e300td w210: cat and fuel economy question - PeachParts Mercedes-Benz Forum

mojo7676 · #1 06-18-2007, 06:37 PM

I have pretty poor consumption (still) on my e300 td estate 1998. i get in the region of 15-20 mpg (uk gallons) whether local or mway at steady speeds. Done all the usual stuff - filters, oil etc. Also checked brakes, checked underneath for leaks and also changed all poly pipes from and to fuel pump. no diesel sitting in injector wells, no other leaks i can see and no black smoke out the back. Used plenty of diesel redex - one bottle poured neat into a new fuel filter. Thanks to Parrot's DIY, cleaned the MAF (which didn't look too bad) but still, i've had no improvement on economy since the day i bought the car. no fault codes, nothing comes up when the OBD is scanned, either. Despite the poor economy, the car runs very well, i think. smooth, quick and nothing untoward - no splutter or misfire (so far). However... have noticed a bit of an occasional rattle when the engine is idling. I'm suspecting the cat might be on its way out but as i said before, performance seems great and there's isn't much noise that suggests the cat is actually falling to pieces - just an occasional sort of rattle. Can a broken cat section of the exhaust cause severe impact on fuel economy? I've done a trawl but not come up with any hits/matches, btw - also posted to another forum with no results. any advice, as ever, appreciated.

mojo

dukegrad98 · #2 06-18-2007, 06:43 PM

Stupid question...where is the catalytic converter on these cars?! I have the 1998 E300TD sedan. I expected to see a cat just downstream of the turbocharger. Uh...no. I wonder if the factory didn't install one? Or did a prior owner remove it in favor of the pipes that are under there?

Sorry to hijack the thread --

Cheers, John

mojo7676 · #3 06-18-2007, 07:42 PM

as far as i know, the cat is situated down from the turbo - and toward the middle. i've been told that it is possible to remove the cat and run the car without - just weld a piece of straight pipe ont where the cat section was, i suppose. given the price of a replacement, decat-ing sounds like an option but don't know what impact it would have on running/performance/starting/etc and also, whether or not it will cause problems passing emissions/particle tests.

aklim · #4 06-18-2007, 07:56 PM

Quote:

Originally Posted by dukegrad98

Stupid question...where is the catalytic converter on these cars?! I have the 1998 E300TD sedan. I expected to see a cat just downstream of the turbocharger. Uh...no. I wonder if the factory didn't install one? Or did a prior owner remove it in favor of the pipes that are under there?

Sorry to hijack the thread --

Cheers, John

On my 99, if you go underneath the car you see the exhaust pipe run along the bottom of the car parallel to the ground. As soon as it turns up towards the turbo, you will see a coffee can thing and that is the "cat" so to speak.

F18 · #5 06-18-2007, 10:04 PM

Mojo......you must be hemorrhaging fuel from somewhere! You are only getting 12 to 15mpg ( US gallons). I know some 18 wheelers that get that kind of mileage. Double check and clean the MAF and its plug again. If you are not seeing any visible leaks at the tank or fuel lines then you are running way to rich because of a faulty/dirty MAF sensor (or its plug) or vacuum leaks, clogged cat or exhaust manifold. If the Cat has been on its last legs for a while it could now be partially plugged up with carbon/oily soot and creating alot of backpressure......that could screw up the mixture.. But either way you would see alot of unburned fuel coming out of the exhaust either as white/grey smoke under light load to black when hard accelerating.

I think that the car has been gradually losing performance over time and you think its still running pretty good...but its not. Fuel just does'nt disappear....its either drizzling on the ground or blowing out the tail pipe......

TMAllison · #6 06-18-2007, 10:08 PM

You can also see the catalyst from the top.

It is 12-18" (30-45cm) aft of the turbo.

F18 - most of the items you mentioned are going to cause the CEL to turn on if performance has dropped so significantly. Maybe someone has been helping themselves to fuel after you fill up? Do you have teenagers?

F18 · #7 06-18-2007, 10:39 PM

Quote:

Originally Posted by TMAllison

You can also see the catalyst from the top.

It is 12-18" (30-45cm) aft of the turbo.

F18 - most of the items you mentioned are going to cause the CEL to turn on if performance has dropped so significantly. Maybe someone has been helping themselves to fuel after you fill up? Do you have teenagers?

