TheWags

I just bought a 2004 E500 4matic wagon with about 90k miles on it. I'm familiar with this 5L motor and have driven it in two other M-Bs, both with 4matic. In those cars, with my heavy foot, I was still used to getting around 15 mpg (US gallons) or more. Heavy acceleration, lots of city driving, in the winter (which in my part of the country means MTBE, and our gas has 10% ethanol year-round), I would still get at least 14 mpg.

After 3 tanks of 93 through this E500, I'm getting about 9 mpg. Yes, NINE!

Obviously, something is wrong. The acceleration has seemed a little sluggish at times, but not bad. Engine compartment looks fine - no apparent leaks or smoke. My mechanic has already had the car for one other issue and didn't find anything wrong (although I hadn't told him about the poor mileage, since I had just got the car). Seems to me that there has to be a lot of unburned fuel or some timing or air/fuel problem. No error codes (other than Tele Assist). The engine seems to run a little rough at idle. What should I tell my mechanic to look at? Ignition coils? MAF sensors? Spark plugs?

WEBSRFR

Do you have the service history?

TheWags

I do not, but I believe it was serviced locally (well, relatively locally - the dealer in a nearby suburb) so I expect if I go to the dealer they will let me know how it looks, or maybe print it for me if I am having some work done.

chairman

I believe that if you ask the sevice department, they can run a service history using the cars VIN. Since the car has 90k on it, has the timing belt been changed?

fmj901

My '04 E500 4Matic gets 23mpg most days - sometimes 25mpg.. I drive 90 miles each way to work - 180 a day (usually 3 times a week) to work.

TheWags

I'll try to determine whether the timing belt has been changed. Is that something likely to be causing very bad fuel economy?

Efivehundred

I don't think there is a timing belt to change.

TheWags

That's consistent with what I have read - that there's a timing chain and it doesn't need to be changed unless it is removed for other repairs or damaged, i.e. there is no applicable maintenance interval.

mountainste

I'll try to determine whether the timing belt has been changed

edwinwalke

The timing chain would not be your problem. these cars run several hundred thousand miles with no timing chain issues.

I think you have an issue with the engine management systems that will require someone with proper equipment (STAR diagnostic software) to isolate the issue.

Flash Gordon

With that kind of mileage you are getting, the car needs a "full tuneup". You know that the previous owner has neglected to maintain the car properly. I would replace plugs, filters first to see any improvement before doing anything else.

Speaking of plugs, stay away from Bosch. Bosch plugs are not the same as before. They are mass produced, mass selling at Walmart. I recently replace the plugs in my G35 with Bosch. These plugs made the car misfired! Had to replace the Bosch with NGK. Replacing the plugs in G35 is such chore and I had to do it twice, not counting the time troubleshooting!

vettdvr

The only time I have seen mileage that low was with a plugged cat converter causing very high backpressure in the exhaust system. I suspect you have a bad cat.

PlatinumPi4u

Let us know if you get to the bottom of this.

TheWags

It's going in tomorrow - I'll tell my mechanic the diagnosis and that he owes me a discount, then I'll report back.

TheWags

Ok, more than a month later, here's an update. The car apparently had a bad MAF meter, which was reporting a constant intake air temperature of 180 F, which is the maximum value. This was screwing up the air/fuel, the timing and probably all kinds of stuff. It seems a little counterintuitive that falsely high intake air temperature, which should mean the computer is putting less fuel in that that (really lower) air temperature would dictate, but obviously there is a lot of monitoring and adjustment of engine dynamics in a modern engine, so it does make sense that bad data and maybe some sort of unreported fault cycle would make the engine run poorly.

With the new MAF, the car is getting consistently above 20 mpg at 75 - 80 on the highway with the air on, so that seems to be in the range of what I should expect. I'm still a little disappointed with the mileage around town, which seems to be a little lower than what I've had in the past with a similar car. Around town, I'm around 13 or 14 mpg overall, but sitting in traffic for a little bit will still drive it down into the very low double digits. I'm keeping a close eye on fuel consumption and will report back, there may still be something else going on.

sosh

There is no timing belt!! MB uses a chain which usually lasts until engine overhaul. Why not stop providing information thats erroneous. Learn something about the subject before you claim to be a self proclaimed expert.

NorseWagon

Seems about normal: I got the same car, same milage and it has been well maintained before and after I bought it. Keep in mind the 4-Matic Wagon is 500 lbs or so heavier than the sedans..

I am averaging 14.5 mpg with 50/50 city highway, expensive, but love the power...

TheWags

The specs have this car at about 60 lbs heavier than the W220 S500 4matic I used to have, so it seems like the mileage should be about the same. Right now it seems just a little bit less around town.

It's not like I am easy with the right foot, so in the 14-15 mpg range is pretty good, compared to 8 mpg!

ozusa

I do not question the diagnosis and fix. But I am surprised that something that must have made the fuel trim so awfully rich produced no codes and no check-engine light. No MIL light came on, correct?

TheWags

ozusa, I was surprised, too, that there were no codes or "visit workshop" messages, but that's how it was.

clkwork

I had sticking fuel injectors that were causing a similar problem. Had them all replaced (under warranty thankfully) and my fuel economy nearly doubled.

SmashF15C

Nice BS!

Smash

chairman

Never said I was a "self proclaimed expert". Mistakes will happen, arrogance is not becoming. This is a forum, I made a mistake and am willing to accept my "punishment", yawn.

XLR82XS

Highway miles will help increase average in addition to a light foot. I average 17-18 city with a heavy foot.