Hello: I am brand new to this forum and very much a novice to electronic projects. I am very excited to attempt an auto related modification project but have questions that are keeping me from getting started with actually cutting the wires and attaching my device (which I have already made up) . Seems I should describe the project and purpose along with what I (think) I know. This involves the electronic throttle control of my truck which as I understand is nothing more than a potentiometer. If what I have recently learned about (pots.) is correct they have 3 wires. One is a power supply into what seems to be a resistance coil winding, and the second is out to ground. The third wire is the "wiper" connection which depending on it's contact position along the coil varies it's output voltage. In MY case the supply voltage from the vehicles PCM (power control module) is 5 volts. Sorry if I am just writing stuff you folks already know. I just want to make sure I cover all the details of what I think I know to see if (YOU) have information to correct my understanding of things. The "project" involves creating what is called an AIC (auxiliary idle control) for the purpose of being able to increase the engine RPM while the vehicle sits running. (I will not get into why this is needed for diesel trucks). My (device/project) for doing this is to use a relay to create a bypass circuit through my own set up of pots. which will actually be used as rheostats. (My understanding is the only thing making (it) a pot. or a rheostat is weather you hook up three wires (as the throttle pedal described above works) or Two wires (one a voltage input & the other wire connected to the "wiper" terminal as the varied voltage output). My plan was to cut the wiper OUTPUT on my existing throttle pedal (that's the middle wire sending varied voltage signals back to the vehicle PCM). Then redirect that out to the relay. (I'm not sure of the proper name for the type of relay I am using but its the somewhat typical type...Terminal's 85 & 86 are the coil that make it work. Then there is 87 - 87a - 30. The N/C (normally closed) is between 87a & 30. When the relay is "activated", 87 & 30 make the circuit and the other (87a) is broken (open) so basically it (toggles) between those two terminals (87 &87a) and (30) can be the output. To keep the "NORMAL" operation of the throttle I would SPLIT the output wire I cut at the pedal, and direct one (leg) of the wire to terminal 87a (input and N/C to terminal 30) Then I would direct the terminal 30 wire back up to the other end of the cut wire at the pedal to continue the circuit back to the vehicles PCM. This takes care of keeping it working "normally".
The OTHER leg (from the output wire which I will have "split" would be directed through to the input of (my) pots. (or I guess to be more precise) my rheostats. There will be two of them wired in series. Then from the output of the second pot. I will direct to terminal 87 of the relay.
So it would seem to me that when I "activate" the relay, the signal voltage back to the vehicles PCM is now controlled by MY adjustment of the "Linear Taper Potentiometers through this (bypass) circuit. Now from my studies there have been some Ohms values associated to what I should have for my pots. The first is supposed to be a 10K resistor (But some suggest that it's better to use a pot. so you can "dial in" for a proper IDLE. Otherwise, because of various reasons & different vehicles you would have to have on hand an assortment of resistors of say between 1K and 10K and any number "K" in between to experiment with to get the correct IDLE reading). (The point is that the vehicle PCM does not just use Zero volts or 5 volts as the starting point for the reference signal voltage for IDLE. So the first pot. in (your) bypass circuit is to "dial in" for the IDLE and then you either tape it into position or glue it there or protect it from moving in whatever manner you choose. Now you go OUT this first pots. "wiper" terminal (the middle one) and send it into the second pot. (this is the one (you) would mount through your dashboard with a knob attached to roll through and make the further varied voltage/resistance values and sent back out the "wiper" terminal of this pot. to terminal 87 on the relay (87 is "making" with 30 when the relay is "on"). Terminal 30 is the relay OUTPUT back to the vehicles previously cut wire back to the PCM.
Now, Having planned all this out in my head and actually wired up the device, NOT to the vehicle YET, (I actually use TWO relays , but that's just another switch that has to be bypassed and "activated" and it's just that, "a switch" so no problem there), I thought I might have MISSED SOMETHING that could make this project NOT WORK the way I expected it to.
And FINALLY I will get around to asking the questions..... The FACT that I am using the vehicles throttle pedal pot. "wiper" as the OUTPUT supply voltage to (my) pots. Is this going to (invalidate) the whole thing from working properly? My thought is (and I have not checked this or am not sure how to check it), What is when my vehicle sits with the throttle pedal at IDLE, the potentiometer is "set up" or designed that it is sending out the LOWEST voltage. (I guess that would mean that the "wiper" connection in the pot. is making contact with the winding at a point where the supplied 5 volts has "encountered" it's maximum resistance, and is sending this REDUCED voltage signal out to the PCM. Naturally, if I am using (cutting and redirecting) this output wire to (my) pots./rheostats , then I am only getting a very low voltage as the SUPPLY voltage to my redirected system. Further increasing the Ohms resistance will just continue to lower the voltage signal back to the vehicle PCM to a point where it is BELOW the lowest number the PCM is programmed to receive as a "normal" number. Either causing the PCM to throw a code (check engine light) or possibly just cause it to stall out.
