Loud Kncking from the Engine

[sviveknaidu]

can some one advise me

I have a 1997 E 250 D with a rather peculiar problem. The engine RPM will increase steadily as i depress the accelerator slowly up to 2000 rpm and then with the accelerator held steady at that point the RPM rises on its own till the Maximum.

My mechanic thought it was a furl pump problem and had it taken out and checked and when he fitted it back, the engine has a very loud knock at idle and upto 1500 rpm as i depress the accelerator. after 1500 rpm the engine smoothens out but does not have the same power as earlier.

also earlier the idle rpm was about 600 and now it is closer to 900 rpm.

can anyone please advise what i should do to soften the engine noise and get back the power of the engine and what could be a possible cause for the engine revving to maximum on its own after 2000 rpm.

also the mechanic had removed the injectors and replaced them after checking them., Are the injectors cylinder specific as they were randomly fitted back after cleaning.

 

[turbopete]

hello and welcome to the forums.

i hope im wrong and that someone will tell me so, but this sounds like a serious problem. the loud knocking at idle speed is probably related to the injector pump timing. either it has been re-fitted in an over advanced position, or something has gone wrong inside the pump, like a broken spring or similar internal fault related to the pump/pump timing. this may well also be the cause of your increased idle speed as the electronics connected to the pump attempt to rectify the problem by increasing fuelling and raising the idle rpm to suit. a pump problem in the advance unit would also explain loss of power. injectors will not be cylinder specific.
engine revving to max on its own above 2000rpm worries me. im assuming this is the reason the fuel pump was removed in the first place. it may be an electronic fault, but id guess more likely that it smokes a lot more than usual when revving at max rpm, meaning that the engine is running on a secondary fuel source. check oil level isnt too high. commonest cause of this after high mileage is that the engine breathing system carries oil vapour in it. on a hard worn engine, the engine can run on this oil vapour and COULD (worst case scenario) blow up the engine. start by checking/cleaning all of the breather pipes etc

 

[Number_Cruncher]

I agree with Pete on both main points.

The injection timing is now wrong - the pump should not have been touched in the first place. These pumps are very easy to time correctly - there's a mark on the crank to align, and a peg inside a viewing hole in the side of the pump to line up - there's no excuse for getting it wrong.

The engine is probably running on a secondary fuel source - how much oil does it use, and how smoky is the exhaust when the engine revs up?

The injectors aren't cylinder specific.

 

[simon_wall69]

I'd be a little concerned that the mechanic has returned the car in this condition.

 

[sviveknaidu]

thank you all for your inputs and your quick responses
well to answer the points that you have raised.

you are correct the the pump was removed because of the revving problem.
the pump was given to the Bosch service center and they said that the pump was alright and they calibrated it, cleaned the nozzles and returned it. The pump was locked in place and fitted back in the same way and the engine started to knock at a high idle rpm on having been put back. It was a very smooth sounding engine before the removal of the pump.

another point to note is that i did not replace the washers for the nozzles when they were put back. I read some where on the forum that you need to replace the copper washers every time the nozzles are removed and put back.

the engine does does not smoke when it is revved up.

i use only Mobil 1 and there is no perceptible consumption of oil at all.
the engine has not done too much mileage either the odometer reads 1,06,000 kms and not miles

i use a K&N air filter and when the nozzles were removed i didn't see much of oil residue in the breathing inlets , but would like to know how to check for it.

Honestly the mechanic has tried to do his best and just hasnt been able to get the engine back to what it was before he removed the pump.

I would welcome any advice on where to start and get the engine gunning right.

Actually have been really heart broken as i just cant get to use this wonderful machine.

 

[turbopete]

if a breather hose is blocked, this will allow the crankcase to build up pressure and then the engine may start to run on the crankcase fumes and rev itself up. any excessive knock will be due to incorrect injector pump timing. you could try starting the engine and remove the oil filler cap for a few seconds. if theres any noticable smoke comes out, its a sign of a breather problem usually

 

[sviveknaidu]

thanks will do that in the morning and check back with you.

 

[Parrot of Doom]

i use a K&N air filter

If that's an oiled filter, and if your car has a MAF, I suggest changing it back to the MB filter.

 

[ALFIEBEARD]

can some one advise me

I have a 1997 E 250 D with a rather peculiar problem. The engine RPM will increase steadily as i depress the accelerator slowly up to 2000 rpm and then with the accelerator held steady at that point the RPM rises on its own till the Maximum.

