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drs_resistor
I put a DIPx8 socket in line with the grey wire. The 4 pins on each side are stapped together. So I can put a variety of small resistors (22ga leads) into the socket in parallel to get differenct effective resistances. To grey wire is the one of the three that is at the far end from the ground wire, which is black. To confirm that the wire that you are cutting is the right one, measure the resistance from the contact on the harness lead (disconnected) to ground. You will detect the resistor the goes to ground in the ECU. This measured at 960 ohms on my Fluke 77 DMM.
I put in 3 100 ohm resistors and a wire shunt, to get zero resistance. Then I let the engine warm up for quite a while to get the O2 sensor working. Then I shut down and pulled the wire shunt and started right up again. The engine did not have any running issues at all. So I went for a spin to let the ECU do whatever adaption it wanted to do. Then I pulled one resistor to go from 33 ohms to 50 ohms. No prolems there either.
So I was able to find one fuel cut on the drive to work. It was in the mid 30's. I adjusted the pop-off valve so that it was out of range and not venting that I could hear. So this is a big improvement. I might pull one more resistor to get 100 ohms. My boost seems to be around 16 PSI now. Hard to say how acturate these VDO or other guages are. The are graduated, not calibrated! They are good for reference only. And like many of the VDO's, the needle at rest is a bit below 0 PSI guage. But I am at a pressure slightly higher than I have ever run continuously.
So my objective to increase the boost range by a minor amount, to shift the fuel cut pressure up, to get more head room for my MBC's pressure overshoots. I have the MBC presssurized from the throttle body, which is a worst case location as far as pressure overshoots go. But I must note that it seems that the Viggen IC does reduce this tendancy somewhat.
With 50 ohms, the stock boost indicator still reads at zero when the engine is not running, ignition on. For folks who do major resistor modes and use the BPC for boost control and modify the fuel rail pressure, the indicator will read well below 'zero'. I am suspisious that for minor resistance changes, the ECU is detecting what a zero reading should be from before the engine is started. So the minor resistor mods might be quite stealthy. For larger changes the ECU perhaps cannot compensate the display that much. If I do the 100 ohms, then perhaps that might change the stock boost indicator. Whatever the outcome, you probably will have no use for an inline socket. You can just solder in a resistor and be done with it. For me it make for easy changes.
If this works, and I am able to get rid of fuel cuts with the pop-off valve adjusted to be a non-player. Them there is the potenial that folks with MBC's can do a 50 or 100 ohm resistor mod, and locate the MBC pressure tap to the TB. The desired outcome would be no or very few winter time fuel cuts and the boost pressure will not roll off at high RPMs. The high RPM boost rolloff is the result of feeding the MBC pressure from upstream of the IC. And the hose barb on the turbo compressor housing is the worste case location. So perhaps we will be able to eliminate the two down problems that MBCs have, other than been affortable and easy to install!
This applies to T5 ECU's. Don't even think about doing this to a T7 ECU or any other management systems. It might be possible, but not to my knowledge.
Stay tuned!
95SET, various intake mods, Viggen IC and a funnel mod which I need to take to a duct mod this winter.
(I don't consider my 'engine' highly modified, I consider it highly optimized, Bruce will probably take issue with this :0 )
(PS, if you do a major resistor mode, you will have fueling and running issues. The fuel rail pressure is not high enought. And with any changes to boost or the engine management system, you are your own warranty. You need to know what you are doing and be well aware of the issues. I can't go into all of that in this post. Thats what this BB is all about.)
posted by 208.24.179...
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