using the OM603 ELR/ EDS with a switch for high idle? - PeachParts Mercedes-Benz Forum

BenzTurbo · #1 12-08-2014, 04:43 AM

Could you install a toggle switch in the cabin for a "high idle"? in a lot of newer diesels (mostly trucks) you can turn on a preset high idle and even control the high idle speed. most seem to go to 1000+ rpm. i don't see why you can't do that on one of our 603 powered cars with it's ELR solenoid. we already have some control over the electronic idle so all we have to do is tap into the idle adjust knob. from what i can see, the EDS computer looks at the resistance coming from the adjustment knob to set the idle speed. the less resistance between it's 2 pins, the less the EDS tries to control the idle until the mechanical governors keep it at 500rpm or so. so increasing the resistance must tell the EDS to keep the idle at "X" many rpms higher? so with the correct resistor or potentiometer you could either have full control over governed idle speed or a preset governed idle speed with the correct resistor and toggle switch. i know this may seem nonsense but i am very curious to do this!

does anyone have internal wiring diagrams of the EDS system's idle control or understand it better than i do and can offer some input? i don't want to fry my EDS computer or ELR solenoid somehow by putting too much resistance over the idle knob pins. any ideas on what resistance would equal about 1000 rpm for a starting point? i guess you could calculate it since you can see each of the resistors and they make a certain rpm increase at of idle. i think the ELR solenoid would have no problem maintaining that high of idle. if you unplug it while at idle then plug it back in, the engine jumps to a high idle very quickly before settling back to it's set rpm so it must be able to move the fuel rack a good bit? the high idle may be useful in quite a few instances! warming up faster, jump starting another car or when needing more alternator output, long idling on hot days for better a/c performance and your fan and water pump spinning faster, maybe even better lubrication if sitting for a long time?

Jeremy5848 · #2 12-09-2014, 11:10 AM

Good idea—would be handy for powering a large inverter or jump-starting the neighbor's car.

Mxfrank · #3 12-09-2014, 01:11 PM

I haven't looked at this closely, but I think there's a thermal sensor in the block that the ELR or EDS uses to do it's magic. I'm not sure about this, but it may be possible to put an on/off switch on this sensor to accomplish what you're looking for.

BenzTurbo · #4 12-09-2014, 03:19 PM

Quote:

Originally Posted by Jeremy5848

Good idea—would be handy for powering a large inverter or jump-starting the neighbor's car.

exactly! i think it could be useful at times!

Quote:

Originally Posted by Mxfrank

I haven't looked at this closely, but I think there's a thermal sensor in the block that the ELR or EDS uses to do it's magic. I'm not sure about this, but it may be possible to put an on/off switch on this sensor to accomplish what you're looking for.

is the sensor only for the EDS system or would it affect the dash temp gauge as well? i wonder what the preset "cold start" high idle is supposed to be? good idea!

Jeremy5848 · #5 12-09-2014, 05:12 PM

IIRC the EDS temperature sender is not the one used by the coolant temperature gauge. Messing with the former will affect EDS. The only question would be, what else gets changed by EDS if the idle speed is adjusted up, and would there be any negative effects on the engine. You might actually want the "high idle" switch to replace the signal sent from EDS with an "artificial" EDS signal created with appropriate electronic components. EDS won't be affected and the IP won't know it's getting a modified signal. Will check the wiring diagrams to see what all is in there.

Jeremy

compu_85 · #6 12-09-2014, 05:41 PM

If it won't burn the rack kicker out you could simply supply it a constant voltage.

The FSM has you do this when testing it, but then warns you should only apply +12 to it for a brief period.

-J

BenzTurbo · #7 12-09-2014, 05:48 PM

the EDS on my car and i'm assuming many others only manages the idle speed and tach output. i have removed the entire emissions side of it's wiring. no more air flow meter, switchover valves, or rack position sensor. the idle control side seems unaffected by all this. it does a great job over governing idle to a set rpm so i'd like to keep that feature. ideally you want to "set" the high idle speed and let the EDS computer keep it there based on load/ ect. i think it would be very difficult to make a controller to run the ELR solenoid on the pump. i think the idle adjust knob would be the best place to modify the idle since it already can adjust it but only to a certain extent.