M103 Excessive fuel consumption - Page 2 - PeachParts Mercedes-Benz Forum

tinypanzer · #16 08-14-2009, 07:53 PM

When the fuel pump was swapped, did they remember to re-connect the wire to the air intake temp sensor? Look on the air intake hose on the side. There should be a temp sensor with a two wire hookup. It's easy to forget to put that back on when removed.

If that looks okay, remove the air filter top and make sure that the air meter flap is closing all the way, and that it is moving freely and not binding to the air funnel. Also push down the air flap and shine a light down into there and see if there is any fuel puddling up.

pawoSD · #17 08-14-2009, 08:19 PM

Quote:

Originally Posted by alienman

Hi pawoSD,

While I haven't done it before, I agree that it looks like a pretty easy job to those swap gears. Unfortunately, my situation is that I don't have a garage to work in and have to make do with street parking. I already have the replacement gears and am looking forward to the opportunity to swap them and to also paint the needles while I'm in there.

You don't need a garage to work on the instrument cluster....pull it out and bring it inside on the kitchen table on a towel or newspaper or something.

That's what I do....

ps2cho · #18 08-14-2009, 08:52 PM

Quote:

Originally Posted by alienman

Hi guys,

I pulled the plugs today and found that my mechanic replaced them with NGK TR5's on the last tune-up. Other than being the "wrong" type of plugs for the engine, they looked okay to me. I'm going to pick up a set of H9DC0's from the dealership tomorrow and swap them this weekend, though I don't think that's the cause of my loss of fuel economy.

I am following this thread. I also get 12mpg average in my 300TE. I don't think plugs are your problem either.

Pawo: Since we are talking gear replacement get this -- I pulled the odo in my 260E and ran a drill on the back...the odo span fine. I plug it back into cluster and it would get to about 2/10 of a mile then stop. Any ideas?

There was a sticker on the back from a shop in LA who fixed it before...obviously didn't last long as it was noted at 80k miles...so it lasted 3k before failing again.

tinypanzer · #19 08-14-2009, 10:32 PM

Quote:

Originally Posted by ps2cho

I
Pawo: Since we are talking gear replacement get this -- I pulled the odo in my 260E and ran a drill on the back...the odo span fine. I plug it back into cluster and it would get to about 2/10 of a mile then stop. Any ideas?

Sounds like the cable is bad or kinked, or maybe it's buggered up where it meets the transmission. I recall seeing a Diesel that had the gear that drives the cable totally chewed up.

ps2cho · #20 08-15-2009, 06:56 PM

Quote:

Originally Posted by tinypanzer

Sounds like the cable is bad or kinked, or maybe it's buggered up where it meets the transmission. I recall seeing a Diesel that had the gear that drives the cable totally chewed up.

But my speedometer works perfectly fine...so could it still be the cable?

cliffmac · #21 08-15-2009, 09:23 PM

nope, not the right solutions...it's much simpler than that

cliffmac · #22 08-15-2009, 09:28 PM

yep, tune the car up with an oil change, proper Bosch cap, rotor, wires, plugs. it'll run great...you won't even believe it.....

alienman · #23 08-16-2009, 07:46 AM

Hi guys,

I swapped the plugs yesterday afternoon and went for a drive. The engine seemed to run a tad bit smoother on idle.

tinypanzer: the air intake temp sensor is/was plugged in and the resistance readings seemed to be ok. I also checked the air meter flap and found it to be closing properly and moving freely. I didn't see any fuel pooling under the flap, but will check again in the morning with a better flashlight.

To recap, here's what I've done so far:
- New cap, rotor, wires (about a year ago)
- New spark plugs
- New air filter

- Resoldered OVP
- Cleaned out the ICV (idles at about 650rpm in gear, 750rpm out)
- Checked coolant and air temp sensors
- Checked for vacuum leaks
- Checked and adjusted duty cycle to 50%, fluctuating
- Checked O2 sensor

I think the next thing I'm going to do is swap in a new fuel filter, since it's relatively cheap

86560SEL · #24 08-18-2009, 01:14 AM

Not sure, but yow, that is LOW mpg for that car. I get 20 mpg in town with my 300SEL. I think I have a failing o2 sensor, as I am getting an occasional check engine light after the car has been running for 2 minutes and goes off after 5 minutes. Quite strange.

alienman · #25 08-18-2009, 04:02 AM

Yep, I used to get around 20mpg as well, but something's gone amiss!

samiam44 · #26 08-18-2009, 01:05 PM

Are you sure it is running rich? Ie is it a mechanical/electrical problem with the fuel system or do you simply have an odometer problem?I ask as these bosch odometers have soft plastic gears and the can crack (slip) or miss a tooth or two. I have encountered the missing tooth and it made about the same difference as you are talking about.Fuel system, you need to go through the FSM troubleshooting. Need a set of FI gauges for KE injection.Michael

alienman · #27 08-19-2009, 05:19 AM

Hi guys,

I finally got in touch with the mechanic that did the water pump and thermostat work. He said that the 87C degree thermostat was used. Since the car runs at about 80C, his guess is that the thermostat is toast and is probably the reason for my poor fuel economy. Going to find out if he's going to replace it since it's only a couple of weeks old.

tinypanzer · #28 08-19-2009, 06:30 PM

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.

alienman · #29 08-20-2009, 01:16 AM

Hello tinypanzer,

I agree with you that the thermostat is probably not causing the loss of economy as I am able to check and set the duty cycle which, as I understand, means the car is getting into closed-loop mode. The engine used to run at about horizontal on the gauge (whatever temp that is), but now sticks to around the 80 degree marker and gets there quickly from a cold start after which it idles relatively smoothly.

There currently isn't any visible smoke coming out the tailpipe, but I will try to see if I can see any at night with a flashlight. I also rotated the coolant temp sensor connector 90 degrees per your tip, though the two elements in there seemed to have matching values when checked with a multimeter.

No fuel odor around the fuel filter/pump area. The plugs installed by the mechanic on a previous tune-up were NGK TR5's, and I've swapped them back to H9DC0's picked up from the dealer. The TR5's looked ok, didn't seem to show any rich mixture. The cap and rotor appear to be ok, though I swapped them this afternoon while I had the cap off with my fresh backup set just to be safe.

I don't know if a leaking injector can affect start up, but the engine starts up on first crank almost immediately, hot or cold. I will leave the car parked for a couple of days to check again for fuel pooling under the air flap. There were no signs the last time I left it overnight, but maybe it evaporated? I will also check the plunger while I'm there.

I spoke with my mechanic again today and he said that the only other thing he could do besides replacing the thermostat was a tune-up, which doesn't sound right to me at all. I'm really hoping that it's not the fuel distributor - that part is quite a few pennies!

alienman · #30 08-23-2009, 04:23 AM

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!