M103 Excessive fuel consumption - PeachParts Mercedes-Benz Forum

alienman · #1 09-08-2009, 03:27 AM

Hey ps2cho,

My car's a w126 which has a 20 gallon or so tank

Thanks for the tip on the EHA, I'll try to see if I can find one at the junkyard. By the way, have you checked your EGR valve (if you have one) for leakage? It seems that they can get stuck open and cause a big vacuum leak. I'm going to test mine out this week when I get my mityvac back!

tinypanzer · #2 09-08-2009, 09:10 PM

If your EGR valve diaphragm is shot, you can find out without a mityvac, although it does help. I just use my cheeks to suck the line down, which is usually plenty. If the diaphragm is torn, you'll find out very quickly. You'll suck it down and very shortly afterwards, the EGR pintle will move back into its original position.

You can also just plug the line to see if symptoms improve. Thing is, a vacuum leak will make you run lean, unless something is adjusted to compensate for it. This happens all the time when people can't figure out why their car won't idle so they richen up the fuel mixture thinking they're pretty clever. The car seems to run okay for a while but the rich running fouls out the plugs, etc., mileage sucks.....

I'm not suggesting you did any of that...... But, one thing I always keep in my glove box is a kit of vacuum line plugs. You can get them for a few bucks at autozone or advance. They're great when you're out on the road and you spring a vacuum leak. I haven't used EGR in a while. My diaphragm is torn, and I don't feel like spending $350 just for EGR. So, I just plugged the line going to it. Problem solved. No emissions tests in my state.

Anyhow, I don't know why I thought you had a 124. Must have misread something. So, you need the 12 tooth gear from odometergears.com and it's pretty easy to install if you are good working with small things. I recommend putting a dab of grease on it because the new one tends to click a bit.