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Registered
1994 S500
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50 Posts
Discussion Starter #1 (Edited)
First of all, I love you all and thanks for all the answers and support. This forum has helped me alot with my new 1994 w140.

My MPG is 10 freeway and 5 city. yes you read that right. with A/C OFF.

110,000 is the mileage. I bought it last week.
It runs great with the engine being so smooth.
No gas leaks whatsoever.
New oil change.
New filters.
Brand new tires.

i want to diagnose it. where should i start? any ideas?

I've seen people saying that they have misfires in cylinders. how can I test for that?
and how can i check the O2 sensor? since this car doesnt get tested by regular tools?

this is killing my pocket, full tank gets to empty in no time. need to do something about it please help. and yes I know its a V8 but this is insane even for this car right?


----------------------------------------------------------
Another Major issue for me.

when exceeding 65mph, a weird noise comes through the cabin like "Whoooo" like being on an airplane sound. when i go down below 65 it goes away. any ideas?



thanks in advance
 

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Moderator
1995 Mercedes S420, 1995 SL320, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
Joined
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1,734 Posts
Yeah, 5/10 is wildly bad mileage for an S500. First question is... are you sure? Are you actually doing the math or going by the mileage gauge? These cars do use a lot of gas compared to modern cars, and even my 420 burns through a full tank startlingly fast. But my mileage is about 12 city and 24 highway, which is more than double what you claim to be getting.

If you're sure you're only doing 5/10 there's a few things you'll need to check. First, you say the engine is very smooth, so that tells me you likely don't have a misfire. You'd be down on power and running rough if the car was misfiring, plus the exhaust would smell very rich. If you have none of those symptoms, we can probably rule out misfires.

You mentioned that you checked for leaks, I'd double check just to be sure. But again, if you don't smell gas anywhere then you probably don't have a leak. I'd want to check the fuel pressure also, just to see what that's doing, along with the injectors.

Next there's the mass airflow sensor, which could be telling the computer to dump too much fuel into the system. But that's something you'd smell in the exhaust also. And if the sensor was totally bad, it would throw a Check Engine light -- ditto for bad O2 sensors. Still, doesn't hurt to spray the MAF sensor with some cleaner just to be sure.

Have you pulled the spark plugs? Do they look fouled or washed? These engines are very sensitive to the correct spark plug type, and the vast majority of owners (and service centers) have no idea how important they are, installing the 'latest and greatest' deluxe quad-point iridium super plugs, when in reality the engine requires plain copper resistor plugs, nothing more nothing less. This could be at least part of your issue. Just do a plug replacement as a preventative measure, it's cheap insurance.

After all that, we're left with friction. Are you completely sure none of your brake calipers are sticking even a little bit? I had a rear caliper begin to stick on me and it was almost imperceptible while driving. I only noticed because the wheel was producing more brake dust than the others.

You said you have new tires, so I'm assuming your tire pressure is good too.

How's your transmission? Is it shifting okay? Not holding gears for longer than it should? No weird noises or whines? I know you mentioned the noise you're getting above 65mph -- where does that sound like it's coming from? Could it be the transmission?

Something like this could be hard to diagnose on your own. Do you have a local specialist that you trust, in case all these end up being brick walls?
 

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Registered
1994 S600 Coupe, 1995 S600 Coupe
Joined
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1,997 Posts
First of all, I love you all and thanks for all the answers and support. This forum has helped me alot with my new w140.

My MPG is 10 freeway and 5 city. yes you read that right. with A/C OFF.

110,000 is the mileage. I bought it last week.
It runs great with the engine being so smooth.
No gas leaks whatsoever.
New oil change.
New filters.
Brand new tires.

i want to diagnose it. where should i start? any ideas?

I've seen people saying that they have misfires in cylinders. how can I test for that?
and how can i check the O2 sensor? since this car doesnt get tested by regular tools?

this is killing my pocket, full tank gets to empty in no time. need to do something about it please help. and yes I know its a V8 but this is insane even for this car right?


----------------------------------------------------------
Another Major issue for me.

when exceeding 65mph, a weird noise comes through the cabin like "Whoooo" like being on an airplane sound. when i go down below 65 it goes away. any ideas?



thanks in advance
What year is the car? The engine management system changed in 96, so knowing which version you have would help.

Jon
 

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W140 Moderator
"CHRIS" Merc 92 600SEL / Sold > 93 600SE / 93 S500 / 89 560SEL / 413CDI / B180-CDI /A170-CDI
Joined
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7,606 Posts
On my other car the fuel consumption was bad as well, i investigated why & it ended up being the Oxygen Sensors faulty . Changing them improved the consumption a lot ,Like from being a heavy Alcoholic to a Mid range drinker , know i'm trying to teach this car not to drink at all but it's not working out to well ,lol.

