Engine 'knocking' when coasting/not under load?

[dougmcdonald]

Hi All,

I wondered if anyone could help me identity some/any possible cause of a knocking sound I seem to be experiencing from my LC.

Basically, the knocking occurs when the car is not under load, so either when just at a constant speed on a flat/downhill bit of road where the throttle isn't used much, or when out of gear and just coasting to a stop (like the stop/ start in first in a queue, or slipping it into 2nd when approaching a roundabout for example.)

The knocking sound sounds like its coming from the engine area in general, more on the drivers side than the passenger side, but it's not particularly directional, it just sounds like the 'front' as a whole. When breaking with the clutch down, if the knocking occurs I can sometimes slightly feel it through the peddles but not like a strong judder or anything, just like the residual vibrations of something physically knocking in front of the peddles/in the engine bay.

The knocking 'frequency' if that's the right term! seems related to the speed I'm travelling, so in 1st in a queue the knocking has say 0.5-1.0 second inbetween knocks, but at say 30 coming up behind something and letting off the throttle it the frequency would be perhaps 3-4 times a second.

This is all on straight roads and when pressing the throttle the knocking goes away.

I did some searching on here but couldn't track anything down which seemed to be similar enough to hijack a thread!
I will take it to the garage as soon as I can, I just wondered if anyone had seen (heard!) this type of problem before and could suggest anything I could either look at myself, or suggest to the garage to narrow down their search.

Any ideas?

 

[dougmcdonald]

As additional info, in case it helps I did have a engine warning light cleared a couple of days ago which was a 'pressure drop between 'something' and the engine inlet manifold'
(I'm afraid I can't remember exactly what the guy said :s I really must start listening to mechanics) he seemed to think that was quite common an if it doesn't re-occur isn't nothing to be too worried about...it does worry me a bit though as the car about 5 years ago had some work done in the SEAT main dealer with a very similar description on the receipts.

I've also had some new front tyres fitted about 1000 miles ago, but it doesn't sound like a tyre issue particularly

 

[LEE69]

Check your wheel nuts to be safe.
Might be the dog bone mount or another mount gone?

 

[Jaylw04]

Could it be a knocking from your exhaust hitting a bracket somewhere? Or maybe wheel bearings? I had a similar problem with my seat ibiza last year but this was when under load, that turned out to be a bearing in the gearbox, so thats what is making me think maybe you have a bearing playing up somewhere? Im not a mechanic though so dont quote me Hope you get it sorted soon!

 

[dougmcdonald]

Thanks for the quick responses guys:

Lee - I will definitely check the wheelnuts, although I did watch the guy tighten them up and things did look ok at the time! he even showed me what torque he'd tightened them to!
I will mention the mounts at the garage too, I was unable to replicate the sound at the time so hopefully if they can hear it they will have an idea what it is.

Jay - Interesting comment on the exhaust, as i do think I have an exhaust issue at the moment as well. That one is strange, with 2 people in the car at the front it's not noticable, but with one person in the back on the exhaust side there is a horrendous virbration/noise from the rear left exhaust area which basically sounds like the exhaust isn't attached properly.
I had it looked at 4-6 weeks ago and the guy welded part of the mount which was loose appararently but I think it's come off again over all amount of times it was used as a snowplow over december :s
I will also get the bearings checked and see what they say.

 

[Jaylw04]

Thanks for the quick responses guys:

Jay - Interesting comment on the exhaust, as i do think I have an exhaust issue at the moment as well. That one is strange, with 2 people in the car at the front it's not noticable, but with one person in the back on the exhaust side there is a horrendous virbration/noise from the rear left exhaust area which basically sounds like the exhaust isn't attached properly.
I had it looked at 4-6 weeks ago and the guy welded part of the mount which was loose appararently but I think it's come off again over all amount of times it was used as a snowplow over december :s
I will also get the bearings checked and see what they say.

My last exhaust issue on my ibiza was a knocking which sounded like it was from my gearbox, i took it to a friend with ramps and the backbox had snapped away so he welded it for me, when i left it was still knocking so i took it back and it was resting on a bracket at the front aswel, he pushed this back up and problem solved....hopefully it will be something simple for you too, maybe just a build up of a few little easy fix things causing a big noise.

Let me no how you get on pal.

