Growling Noise Under Acceleration

[Muggle]

Hi everyone, I have now had my 2006 C5 2.0HDi Exclusive estate for nearly 3 years and (I know I'm tempting fate here, but..) although the first year was paying out money left right and centre putting right the lack of maintenance by the previous owner, for the last 18 months all has been mostly sweetness and light.

 

Apart from one problem that will not go away.

 

The last work I had done was the A/C failing and since I had a warranty from WD, which covered most of the cost I had it repaired. The condenser had failed and 2 pipes which connect to it had corroded and needed changing. These pipes went all around the back of the engine and seem to be tailored to each nook and cranny on the way. It cost a small fortune (£1300!!), but I only paid 15% of that, so got it done.

 

Unfortunately, ever since that repair there has been a heavy, growling sound from the engine when I accelerate quickly in the first 2 gears, especially when I've got my caravan hitched to it.

 

The sound is the sort of noise you used to get when you fitted a sports air intake filter to the carburettor on a petrol engine trying to a get the last couple of bhp out of it, but heavier with a sort of deep 'knock' as if something is banging against the bulkhead due to weak engine mounts.

 

It doesn't come in gradually, but all of a sudden when the throttle is opened to just a particular point. As the throttle opens bit by bit it comes in all at once. Although it is most obvious in the lower gears, I can make it happen with full throttle in other gears as well. It isn't related to engine revs, just seems to be at a particular throttle setting.

 

As you back off the throttle to cruise or accelerate gently the noise disappears just as suddenly as it started and the engine is as quiet as normal.

 

I've been back to the garage who did the job, several times and they've checked for loose bits, worn mounts, anything near the a/c piping and the bulkhead - in general everything that they and I can think of checking, but finally I just gave up and lived with it.

 

I am not looking forward to my next caravan outing (to France, not just down the road) all because of this noise. I had a friend drive it past me and it didn't sound at all loud, just another diesel in a hurry, but it's still there when you're in the cab. 

 

I know it's weird, but - anyone got any ideas?

 

KC

[paul.h]

Did you check for any air leaks in the air inlet or exhaust or maybe a hose that has gone soft or the air filter. If it was a gearbox worn bearing problem this tends to be a bearing whine as you accelerate. On our C4 that developed a rattle after a service and it turned out to be the air inlet duct was vibrating at the front since it is a slightly loose fit in to the box section at the radiator end - this was fixed by tightening it with a tie wrap and apparently this is a common problem since the dealer knew what to do.

[Parkesie]

A piece of sound deadening or a cover of some sort been discarded/dislodged or fitted out of place?

[Muggle]

Hello again guys and thanks for your suggestions. As it happens, I've already tie-wrapped the air intake and checked for loose plastic covers and so on, but to cover everything, I have had another look under the bonnet to check the hoses and so on. I can't find any 'soft' pipes or loose bits at all. 

 

I was wondering if the top engine mount might be a little tired (the car has done just over 90k) and under high throttle settings might allow the engine to rock back and so make contact with the bulkhead? I vaguely remember having similar problems with the top bracket on a mini back in the day. The current technology means that the top bracket is nothing like the simple rubber bush on the mini - does anyone know of any sort of test I can do to check the top engine bracket?

 

It doesn't seem at all loose, but I understand that the engine can rotate with a lot of more force than I can generate with a quick shove and a pull. I can't seem to make it move myself, but i guess I wouldn't really expect to be able to move it.

 

I can't really see right down to the bottom between the engine and bulkhead (old age and a bad back, etc), but when the weather improves a bit, I think I'll put the car up on stands then remove the bottom cover and give it a really close examination, but I don't expect to see anything since the garage that moved the engine about doing the aircon had it back several times looking for bits that might make contact.

 

Maybe the only way to eliminate the top engine bracket is to get it changed just in case - I haven't found any online mention of this part being a failure point, but you never know.....

 

KC

[paul.h]

If it was an engine mounting that is worn, the one at the back is most likely to let the engine rock. However, there are heat shields down the back of the engine and along the top of the exhaust. If one of these was a bit loose or had been bent whilst fitting the air con pipes, then they could possibly make the noise you describe. These shields tend to be alloy/aluminium and the bolt holes in them corrode and get larger so they can become loose - on our previous C3 a repair was done using larger penny washers to hold it in place. These can be bought from such as Toolstation and B&Q http://www.toolstation.com/shop/p86424?utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&mkwid=b7eUiBxi&pcrid=46334058743&gclid=CN-d8Y2Hv8QCFTHLtAodvG8A6Q

[Muggle]

That sounds like a good possibility, can the heat shields be seen and fixed from the top or will they have to wait until I can get under it? If there is nothing loose then I'll look for a quote on the bearing.

Thanks to everyone who has helped with this, I was totally out of ideas!

Cheers

KC

[MikeLane]

This sounds very similar to my post:

"C5 Loud "rumbling" When Accelerating Hard"

so I'll keep my eye on this one and check suggestions.

(Also will swap wheels back to front as I inadvertantly fitted a pair of reinforced tyres on the front wheels recently!)

[MikeLane]

This sounds very similar to my post:

"C5 Loud "rumbling" When Accelerating Hard"

so I'll keep my eye on this one and check suggestions.

(Also will swap wheels back to front as I inadvertantly fitted a pair of reinforced tyres on the front wheels recently!)

Oh Dear! My C5's DMF fell apart yesterday - engine nice and quiet after that but no drive! My indie's lent me a C3 Desire"until he calls"! Desire? I think not!!

[MikeLane]

Just had my DMF etc. replaced with the (solid) Valeo conversion kit.

It might be my imagination but I (think I) have a slght judder under around 1800 rpm if I accelerate. However I can still use cruise control set to 30 or so in 4th gear in the dreaded villages where speed vans hide under the trees so....

Total bill was about £200 less than replacing DMF etc..

[Mossy76]

Just a quick note, I now own above noisy car :) and the issue as since been identified as worn injectors, was informed that this wold cost around £200 per injector plus fitting so live with it, has been running fine for previous owner (father in law) for last 2 years so i'm not touching it, just wanted to update the site while I'm here :)

thanks

neil

[paul.h]

Welcome to the forum and thanks for the update. I guess you will also be living with the growl.

[Rookie2]

Hmmmmm. dont we all live with a "Growl" Paul ?, mine 's just took the kids to school. :)

[Mossy76]

Thanks paul and yes Rookie2 most of us do live with a "growl" :D