YES, with most of those perfomance malfunctions a CEL/ defective message would be staring you right in the face. The stored fault codes need to be read.

mojo7676 · #8 06-19-2007, 07:40 PM

Thanks for the replies all. F18; i do take your points and will mess around with the MAf some more but as i said, codes read and nothing doing. the only warning i do get is an occasional 'battery charge' on a coldish morning and a bulb out warning because one the kids has slammed the tailgate shut!

i;ve also noticed a sound - a whirring (only when the engine's just been switched off) that comes from the egr vacuum doohickey on the right hand side of the engine bay - there's a couple of rubber pipes going into it. apparently, it's supposed to make that noise - but when i pull off one of the rubber hoses, the whirring stops. not sure if it's important, but possibly worth mentioning.

there's no black smoke detected - even when i topped up the fuel filter with cleaner, started up and revved the nuts off it, nothing happened out the exhaust. i'm just about to buy some stuff called Forte, off ebay, and give that a go as it comes highly recommended from a couple of mechs i've talked to. i can't see any fuel leaks and have taken off the sump guard thing just so i check for puddles under the car - not a drop noticed.

as for not noticing power dropping gradually, hard to say, really as i've only had the car about 3 months or so and it's been running this way since i bought it - so i don't have a benchmark/comparison, as such - other than what people tell me. however, a friend did have one and says mine (an estate) seems to pull better than his did (a saloon). having said that, i do notice that when the accelerator is floored, there's a kind of over-rev when the gears change - it's only slight, but noticeable - not sure if it means anything.

am planning on taking it to a local mech who i've spoken to on the phone a couple of times - a diesel specialist who runs a non turbo w210 himself and seems like a decent sort of chap who says he can have a look and give me his view before suggesting anything too drastic. re: the cat, same mech did say it is okay to just remove it and replace with a straight pipe as it won;t impact the emissions for the MOT - not 100% sure about that and what potential harm it might do; any comments/advice appreciated.

for reference: from a full-full tank (i could see the diesel at the top of the filler), the car's done about 48 miles, local driving. The needle is now showing a third over the three quarter line - about 3 gallons, i think, at least to top up to full again. about 16 to a uk gallon... bugger!

i guess i'll just have to wait and see what happens... i'll nail the sodding thing, eventually. or die (skint) trying.

mojo

F18 · #9 06-19-2007, 08:33 PM

Mojo....I just have this suspicion that your economy issue is related to your Cat. if everything else is in order. I could be wrong, but the early diesel cats were not part of a sophisticated monitored/ sensor system like the gas engines. I believe there are no forward and aft O2 sensors to allow the computer to compare the performance of the Cat... so it can very well go bad and plug up without throwing a code. When I get a chance I will go out and take a look at my 98 sedan E300......but US emission equipment may have been different than in the UK.

aklim · #10 06-19-2007, 08:57 PM

Quote:

Originally Posted by F18

Mojo....I just have this suspicion that your economy issue is related to your Cat. if everything else is in order. I could be wrong, but the early diesel cats were not part of a sophisticated monitored/ sensor system like the gas engines. I believe there are no forward and aft O2 sensors to allow the computer to compare the performance of the Cat... so it can very well go bad and plug up without throwing a code. When I get a chance I will go out and take a look at my 98 sedan E300......but US emission equipment may have been different than in the UK.

I KNOW mine has no sensors because I have looked and not seen them on my 99 E300

F18 · #11 06-19-2007, 09:10 PM

Quote:

Originally Posted by aklim

I KNOW mine has no sensors because I have looked and not seen them on my 99 E300

My 94 K1500TD Blazer was the first year they required a Diesel Cat. on a non-commercial diesel vehicle in the US. And it had no Oxygen Sensors either. The cat was not tied into any of the emission system electronically...... so you never new if it was working OK.

mojo7676 · #12 06-20-2007, 01:17 PM

so - am still not much clearer as to whether decatting will make things better/worse... thoughts?

mojo

mbehensky · #13 06-20-2007, 01:54 PM

A UK gallon is MORE than a US gallon, so 15-20 mi/UKgal = 18-24 mi/USgal. I checked on the us fueleconomy.gov site, and for the 1987 300TD (the last diesel wagon MBZ imported into the US) the fuel economy was 21-25 mi/gal. These US economy numbers tend to be optimistic, though, so 18-24 might be reasonable.

Of course, this is for a 124 chassis with a 6 cylinder motor and no cat, but it doesn't seem like your mileage is abominably bad, anyway.

I don't have any real world experience yet; I just purchased an 87 300TD, but it overheats and needs to have its head pulled..

Max Behensky

KarTek · #14 06-20-2007, 02:14 PM

I'm thinking you may have the formula backwards. It would be something like this:

UK MPG/4546.09 = US MPG/3785.41 (Gallons expressed as cc's)

Ex to solve for US MPG:

20 UK MPG/4546.09 = .0044

.0044*3785.41 = 16+ US MPG

F18 · #15 06-20-2007, 02:22 PM

Max...the US Gallons are approx. 24% smaller than the Imperial Gallon so to convert you need to reduce the UK mileage by 24% which gives him a range of approx. 12 to 15miles per gallon US.

Mojo I would defer to your mechanic.....I have never removed a cat on any of my diesels. The cat is not sensored so it does not give any feedback to the computer and will not throw any codes if removed or is malfunctioning.
How effective it really was for diesel emmissions in the first place is questionable.....I think it was just "window dressing" to keep the environmental people happy!