e300 diesel (606) intermittent power loss

[mjrose]

I'm having some intermittent power loss (usually at cruising) on my 95 w124. The power will start to bleed off and on causing erratic (but gentle) decelaration and acceleration. Following this two things happen, either it will return to normal or the power bleeds off almost completely, car slows and lots of smoke appears out back from the exhaust.

If you stop the car, it will stall but start again, albeit roughly and then quicly return to normal.

The engine is otherwise in fine health; smooth, strong and no smoke.

I was thinking fuel starvation, but last time it happened i opened the bonnet (when running rough at idle after restarting) and there seemed to be plenty of fuel in the lines???? I couldnt tell whether it was flowing though!

Has anybody had a simialr problem??? PS i'm running straight diesel, and the filters were changed recently.

 

[SilverSaloon]

PS i'm running straight diesel,

why? good car for veg

seriously though, was the fuel pre-filter changed/cleaned?

any signs of fuel leaks?

what about the fuel tank strainer? i have a similar issue when my tank gets to 1/4 full.... i believe it to be a clogged strainer.

 

[mjrose]

Yes, veg is the next step, but i thought i better get this problem sorted first!

Both the pre and main fuel filters were changed and look fine still. I did have a small fuel leak but was it was sorted with a new pipe leading into the pre-filter.

Clogged tank strainer sounds plausible, any idea how you get to it??

This happens all all fuel levels, so need to get sorted really. Are your symptoms the same at 1/4 tank?

 

[SilverSaloon]

Clogged tank strainer sounds plausible, any idea how you get to it??

This happens all all fuel levels, so need to get sorted really. Are your symptoms the same at 1/4 tank?

it may not be the strainer but...

i believe on a estate it is underneath the fuel tank in the middle (accessed from under the car).... on a saloon i think you access it from the wheel arch. Obviously tank needs to be almost empty as it will drain out

it only happens for me at 1/4 tank and that is on veg - but i guess it could depend on how badly its blocked.... the engine basically looses all power and conks out or idles rough, until (i assume) the blockage is passed.

Worth checking out though i would say.

 

[mjrose]

Sounds like somewhere to start, thanks!!!

BTW is there fuel still showing in lines lines when that happens?

 

[SilverSaloon]

Sounds like somewhere to start, thanks!!!

BTW is there fuel still showing in lines lines when that happens?

i think so... its been a while as i've only let it do it a few times - now i just dont let it go past 1/4 tank

 

[Dieselman]

The smoke makes it sound like either fuel starvation or the timing is retarding significantly. I would doubt it being the timing as that is mechanically controlled by a gear with bob weights.

It does sound like fuel starvation. If it persists rig a vacuum gauge upto the fuel line and you will be able to se if the line suddenly goes under higher vacuum.

Is the fault more prevelant when teh engine is under more load, such as when driving up a long hill?

The strainer is fitted into the underside of the tank, but it's possible for the inlet into the plenum inside the tank to become restricted also, so worth checking ho well fuel flows once the srainer is out.

In addition check the EGR valve isn't going fully open when driving as this will starve the engine of oxygen. Best to blank it off.

 

[bolide]

What colour is the smoke?

Assuming air is getting to the engine the only thing that can cause loss of power is lack of fuel. Rough running after a restart seems to back this up

I'd start with the new filters - check the O-rings haven't split or been misplaced. Then I'd look for air/diesel leaks by the filter / IP. Then I'd think about the fuel system from the tank to the lift pump, then the lift pump and IP

Nick Froome
www.w124.co.uk

 

[mjrose]

Fault is definately more prevelant at constant load, has so far it has only happended whilst crusing at 75-80. It does not seem to happen at varying loads (i.e. whilst pottering around town).

EGR is disconnected from vacuum system and therefore should stay shut!? Is it possible for this to be pulled open some how? The EGR was disconnected following a problem some time ago with a very gentle power on/off at 55-60 mph which was diagnosed to be the EGR and therefore disconnected (fine ever since). How do i check this is staying closed?

I'm not sure about the colour of the smoke, it was late evening when it happened last...

I'm pretty confident that the fuel filters are OK, it has done less than a thousand miles since service. But i will certainly have a look. There are no obvious fuel leaks and the lines are almost completely air free (except for one little bubble next to the fuel pre filter!).

What got me stumped originally was that there was fuel in the lines when it was running rough, which led me to think there was a blockage somewhere before the ip reducing pressure to the injectors but not starving the lines of fuel??? But if its a blocked tank strainer or plenum inlet, then why would the problem clear when the engine is off load (i.e. after restart, at idle?).

