Don't know about the I5's, but the BANKS AUTOMIND tunes for the 5.3 raises the idle rpm to 700. How high do you want to go?
I'd prefer the idle for normal driving to remain unchanged. When negotiating offload obstacles, being able to manually select engine speeds in the ~1000-1500RPM would be preferred. I don't think I want to program a different base idle speed.
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The I5 can benefit from a tune, not that it will make it a power house. But reducing torque management, making it go into power enrichment sooner(like immediately after pushing the skinny peddle), raised idle, shorten shift times in the auto, ect.....GM did no justice to the tunes in many of the light duty trucks. I would have to look at a stock I5 tune again, but they prevent going into PE to help with emissions. But commanding a 14.7:1 afr under load is not good for power or the life of the engine.
I may have to look into this further, as the torque on the bottom end of this engine does "feel" weaker than I would expect given the displacement/sophistication etc. Feels like it is holding its breath until ~4500RPM+. So who is in the reprogramming business for these? Any recommended direction for that?
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They are potentiometers, shows it on the schematic and it's wired directly into the ECU, not the bus.
Excellent! Thank you!
While the theory has merit, it's also going to be extremely difficult to execute due to a number of factors. The main one is that you'd have to have it inline with the accelerator pedal and would then have to make sure that it is able to go down to 0 ohms on both sides so that it doesn't inadvertently always make the ECU think the pedal is being pushed down more than it is.
It is highly unlikely that the accelerator position sense pots would have to accurately approach 0 ohms to command an idle. It is also highly unlikely that the sense input on the PCM is anything less than many thousands of ohms. Very low impedance requirements in any part of this circuit besides the reference output impedance would be a poor design susceptible to variation from oxidation, contact resistance, termination, etc. It also would require a very high current reference source to drive, which is not practical either.
I just pulled up the diagram that Schwarttzy has hosted, and it appears to be a pair of pots used as voltage dividers from a 5V reference. The PCM is likely comparing the sense input from each pot, assuring both pots are operating within a defined tolerance of each-other. The PCM might also be looking for combined voltage from each divider to add up to something very close to the reference voltage (will never completely match the reference voltage)... That could complicate things...
In order for such a circuit to work well, I would expect the output impedance of the 5V reference to be relatively low (<1ohm), the impedance of the accel-sense inputs on the PCM to be relatively high (approximately 10-100X the POT resistance), and the pots in-between to operate somewhere in the neighborhood of tens to thousands of ohms.
The other main factor is that the values need to match exactly or the ECU might freak out.
They don't need to be exact, they need to be within the tolerances allowed. We don't know the tolerances, but I suspect that the biggest issue that could put the PCM into a lockout/safety mode regarding the throttle, would be if the tolerance between the 2 pots varied too much. As long as they are within allowed tolerance, any remaining tolerances would not need to be very tight for this to work well. There's a possibility, that the PCM also expects the combined voltage from each divider to "add up" to a particular level, which could be a problem for such a modification, but is less likely.
The simplest way to accomplish this is to just get another pedal and use the internals, but after the cost and effort of sourcing the part, modifying it, splicing it in, and hoping it works,
If we simply splice in another pedal's electrical guts, low side in series, high side in parallel, then we will have doubled the resistance of one side of the divider, and halved it on the other for its maximum and minimum range. If the input impedance of the PCM sense for this, is say, 100X greater than the highest impedance of the POT's, then splicing in an equivalent set of POTs would have less than 1% effect on the sense input voltages and low reference voltages. However, if the input impedance of the PCM, is only say, 10X greater than the highest impedance of the POTs, then we would be changing the sense and low-reference sense voltages by as much as 10%, which would likely be out of range for where idle and max throttle belong.
My thoughts, are that I would NOT approach this by using another of the same "gas pedal." I think a smarter approach, would be to use a set of POT's sharing a common shaft, that are selected to only effect a change in resistance of ~10-20% of the total range that the pedal is capable. This way, we're less likely to throw things out of range on the sense inputs for where idle and WOT are supposed to be by accident, and furthermore, for safety reasons, a hand throttle probably should not be capable of increasing engine speed with no load more than maybe 1000-2000RPM.
you could have just bought a choke cable and installed it to control the pedal manually and be done. It has the lowest risk and impact which when you're talking about the part of the vehicle that makes it go faster is probably a better and safer option then messing with the electronics involved.
After taking a close look at the pedal itself, I don't think the installation of a cable actuated mechanism to move the pedal will be as simple as it seems on the surface. This would have to be done in such a manner that does not interfere with foot-well clearance around the pedal and does not prevent the pedal from its full range of motion, while also incorporating...
To make it even safer I'd rig it so that it can only depress the pedal just enough to bring it up to maybe 1500RPM max.
...bingo.... a method that only can actuate it partially....
I see a fair bit of fabrication/experimentation and likely numerous "beta stages" to come to a long term reliable solution for this. I actually think, looking at it closer, that an electrical solution might be easier.
