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  #1  
Old 11-15-2016, 09:41 PM
Foo Foo is offline
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Normal RPMs for M104 engine at 60mph?

Hello all. Wonder if anybody can help me out with this. My 93 300e has usually run at around 2500rpms (+-100) doing 60. As of recent it's been a bit odd due to the rpms being at roughly 2900 when doing 60, but then if im doing 80 the rpms are just barely over 3k. The transmission has just been rebuilt and was doing perfectly fine until i noticed the rpms running higher (there is a delayed shift from 2nd to 3rd which is kind of annoying). Not really sure if this would affect anything as I am used to the car averaging roughly 15mpg due to it being lowered 85-90mm. Im big on preventative maintenance and new to working on Mercedes, if someone could post their rpms at 60 or shed some light on this I'd appreciate it.

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  #2  
Old 11-16-2016, 12:08 AM
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Quote:
Originally Posted by Foo View Post
Hello all. Wonder if anybody can help me out with this. My 93 300e has usually run at around 2500rpms (+-100) doing 60. As of recent it's been a bit odd due to the rpms being at roughly 2900 when doing 60, but then if im doing 80 the rpms are just barely over 3k. The transmission has just been rebuilt and was doing perfectly fine until i noticed the rpms running higher (there is a delayed shift from 2nd to 3rd which is kind of annoying). Not really sure if this would affect anything as I am used to the car averaging roughly 15mpg due to it being lowered 85-90mm. Im big on preventative maintenance and new to working on Mercedes, if someone could post their rpms at 60 or shed some light on this I'd appreciate it.
Depends on your gearbox. My 5 speed gives me about 2500 rpm at 60 mph if I remember correctly.

Are you getting 15 mpg in town? I get 15 mpg stop/start in Paris. 35 on a run of 500 miles. My UK gallons are a little bigger but not that much bigger.

Something must be wrong unless you're always in town or have a leaden right foot!

RayH
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Old 11-16-2016, 09:42 AM
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How many RPM's you're doing at a certain speed depends on the gear ratio in the transmission and the rear end final drive ratio, not the engine itself.

If nothing has been done other than having the transmission serviced, but now you have a difference in RPM at a given speed (400 RPM difference is significant), I'd suspect you may have a low fluid level or a slipping transmission or even the wrong fluid in the gearbox. Start with the easy stuff, go get the transmission hot and check the fluid level with the engine running.

15mpg is terrible fuel economy unless it's all in-town driving stop/go stuff.
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Old 11-16-2016, 05:39 PM
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Ill put it to you this way. Takes me 20 minutes to go 7 miles through downtown where I live. My extent of highway driving is going one or two exits down 85. The rest is all city driving and to school and back. Traffic is always terrible here too, so that tells me its normal. The transmission is still under warranty so I'll take it to the Autowerks shop and let them check it out, can't beat free lmao.
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  #5  
Old 11-17-2016, 01:34 AM
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Takes me 20 minutes to go 7 miles through downtown where I live.
Or 21 mph.

15 mpg, especially on small gallons, may be reasonable.

Give yourself a treat one day:
1. Fill the tank.
2. Go for a long, relaxing drive of 100+ miles, OUT OF TOWN.
3. Fill the tank.
4. Calculate the consumption.

I would expect 30-ish under those circumstances.

RayH
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  #6  
Old 11-17-2016, 06:53 AM
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my S does about 2100 at 60 mph,I'm planning to find a 92 rear end to put in mine to drop it lower.
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Old 11-17-2016, 10:29 AM
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You need low end torque to make taller gearing work properly. In most cases MB picked the correct ratio for your engine's torque curve and weight. If you swap in a taller diff you will be giving up some acceleration.
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Old 11-17-2016, 12:46 PM
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A strong '94/95 E320 with stock 2.65:1 rear screw will light the tires on dry pavement, it has adequate torque for that car's weight and gearing and the torque converter makes it all come together.

Your TC can be tired, there is no lockup TC on these transmissions so you're at the mercy of the TC at speed.
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Old 11-21-2016, 11:03 AM
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Interesting, my '97 CL600 sits at 2200RPM at 80MPH burning gas at the rate of 20MPG.
Anziani
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Old 11-28-2016, 02:37 AM
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Sounds like the difference between overdrive in and overdrive out (5th if you have it). If so you could try shifting from 5th to 4th and see if it makes any difference.
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  #11  
Old 11-28-2016, 08:34 AM
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Most 1993 300e models in the USA had the 2.8 liter variant of the m104. Only a small minority were 3.2 that year. This car also has a 4 speed automatic, no overdrive, and no lockup torque converter. It's been a number of years since I sold mine so I don't recall exactly how fast the motor spun on the highway, but it was geared on the short side. I think about 2400 at 60mph is about right. Outside the city at Texas nominal it turned about 3k rpm. Mine never delivered great mpg, about 24-25 on road trips and 20ish around town.

Sounds like the OPs car is in third at 60. Possibly the Bowden cable that controls shift points is too tight, delaying the upshift to fourth. I think it's a simple tension adjustment at the throttle body, like other MBs of the era. This is an early drive by wire throttle though, so may be a bit different.

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