M103 Excessive fuel consumption - Page 3 - PeachParts Mercedes-Benz Forum

ps2cho · #31 08-23-2009, 12:05 PM

Quote:

Originally Posted by alienman

Hi guys,

I went ahead and bought a new 87c Behr thermostat on Friday and installed it this afternoon because my mechanic refused to swap it out under warranty. To my surprise, the thermostat that my he put in was rated for 75c! I don't know what brand it is, but stamped on one side was "G7 2.08675 BTT Made in Germany." It was immediately apparent that the check valve was broken off by force, as the four strong metal tabs that hold it in place were badly mangled. What was left was a small hole that would seep coolant when the thermostat was supposed to be closed.

I called up my mechanic to find out what the deal was and he blamed me for breaking the thermostat which was the wrong one to begin with! So now, in addition to using the wrong coolant and spark plugs, he used the wrong and very broken thermostat!

Anyhow, I took the car for a spin and found that there was no soot at the tailpipe to report, and the area under the air flap was clear after two days of sitting. The car felt more responsive with the new thermostat, but it might be some kind of placebo effect. In regular driving conditions, the engine temperature is now where it was before this whole ordeal started (~87c) and slowly creeps up to about 100c when idle for a while, at which time the aux fans turn on.

Lambda will be checked and adjusted as needed tomorrow, followed by a fresh oil change and test drive to see if my fuel economy has been restored to acceptable levels. After that, I will try to find a place to tackle the odometer gears and will also be on the quest to find a reputable and knowledgeable mechanic!

If you are used to 20mpg, then 12mpg should be noticable just by general driving. My 300TE (which has the same overfueling as you) lasts me about 1 + 1/2 weeks @ 12mpg while my 260E lasts me over 2 weeks.

They have about a 210 vs 310 mile range...that's a big difference that you should know just by the distance you travel!

Definitely get rid of that thermostat and never go back to that mechanic.

Make sure to post your bad troubles in the mechanic section of this forum so we can avoid this person.

alienman · #32 08-24-2009, 04:22 AM

Hey ps2cho,

I'm *really* hoping that the thermostat was the cause of the loss of fuel economy and am definitely not going to spend another dime at that shop!

After putting in fresh oil this afternoon, I filled up the tank with 91 octane and drove about 30 miles on the highway and, with the engine nicely heated up, checked and adjusted the lamda. I found that the engine was running slightly rich, so I adjusted it from ~40% back to ~50% and found that it retained the same setting 30 miles later when I arrived at home.

The trip used up about 1/8th of the capacity of the fuel tank. This seems about right to me, as the trip previously used up about a 1/4 tank. However, I'm going to fill up the tank again and drive it just to/from work and count the number of trips I can get out of a tank, as I know how far the trip is and because I have a jumpy fuel gauge.

Thanks to everyone who contributed to this thread! I hope that this resolves this issue and will report back in a few weeks with the results.

alienman · #33 08-24-2009, 04:58 AM

Just a slight correction to the lambda setting posted above. I just realized that the wires on the multimeter were reversed, so the car was actually running leaner than it was with the 75c thermostat, not richer. So, it was running at ~60% and was adjusted to ~50%. I will check it again tomorrow with the correct polarity and adjust if necessary before filling and burning a tank of fuel.

pmckechnie · #34 08-24-2009, 07:31 AM

I hope the thermostat, plugs and adjustment helped but I thought of another thing that can effect fuel mileage and would not show up making the adjustments. Ignition timing can greatly effect MPG. I know it is not adjustable on that engine for if it looses vacuum at the ICU then it will not advance correctly. I don't know right off what the specs are but you can check the vacuum line at the ICU and make sure there is vacuum there. You may have to raise the RPM to find vacuum though.

Paul

alienman · #35 09-07-2009, 07:40 AM

Well, here's another update.

So far, I've driven around 255 miles and the fuel gauge is just below the quarter tank mark. At this point, it appears that I'm getting about 15mpg, as I'm burning a quarter tank every 75 miles. That would mean I'd get about 300 miles per tank. I'm going to try filling up at other stations to see if I get a better result after going through this tank, though I'm wondering if too much ethanol in fuel can have such a huge effect on fuel economy (20% drop!). The only place I can get gas without ethanol gas is at the marina, so I'll try to see if I can fill up a tank there to rule out the ethanol.

tinypanzer · #36 09-07-2009, 09:24 PM

I dunno, Ethanol is supposed to be 10% less energy per unit than gasoline, and gas is supposed to have no more than 10% ethanol in the blend, therefore 10% of your fuel is 10% less powerful, meaning a total of 1% less energy in a gas-methanol blend of 90% gas 10% ethanol. In other words, in theory, you should only see a 1% drop in mileage with ethanol blended gas.

