Tapping Noise W202

[Nik_Endeavour]

For the last week or so I have noticed that my w202 was getting some slight tapping noise but annoyingly enough never when I went to the garage.

I have also noticed that the breather hose has "bled" oil which had never done before. I do feel that the car had lost some power but nothing dramatic to notice.

Also at occasions it the engine wouldn't stay on unless I held the accelerator pressed. The car also would vibrate slightly when at the traffic lights. The thing is that it does these things at random no exclusively when hot or cold so I am confused.

Yesterday I went to Heathrow and it was very smooth (sat on the driveway all night).

Today it was making a loud tapping noise every 3-4 seconds and the car was vibrating noticeably on the traffic lights. It barely made up a hill and I thought it had it. When it got warm though (reached 80 C) it stopped the tapping noise?

I would have blamed the MAF (lack of power) but it was changed last year and the tapping noise made me think otherwise. It sounds like the mixture is not right and too much air or petrol is put onto the mix.


Help please!

 

[Dieselman]

It sounds like it could be firing on 3 cylinders hence the lack of power, but why.
The blowby doesn't sound good as that indicates combustion gas is entering the crankcase which indicates broken or blown rings.
You really need a compression test/leak off test performed to decide.

It may also be due to sticking hydraulic tappet causing an exhaust valve to stay closed.
A flush with flushing oil may sort that.

Listening round the engine with an engine stethoscope would possibly reveal where the noise is coming from if it's mechanical.

Also for the noise don't rule out a cracked exhaust manifold, which in turn will upset the mixture due to drawing in air.

 

[Nik_Endeavour]

I did think of the exhaust manifold as well, judging by the noise and the fact that it goes away when hot as it expands. The

 

[grober]

Could be a faulty ignition coil/wiring-- well known fault with these models. Best not to leave it since the faulty coils end up damaging the ECU. If it is a coil its best to renew both coils. I am assuming your "noise" is a misfire? The other possibility is the the inlet cam timing adjuster is jamming.

 

[Nik_Endeavour]

This is getting joyful :-(. It might be a misfire but it sounds more like a mechanical tap onto a metallic object.

 

[grober]

If its the cam adjuster then an a good engine oil flush like Dieselman suggested might help both hydraulic tappets and the timing adjuster? When was the oil changed last?

 

[Nik_Endeavour]

Not that long ago, in February. I will start with the oil first. Time to book it with the garage and rent a car.

 

[Dieselman]

Not yet it isn't...
Go to a local motor factors and get some flushing oil and engine oil.

Given the recent change you don't NEED a new filter but given the choice.

Drain the oil, 1/2 fill with flushing oil and run it for 30 mins. (normally 10mins or so but a long flush might help).

Drain flushing oil and refil with engine oil.

If you can get a spark tester as well as grobers point re the coil is a good one.

Before doing anything check the oil and coolant for any mixing.

 

[Nik_Endeavour]

I will give that a go today. I know that the engine would have not been flushed since I got the w202 as the garage I do normally service does not like flushing (the more harm than good theory).

With the ignition coil I would now where to start but if that is faulty, anybody has any ideas how much they cost.

 

[Dieselman]

Well yours is defenately knocking and has blowby so I can't see it's going to get any worse.

The theoretical risk with flushing is that it could release chunks of carbon sludge which could then block the oil supply system.

I have once heard of this on a Golf git (OOps, Gti ) oil pickup strainer but that must have been in a bad way anyway. I also know someone that his Gti strainer blocked without ever being flushed, so make up your own mind.

I've flushed some really bad engines and never had a problem. That includes Ford CVH engines which were known for dying due to 'black death'.

It's worth checking your breather system before doing anything as it could be blocked so causing crankcase pressure which will then blow out every now and then.

If the engine rattles after flushing it could be a broken ring. It's already broken if that is the case, they break due to getting trapped into the grooves by built up carbon.

Of course this is only a suggestion, don't feel any compulsion...

 

[grober]

You will find the ignition coils under the flat plate on top of the cam cover. You will need a torx or allen key to undo the bolts holding it on. You will also have to remove the inlet cross over pipe which links the air filter and MAS to the throttle assembly. Easy after you have done it once but fiddly if not as you can easily break plastic bits. http://www.detali.ru/cat/oem_mb2.as...GM=716.624&CT=M&cat=68Z&SID=15&SGR=060&SGN=03
coils £28-51 +vat+carriage from Inchcape.http://www.mercedes-benz-parts.co.uk/

but get them tested first.

 

[Nik_Endeavour]

Dieselman, Grober thanks gents. I am already planning a trip to Halfords (they are the only ones open today after 4. (I am stuck doing some out of hours work until then). Just a reminder which oil grade should I get and how much flush>

 

[Dieselman]

5L flush (you only need 1/2 normal capacity)
Whatever oil your car runs on...10W-40. Go for semi synth.

Re reading your original post does make me agree with grober and think there is an HT leakage. Just have a good listen for a loud crack noise every 4th firing.
If you can get into somewhere dark you may see a flash.

The oil breather though being a problem may be a red herring at the moment.

 

[Nik_Endeavour]

Re reading your original post does make me thing there is an HT leakage. Just have a good listen for a loud crack noise every 4th firing.
If you can get into soemwhere dark you may see a flash.

I thing you have got it. That's what it was doing this morning. It was a very distinctive noise at semi regular intervals (which might be the 4th firing, didnt pay notice at that). I will have to wait for night fall for the flash though.

Now the ignorant part, I presume HT means High Temperature but what does it all mean in the great scheme of things.


Nik

 

[Dieselman]

See where it's coming from first. It could be anything from a duff plug to a loose or damaged HT lead.

In the great scheme of things.....cheap..

Oops, didn't answer you. HT means High Tension. It's the high voltage that the spark plugs use.

 

[Nik_Endeavour]

Sorry to be not so not knowledgeable about this but will this also explain that it goes away once the engine gets hotter. Also looking at the engine where are the HT leads -(Sorry again, but I write computer programs, not usually fix cars)

 

[Dieselman]

On your car there are no fly leads as such. It uses the straight connectors, item #40 in grobers link.

Just remove the cover and have a look/listen and even a smell. Then if necessary remove each coil and inspect how well the connectors clip on and for any signs of arcing.

The fact it gets better when warmer suggests they are drying out, there could be water in the plug wells.

 

[Nik_Endeavour]

It might well be. I will have a look when I get home though. I tried it now and it was absolutely fine.

I had a look at a Haynes manual and seems OK enough to dismantle.

I also found something odd, might be a red herring again but there is oil here:

Checked the oil level is low (next to min), might be unrelated though might be something else.

 

[grober]

The coils are under that plate to the left of the oil filler cap and breather pipe. The pipe in the second photograph is taking the automatic transmission fluid to the heat exchanger in the radiator and has nothing to do with your present problem.

 

[Nik_Endeavour]

Last point guys and I promise I will keep quiet for a while. I also have a problem with the throttle cable:

The registering screw (plastic) has broken and was wondering how much do they cost and how difficult is to replace it. Also would this have anything to do with the iffy idle?