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  #1  
Old 01-19-2011, 02:17 AM
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M104 HFM 2.8 rev is limited to 4000rpm

I tested my car and realized that its rev is limited to 4000rpm. I tested it without load and the rev limit was around 4000rpm too. Cam adjuster connector was tested and showed 8v when the rev was less than 4000rpm, jumped when the rev reached 4000rpm.

Do I have my cam adjuster failed?

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  #2  
Old 01-19-2011, 04:38 AM
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If you did it in N or P then this is how it it's meant to be. If you drive it you'll notice the rev limit is much higher. It's a safety thing Mercedes incorporated in.

Btw, what HFM?
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  #3  
Old 01-19-2011, 01:09 PM
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Quote:
Originally Posted by Spetz View Post
If you did it in N or P then this is how it it's meant to be. If you drive it you'll notice the rev limit is much higher. It's a safety thing Mercedes incorporated in.

Btw, what HFM?
Unfortunately 4000rpm was also what I got on highway. Note that 4000rmp was the threshold that the cam adjuster kicks in to retard the inlet valve timing, leading me to the thinking that there might be something wrong to the cam adjuster. Some tell me it's got to do with the ECU, it was programed that way.

In some market automobile manufacturers have to bring cars' power down to comply with local laws. Did it apply with the E280 when it was imported to certain markets?

HFM stands for hot film mass air flow sensor meaning that the system meters air amount sucked in by means of a hot film. Before HFM was KE Jetronic, LH jetronic was after, etc.
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Old 01-19-2011, 02:27 PM
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A failed cam adjuster will not keep the engine from revving. (barring any catastrophic failure that would affect all engine speeds) The power may be a bit off but it should pull to the redline regardless.
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  #5  
Old 01-19-2011, 04:14 PM
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Note that the M104 has a transmission overload protection switch (S65) and its connector (X22/1). Can failure of either of the two cause the god dammed 4000 rpm limit?
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  #6  
Old 01-20-2011, 01:12 PM
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If the Mass Air Flow sensor reports too little air (which is usually how they fail), you may experience fuel starvation at higher RPM. As the condition worsens, the maximum RPM you'll be able to attain will drop. I've seen this happen many times on the older HFM-SFI systems.
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  #7  
Old 01-21-2011, 12:57 AM
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I've got some updates on this.

My car sprints like a beast when I floor the gas pedal. It revs all the way to 5500rpm then shifts to second gear. I believe its speed is restricted to 150km/h, not its rev. At 4th (final) gear and 150km/h its rev coincidentally is 4000rpm which is also rev limit when the car in Park.

I don't know why some idiot restricted my car's speed limit.
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Old 01-21-2011, 01:00 AM
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Originally Posted by ILUVMILS View Post
If the Mass Air Flow sensor reports too little air (which is usually how they fail), you may experience fuel starvation at higher RPM. As the condition worsens, the maximum RPM you'll be able to attain will drop. I've seen this happen many times on the older HFM-SFI systems.
I didn't see any sign of fuel starving. It runs as it should until it reaches 4000rpm. Fuel is cut off when above 4000rpm then resumed as long as the car reaches 4000rpm again.
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  #9  
Old 01-21-2011, 01:12 AM
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My E280 doesn't have sensor for speed signal. I wonder how the ECU recognizes the vehicle's speed. Can any one tell me at which pin the ECU receives the vehicle's speed?
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  #10  
Old 01-21-2011, 11:48 AM
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Originally Posted by glpro160 View Post
I don't know why some idiot restricted my car's speed limit.
I seem to remember that this was a gentleman's agreement between luxury car manufacturers Mercedes, BMW, Audi and Porsche. Each were building cars that were just as fast (if not faster) than the others, and an agreement was that no cars would be made that would go faster than 250 km/hr or 155 mph.

I think that the first car to be built with the limiter was the V12 BMW 750i in 1987.
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  #11  
Old 01-21-2011, 12:48 PM
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Originally Posted by glpro160 View Post
I've got some updates on this.

My car sprints like a beast when I floor the gas pedal. It revs all the way to 5500rpm then shifts to second gear. I believe its speed is restricted to 150km/h, not its rev. At 4th (final) gear and 150km/h its rev coincidentally is 4000rpm which is also rev limit when the car in Park.

I don't know why some idiot restricted my car's speed limit.
Doesn't sound right. I have the same basic car - 1993 USA model 300E 2.8 (e.g. E280). The USA models are limited to 130MPH maximum speed because they were delivered with "H" speed rated tires. Mine pulls right to redline before upshifting - 6400RPM.

