GM Drive By Wire High Idle Control

[Provience]

I'm at a mental block for drive by wire stuff

2005 GM LM7 drive by wire, stripped harness and stripped ECU.

I'm trying to see if anybody knows an easy way to click on high idle for PTO use, not looking for much but 1200-1500 rpm would probably be just dandy.

would the easiest thing be to hack into the Accelerator Pedal Position signal wires, send them through a switch normal one way, and then send the other leg of the switch through some whatever sized resistors to make the ECU tell the Throttle Body that the pedal is depressed a couple degrees?

GM Gen III LS PCM/ECM: Electronic Throttle Equipment Guide (lsenginediy.com)

 

[arse_sidewards]

Put a potentiometer (dimmer) inline with the wire from the pedal to give you a tune-able high idle and I'd wire up a switch to bypass the potentiometer for when you want it to idle normally.

A $5-10 universal headlight switch with dimmer should provide everything you need in a nice simple package. You might need to add a relay if you want "behave normally" to be the pushed forward position on the switch.

 

[Provience]

Put a potentiometer (dimmer) inline with the wire from the pedal to give you a tune-able high idle and I'd wire up a switch to bypass the potentiometer for when you want it to idle normally.

A $5-10 universal headlight switch with dimmer should provide everything you need in a nice simple package. You might need to add a relay if you want "behave normally" to be the pushed forward position on the switch.

it's got 2 positional signal wires, probably no reason to not run them both thru 1 switch right?

good call on the dimmer. take a bunch of the guess work out of it

 

[Chief Rocka]

Put a potentiometer (dimmer) inline with the wire from the pedal to give you a tune-able high idle and I'd wire up a switch to bypass the potentiometer for when you want it to idle normally.

Appreciate the discussion. Be great to find a better solution to control idle for an on-board welder (premier) with an E40 ecm. Other than the pedal, the only way I've found to control idle is thru HPT>VCM scanner> vehicle controls and special functions.

Will the DBW throttle respond correctly if only one of the two signals is changed? It looks like sensor 1 needs to see a sweep to 5v and sensor 2 needs to see a sweep towards 0v, simultaneously. If not, code pops and goes into REP mode.

OP, I know you said easy but it looks like these guys have something that might work.
http://www.offroadengineering.com/product-gmsuv.html

 

[Provience]

Appreciate the discussion. Be great to find a better solution to control idle for an on-board welder (premier) with an E40 ecm. Other than the pedal, the only way I've found to control idle is thru HPT>VCM scanner> vehicle controls and special functions.

Will the DBW throttle respond correctly if only one of the two signals is changed? It looks like sensor 1 needs to see a sweep to 5v and sensor 2 needs to see a sweep towards 0v, simultaneously. If not, code pops and goes into REP mode.

OP, I know you said easy but it looks like these guys have something that might work.
http://www.offroadengineering.com/product-gmsuv.html

easy is relative.

i didn't even consider that they sweep opposite directions, just figured it was 2 sensors for redundancy that mirrored each other obviously i didn't read the whole link in the first post if that info was in there.

kind of a bummer they don't have even a rough price on the unit online, but the fact that it exists and just plugs inline with the pedal is a good sign and also points to throttle signal manipulation as being the 'easiest' way to go about it.

hell, maybe that is what the scantool is using to control the idle through the menus

 

[Rangerrod]

On a Ford application Im dealing with right now you can have the tuner have a high idle put in where the input was from the ac compressor.

I don’t know if this is possible on gm stuff or if you’re actually running ac.

 

[arse_sidewards]

Appreciate the discussion. Be great to find a better solution to control idle for an on-board welder (premier) with an E40 ecm. Other than the pedal, the only way I've found to control idle is thru HPT>VCM scanner> vehicle controls and special functions.

Will the DBW throttle respond correctly if only one of the two signals is changed? It looks like sensor 1 needs to see a sweep to 5v and sensor 2 needs to see a sweep towards 0v, simultaneously. If not, code pops and goes into REP mode.

OP, I know you said easy but it looks like these guys have something that might work.
http://www.offroadengineering.com/product-gmsuv.html

I totally forgot about that second wire. That makes my suggestion not useful. You'd need additional electronics to control the second signal simultaneously. I don't know enough about analog electronics off the top of my head to think up something clean.

 

[RustyC]

Depending on your PCM hardware it may be possible to signal the PCM with a physical request (12v+ positive signal on Pin 17 on C2 PCM connector).
This will only work for the following PCM service #s 12576106, 12581565, 12586243, 12589462, 12602801.
This is how GM elevates the idle while air conditioning is being used. Program the PCM to set the idle to 1500 rpm while the ac/winch/welder/compressor is being used.
Being that you have a 2007 PCM chances are high the it is a serial data to the can bus and all the above would not work. Depends on the PCM hardware#.

