Hey everyone new member who finally got his dream car: a '99 E300!

This car has 250k miles on it so I fully expected it to have issues that needed addressing. First on the list of thing to fix is excessive fuel loss at motorway speeds. Driving 50 miles the fuel gauge indicated I burned through 1/4 of a tank. I could smell no diesel and could see no fuel leak anywhere. Thinking it might be a stuck injector I took a heat gun to the exhaust manifold ports of each cylinder as well as the exhaust side of the turbo charger, here are the temperatures in degrees F at operating temperature and being driven for a bit:
1)255
2)288
3)293
4)285
5)275
6) 270
EX turbo) 310

With a variance of temperatures right at 10% at the exhaust ports, that seems okay. Great! No fuel leak and no abnormally large variance of exhaust temps, now what? I noticed on the short drive back that at 70-80MPH engine speed was hovering at or in excess of 3K RPM. I've driven other 5 speed autotragics before and at that same speed with similar gear ratios and diff gears that I'd be at 2500RPM max. There were also some intermittent hard shifts but could no replicate on demand. There is also an intermittent CEL for the turbocharger wastegate solenoid. My thoughts on the problem are either:
A) Transmission is not shifting into 5th for some reason strictly with the transmission
OR
B) The wastegate CEL is related to not being able to shift into 5th and is also at least partially responsible for the intermittent hard shifts

Thoughts on this problem? Could it be something else I've missed or not thought of? Any help or insights would be greatly appreciated!

Welcome to the club.

You will need to get a scanner with a 36 pin connector to read the transmission codes. Get it read and update info. It may just need a conductor plate. Also look for the transmission control unit in the plastic box under hood at base of windshield on passenger side and see if it has transmission fluid in it. If it does you will need to clean it up and replace the sealing bushing at the transmission.

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Jim

Verify odometer accuracy before checking fuel economy. Interstates are measured miles.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thanks for the info! Took it to a local transmission shop and they pulled some codes, here are the codes they pulled:
P0703
P1470
146 tranny code
147 tranny code

Even more information!!!

Filled up the tank to do a 100 mile test to see what my fuel economy is. Did over 100 miles and filled up again to see how much fuel I used. Apparently I only used 1.5 gallons. When I put the nozzle back i noticed that there was fuel right up to the brim of the filler neck! I shook the car a little bit and diesel came gushing out and went down the side of the car. Drove home and parked and checked the filler neck again, more diesel came out. I know think I know what's going on: fuel is somehow getting into the filler neck and cannot get into the tank. When I'm doing left turns, the more fuel is going into the filler neck and escaping out into the overflow and spilling onto the ground. But I don't know why. Anyone ever heard or experienced something like this???

The fuel tank is vertical with the top of the tank near the filler neck. If you have a loose fuel cap it will spill out on right turns if the tank is full.

You can shift from 5th to 4th by just pulling the shift lever toward the drivers side, if you are left hand drive. If you hear an rpm change you were in 5th. Your winter/summer switch should be in S so it will start out in first gear. Then you should be able to count the shifts.

I have the naturally asperated version of your car. The rpm figures you mentioned sound normal for my car, but the rear end on your turbo might be different. Mine runs at about 2700 at 70 mph in 5th.

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'97 E 300 D

I am turning the filler cap as far as it will go but diesel is still filling up to the brim and spilling out. There's not a gasket/O-ring for the filler cap is there? I can see where there's a space for what could be a filler cap, but have not seen a part number for it or a gasket/O-ring called for in the fuel tank & fuel system diagram I got from Mercedes