My mechanic thought it was a furl pump problem and had it taken out and checked and when he fitted it back, the engine has a very loud knock at idle and upto 1500 rpm as i depress the accelerator. after 1500 rpm the engine smoothens out but does not have the same power as earlier.

also earlier the idle rpm was about 600 and now it is closer to 900 rpm.

can anyone please advise what i should do to soften the engine noise and get back the power of the engine and what could be a possible cause for the engine revving to maximum on its own after 2000 rpm.

also the mechanic had removed the injectors and replaced them after checking them., Are the injectors cylinder specific as they were randomly fitted back after cleaning.

Hi I purchased a brand new E250D in 1995 and I noticed that if you held the throttle at 2000 rpm the revs rose right up to 4000 od rpm, this is normal with your type of pump,you will notice it does,nt do this whilst driving, mine done it from new and I took it back to the dealer and he showed me another brand new car do exactly the same, it is a characteristic of this lovely 5 pot engine, on the other hand I reckon that either the pump timing is out or somehow it is overfuelling after being stripped causing the low power and knocking. I am afraid your pump has been taken apart needlessly, ask for another member who owns the same type of engine to try theirs I bet they come back to you and say they do rev up on their own only off load though.
Hope this helps
Alfie B

 

[Number_Cruncher]

>>this is normal with your type of pump

You raise an interesting point. I take it you mean that the revs gradually drift up a bit, rather than a fast revving up to the limiter (or beyond!)

To the OP - do the revs raise quickly up to the rev limit?, or, do they just gradually drift up a bit?

Usually, if the engine were running on its own oil, I would expect both some smoke, and some oil consumption.

Get some new injector washers in there ASAP, before your injector nozzles become damaged via overheating, then, aim the K & N towards the bin, where it belongs!

 

[ALFIEBEARD]

>>this is normal with your type of pump

You raise an interesting point. I take it you mean that the revs gradually drift up a bit, rather than a fast revving up to the limiter (or beyond!)

To the OP - do the revs raise quickly up to the rev limit?, or, do they just gradually drift up a bit?

Usually, if the engine were running on its own oil, I would expect both some smoke, and some oil consumption.

Get some new injector washers in there ASAP, before your injector nozzles become damaged via overheating, then, aim the K & N towards the bin, where it belongs!

If you rev the engine gently to 2k then hold the throttle there will be a slight pause then the revs will carry on rising until it reaches the governed speed, they dont shoot up to the max they just carry on rising, this only happens off load, It amazed me when they showed me another new car do the same.

Alfie B

 

[brianbrian]

When you fit new Injector washers make sure you put them in the right way up, also you need a torque wrench, injectors must be taught down appropriate

 

[Cole@MBS]

When you fit new Injector washers make sure you put them in the right way up, also you need a torque wrench, injectors must be taught down appropriate

7NM +90+90 to be correct!!!

 

[Number_Cruncher]

>>7NM +90+90 to be correct!!!

Those numbers are right for a CDI engine, but, I would hesitate and double check before applying those torques/angles to an injector in this engine.

 

[sviveknaidu]

thank you guys, am sending the car back to the mechanic this morning and will fill him in with all these information.

i wish i had logged into the forum before i gave the car in for a check up and would have saved myself a lot of heart ache.

i have in the meantime checked back with the Pump service guys and they have confirmed that the pump was checked and is alright and and was then calibrated by them.

Is the K& N Filter not suitable for the Mercedes?

will post an update on the progress of the repairs on the car.

thank you all for your inputs and advice and any more advice in any form is more than welcome.

 

[rpe2]

I think that the 7nm +90+90 is for CDI injector clamps. sviveknaidu had a 250D whi will have direct injectors that screw into the head, not too sure about what the torque settings would be for these.

Sorry to question such eminent wisdom....

Best Regards

 

[Number_Cruncher]

The injector torque is 40 Nm

 

[sviveknaidu]

hi guys ,
its been a while since i replied but have been working with my mechanics on the car in a sort of a easy but very thorough way.

thank you all for your inputs have been able to sort out all but one of the problems. That is the engine still knocks at the idle rpm of 800 but the knocking eases off as the rpm increases above 1000. i was wondering if any body had information regarding the amount of diesel delivery from the fuel pump at idle rpm. I was told it is 32 cc. i have a feeling that this maybe a little low so would like to confirm this and also the setting of the pump which i am told is 14 degrees TDC .

thank you once again all your input have been very useful