 

[Provience]

Depending on your PCM hardware it may be possible to signal the PCM with a physical request (12v+ positive signal on Pin 17 on C2 PCM connector).
This will only work for the following PCM service #s 12576106, 12581565, 12586243, 12589462, 12602801.
This is how GM elevates the idle while air conditioning is being used. Program the PCM to set the idle to 1500 rpm while the ac/winch/welder/compressor is being used.
Being that you have a 2007 PCM chances are high the it is a serial data to the can bus and all the above would not work. Depends on the PCM hardware#.

well that pretty solidly confirms that GM is using the throttle blades to control idle rather than a different bypass circuit.

next step would be determine what voltage = what angle and either faking that signal on the pedal side or sending that reference to the throttle body

 

[Twankie]

This has been on my list for years to do with factory parts and I always get frustrated and give up researching pto and ac functions (my truck has an 05 pcm) from what I gathered the last time around the ac is pwm and that stopped me.

03+ dbw is all throttle blade controlled iac.

02 down dbw stuff (more rare than dbc) has a separate iac valve.

interested for my York if you come up with anything

 

[Provience]

This has been on my list for years to do with factory parts and I always get frustrated and give up researching pto and ac functions (my truck has an 05 pcm) from what I gathered the last time around the ac is pwm and that stopped me.

03+ dbw is all throttle blade controlled iac.

02 down dbw stuff (more rare than dbc) has a separate iac valve.

interested for my York if you come up with anything

Holley 300-130 Holley Dual Plane Intake - GM LS1/LS2/LS6

Brawler BR-67253 570 CFM Brawler Diecast Carburetor Vacuum Secondary (holley.com)

for ~$600 it could be about a done deal

i sent offroad engineering an email about their plug and play solution.

 

[Twankie]

Holley 300-130 Holley Dual Plane Intake - GM LS1/LS2/LS6

Brawler BR-67253 570 CFM Brawler Diecast Carburetor Vacuum Secondary (holley.com)

for ~$600 it could be about a done deal

i sent offroad engineering an email about their plug and play solution.

And what? A choke cable to the throttle linkage?

i could do that now with the dbw gas pedal..

 

[Provience]

And what? A choke cable to the throttle linkage?

i could do that now with the dbw gas pedal..

yeah that was my thought. everytime i look at this motor, all i can think is "man, a carb would sure be nice about now"

adding an extra cable for the choke/high idle would be much easier than looping a cable around the peddle assembly. I don't think the throttle blade servo would much like being forced by a cable

 

[06h3]

bump from the dead.....

Appreciate the discussion. Be great to find a better solution to control idle for an on-board welder (premier) with an E40 ecm. Other than the pedal, the only way I've found to control idle is thru HPT>VCM scanner> vehicle controls and special functions.

Will the DBW throttle respond correctly if only one of the two signals is changed? It looks like sensor 1 needs to see a sweep to 5v and sensor 2 needs to see a sweep towards 0v, simultaneously. If not, code pops and goes into REP mode.

OP, I know you said easy but it looks like these guys have something that might work.
http://www.offroadengineering.com/product-gmsuv.html

I have a premier and am sick of having a person man the pedal while welding. I looked to see if I could create a hook system that hooks the pedal somewhat depressed at the firewall but there isnt much room.

Can an arduino controller do 2 outputs one from 0v to 5v while its sending the other from 5v to 0v at the same time?

 

[Skinny]

Not sure but I remember seeing an input switch for PTO on the ECM in the wiring diagrams over the years. I'm sure the larger trucks have a switch which enabled a high idle or set target RPM when the ECM sees an input or ground on this terminal. So may be worth digging up tuning on a 2500/3500 or maybe even the next size up truck to see if this is a thing. Maybe even look at PTO kits to see what they do because you want that just minus the PTO.

Also may only be an Allison equipped option. Not sure.

Plan B...is there any option to get the ECM to seek a higher target idle RPM? Like are there any flags or pids (thinking trans too hot or limp mode) where you could trick it into using another value which gets you the higher revs?

If none of that works out I'd use an air solenoid to bypass the throttle plate. The ECM may not like it so maybe try it before buying the hardware. Create a big ol vacuum leak from after the MAF to the intake manifold. This will cause it to rev up but at least it's with metered air. See if the ECM will play nice with it. Sure it's going to chase the leak but it can only close the throttle plate all the way and it's still going to get air. May throw a code, not sure.

If that didn't work I'd use a small electric servo to push the pedal down slightly. Or rig up a locking throttle knob (small airplane style) to actuate the pedal.

I've run out of ideas...

 

[Skinny]

Damn didn't see the original post date 🤣

 

[Bebop]

Not sure but I remember seeing an input switch for PTO on the ECM in the wiring diagrams over the years. I'm sure the larger trucks have a switch which enabled a high idle or set target RPM when the ECM sees an input or ground on this terminal. So may be worth digging up tuning on a 2500/3500 or maybe even the next size up truck to see if this is a thing.

You can do that with the right firmware, yeah.