150KPH is only ~95MPH - that's awfully slow. IIRC redline in 3rd gear is marked on the speedometer at 120MPH - are you sure it's shifted into 4th gear when you reach terminal speed?

I'm thinking ILUVMILS is on the right track here - perhaps you are down on power and it simply can't pull past 4K RPM at speed. Do you have a code reader to pull the fault codes from the OBD diagnostic system? There are many articles here on how to build, read, and interpret the codes.
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  #12  
Old 01-22-2011, 01:10 PM
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Originally Posted by jcyuhn View Post
Doesn't sound right. I have the same basic car - 1993 USA model 300E 2.8 (e.g. E280). The USA models are limited to 130MPH maximum speed because they were delivered with "H" speed rated tires. Mine pulls right to redline before upshifting - 6400RPM.

150KPH is only ~95MPH - that's awfully slow. IIRC redline in 3rd gear is marked on the speedometer at 120MPH - are you sure it's shifted into 4th gear when you reach terminal speed?

I'm thinking ILUVMILS is on the right track here - perhaps you are down on power and it simply can't pull past 4K RPM at speed. Do you have a code reader to pull the fault codes from the OBD diagnostic system? There are many articles here on how to build, read, and interpret the codes.
I am 100% sure that it was at 4th gear when struggling with 4000rpm threshold. I goes past 4000rpm to around 5000rpm when upshifting from 1st to 2nd gear. I can't find one that has adapter to read 16-pin OBD I, so don't know where the fault is.

The car has a history anyway, it was first imported to Vietnam for embassy's use, then sold out for private use. It might be the reason for that awfully low power limit.

A guy told me that the limit can be removed by loading ECU's chip with firmware from unrestricted car.
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  #13  
Old 01-22-2011, 02:00 PM
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I was wondering in what region you lived. Perhaps there were speed restrictions applied via the ECU firmware. If the car is running properly it should still be accelerating quite strongly at 150KPH. Does it stop accelerating quite suddenly at 4000RPM?

It is quite easy to build a code reader for the 16 pin OBD. Only a few basic electronic parts are required - a 12 volt LED, pushbutton switch, and a few banana plug leads. These are easily available in the U.S., though cannot speak for your locale. You can find the instructions, wiring diagram, and code lists in old posts here. Suggest searching using the terms "Arthur Dalton code reader" and go from there.
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  #14  
Old 01-23-2011, 06:45 AM
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Quote:
Originally Posted by jcyuhn View Post
I was wondering in what region you lived. Perhaps there were speed restrictions applied via the ECU firmware. If the car is running properly it should still be accelerating quite strongly at 150KPH. Does it stop accelerating quite suddenly at 4000RPM?

It is quite easy to build a code reader for the 16 pin OBD. Only a few basic electronic parts are required - a 12 volt LED, pushbutton switch, and a few banana plug leads. These are easily available in the U.S., though cannot speak for your locale. You can find the instructions, wiring diagram, and code lists in old posts here. Suggest searching using the terms "Arthur Dalton code reader" and go from there.
I live in Viet Nam, South East Asia region you may know. It was originally used by some foreign embassy here which I don't know. But the fact is that its speed is restricted. I can vividly feel that when the car reaches 150kph/4000rpm (not sure which of those is the determinant) fuel supply is terminated. When under 150kph my car can pass basically any car at ease. Yes, it stops suddenly at 150kph/4000rpm.

I wonder these things: if the ECU restricts the car's speed then there must bee speed signal input for the ECU, or if the ECU governs the car by rev limit then tach signal must be an input for the ECU. I read the ECU's pinouts seeing that ECU takes speed signal from pin A8, but my car's speedometer is the rotating type, not the sensor type, so where does it take the speed signal from? Can it be the speed sensor that the ABS also utilizes? The thing is that the ABS is working properly. Pin A18 receives engine speed signal to revolution counter.

Whatever it is I sort out 3 possible reasons for my car seemingly speed restrictions:

- ECU's firmware: nothing can be done unless reinstall the firmware
- speed signal sensor is wrong
- engine speed signal is wrong

Anyway I will learn how I can make a code reader.

Any input is welcome.
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  #15  
Old 01-24-2011, 12:02 AM
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Originally Posted by glpro160 View Post
It was originally used by some foreign embassy here which I don't know.
The embassy wouldn't have required armour plating, would it? It would certainly reduce maximum speed, not sure about power output.

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