Independent Renault Forums banner

1 - 10 of 10 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter #1
Hello.

2008 Megane 1.5 dci, bought last August, had new cambelt fitted and oil changed by authorised Renault service centre right after that (as a measure of precaution).

Hopefully, someone here will help me with this problem.
Namely, when the engine is cold, upon acceleration, in range 1500 - 2100 rpm there is a clearly audible tinny knock that is in sync with engine's own 'dieseling'. More pronounced if I press throttle more (turns into roar almost). As the revs climb through this range, knocking seems to change pitch, the frequency and loudness remain the same.
Once it reaches operating temperature, knocking almost disappears.

At first I thought something is knocking against a heat shield, checked, all ok. Engine is bone dry, no cracks on exhaust, dogbone mount appears intact.
Had it checked at local Renault garage, they ruled out big end bearings, fuel supply (low and high pressure) and DMF (as most obvious noisemakers), and attributed this knocking to normal operation noise of piezo injectors. Also, slight weeping of injector return lines was dismissed as not dangerous, apparently one of the O rings got some slack.

Also, once warmed up, revs fall to 800 mark and the whole car starts to shake and sounds almost like a sewing machine. This would probably be due to worn hydraulic mount and/or additional mount that sits right next to it.

The car otherwise runs like a dream, pulls like a train, moderate consumption (given it's used mostly in the city), starts right away no matter how cold it is. Apart from this nuissance, no other complaints.

Any tip/idea would be greatly appreciated.
And sorry for a lengthy post (although I still have a feeling I left something important out :eek:)
 

·
Super Moderator Technical Supremo Platinum Member
Joined
·
24,220 Posts
.......... Also, slight weeping of injector return lines was dismissed as not dangerous, apparently one of the O rings got some slack.......
Prefer posts that give some details then the help my car is rattling variety :d

The bit I've quoted made me pause.
one of the common reasons for DCi problems we see is air in the fuel system, often because of minor leaks due to slack O rings.
Many return lines go back to the filter (not sure on yours) so if air in the returns you immediately have air in the fuel system.
Which can cause misfire, hard starting, rough running etc as well as creating excessive wear on the pump...google cavitation... it's where little air bubbles are bounced around in hydraulic systems and can wear out a pump as fast as sand.

Not saying that is your noise or even the rough running issue....but could be and needs sorting anyway.
 

·
Technical Supremo, Platinum Member
Joined
·
7,872 Posts
If the noise wasn't there before the belt change and appeared after it I would be a bit suspicious if they had got the timing right.
 

·
Registered
Joined
·
3 Posts
Discussion Starter #4
Thanks.
Now that you mention it, I did notice air bubbles in fuel line between the filter and the HP pump. In idle there are quite a few, I can just imagne what it's like under load. However, I read siemens vdo HP pumps are self bleeding, so didn't pay much attention to that.
I'll start by changing the fuel filter and the return lines (they do connect to the filter via a bypass valve thingy, probably to warm the fuel as quickly as possible).
And, yes, cavitation is a [email protected]***h :d
 

·
Super Moderator Technical Supremo Platinum Member
Joined
·
24,220 Posts
Virtually all common rail systems are supposed to be self bleeding. But IMO this means that they should self prime (often don't) and don't need fuel lines cracking open to get rid of air as was often the case with direct injection systems.

But I'm not sure they handle air bubbles too well :d
 

·
Registered
Joined
·
2 Posts
Hello.

2008 Megane 1.5 dci, bought last August, had new cambelt fitted and oil changed by authorised Renault service centre right after that (as a measure of precaution).
Hello
My car is the same model, same year 1.5 dci 106 bhp and I have the same problem. Did you fix it? What was?
Thanx in advance
 

·
Technical Supremo, Platinum Member
Joined
·
7,872 Posts
Don't know the outcome of this thread but common rail
engines sometimes suffer from injector pies ringing this
does sound like a knock, with engine ticking over try
just applying light pressure on each pair of injector pipes
were the plastic bridges are if it stops the noise then tightening
those bridges may sort it.
 

·
Registered
Joined
·
2 Posts
Hahaha!!! So apparently, went to Renault guys and they said it may be the injectors. And they told me that Oil in the engine needs to be added like 0.5 litters. So I went to a private garage, checked the injectors=everything's fine, EGR-fine, added Oil in the engine(the computer said Oil Level Ok before I added) the result, after driving it on highway for 5 miles=the noise is gone forever!
The guy at the garage adviced me to get a bottle of injectors cleaner and to ad it in the tank and race a bit on highways. THAT'S IT!
 

·
Technical Supremo, Platinum Member
Joined
·
6,588 Posts
Never rely on the oil level gauge check at least once a week via the dip stick
also if you are near or shop at asda 4-5 times a year they do a deal on redex worth it for the injectors
 

·
Registered
Joined
·
10 Posts
OK daft as it sounds there proper fuel filters & cheap ones the proper ones have a bi metal strip and a ball bearing when it detects warm fuel it shuts off the fuel return to the pump and sends it to the fuel tank along with the air bubbles ,cheap filter do not have the bi metal & bearing so will push the air bubbles straight to the pump .

The fuel harness has connectors and sometimes the seal leak , the bulb is prone to leaking air into the system .

long cranking can be the non return valve in the tank unit not working.

Air can also get into the system via a faulty injector compression will blow by and put air into the system .

I have air in my system so am replacing the pipe harness as there is a crack in the primer bulb ,if that dont work i will be checking out all the above .
Hope it helps Megane 2 owner /UK
 
1 - 10 of 10 Posts
Top