OM616/7 Electronic Idle Control
 

Morning Everyone,

Our one 300SD does not really enjoy idling on first start up in these cold temperatures. You have the throttle up in order to keep the engine from stalling out. I might have the wrong oil for these temps in there but I can't remember at the moment.

Currently there's no benefit from starting the car and letting it run for a bit to get some heat in the cabin as the driver has to sit there and hold the pedal for a bit before its even stable and at that point might as well drive off in a lower gear and heat it up.

So I was thinking, is there a way I can do this electronically. It would be nice to just have a knob in the cabin to set the idle speed. Since the 617 is a purely mechanical design there's no electronic device like the ELR on 602. Aside from a mechanical "hold" cable there's nothing to use..

OR IS THERE?!

When it warms up a bit I plan on experimenting with using the cruise control system as an idle controller. Certain safety mechanisms would be designed as well but the general idea of operation would be, hold pedal to desired RPM, up tick cruise switch to hold.

What do you guys think of this approach?

That is how it works in our International 4900 truck.

Would be great if the MB could do the same

I was going to design a little black box that would essentially switch the signal input to the cruise amp based on the gear selection and speed.

I think its entirely do-able.

I've thought about installing the "gorilla knob" and cable from a 240d parts car

That's one way to go about it, but I don't/didn't want to really modify the interior to accommodate a new item like that. I wanted something clean and mostly seamless.

I think this will be fun to do. I'll probably order up some parts and start on the first gear start project too.

Hmm
 

What is your normal idle RPM ?

It should be 750 - 800 RPM..

The only way to get quick heat from the 616 - 617 is a block heater.

Heat generation at idle is relatively low, air flow, and ambient temperature seriously impact the time required to reach operating temperature.

Partially blocking radiator air flow, and brake torquing the transmission will speed up the process.

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It does normally idle in that range, once the engine is warmed up a hair.The block heater does work and is plugged in during the nights and on a timer that runs from 2am to 7am (617 leaves around 630AM, my 602 leaves around 7)

I think a lot of the stalling issue has to do with the fact that I probably have 15w40 oil in there still. I think if I changed that out for some 5w40

My 602 can idle for 10-15 minutes and give me some heat at the vents, the gauge does not show much heat but the ambient temp in the cabin is more comfortable and tolerable.

That's my goal with the 617, using the proposed "idle control" system, bump the idle to 1K or so for 10-15 minutes and get a more comfortable temp in the cabin.

It might not be an absolutely necessary little device but I think it could have its uses and be fun to design/implement.

Answer
 

If the block heater is working correctly, you should have instant heat.
I suspect either cord or heat element damage.

Using the block heater (ambient -2° F), my 240D puts out 86° F within seconds.

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I'll have to investigate it a bit more tonight. I've been meaning to break out my KillAWatt to check power usage on the block heater but haven't dug it out yet.

How long do you run your block heater for?

Answer
 

Two hours, unless ambient is -20° F or lower where I leave it on all night.

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Sounds about right. I did a test last week where I plugged in the block heater for an hour at ambient 15F and shot the cyl. head with an IR thermometer and got 68F.

If you do or figure out a way how to, let me know! I spend quite a bit of time idling my car so this would be good in really hot weather too! Speed up a/c compressor, clutch fan, and have good charging voltage. In at least the new duramax's you can set the cruise at idle and the engine will jump to 1000rpm. It just seems like if i try to hold lets say 1100rpm in my car, once the turbo spools a little and there is a bit less drag from some of the belt driven accessories the engine "takes off" so the cruise amp would have to somehow prevent that without it being jmpy. If not, it's a runaway switch :D

I ohmed out the 300D and 300SD. Couldn't find the kill-a-watt meter.

300D: 26 Ohms, At 120V = 553 watts
300SD: 31 Ohms, At 120V = 464 watts

These were measured at the AC plug so I can take away that my elements are fine as well as the cord.

Assuming constant draw (false assumption really it's going to change as the element warms up..but best I can get right now) running them from 2 am to 7 am, 5 hours:

5.085 kWH @ $0.0946 cents per hour = $0.48 per night.

The cruise control *should* be able to regulate the speed, that's what it does with the speedometer signal anyway, I'm just going to be feeding it a different signal.

It should detect frequency increase on the signal line and back off the actuator. I plan on doing some testing when it get a bit warm.

I also plan on--somehow--adding in some safety items like a multiple cutout mechanisms. One would cut the signal if engine RPM approached X Hz, or if the gear selected was moved. The brake pedal too will be a cutout as it naturally is for the cruise system.

Lots of cool possibilities. I actually had no thought about the hot weather applications like increased A/C output or alternator charging.

Hmm
 

That is cheap for guaranteed starting, on the few days per year it may be needed.

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