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No fuel cuts on the way home from KC. But not much opportunity to get on boost on the commute.
So in town I stopped and yanked one more 100 ohm resistor, now there is one left and the inline resistance goes from 50 to 100 ohms. The stock boost indicator now shows a change for the first time. Its now shifted about two needle widths to the left of 'zero' when the engine is not running.
So no fuel cuts on the way to the house, as expected. But the strange thing is that the engine seems more powerful, and the boost is a bit higher, which does not make any sense at all. Perhaps with the ECU faked out, it was previously cutting back on the ignition timing when it saw that it was near the fuel cut pressure. That is wild speculation. I can't explain why going to 100 ohms from 50 also increased the boost a bit. The MBC can't know whats up. But if there is more exhaust energy, the wastegate would need to be closed more than usual to maintain pressure, and the MBC will not compensate fully for that. So that would be consistant with the previous speculation. Well I guess that is better than the boost going down.
I am thinking that a resistance between 50 and 100 would be better. Less of a stress on the O2 sensor adaption algorithm. If there is a problem, there will be a CEL. My commute at 75 mph to KC should resolve that issue, if there is one. Some engine packages adapt very easily to these things, some do not. Variations in the fuel pressure regulators etc. So some variation in vehicle response is known to happen and is expected sometimes. There is no need to have a resistance greater than a value that provides relief from fuel cuts. That might be a different value in the dead of winter. ( I have been getting the wisdom of someone more experieced in these things.
So what is the impact on MPGs? Well on the way home at 50 ohms I got around 30 mpg-US with a small side wind. So no effect there. Will see tomorrow how that goes with 100 ohms. In theory with the ECU readapting to things, there should be no effect on the MPGs.
So I am feeling that this will work out very well.
Restating the objectives:
Use a MBC, move the pressure tap to the TB to eliminate high RPM boost droop or taper. And do the resistor hack on the MAP sensor to shift the ECU's view of what the pressures are. Continue to seek around 15 PSI of boost on the MBC, not higher. The fuel cuts from pressure overshoots will be eliminated. This should address the main complaints with the MBC's other than the high cost ($35US).
One may have to spend pocket change on a resistor and some longer VAC line. I don't know how easy it is to tap into manifold pressure on the various years. The hoses to the small orifices at the throttle plate should not be used. Do not use the hose to the MAP either. I made up a 3/4x1/4x3/4 TEE by bonding a hose barb into a 3/4" hose. I think that there is a plastic heater hose component for Fords on the racks to that might do. It could be splice inbetween the TB and IAC valve. There is a provision for a port on my TB which could be drilled out and tapped. So such details need to be worked out. My current rig with the pop-off valve is very much deviated from what you might want to do.
It will be possible that one could go for more MBC boost pressure. You are on your own with that. And again, you do this stuff, you are your own warranty. Don't get negative if something goes wrong. If you are not comfortable with such things, don't do it at all, or wait and see if anyone on this particular bleeding edge gets hurt. :)
What next? I think that the ECU gets chicken when its really hot and cuts back on ignition timing. The intake air temp sensor is around 2K when cold and around 100 or 200 ohms when hot. So make it think that it is not too hot. Add a small amount of resistance. The error of this when cold is minor as the resistance is quite high. When its hot, make the ECU think that its a bit cooler. If the ECU is doing what I am thinking that it is doing, then there will not be that power wall at around 90 to 100F. The ECU will adapt via the O2 senor as usual and will aquire new adaption and correction factors. So that will have to wait for next summer.
posted by 65.68.10...
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