E300td intermitant fault

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R Phillips

Member
Joined
Aug 8, 2003
Messages
53
Location
Epping
Car
E350 W212 estate
1999 E300td, car runs fine for 99% of the time but every now and then on start up I get a small rumble of a missfire, when this happens the car then has no power. to drive, it feels as though only the first 20% of the throttle is working. The engine sounds fine but is down on power. It has never cleared while on the move, but after it's been left on restart it tends to be fine again. It happened about 3 times in the first 5/6 years (I've had it from new) but now seems to happen more often.
 
I did think it could be the MAF, but most of the time it runs fine. It's almost like the engine goes into a safe mode after detecting a fault.
 
No, I'll try and get that read.
 
My old 250TD would occasionally feel like it lost half its power (a serious problem with a 250, I can tell you) and the cause was the fuel shut-off valve not opening fully. On that car it was pneumatically operated - if you started it, turned it off immediately then restarted it it would either stall or limp along

As your car does this so infrequently I'd suspect somethng mechanical and not electrical. The shutoff valve is one possibility

Nick Froome
www.w124.co.uk
 
Pretty strange fault here but given that the fuel system is mechanical with electric control I would look at the fuel pipes for air leakage and the connections onto the back of the fuel pump.
 
Strange you should say that because something else has happened in the past, should the fuel tank be low (less than 1/4 tank) and the car is parked with the nose up, I have had to let the starter run for it to start.
 
Check the o-ring on the fuel pre-filter. Its just to the left of the main filter, held down by a small plate of metal. Remove that plate and then remove the pipe that supplies fuel to it, then the prefilter will lift out.

If the o-ring has a square cross section, get a new o-ring from the parts desk of your local dealer.

Also feel for any damp diesel under the injection pump and around that general area. Leaks here are a common problem but not a big deal to fix.
 
Is this the pre filter?
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Sorry it's a bit small, taken on my phone.
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another try.
 
The pre filter is in the left under the black plate. It's retained by the bolt to the right of it. The main filter is to the right

Do a search of this forum for diesel air leaks and you'll find lots of information about it. A couple of hours work and about £10-worth of O-rings will solve the problem. The connections on all those transparent pipes are suspect

Nick Froome
www.w124.co.uk
 
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can you tell me how to solve this known air leak problem with the mercedes diesels 220d 250d 300d so on,, everyone knows its commom yet no one knows answer???
 
I really do not think that it is an air leak problem. If it was it would be difficult to start pretty much every morning or after its left for a few hours. Get the fault memory read and see what the fault codes say. Another possible cause is the vacuum transducer sticking intermitantly. This would cause your lack of power.
 
Well it's back again, I don't think it's an air leak as it doesn't happen that often (been approx 3 months now)
So it's done it again, it started just after heavy rain, not sure if that could be connected.
But to define it better it is fine from a cold start and starts when the engine temp gets to about 70 deg (just before normall)
 
The only things that can cause a misfire are the IP, injectors or air leak.

Bolides suggestion of the fuel shut off is a good one as it could cause fuel starvation but I would expect that to be Ok under light load and worse as the load/speed increased.

Exactly what happens, is it when idleing or only under load.
 
No it Idles and runs fine, the slight missfire seems to have gone, to drive it just feels as though it only has the first 15% of throttle working.
From cold it is fine until 70deg then it feels as though the power has gone, not smoking, a passenger wouldn't notice anything but think that you may be driving slow. It will still kick down you just don't go anywhere!
 
No it Idles and runs fine, the slight missfire seems to have gone, to drive it just feels as though it only has the first 15% of throttle working.
From cold it is fine until 70deg then it feels as though the power has gone, not smoking, a passenger wouldn't notice anything but think that you may be driving slow. It will still kick down you just don't go anywhere!

When it does it pull up and open the bonnet and check to see if the turbo wastegate has been released. I bet it has due to the ECU going into limp home mode.

I suspect the EGR valve isn't working. Thiss will allow xx many cyccles at idle before tripping limp home, roughly about 5 mins driving.

You can check the EGR valve by sucking on the tube that feeds it. The modulator is just behind hte ABS block and screen wash bottle.

The modulators can leak vacuum as well so try swapping EGR and wastegate modulators.

It could also be the wastegate modulator leaking.

Because the IP on these cars is mecahnical it can't perform differently for different cylinders so this creates less problems.
 

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