81 240D- Horrible fuel mileage - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 04-01-2018, 02:52 PM

My 240 was running great, and getting decent mileage. It still runs pretty good, but now gets what seems to be 10 MPG. My friend is using it, and he ran out of fuel twice. After putting in several gallons, he was only able to drive few miles before running out again. It also smells like raw Diesel from the exhaust pipe. The only thing I can think of, is that the injectors are all bad. I can't imagine the IP forcing more fuel than the injector can take, so I think I can rule a bad IP. I know that it does not help the situation that the fuel gauge reads full all the time, so I need to at least fix that. Any ideas?

Diseasel300 · #2 04-01-2018, 03:02 PM

Look for a leak. If the IP were the issue, you'd be rolling serious coal or having serious running issues to have that kind of fuel economy.

ROLLGUY · #3 04-01-2018, 03:21 PM

Quote:

Originally Posted by Diseasel300

Look for a leak. If the IP were the issue, you'd be rolling serious coal or having serious running issues to have that kind of fuel economy.

There are no fuel leaks that I can detect. I have not noticed much coal at all from the tailpipe when I have driven it, either before or now. It just seems that fuel gets put in it every day, and it only gets driven a few miles. Again, the exhaust smells like raw fuel. It has not smelled like that before. I do have a set of injectors that have a couple thousand miles on a rebuild (from another engine) that I can install, but am not sure if it is worth the effort. After I fix the fuel sender, I will fill the tank and write the mileage down and check the MPG at the next fillup. My guess is it will be nowhere near 25 (I would expect a 240D manual to get at least that around town).

gastropodus · #4 04-01-2018, 04:12 PM

Does the fuel door still lock when you lock the car? Any sketchy neighbors driving diesel Ram pickups?

leathermang · #5 04-01-2018, 05:16 PM

Be sure and check your oil level often....

psaboic · #6 04-01-2018, 09:21 PM

Is the fuel return system working ok? Check for fuel leaks at the tank, all the lines, the filters, etc........gotta be leaking somewhere.

Mxfrank · #7 04-01-2018, 09:36 PM

Quote:

Originally Posted by Diseasel300

Look for a leak. If the IP were the issue, you'd be rolling serious coal or having serious running issues to have that kind of fuel economy.

+1 If you haven't found a leak, you aren't looking in the right place. I had a problem like this that turned out to be a bad hard line over the rear axle.

moon161 · #8 04-02-2018, 08:32 AM

Quote:

Originally Posted by Mxfrank

+1 If you haven't found a leak, you aren't looking in the right place. I had a problem like this that turned out to be a bad hard line over the rear axle.

Yes. With this level of comsumption, you should be able to park it over newspaper and let it idle for a while and find a puddle.

leathermang · #9 04-02-2018, 09:30 AM

Given the symptoms expresses.... .I am going to ask a logical question I think...
is there ANY way the fuel could be entering the exhaust system past where it would ignite.. thus not causing any smoke but allowing for the use of so much fuel ?
I can not imagine this happening.. just going by the description so far... of course it may only be leaking while out on the road... ?

Diseasel300 · #10 04-02-2018, 11:10 AM

We weren't being trolled for April Fool's day?

ROLLGUY · #11 04-02-2018, 11:18 AM

Quote:

Originally Posted by Diseasel300

We weren't being trolled for April Fool's day?

I hadn't even thought of that, so NO. I don't have access to the car until this afternoon, but when I get it back I will park it on some cardboard and run the engine. I do know that the engine bay is squeaky-clean, no leaks there.

Diseasel300 · #12 04-02-2018, 02:10 PM

Quote:

Originally Posted by ROLLGUY

I hadn't even thought of that, so NO. I don't have access to the car until this afternoon, but when I get it back I will park it on some cardboard and run the engine. I do know that the engine bay is squeaky-clean, no leaks there.

Just had to check! You can't trust anyone on April 1st

In addition to checking for leaks, check timing and compression if you find no leaks. Low compression or really retarded timing can cause incomplete combustion leading to that smell and low power thus requiring more throttle.

If you have a fuel leak somewhere causing air ingress, you can also get that raw fuel smell and possibly blue/white smoke due to weak combustion.

Then of course, there's always the blocked tank vent causing the fuel tank to collapse/implode. If the guy is putting in a few gallons and the tank is "full" but keeps running out of fuel with no leaks, it's sure a possibility since the fuel gauge is non-functional.

Mxfrank · #13 04-02-2018, 03:27 PM

Quote:

Originally Posted by leathermang

Given the symptoms expresses.... .I am going to ask a logical question I think...
is there ANY way the fuel could be entering the exhaust system past where it would ignite.. thus not causing any smoke but allowing for the use of so much fuel ?

Sure. A broken exhaust valve spring, cracked head, dropped valve seat, leaky injector, really bad cam timing, or anything else that would cause low compression, overfueling or late ignition. But anything like that would be accompanied by poor power and rough idle. Since it still "runs pretty good", it has to be a leak.

BillGrissom · #14 04-02-2018, 03:39 PM

I don't think the injectors could account for increased fuel flow directly, from what I know of how the fuel system works. Each IP cylinder delivers a fixed volume of fuel per stroke, dependent upon how far you push the accelerator pedal. Thus, even a stuck-open injector would not increase the fuel flow. However, it would send unburnt diesel thru to the exhaust, which could account for the smell. It would also lower efficiency, so perhaps you could realize 10 mpg, especially if 2 injectors were not spraying properly.

It might be pretty hard to tell that you are having to press the pedal further to get the same engine output. The best indicator would probably be timing how fast you could drive up a steep hill with it floored, assuming you had past results to compare.

ROLLGUY · #15 04-02-2018, 09:43 PM

Thanks all. The car actually has good power, maybe even more than it had before the low MPG. I still have not gotten the car back, but should get it tomorrow. I will check for leaks with it parked on cardboard......Rich