However if its the EGR somehow opening then it would probably shut at low loads (i.e. at idle) wouldnt it???. Even though it has been disconnected from the vacuum system!!?? Can it get sucked open?.

Confused

 

[OneTwoFour]

Hi MJROSE, did you ever resolve the issue with the car intermittently slowing. I am experiencing the same on my 1996 124 300 Diesel Estate. Have replaced the clear fuel lines, checked & replaced the fuel strainer in the tank and the 2 in the engine bay. Ran some injector cleaner through the engine & it was okay for half a day then returned. Most recent change was to have the EGR valve cleaned when they also checked the vacuum and EGR operation was okay. After this last change it ran perfectly for a day and a half then the problem gradually came back. It seems to be partly temperature related, only appearing when the engine is up to temperature and comes and goes fairly randomly. It's driveable and I am commuting in it but overtaking requires some care and anticipation just in case of power loss. The sensation is of the brakes being temporarily applied but negligible speed is lost. There is also and audible tick, tick tick from the engine which sounds a bit like pinking. I'm sure the fault must be somewhere in the induction system but am running out of ideas.

 

[SilverSaloon]

have you tried blanking off the EGR with a bolt to see if that cures it?

personally my EGR has been blocked off like this for 5 years.

 

[OneTwoFour]

Hi Silversaloon,

I haven't tried that yet but given the change after EGR valve cleaning it should be worth a try if only to eliminate it as a possible cause. The car is pushing 250K miles so maybe the content of the exhaust sent via the EGR is now such that it is enough to gum up the valve, 'though it wasn't that dirty. Thanks for the suggestion.

 

[SilverSaloon]

well worth blanking off whether it fixes the problem anyway. I reckon it may since you saw an improvement when things were cleaned.....

i run two W124 E300D estates with 606 engine and both have had this blocked off for a long time (one at 250k and the other at 280k) with no ill effects.

Are you running standard diesel? I run both my cars on waste vegetable oil

 

[OneTwoFour]

Yes running on standard diesel.

So what are the economics and are there any issues running on waste vegetable oil, where & how do you source it & does it need any pre-treatment before use?

 

[SilverSaloon]

look at www.vegetableoildiesel.co.uk forums

 

[OneTwoFour]

Has anyone tried Terraclean on a 124 diesel? I've looked at a number of the posts but haven't yet noticed a 124 as the subject. Results on other models seem to be generally positive 'though it seems older/higher mileage vehicles show a better improvement (not surprisingly I suppose)..

 

[Dieselman]

I'm still skeptical that it works better than any other quality injector cleaner.

 

[OneTwoFour]

One of the arguments was that injector cleaner is usually administered via the fuel tank and so gets diluted.

We did try this at one point and it improved things for maybe half a day before the problem gradually resurfaced.

As I understand it, with the Terraclean system the fluids are administered directly to the engine bypassing the existing fuel supply so retaining their concentration.

It is also supposed to treat both induction and exhaust sides of the engine, so if we're seeing a problem due to eg. exhaust valves then maybe this would help.

I'm not sure but I'm willing to give it a try and my local agent has said that they will assess things first before going ahead (eg. by using diagnostics) and if they don't think Terraclean is worth trying then they won't do it, which on the face of it seems fair enough.

 

[OneTwoFour]

Okay had the Terraclean process done (not particularly cheap at around £144) and 'though it is still early days I have had no further hint of the problem. The engine seems to be running better and back closer to how it used to run before the problem was encountered. I have still to check the mpg as I wasn't about to fill the tank until I had some confidence that the problem was fixed. I'll check the mpg before the weekend as I will have new tyres fitted this weekend (also something I was delaying until I saw how things had worked out) and I want to compare like with like as much as possible. So time will tell but so far it looks promising, the only slight frustration is that if this does fix it I will never know exactly what was causing the problem, 'though it would seem to be related to carbon deposits somewhere in the engine.

 

[OneTwoFour]

Spoke a bit too soon! The car ran fine for about 5 days then I detected the problem coming back again and it died a couple of times on me when cold. So I have now blanked off the EGR valve and it has been running fine ever since! I'm sure that cleaning out all the carbon deposits has also helped and the engine seems to be running quite smoothly. Just passed the 250K miles mark last week too so on to the next 250K.

It'll be interesting to see what all this has done to the emissions relative to the MOT test.

Those of you who have blanked off or disabled the EGR valve and are still running on diesel, do you re-enable the EGR valve for the MOT or is it not an issue for the emissions test?