My MPG is 10 freeway and 5 city.
My ex S500 (June 93 Build) used to drive around 700km before i needed to fill up . You would be doing 110 with a full tank including Reserve .
 

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Premium Member
'97 CL600
Joined
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2,915 Posts
Fill the tank. Write down mileage. Drive for a month, recording every drop that you put in. At the end of a month, fill to top and record mileage again. Subtract beginning mileage from ending mileage and divide this number by gallons used. I have a 12 cylinder CL600 and get 12 around town with full AC and 20 on the freeways at 80+ Something is wrong with your calculations if you say the car runs well.
Anziani
 

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Moderator
1995 Mercedes S420, 1995 SL320, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
Joined
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1,734 Posts
Yes, what Anziani said. Before you go trying to diagnose or replace parts, get a REAL calculation and be 1000% sure.
 

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Registered
1994 S500
Joined
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50 Posts
Discussion Starter #7
On my other car the fuel consumption was bad as well, i investigated why & it ended up being the Oxygen Sensors faulty . Changing them improved the consumption a lot ,Like from being a heavy Alcoholic to a Mid range drinker , know i'm trying to teach this car not to drink at all but it's not working out to well ,lol.


My ex S500 (June 93 Build) used to drive around 700km before i needed to fill up . You would be doing 110 with a full tank including Reserve .
was your engine check light on or you just replaced them on a guess? asking because my check engine light is not on so do you think It would be good to change them anyway considering it has 110000 miles on it ? also i couldnt find a guide or video on how to do that (since I do everything myself nowadays), any idea if theres any?
 

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Registered
1994 S500
Joined
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50 Posts
Discussion Starter #8
Yeah, 5/10 is wildly bad mileage for an S500. First question is... are you sure? Are you actually doing the math or going by the mileage gauge? These cars do use a lot of gas compared to modern cars, and even my 420 burns through a full tank startlingly fast. But my mileage is about 12 city and 24 highway, which is more than double what you claim to be getting.

If you're sure you're only doing 5/10 there's a few things you'll need to check. First, you say the engine is very smooth, so that tells me you likely don't have a misfire. You'd be down on power and running rough if the car was misfiring, plus the exhaust would smell very rich. If you have none of those symptoms, we can probably rule out misfires.

You mentioned that you checked for leaks, I'd double check just to be sure. But again, if you don't smell gas anywhere then you probably don't have a leak. I'd want to check the fuel pressure also, just to see what that's doing, along with the injectors.

Next there's the mass airflow sensor, which could be telling the computer to dump too much fuel into the system. But that's something you'd smell in the exhaust also. And if the sensor was totally bad, it would throw a Check Engine light -- ditto for bad O2 sensors. Still, doesn't hurt to spray the MAF sensor with some cleaner just to be sure.

Have you pulled the spark plugs? Do they look fouled or washed? These engines are very sensitive to the correct spark plug type, and the vast majority of owners (and service centers) have no idea how important they are, installing the 'latest and greatest' deluxe quad-point iridium super plugs, when in reality the engine requires plain copper resistor plugs, nothing more nothing less. This could be at least part of your issue. Just do a plug replacement as a preventative measure, it's cheap insurance.

After all that, we're left with friction. Are you completely sure none of your brake calipers are sticking even a little bit? I had a rear caliper begin to stick on me and it was almost imperceptible while driving. I only noticed because the wheel was producing more brake dust than the others.

You said you have new tires, so I'm assuming your tire pressure is good too.

How's your transmission? Is it shifting okay? Not holding gears for longer than it should? No weird noises or whines? I know you mentioned the noise you're getting above 65mph -- where does that sound like it's coming from? Could it be the transmission?

Something like this could be hard to diagnose on your own. Do you have a local specialist that you trust, in case all these end up being brick walls?
Thank you for taking the time to reply.

Yes, even though I dont hear any knocking or misfires, i am going to check the status of my spark plugs today. previous owner told me he changed them so I am not sure what to expect. maybe he put in the wrong ones?

i will get back to you with an update
 

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Registered
1994 S500
Joined
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50 Posts
Discussion Starter #10
Yes, what Anziani said. Before you go trying to diagnose or replace parts, get a REAL calculation and be 1000% sure.
Unfortunately my calculations are a 100% correct. its not rocket science to calculate the mpg lol
 

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Registered
1994 S600 Coupe, 1995 S600 Coupe
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1,997 Posts
Is your transmission shifting into 4th? Running in third would kill mileage. Pre-96 cars normally start from standstill in 2nd, so you should have two upshifts.

If you let us know where you live, someone close by might have the STAR diagnostic system. You really need to see real time data from the MAF, throttle body, O2 sensors, etc.

Does your engine oil smell like gas?