Now (If) the vehicle is set up to START at the higher voltage at IDLE (say the full 5 volts), then I don't think any of this would be a problem.
So the questions are....Do I need to cut the 5 volt supply line and send that as the redirected bypass line and INPUT THAT into (my) pots. and then "adjust that 5 volts (via. my pots.) and send that back to terminal 87 on the relay then out terminal 30 line back to vehicle PCM?
OR do I only know how to wire it AFTER I find out what the IDLE voltage is out the "wiper" wire from the original pedal pot. ???
Seems if the IDLE voltage is the HIGH output voltage, I could use the "wiper" (center wire) from the throttle as the input to my pots. for supply voltage for the (bypass) circuit. Otherwise I NEED to "tap" that 5 volt supply line (sorry, I think I said I was going to cut it above somewhere) I meant "tap" it.
Gee wizzzzz I sure hope this makes scene to someone!
ANY HELP or response sure would help out here. I just don't seem to know where else to get this kind of information. Thanks so much if you have read this........ Bob
The OTHER leg (from the output wire which I will have "split" would be directed through to the input of (my) pots. (or I guess to be more precise) my rheostats. There will be two of them wired in series. Then from the output of the second pot. I will direct to terminal 87 of the relay.
So it would seem to me that when I "activate" the relay, the signal voltage back to the vehicles PCM is now controlled by MY adjustment of the "Linear Taper Potentiometers through this (bypass) circuit. Now from my studies there have been some Ohms values associated to what I should have for my pots. The first is supposed to be a 10K resistor (But some suggest that it's better to use a pot. so you can "dial in" for a proper IDLE. Otherwise, because of various reasons & different vehicles you would have to have on hand an assortment of resistors of say between 1K and 10K and any number "K" in between to experiment with to get the correct IDLE reading). (The point is that the vehicle PCM does not just use Zero volts or 5 volts as the starting point for the reference signal voltage for IDLE. So the first pot. in (your) bypass circuit is to "dial in" for the IDLE and then you either tape it into position or glue it there or protect it from moving in whatever manner you choose. Now you go OUT this first pots. "wiper" terminal (the middle one) and send it into the second pot. (this is the one (you) would mount through your dashboard with a knob attached to roll through and make the further varied voltage/resistance values and sent back out the "wiper" terminal of this pot. to terminal 87 on the relay (87 is "making" with 30 when the relay is "on"). Terminal 30 is the relay OUTPUT back to the vehicles previously cut wire back to the PCM.
Now, Having planned all this out in my head and actually wired up the device, NOT to the vehicle YET, (I actually use TWO relays , but that's just another switch that has to be bypassed and "activated" and it's just that, "a switch" so no problem there), I thought I might have MISSED SOMETHING that could make this project NOT WORK the way I expected it to.
And FINALLY I will get around to asking the questions..... The FACT that I am using the vehicles throttle pedal pot. "wiper" as the OUTPUT supply voltage to (my) pots. Is this going to (invalidate) the whole thing from working properly? My thought is (and I have not checked this or am not sure how to check it), What is when my vehicle sits with the throttle pedal at IDLE, the potentiometer is "set up" or designed that it is sending out the LOWEST voltage. (I guess that would mean that the "wiper" connection in the pot. is making contact with the winding at a point where the supplied 5 volts has "encountered" it's maximum resistance, and is sending this REDUCED voltage signal out to the PCM. Naturally, if I am using (cutting and redirecting) this output wire to (my) pots./rheostats , then I am only getting a very low voltage as the SUPPLY voltage to my redirected system. Further increasing the Ohms resistance will just continue to lower the voltage signal back to the vehicle PCM to a point where it is BELOW the lowest number the PCM is programmed to receive as a "normal" number. Either causing the PCM to throw a code (check engine light) or possibly just cause it to stall out.
Now (If) the vehicle is set up to START at the higher voltage at IDLE (say the full 5 volts), then I don't think any of this would be a problem.
So the questions are....Do I need to cut the 5 volt supply line and send that as the redirected bypass line and INPUT THAT into (my) pots. and then "adjust that 5 volts (via. my pots.) and send that back to terminal 87 on the relay then out terminal 30 line back to vehicle PCM?
OR do I only know how to wire it AFTER I find out what the IDLE voltage is out the "wiper" wire from the original pedal pot. ???
Seems if the IDLE voltage is the HIGH output voltage, I could use the "wiper" (center wire) from the throttle as the input to my pots. for supply voltage for the (bypass) circuit. Otherwise I NEED to "tap" that 5 volt supply line (sorry, I think I said I was going to cut it above somewhere) I meant "tap" it.
Gee wizzzzz I sure hope this makes scene to someone!
ANY HELP or response sure would help out here. I just don't seem to know where else to get this kind of information. Thanks so much if you have read this........ Bob