Mercedes 300E 24v gearbox issue??

[mrnick969]

Hi there
I have a Mercedes 300e 24v, it has the 4 speed automatic gearbox. It runs perfectly except for one thing. The red line is 7000rpm but mine will only rev to about 6500 rpm. I am aware this is only a matter of 500 rpm but I still feel like I am missing out on a little bit of performance.

Do I have some kind of issue with my gearbox or is it normal for it to change at 6500 rpm

Thanks

Nick

 

[trapperjohn]

Cue Ian Walker. He has two of these a Coupe and a Saloon.

Not sure even Ian holds it in gear than long. On a private test track I have noticed his Coupe will "kick down" at 90MPH. Wasn't looking at the rev counter, was more intent on looking for a four point harness at the time

 

[neilrr]

Has it ever revved to 7K while you've owned it?

 

[carat 3.6]

Sounds like your car is fitted with the fuel pump relay from the 12v m103 300e.

 

[trapperjohn]

Has it ever revved to 7K while you've owned it?

Not as I'm aware.

 

[neilrr]

Sounds like your car is fitted with the fuel pump relay from the 12v m103 300e.

300E-24v engines use a much bigger relay than M103 engined 300Es which (IIRC) does a couple of other things as well as fuel.

 

[Ian B Walker]

Cue Ian Walker. He has two of these a Coupe and a Saloon.

Has it ever revved to 7K while you've owned it?

My Coupe will happily rev to 7k. The saloon revs just shy of 7k.

 

[RBYCC]

300E-24v engines use a much bigger relay than M103 engined 300Es which (IIRC) does a couple of other things as well as fuel.

The FPR's are all interchangeable with the differences being the high RPM limit cutoff setting.
The RPM limit is sometimes stamped on the relay.
The FPR controls not only the fuel pumps but kickdown on automatci transmission vehicles and max rpm limit cutoff points.
Installing a W126 V8 FPR will increase the limit RPM if you can't locate the correct FPR for the high RPM early M104-24V CIS-E motor

 

[neilrr]

The FPR's are all interchangeable with the differences being the high RPM limit cutoff setting.
The RPM limit is sometimes stamped on the relay.
The FPR controls not only the fuel pumps but kickdown on automatci transmission vehicles and max rpm limit cutoff points.
Installing a W126 V8 FPR will increase the limit RPM if you can't locate the correct FPR for the high RPM early M104-24V CIS-E motor

You sure?

The LH one is from an H reg 300CE-24, the RH one, MB part # 003 545 24 05, from a G reg 190E 2.6.

 

[RBYCC]

You sure?

The LH one is from an H reg 300CE-24, the RH one, MB part # 003 545 24 05, from a G reg 190E 2.6.

Depends on the year...I believe up until a transition point in 1990 ( possibly 1992 dependent on country ) the CIS-E engines used the smaller separate fuel pump relay.
The later M103 and M104 used the combined MAS engine systems control unit which incorporated the FPR, KLIMA, etc....

My comment was based on an earlier post that the vehicle may have an early M103-12V style FPR...

 

[carat 3.6]

Depends on the year...I believe up until a transition point in 1990 ( possibly 1992 dependent on country ) the CIS-E engines used the smaller separate fuel pump relay.
The later M103 and M104 used the combined MAS engine systems control unit which incorporated the FPR, KLIMA, etc....

My comment was based on an earlier post that the vehicle may have an early M103-12V style FPR...

Mine is a 1990 24v and has the smaller relay, I think the change to the bigger relay was at the same time as mercedes started fitting catalic converters, 02 sensors, and air pumps to these engines.

I could be wrong though

Just out of intrest, what the rev limit theoreticly be increased to if I fitted the v8 fuel pump relay?

 

[RBYCC]

Mine is a 1990 24v and has the smaller relay, I think the change to the bigger relay was at the same time as mercedes started fitting catalic converters, 02 sensors, and air pumps to these engines.

I could be wrong though

Just out of intrest, what the rev limit theoreticly be increased to if I fitted the v8 fuel pump relay?

There is a long running thread "Tuning with CIS-E" on Peachparts.com - shop forum-performance paddock..in which "400Eric" has been experimenting with various FPR's and EZL's.
He indicates the 126 V8 FPR will go to about 7300 rpm.

Ed A.

 

[mrnick969]

Thanks for all of your replies, I have not posted again because I am unable to connect to this site from my home computer for some reason. I have looked under my bonnet and I have the large MAS unit as shown in neilrr's picture. It says m104 on it so I assume it must be the correct unit for my engine. Does this suggest there could be a fault with it? I will be giving my car a full service in the near future so it will be interesting to see if that makes any difference. If not the FPR from a w126 v8 could be worth trying. 7300 rpm would be nice! Although I am not sure if it would be possible to fit to my car as it has the later all incorporating MAS unit.

 

[Scott_F]

As your car is 20+ years old maybe it's time to give the old girl a break and stop revving her to 7000rpm !!

 

[trapperjohn]

As your car is 20+ years old maybe it's time to give the old girl a break and stop revving her to 7000rpm !!

That works for me too.

If you want to rev the nuts off something get a BMW

 

[Scott_F]

That works for me too.

If you want to rev the nuts off something get a BMW

I feel guilty when I rev my car above 4500 rpm !

 

[mrnick969]

As your car is 20+ years old maybe it's time to give the old girl a break and stop revving her to 7000rpm !!

Whilst I am sure that is sensible advice I would rather enjoy the car to its fullest extent!

 

[trapperjohn]

Whilst I am sure that is sensible advice I would rather enjoy the car to its fullest extent!

Fair do. Each to their own.

 

[mjcr666]

an old car like that shouldnt be revved that high anyway!

 

[bolide]

an old car like that shouldnt be revved that high anyway!

Why not? The redline is there for a reason but the rest of the rev range is designed to be used, not saved for a rainy day

Nick Froome
the independent Mercedes Estate specialists