Is the boost being bled constant or boost dependant itself?
it's basically the same as a mbc controller, only the spring/ball bearing is adjusted totally loose, so all boost can get past it whenever it wants, the only reason it's there is to shut off when vaccum in present and the vacuum flows through the other checkvalved line.
So the boost comes up to the ball bear and immediately pushes it out of the way, and from there it either goes off to the fmu or a certain amount is bled off with a ball valve or something. you adjust how lean you want to go by opening /closing the ballvalve a certain amount.
The next question I have is, if you have a bleed setup that bleeds say 1.3 psi at 2 psi... will it bleed 1.3 psi at say 6-7 psi, or will it bleed more like 4 psi at that level? Is the boost being bled constant or boost dependant itself?
