Mercedes 300D idle problem

[tonychunk]

Hi I have a 300d w124 1991. My problem is I had a poor start issue and plug lamp illuminating about 2 mins into journey so replaced glow plugs. Starting was cured but lamp still illuminated after about 2 mins as before. Lamp has stop illuminating apart from from initial cycle. Problem now weather warmed is that car starts ok but if you rev it it cuts out. Start it again and idle is really lumpy til you start to accelerate then there is like pre ignition type noise some smoke then it clears. Car will then run fine, accelerate nicely and is a smooth ride. Will idle fine too. But when left for a short time the problem appears again... Can anyone help please.

 

[Number_Cruncher]

Check for air in your fuel pipes.

 

[Rousha]

Sounds like a similar problem to mine '250TD Fuel Starvation' - I can actually see air bubbles coming up the fuel intake pipe into the main fuel filter and when the airlock gets big enough it stalls the engine -which then restarts lumpy until the airlock clears -then goes OK for a few miles and stalls over again. The suggestion is it's either a pipe loose on the fuel pump or the tank strainer. We're checking it out tomorrow so will let you know the outcome shortly.

 

[brianbrian]

I would change large filter, and small filter just under air filter box, when you take the air filter box off check all fuel pipes as after 18yrs they do tend to perish you can buy a lenght of pipe also buy new jubillee clips. Hope this helps

 

[tonychunk]

UPDATE.

I cannot see any air in any of the pipes you have mentioned. All filters were changed (incl tank strainer) a couple of hundred miles ago. When i am cranking the engine from cold it seems like there is no compression til i press throttle then she judders into life. The pre ignition type noise is stilll prominent when first revving and is accompanied by some smoke from first starting. once this clears engine runs fine.

 

[simon_wall69]

Could there be water in the fuel? Are you running it on diesel or some alternative fuel? What colour is the smoke?

 

[Hertfordshire Merx]

Check your injectors for fuel leaking back to the tank from the spill pipes. I would imagine thats the issue and you will need to replace the faulty ones, and their seals.

 

[tonychunk]

Thank you all for your replies. Can you tell me how i check the injectors please, woukd it be safe to say that this is caused by air in system as there is the knocking with smoke which clears after revving and then runs/idles fine til is left again?

The fuel is free from water as the tank was changed for one out if a petrol car due to it being full of black sludge which stopped the fuel light working at the same time all the filters were changed. The fuel i took out of the original tank had a slight green tint to it!

 

[Number_Cruncher]

>>Check your injectors for fuel leaking back to the tank from the spill pipes.

I think this check is much more applicable to common rail injection engines.

However, I would be tempted to do two things which have a certain amount of overlap.

Remove the injectors (capping the pipe ends to prevent contamination), and have them tested for;

- opening pressure
- spray pattern
- leakage under pressure

With the injectors out, check the engine's compressions.

Owing to the special equipment required to do this work, I would allow an independant diesel injection specialist to undertake the work.

Wen you put this back together, be sure to use new injector seals, and new leak off pipes.

 

[tonychunk]

Had a real baffler today... started on the button no problems. I drove away stopped en route at shop to get paper (about 40 yrds) Came out car turned over and over for about 2 mins was trying to start but wouldnt. Waited ashort while, gave it 2 lots of glow plug was trying to fire but just would nt. after about 5 mins of trying there was some noise like pre ignition you get on petrol engines loads of smoke then she ran like a good un. A blast down dual carriageway reach island ticked over no problem. travelled about 4 miles left for an hour she started ok i drove about 100 yrds chugged on tick over til i revved got the pinking noise again then fired into life again... how strange!

 

[Number_Cruncher]

Has anything other than pump diesel been used to fuel the car?

 

[tonychunk]

it was run on new veg oil for a time. it smelled awful i guess its well diluted now

 

[Number_Cruncher]

Thanks - I would pursue the compression test and checking the injectors.

 

[tonychunk]

Thank you for your help. Is removing the injectors a big job, what tools will I need?

 

[Number_Cruncher]

Before you get the spanners out to take the injectors out, where will you be doing the compression test? You'll need the injectors in to drive there, unless you have a compression tester for diesel engines available to you.

In your shoes, I would take the car to an independant diesel injection specialist, and let them remove & test (and if necessary repair) the injectors, and do a compression test on the engine while they're out. Removing the injectors is not a long or expensive job - doing it yourself will not save you much money.

IF you do take the injectors out yourself, you'll need;

an open ended spanner, or, preferably a flare nut spanner for the injector pipes (17mm I think - better to check than rely on my memory though!)

Undo and take the pipes off at both ends without using any force - do not under any circumstances bend the metal injector pipe, or attempt to only undo the injector and wiggle the injector past the pipe.

plugs/caps for the injector pipes, delivery valves and injectors

27mm deep socket for the injectors themselves

A smaller spanner for the clamps on the injector pipes - make sure ALL the clips and clamps are in good condition when you rebuild. Injector pipes soon fail via vibration & fatigue if they aren't properly supported.

You'll need some new injector heat shields/washers, and it's best to renew all the leak off pipe, and the blank stub on the rearmost injector, when it gets disturbed. Be careful not to scratch or mark the barbs on the leak off pipe stubs on the injector, you want a good seal here.