Jon
 

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Registered
1994 S500
Joined
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50 Posts
Discussion Starter #12
Is your transmission shifting into 4th? Running in third would kill mileage. Pre-96 cars normally start from standstill in 2nd, so you should have two upshifts.

If you let us know where you live, someone close by might have the STAR diagnostic system. You really need to see real time data from the MAF, throttle body, O2 sensors, etc.

Does your engine oil smell like gas?

Jon
Transmission does shift into 4th.

I was wondering who or where you can have all things you said tested. Can a smog shop with "STAR Certified" do this? if the engine is misfiring, does that mean I got the wrong spark plugs in?

I live in San Bruno, California

Thanks,
 

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Registered
1994 S600 Coupe, 1995 S600 Coupe
Joined
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1,997 Posts
STAR diagnostics is the Mercedes specific diagnostic system. It interfaces at the 38 pin port on the right side of the engine compartment. A Mercedes specific repair shop should have the system. Many members here also have it.

There are a lot of things that can cause excessive fuel consumption. That's why you need to have your engine diagnosed. Trying to speculate won't help.

This website has a bunch of diagnostic info specific to the S500.

Jon
 

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Premium Member
'97 CL600
Joined
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2,915 Posts
There is a place on this forum where you can look up recommended Benz repair shops. I poked around a little bit and found places in San Jose. You need a good Benz mechanic that has the Star scanner. It will probably cost some bucks to have him scan the car but throwing parts at it is not the answer. And strange as it may sound, I would call the local Benz service department, tell them you have a 27 year old car and could they recommend someone in the area to work on it. Also contact Thomas Hanson at The Classic Car Center in Irvine and ask him for a service recommendation in your area.
Good luck,
Anziani
 

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Registered
1994 S500
Joined
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50 Posts
Discussion Starter #15
There is a place on this forum where you can look up recommended Benz repair shops. I poked around a little bit and found places in San Jose. You need a good Benz mechanic that has the Star scanner. It will probably cost some bucks to have him scan the car but throwing parts at it is not the answer. And strange as it may sound, I would call the local Benz service department, tell them you have a 27 year old car and could they recommend someone in the area to work on it. Also contact Thomas Hanson at The Classic Car Center in Irvine and ask him for a service recommendation in your area.
Good luck,
Anziani
Thank you, didnt know this forum had such a thing.

I contacted my local Mercedes dealership and asked if they could refer me to someone in the area who could work on my car, their answer was "we have the mechanics certified to work on such a vehicle and you should bring it to us", which in no way in hell am going that. their cost estimates are always through the roof for stuff that doesnt even need changing.

i'll take an appointment from one of the shops listed in that forum and will get back to you with an update.
 

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Registered
1994 S500
Joined
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50 Posts
Discussion Starter #16
=
Is your transmission shifting into 4th? Running in third would kill mileage. Pre-96 cars normally start from standstill in 2nd, so you should have two upshifts.

If you let us know where you live, someone close by might have the STAR diagnostic system. You really need to see real time data from the MAF, throttle body, O2 sensors, etc.

Does your engine oil smell like gas?

Jon
I've just contacted 2 star certified shops and both said that this car is too old to be connected like a regular car and check the engine for real time data. They asked for $300+ to diagnose the car which is really expensive...

Who said Californian's are living the dream....? More like a nightmare to me
 

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Registered
1999 E320, 2000 E320, 2003 E320 Wagon, 2005 C230K SS, 2010 Accord LX w Eibach & Koni FSD's
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2,727 Posts
I've just contacted 2 star certified shops
When you say star certified shops, are you referring to "Star" smog shops? As mentioned by Jal1224, STAR is a Mercedes diagnostic system used by mechanic to scan, code, do adaptation etc. on Mercedes vehicles.

You need to find a shop that specialize in Mercedes repairs. They will have the STAR system
 

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Premium Member
'97 CL600
Joined
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2,915 Posts
Benzdream, I went to google and typed in "Mercedes repair shops in San Bruno, CA" and found at least three independent shops listed. I would start there. And yes, some Mercedes dealers still have an old timer or two on the staff. Usually if they are any good, they go out on their own and open up their own shop. I went to our local Benz dealer (Palm Springs) and wanted JUST an Star engine scan. They quoted me $400 for the whole car but wouldn't scan the engine only. You can also buy a OBDII scanner on amazon for under $100 that you plug in under the dash if you are the "do it yourself" kind of a guy.
Anziani
 

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Registered
1994 S500
Joined
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50 Posts
Discussion Starter #20
UPDATE:

Found multiple leaks. Rear differential leak, fuel filter leak, transmission leak and power steering leak.
all due to old gaskets that need changing (makes sense since the car has been parking for more than 15 years).

Bought fuel filter and spark plugs from the dealership. i will update you all once i put them in if theres any difference afterwards.
 
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