OM603 Idle Speed - PeachParts Mercedes-Benz Forum

tomkanis · #1 01-12-2003, 09:08 PM

Anybody know the correct sidle speed for the OM 603 in my 87 300 SDL?

The indicated (dash tach) speed is about 600 RPM and the engine develops a "lope" of about 50 RPM when idling warm. I noticed that it stops when i raise the speed about 100 RPM with the accellerator.

How is the idle speed adjusted?

TIA

Tom Kanis
www.bravecannons.org

PaulH · #2 01-12-2003, 10:30 PM

Yes - 630 RPM. It is noted on an emission label under the hood near the passenger side headlight. But, the interesting thing is that you can the adjust the idle RPM very easily. Under the hood,just behind the fuse box, near the windshield, on the driver's side is a round Knob with numbers on it going from 1 to 7. Now, you MUST raise the knob slightly BEFORE you try to turn it. It should be set at the "4" setting which is 630 RPM's. So, to change your idle RPM's, just lift slightly and turn. I did this while the engine was off. #1=570 rpm; #2=590rpm; #3=610rpm; #4=630rpm; #5=650rpm; #6=670rpm; #7=700rpm. I set my SDL at #4 in the winter and #5 or 6 in the summer when I have the AC on and sit in a lot of traffic jams in the hot weather. Good luck.

md21722 · #3 01-13-2003, 08:08 AM

There is a chance turning that knob will do NOTHING if the ELR is not working as it should. IF that's the case then come back and ask for some diagnostic information.

(I'm not sure of it myself!)

gsxr · #4 01-13-2003, 06:29 PM

Yeah - what Brian said. Also you can adjust it with the engine running, there should be a very noticable difference between #1 and #7 (factory setting is #4). This is a great system, as it keeps a steady engine RPM when the A/C compressor kicks on & off at idle. Your warm idle "lope" is more likely to be a problematic injector or leaking seal in the injection pump. I had the same problem, and after a local diesel shop rebuilt my injectors & resealed/calibrated the pump, the problem was cured.

If the ELR system is not working, you might be lucky and find a bad connection at the ELR actuator at the top rear of the IP (two wire connector, only one there). If that's not it, troubleshooting gets harder, so let us know what you find...

tomkanis · #5 01-13-2003, 08:25 PM

And there is a noticable difference in the settings. But I still have a "lope", and I've had it for about 70K Miles now. Is this a serious thing with the IP and injectors?

Tom Kanis
87 300SDL 176K
"The Scharnhorst"

gsxr · #6 01-13-2003, 08:54 PM

Cool, your ELR is working. The lope probably isn't serious as long as it doesn't bother you. If the engine is shaking, it could very well be motor mounts, they only last ~50-100kmi or so (or 5-10 years tops). If it truly is a misfire, it's either the injectors or IP. I'd start with the injectors as they're easy to pull out and have tested. Or before you do that, try a can of Lubra Moly Diesel Purge first - follow the directions exactly, it's kind of a pain, but the stuff can work magic if your system just needs a little deep cleaning. If the DP doesn't fix it, you'll need to test the injectors. If they are OK, it may be the IP.

Regards,

sixto · #7 01-16-2003, 10:31 PM

I haven't done anything with the resistor switch but when I disconnect the ELR plug from the IP the SDL won't idle. Does this mean the ELR is working? It idles at a steady 600-ish.

Thanks,
Sixto
91 300SE
87 300SDL
83 300SD

PaulH · #8 01-16-2003, 10:57 PM

On most (older) diesel truck and boat engines you can adjust the "lope " out by simply turning a screw(held by a lock nut) on the side of the IP. It is easy to do. However, I have no idea if MB diesels have this adjustment, althought I suspect that they do. There is another adjustment screw for fuel. MB has an adjustment for fuel. Good Luck.

gsxr · #9 01-17-2003, 12:12 AM

Sixto (and Paul),

yes, the OM603 injection pump has a mechanical screw to set base idle, with the ELR actuator disconnected. I think it gets set at 530rpm or something. However, the engine SHOULD idle at more like 640rpm, with the ELR functioning. Adjusting the trim plug should make the idle speed change, as stated earlier in this thread. If not, the ELR may not be working. Unplug it, if the idle speed is still 600+ then the min speed is too high AND the ELR is not functioning. It sure is nice to have it working in the summer, so the RPM's stay constant regardless of A/C compressor engagement. :p

PaulH · #10 01-19-2003, 12:52 AM

Tom , You've got to love this forum with all the info at a great price. Just DON'T ask about oil!! You'll get a thousand responses !