M103 Excessive fuel consumption - Page 4 - PeachParts Mercedes-Benz Forum

alienman · #46 09-21-2009, 08:56 AM

Hi Mak,

I'll try to see if I can check the cold start valve. I'm guessing that I just pull the valve and let it shoot into a jar while someone else starts the car? I'd probably disconnect the ignition coil just to be safe!

JoeinCA · #47 05-11-2012, 10:34 AM

I'm resurrecting an old thread here. And I know if I spent a few hours searching I could find the answer... But if someone that recently dealt with this could point me in the correct direction, that would be great!

So, I have the terrible fuel consumption problem... The first check the car failed on was the bold text in the below post. I cycled the fuel pump a few times, left the key on, and there was no difference in pressure required to depress the flap. Is a stuck plunger an easy fix... like loosen this thingy, tap on this bastard, or yank this part, clean, reinstall? Basically, does anyone know the quick fix, so that I can get slightly better mileage whilst waiting for some money to come in and I go ahead with the covert Megasquirt and DIS install. (I'm going to make it look as factory as possible, and then if there are any questions when smog time comes, I will attempt to convince them that it is a little know factory option.... Or something, I'm a licensed but disable smog tech and ex mercedes Tech... so, I should be able to figure it out, and explain away any inquiry)

Well, I guess I'm in a wordy mood today, sorry for the long post...

Thanks for your help guys!
Joe

Quote:

Originally Posted by tinypanzer

I'm not sure if I buy the theory that 7 degrees difference on the T-stat is going to be a big mileage buster. Now, if the engine was having difficulty getting to 80c, then perhaps, but 80c is in the normal range.

If it is indeed running that rich, there should be soot accumulating in the tailpipe. Worth a check.

If you really are burning that extra gas, there aren't too many things that can cause it. Leaky injectors, a leaky cold-start injector, a leaky fuel distributor O-ring dumping gas into the air bowl, bad temp sensors, OVP relay issues causing you to run purely on mechanical. I would expect to see rough running and dashboard lights if the OVP was bad, though. Perhaps a stuck plunger on your fuel distributor. You can check for that by putting the ignition to ON with the motor off, the air meter flap should get much harder to push on with the fuel pressure from the pump. But, again, I would expect to see rough running with that scenario.

You could have a leak in your fuel line, and you're just dumping your gas on the road...... Check the banjo fittings on the pump and filter. Mine have leaked in the past..... Something tells me you'd be smelling that, though.

Just for fun, here's an easy thing you can try. Take the plug off the main temperature sensor by cylinder 6, turn the plug 90 degrees and plug it back in. What you have just done is switch which computers are running on which temp sensor element (there are two in there). See if your symptoms change noticeably. If so, probably a bad temp sensor.

Also, make sure you're not running platinum spark plugs, and check to see that your cap and rotor are not damaged.

JoeinCA · #48 05-11-2012, 11:13 AM

I went and started looking around a bit anyhow, still haven't found much more than people lamenting about how difficult it is to work on the fuel distributor, and that you are better off just replacing it.... Which is not an option here.

I need to find some of my MB old tech school literature I suppose. See if i can't dig up my manuals... The unfortunate part is that while I was a MB tech, it was around 2003-2006, so my model familiarity lies with 2000-2007 cars...

Anyhow, I just went out to verify, and there is indeed very little if any change in resistance when fuel pressure is applied to the air meter flap... and I have to forgo my pain meds today because I have to drive... wheee... I can already feel the knives digging into my legs and unmentionables. Do not injure your backs guys, and if you have a predisposition for scarring badly, try to avoid surgery. Just a tip. Life with moderate-sever nerve damage is not pleasant at all.

The funny thing, is that aside from a slightly rough idle, and a very occasional hesitation problem the thing runs pretty well.. Or I just haven't driven enough perfect running m103 cars to know the difference between a well running car, and a dog.

How I long for the days where I could just slap a fuel injected chevy drivetrain in there and be done with it. Which is technically a possibility, if I can cajole enough of my friends into a project of that scale again... On another note, smog laws suck, and the 91 300se should either have come with first gear start and taller rear gears, or an overdrive transmission. I am just bothered by buzzing down the highway above 3k rpm. I must just be spoiled from the 98 Riviera I had, 1200-1800 rpm on the highway, and 28+mpg if you kept your foot out of it. Ugly as sin, but just as comfortable.

Don't get me wrong, I love my w126s, and their brethren, the ride quality, the handling, even the braking isn't too shabby... They are just so darned pricey to maintain.. my 300SDL has been a money pit, and it still needs work. But it never complains about being driven 70 miles a day.

Anyone want to trade a 190D for a very nice 300se with only minor issues? It's got a rebuilt head!... no.... oh well didn't think so.

Thanks again,
Joe

Thanks again for any assistanc