 

[akchappers]

I have just had the same problem fixed on my toledo v5. When it was accelerating no noise and just cruising no noise either but on slowing down and coasting it sounded like i had a really flat tyre!And it was speed related too and the dunk dunk noise slowed as i did! Zfter much head scratching at the garage i use we changed the offside cv joint and hey presto! Silent as a mouse. and mine apart from the thunking noise slowing down or coasting it didnt make a peep! Or click on full lock!
hope this helps.oh and the part cost £122 and an hour to fit! Total was about £190.not cheap but well worth it.was driving me crazy!
ak

 

[LEE69]

Hell!!
You do know the cv joint is a bout £25 on ebay?
Been using one for ages on mine, no problems.

 

[dougmcdonald]

Mine definitely seems speed related too, rather than say, rev related. I coasted in 4th and got the rhythm, then dropped it into 3rd and the knocking rhythm stayed the same.

I'm due to take it in to the garage tomorrow so I'll update here when they let me know what they reckon it is. I will certainly mention the bits mentioned here to see if they agree, thanks again for all the pointers, hopefully sorted soon!

 

[Jaylw04]

Good Luck!!

 

[dougmcdonald]

Ok, I'm officially an idiot....

Loose wheel nut, Lee, right all along. Tyres were changed 2 weeks after service and I have a receipt from eTyres as to the torque and PSI when fitted, but clearly they didn't tighten them enough!

My garage took it for a drive, heard the noise, were concerned, put it up on the ramp, tutted at my exhaust, mentioned cv joint, and asked if I could give them a few.

I took a seat, they came back after 5 and said, and I quote "have your tyres been changed recently?"....yes i said...he handed me my keys and said, loose wheel nut mate, give it a couple of miles and if you hear it again come back, but I'd be amazed if it wasn't that. Have driven 30 miles since without a peep....I'm a muppet :s

Good thing is that is cost me £0, bad thing is, after seeing the state of my exhaust I now want that sorted!

 

[Jaylw04]

Good stuff!! Glad you got that sorted...and free!! I think we have all done somethin similar, I took mine into the dealers the other day to say one fog light keeps comin on, got educated about cornering fog lights...in my defence iv never had a newish car.

 

[akchappers]

Nice one! Glad they sorted it!
ak

 

[mikeholroyd]

Tyres were changed 2 weeks after service and I have a receipt from eTyres as to the torque and PSI when fitted, but clearly they didn't tighten them enough!

This isn't the first time I've heard of problems with eTyres. A work colleague had 2 tyres replaced on his Laguna, at work, and not only did they not tighten any of the wheel nuts on one wheel, they managed to lose his locking key.

And in a separate issue, my neighbour had 2 tyres replaced on his Mazda 2, and they overtightened the wheel nuts so much that it we couldn't remove them with the car wheel brace. I helped out by lending him an extending wheel brace, and split one socket apart before we shifted them. And that was on alloy wheels, so god knows what damage it could have done, or has done, to the wheels themselves.

And I've got laughed at a few weeks ago when I needed a couple of tyres on my Octavia -- I took my (already set up) torque wrench with me, and insisted the tyre dealer used that to tighten the nuts when refitting the wheels.

Mike

 

[dougmcdonald]

There was another online remote tyre fitting site I contemplated using but I went with eTyres when they came in a couple of quid cheaper, slightly regretting the fact now!

Oh well, sorted now, will use something else when I do my backs in May!

 

[traumapat]

Ok, I'm officially an idiot....

Loose wheel nut, Lee, right all along. Tyres were changed 2 weeks after service and I have a receipt from eTyres as to the torque and PSI when fitted, but clearly they didn't tighten them enough!

My garage took it for a drive, heard the noise, were concerned, put it up on the ramp, tutted at my exhaust, mentioned cv joint, and asked if I could give them a few.

I took a seat, they came back after 5 and said, and I quote "have your tyres been changed recently?"....yes i said...he handed me my keys and said, loose wheel nut mate, give it a couple of miles and if you hear it again come back, but I'd be amazed if it wasn't that. Have driven 30 miles since without a peep....I'm a muppet :s

Good thing is that is cost me £0, bad thing is, after seeing the state of my exhaust I now want that sorted!

They probably did them up tight. The problem is you drive off and everything heats and expands and then things can work loose. Always check the wheel bolts if theyve been touched after so long.

Had my new wheels fitted, 50miles later pulled over alls well. Again 50 miles later again, still tight. 20miles from home (total 170miles) and 2 came loose on the N/S front!

I was paranoid for a couple of weeks after that