I'm beginning to think that perhaps something wasn't connected back correctly when the water pump swap was done. Perhaps a vacuum line? Maybe two were swapped accidentally and so everything looks ok? Kinda stabbing in the dark here.

Did you notice soot at your tailpipe? I would expect to see quite a bit of it if your MPG is really that low.

As for the odometer gear, if it's the same as a W126, it's not too hard to swap out by yourself, but I've never pulled a cluster out on a 124 personally.

alienman · #37 09-08-2009, 01:21 AM

Hi tinypanzer,

Thanks for your suggestion! I'm going to recheck the vacuum lines against the diagram, as I only checked for vacuum leaks previously. I don't see any soot or smoke coming out of the tailpipe and am going to fill up without ethanol to see if that makes any difference on the mileage.

Regarding the odometer, my car's a W126 and I'm going to try and get the gears swapped this week. I think I just have to unclip the speedo cable under the floor mats and yank the cluster out with the homemade tool. Hope I don't accidentally break anything while I'm in there!

ps2cho · #38 09-08-2009, 03:06 AM

Quote:

Originally Posted by alienman

Well, here's another update.

So far, I've driven around 255 miles and the fuel gauge is just below the quarter tank mark. At this point, it appears that I'm getting about 15mpg, as I'm burning a quarter tank every 75 miles. That would mean I'd get about 300 miles per tank. I'm going to try filling up at other stations to see if I get a better result after going through this tank, though I'm wondering if too much ethanol in fuel can have such a huge effect on fuel economy (20% drop!). The only place I can get gas without ethanol gas is at the marina, so I'll try to see if I can fill up a tank there to rule out the ethanol.

255 miles a tank would be about 16.5mpg...

Put it this way, my 260E gets about 21mpg and it lasts 310miles a tank.

Something that may interest you as well....I just swapped the EHA on my 300TE and my MPG jumped from 12 to 15. No change in driving or distance. I've tested over 2 tankfuls now and its significantly better. My EHA checked out on the pressure test too, it came out 5.1 BAR dead on spec. Something you may want to keep in mind

alienman · #39 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 · #40 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.

alienman · #41 09-09-2009, 02:30 AM

Hey tinypanzer,

Thanks for your input! I haven't had a change to re-check the vacuum lines against the diagram but got my mityvac back today. I'm thinking that I have a vacuum leak somewhere, though the car idles and runs okay except for the poor fuel economy. I've replaced all the vacuum tubing and rubber connectors previously, and also changed the (4?) rubber hoses that connect to the idle control valve, air filter housing, air injection pump, and the other one that goes on the valve cover to I think the intake manifold. I'm not sure about this, but I think that the only other places that could leak vacuum are the EGR, throttle body boot (not sure what that part is called), and the injector seals?

Regarding my EGR valve, it appears to not have any vacuum lines running to it

. I'm going to try and see if maybe it somehow got stuck in an open position.

Thanks for the tip on the odometer gear, I'm going to give it a shot this weekend!

tinypanzer · #42 09-09-2009, 05:50 PM

Wow, it sounds like you are pretty on top of your rubber which is a good thing. It also sounds like you know all the suspect hoses and have replaced them....

A vacuum leak really should make your motor run rough. I'm beginning to think that you have taken good care of your rubber and that this isn't the issue. What is the issue then....... Looking at your previous posts, it appears that your lambda adjustment is correct. If you're not seeing soot build up inside the tailpipe, it's hard to imagine it running too rich at all.....

This is truly puzzling me. If lambda is correct, then in theory, you should be running at optimum mixture. Yet your mileage would indicate otherwise. I am wondering if perhaps idle mixture is perfect but your driving mixture is off. This is quickly departing my libretto of CIS knowledge.

Hmmmmm.........

alienman · #43 09-10-2009, 02:11 AM

Hi tinypanzer,

I swapped all of those rubber pieces out when I bought the car, as they were disintegrated

The engine shakes around a bit under the hood, but I only feel a little murmur when idle. I'm planning on spraying some carb cleaner around the injector seals and will post back, assuming I don't spray too much

.

alienman · #44 09-21-2009, 07:31 AM

Just a quick follow-up...

I just filled up with about 18 gallons of fuel after driving 240 miles, giving me 13 or so mpg. I've filled up at a different station to see if that makes a difference. Last tank was from Costco.

I've also determined that there are no vacuum leaks around the injector seals, but do have a broken EGR diaphragm which appears to leave the valve in the closed position (same direction that the bolts go in). Not sure if there might be some vacuum leaking from the valve to the manifold because I chickened out and decided against spraying carb cleaner in that area! I'll try to see if I can find a used one at the junkyard and will also re-check the o2 sensor's operation.

mak · #45 09-21-2009, 08:15 AM

that is a drastic drop in fuel economy . could the cold start valve be leaking or not switching off ?
mak
300se/89