Idle control through the ECM 2

[mifel]

I would like to control the idle RPM so that the battery voltage is maintained when the electrical load is increased. I would like to accomplish this through the ECM. The vehicle is a 2002 suburbans with a 6.0 vortec. Unfortunately it has a mechanical throttle control as apposed to a drive by wire. I am trying to avoid a mechanical solution.

 

[GregLocock]

I think you'll find the idle speed is controlled electrically, for emissions reasons. The idle is probably controlled by a separate electrically operated valve, imaginatively called the Idle Control Valve.

I don't know about your engine in particular, but ours is fed a pulse width modulated signal to control engine speed.

The problem you face is that if the vehicle is in drive it will lurch forward from a standstill when the idle speed gets increased. I strongly recommend that you put some sort of interlock in to enable this feature when the car is in Park only and Neutral only. There will be a switch that detects that already.




Cheers

Greg Locock

 

[crashbox455]

GM calls this the "IAC"- Idle Air Control Valve. it's just a stepper motor, but the computer gets fussy if it loses track of where the valve is. the ECM is smart enough to use the PRNDL switch to tell the difference between Park and Drive, so i'm sure you could interface the charging system without too much difficulty.

 

[JRW261]

Alot of newer vehicles will increase rpms, within an acceptable range, when there is excessive battery drain. This becomes apparent when your vehicle has a bad alternater.... if it gets bad enough the engine will idle fairly high for several minutes until it sees acceptable voltage or trips a code. There are also units that will do this mechanically, mostly like a cruise control, and are found on vehicles that have large power inverters or Electonic PTO systems.

For normal passenger vehicles, I believe your ecm will trip a code if it sees excessive RPMs while in park, and think the P-N switch is bad and that you are really in gear.

 

[JRW261]

Why the need for increased RPM?

 

[GregLocock]

Modern passenger car alternators are at the limit of their ouput at idle, typically. I realise that increasing the speed shouldn't help, in simple theory, but it does, in practice.


Cheers

Greg Locock

 

[mifel]

Concering the idle control. Our application is for an aux power system 28 volt 250 amp. This alternator needs to be at 2000 RPM to put out full current. If I changed the alternator pulley to a smaller size, the alternater will exceed its rated RPM(10000) at the shift point with max throttle(5200). So the solution is to sense the load and bump the idle up when the vehicle is in park and the battery is being discharged. I have been talking to a company called Inpower for a solution. They also said that they may be able to control the idle through the ECM even though the vehicle has a mechanical throttle control.

 

[GregLocock]

I am 99% sure that even though it has a mechanical throttle it will still have an electrical idle control valve. Look for the wires on the throttle body.

Cheers

Greg Locock

 

[crashbox455]

what exactly do you mean by "avoid a mechanical solution"?

any time the ECM ups the idle (A/C for instance, or transmission engagement, or PSPS signal, etc... ) it uses the IAC. easy way might be to tap into the A/C or PSPS lines and use that- i have no idea how much extra current you'd get though.

 

[mifel]

The "mechanical solution " is a selenoid pulling on a thottle cable.

I have just tested an Inpower throttle control on a non-ETC 2002 suburban and it seems to work ok. So I have the Suburban idle up problem solved. I now have the same problem to solve on a Mercedes ML500. Your idea on using the AC or PSPS is a good one.

Thanks