W124 250 diesel performance (1992)

EireJames

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Well, I know they are slow and mine pulls quite well in first and second and third. But in 4th and 5th it is completely dead, doesn't seem too interested in going over 85mph to be honest. Now she was off the road for the last year, the air filter is clean. If the exhaust was blocked I presume it wouldn't pull well in the lower gears. When new these were meant to do 109 according to the net. Will exercise improve her gradually ?
 

Number_Cruncher

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First thing to do is to renew all the fuel filters, strainer, primary filter and secondary filter.
 

wireman

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Bcause of the low gear it will seem OK whilst being flogged at low road speeds, besides the filter change job check that you are getting full travel of the throttle lever on the fuel pump body. I would expect black or blue smoke under load if there is much wrong with the engine.
Any signs of missfiring or rough running?
Avoid any style of Italian tune up untill you have sorted out the filters.
 
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EireJames

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Thanks a lot gents, I shall action the filters as soon as I can. There is no black / blue smoke to note.
 
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EireJames

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What's the priming procedure for the main fuel filter ?
I just filled the replacement with diesel and hoped for the best :neutral:
Turns out I was wrong as she won't start. Anything I can do to prime the system, my last diesel had a priming bulb, there didn't seem to be any such thing on the 250 :(

Am in in trouble gents ?
 

simon_wall69

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No, just crank, pause, crank, pause at abot 30 second intervals. Takes a while normally and maybe a battery charge! Also, you should put some fuel on the gasket as well to stop air coming in but I assume you knew this.

It will self-bleed.

p.s. you haven't turned the fuel cut off screw by mistake - it sits above the housing (could be wrong about this bit, by the way!)
 
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EireJames

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Only thing I turned was the nut that screws into the filter :D
Dunno will my batery endure this :neutral:
Thanks for the info and quick reply, fingers crossed.
 
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EireJames

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I was right about the battery, bummer, and she very very nearly started.
 

simon_wall69

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The only other thing that I can think of is that there was already some air in the system leading to the loss of power - it should still start though - sounds as if you are nearly there.
 
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EireJames

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Happy out :)
The battery recovered and she started on the 2nd crank before the battery died again. Stroke of luck. Cheers for help Simon, knowing that it may soon start was a great help.

So where is the inline filter can anyone tell me ? :Oops:
 

Number_Cruncher

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Yes, the system is self bleeding.

Short bursts on the starter of about 10 - 15 seconds each will eventually bleed the fuel through, while avoiding overheating the starter motor.

There's no fuel tap on the filter, as there's a conventional electrical shut off on the pump.

There isn't an inline filter as such.

However, the prefilter is item 26 in the link below. You'll also need a new O ring, part 29.

http://www.detali.ru/cat/oem_mb2.as...GM=717.460&CT=M&cat=19S&SID=07&SGR=120&SGN=04

There may also be a tank strainer - ask at the MB garage about that.
 

wireman

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My 1989 handbook says crank it for up to one minute without pause and keep the starter engaged (dont release it if the engine only catches) untill the engine runs cleanly to bleed the system after running out of fuel.
Having once run out (in Tescos fuel station blocking the entrance 20 feet from the pumps) I can report that not keeping it cranking makes bleeding it a much longer job, if it ever happens again I shall follow the MB instruction.

On mine there is an inline hanging on the flexible pipes below the air filter box.
 

Number_Cruncher

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For some reason, I've got confused between this thread, and a similar one about a C250D - so, I need to revise what I said.

>>There's no fuel tap on the filter, as there's a conventional electrical shut off on the pump.

This was wrong - there is a tap on the W124s, as they have the vacuum shut-off, while on W210s, and W202s, there isn't a tap.

>>There isn't an inline filter as such.

I suspect if there is an inline filter hanging from the pipes, it's probably an aftermarket fitment, or a retro fit of the W123 inline filter, perhaps fitted by someone who didn't know about the presence of the pre-filter in the low pressure fuel filter & distribution body.

There will also be a tank strainer in a W124.

I'm surprised that you can crank as long as a minute. That is quite harsh treatment for the starter motor. But, of course, I won't argue too strongly against advice written in the handbook.
 
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EireJames

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Changing the filter didn't improve things too much I think, to be honest I wasn't expecting it to. She pulls from 50 to 60 mph in 5th, slowly but she does. And will go to 90 in 4th but is just dead. Above 70 in 5th and there is nothing at all.

Can anyone who has / had a 250 diesel comment on what there's is like in top gear over 70 mph.
 

simon_wall69

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Not had a manual one but mine only ever did about 95 flat out with an auto. You do only have about 90 bhp on tap (and a paucity of torque) and some of those horses will have fled over the years. Other things to affect performance could be tyres, old injectors and a lack of compression; I wouldn't get your hopes up too much though.

What is the mileage?
 
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EireJames

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Yeah I was thinking that, 226 000 miles :lol:
I reckon she is as she is. Still she has been resting for a year so maybe she will benefit from use, I sold my Prelude on Saturday morning so the Merc is now my daily driver.
 

Juddian

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Too late for this occasion but with my 300d i always filled the filter with VERY clean fuel before fitting, would fire up straight away then with only a slight hesitancy to clear the last of the trapped air.

Here we go prepare for flaming.
Have you tried a good dose or even regular use of a fuel treatment/injector cleaner such as Forte or Millers.
It may just help to clean up the injectors a little, and by the way did you change the air filter?
 

brianbrian

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w124 250D, SL129-deisel
You have your main filter, you have your inline filter, you have a strainer in the bottom of fuel tank on this model, small inline filter needs to be changed this is the one that normally makes the car a bit sluggish , you need to take air filter box of to get to it, buy a length of fuel pipe and new jubilee clips and replace fuel hoses to make the car reliable as they do perish, the 250d is a bit slow after 70mph on the auto and manual but should do over 100mph, if you decide to take the strainer out of the tank make sure you have a new strainer or O ring. Hope this helps
 

Number_Cruncher

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>>you have your inline filter

If it's an OM602, yes, but, if it's a later OM605 engined 250, then, there isn't an inline filter.
 


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