Quote:
Originally Posted by 320touring
Thanks for the info.
The car runs NO knock sensor, only a crank sensor for timing, and has no ability to advance/retard ignition, hence my concern regarding it's abilities to alter pulse widths..
Also, with some more thinking it occurred to me that the lbs for the engine are devided by 6 (6 injectors) so I need to look at SMALLER capacity 4 cyls, rather than ones with comparable bhp/displacement.
i.e. possible replacement injectors from a 1.4/6 rather than a 1.8/2l
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First, I'm sorry I mistyped a couple of words in my previous post and didn't proofread til this morning. The corrections are in BOLD now.
I don't know exactly what you're running, but even in the older OBD1 systems the spark advance routine (often called adaptive spark) is really separate from the adaptive fueling routine. You can delete your knock sensor and it will not have a direct effect on your pulse width/fuel delivery.
The only function you lose is knock-retard. The spark will still advance as per your programmed calibration values. Again, your fueling corrections will not be hindered by the lack of a knock sensor.
The adaptive fueling keys off of input from your O2 sensor.
Injectors are sized by the individual cylinder size. You have to multiply your lb/hr rating by the number of injectors you have to find total fuel capacity.
The total capacity is always "oversized" in order to cover conditions where you are heavily loading your engine (wide-open throttle) up to the physical RPM limit of your engine, even in very cold conditions (added pulse-width for PE-fuel enrichment, and coolant correction - warm up enrichment), and still be operating at something under 100% duty cycle for the injector at any given RPM. This amount of fuel delivery capacity is FAR more than needed for normal economical driving.
The same fuel injector can be run in either a V8 or an I4, if the cylinder size, volumetric efficiency, and RPM range are about the same between the two engines. An engine with a smaller individual cylinder size will most often have a smaller capacity injector. What I have said here applies to MPFI - an injector per each cylinder. You are right to look at injectors for a smaller displacement engine of the same configuration as yours.
If you've got TBI or a centrally located injector or injector-pair, then the same doesn't apply. A single injector will of course have to feed the entire engine, or entire bank of cylinders. You often run into efficiency troubles with this arrangement because the physical limitation of the injector makes it hard to control fuel delivery when using very small pulse-widths, - at idle for instance. This happens often in performance applications where the injector has been upsized. A better solution is to use a vacuum referenced and adjustable fuel pressure regulator with a smaller injector.
At idle and cruise where vacuum is high, the fuel pressure is kept relatively low, and the smaller injector operates in a very efficient window of capability. The effective load/RPM range of the injector is increased without having to install larger injectors.
This same solution will work with MPFI, and will allow you to downsize your injectors without losing any wide-open throttle capability.
There are people who have cut their injector size down by 50% and have no problems, but they have done so by taking control of their fuel pressure, normally with a vacuum referenced adjustable regulator, and by monitoring their car's fuel trims during operation to make the proper adjustment.
Having control over the ECM tuning (recalibration) is also a big help when doing something like this, but isn't always a must.
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