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this hit me tonight while i was working in the garage. a common problem with cranking up the boost is running out of fuel at higher boost/rpm ranges. many have confirmed this on a dyno. proper way is to go the aftermarket ecu route. however, there have been many attempts to bandaid the stock ecu to make it work. i think i may have another band aid, keep in mind, it is quite crude.
assume a modified engine running 18psi with 30# injectors and rrfpr (just because this is what i am running :) ). my amm is non-adjustable, therefore i need the 300ohm resister to have a proper idle. with this set up, on the dyno, my fuel went lean around 45-5000rpm on up. what i realized (i had thought about this before, but did not give it much time) is that the resistor is used to shorten the injectors pulse width to cause it to deliver less fuel. however, this not only affects idle, but the entire range of the injector. so, we place larger injectors on, and then shorten the pulse width to reduce fuel. granted, we may be more in the optimum range of the injectors that way, but it still seems to contradict the intent.
so, wouldn't it be nice to be able to vary the resistance of the amm while the engine is running? there is something out there called a unichip that can do this, it splices in with the signal from the amm and then 'fools' the ecu to deliver more or less fuel. however, it is almost better to just fork out for the completely programmable system at that point. but, a crude way to do the same thing can be done with relays and pressure switches. picture this, amm set up with 300 ohm resistor for 30# injectors (for good idle quality). now, rig a relay in parallel to the resistor. hook a pressure switch to the relay. the switch can be set for any pressure. again, this is quite crude, since fuel demand is not just based on pressure, but also rpm. however, running 10 psi at 5500 rpm does not require the same fuel as 18 psi at 5500rpm. so for example, set the switch for 10psi. therefore, as long as boost is below 10 psi, the signal will pass through the 300 ohm resistor, thus limiting injector pulse width. but, if boost were to climb above 10 psi, the switch would close the relay and the signal would pass through a normal conductor (lower resistance), pulse width would increase and more fuel would be delivered.
now, since my leaning begins at 4500 'ish, ideally, i would have the relay close at that point. but, max boost is achieved around 2800-3000 rpm. so, any pressure setting for the switch would come on too early (i.e. about 1500 rpm too early), thus the crudeness of this set up. so, maybe set it up for 15 psi or so to delay the extra fuel, and suffer with a little excess richness for 1000-1500rpm or so. note: rrfpr, and 30# at wot are already too rich at lower rpm and wot.
thoughts? keep in mind it's crude, but i may give it a shot since i already have the resistor on and a parallel placed relay will not be difficult to rig. i don't think i'll hop on the dyno for this though. just thought it may spur some other ideas or conversation.
posted by 4.60.1...
, Tue, 5 Feb 2002 11:31:40, Wed, 6 Feb 2002 00:45:49, Wed, 6 Feb 2002 16:21:34
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