Xantia V6 weird engine (?) noise

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Mandrake
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Xantia V6 weird engine (?) noise

Post by Mandrake »

Hi All,

I've started to notice a strange noise on the V6 in the last few days which has got me a bit worried.

When doing speeds around 25-30 MPH in 3rd gear (around 1500rpm) if I put my foot down quite a bit without kicking down a gear there is a low rumble that at first just sounds like a throaty intake noise but with a bit more throttle turns into a definite shudder/vibration which can be felt as well as heard.

I can't for the life of me think of anything that would make a noise like that, nothing I want to consider anyway. :? I checked under the bonnet and found the ECU box doesn't seem to be bolted down properly (how I didn't notice that before I don't know) so I thought perhaps that could be vibrating/rattling with vibration from the engine, but I'm doubtful thats it.

Anyone have any ideas ?
Simon

1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White

2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive
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xantia_v6
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Re: Xantia V6 weird engine (?) noise

Post by xantia_v6 »

I would suggest either the top or bottom engine mount or the bushes on the reaction bar on the top mount.
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Mandrake
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Re: Xantia V6 weird engine (?) noise

Post by Mandrake »

The reaction bar at the top looks fine, top mount looks fine, can't check the bottom mount at the moment, but I don't think engine mounts fit the symptoms, especially when the problem has only been apparent for a couple of weeks, and engine mounts would get worse over time.

I was noticing it again today and the whole transmission shudders badly under load at 1500rpm in 3rd. The pessimist in me thinks its a clutch slipping in the gearbox... :( The shudder feels exactly like a manual gearbox with oil on the clutch. Another possibility that springs to mind is a misfire on one cylinder, as I've noticed the engine is intermittently a little bit down on power.
Simon

1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White

2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive
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CitroJim
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Re: Xantia V6 weird engine (?) noise

Post by CitroJim »

I can put your mind to rest on the slipping clutch thoughts Simon. It's unlikely as if the gearbox detects any slip it'll log a fault..

I'll think on this one but presently my brain is only working at around 20% of it's usual capacity :(
Jim

Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
lexi
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Re: Xantia V6 weird engine (?) noise

Post by lexi »

For a misfire I would be thinking plugs themselves. I bet it is a long time since those rear ones were changed.
There is also possibility of oil in the plug holes from cover gasket leaks.........that is favourite on most V6 engines of all makes. My mK 1 v6 also had a crack in the coil packs on the cast resin block. Heat is the culprit and it can lead to misfires. That one of yours was ok at the front bank but I never saw the rear.

The bottom mounts on Xantias do get oil soaked. It could be a failed one .
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Mandrake
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Re: Xantia V6 weird engine (?) noise

Post by Mandrake »

Another weird thing I've noticed only in the last week or two is the engine fluctuating between two different rev's with a constant throttle - for example doing 60mph on the motorway, steady throttle opening and I can hear (and see on the rev counter) the engine surging slightly and backing off about once per second... very odd. Until a couple of weeks ago the idle speed was very steady and the smoothness overall very good.

This surging only seemed to start after I had the fuse box out the other day, but I can't see any connection to that, other than the battery being disconnected...

I have noticed for a while that the car is sometimes extremely zippy and responsive, (it really zooms away with light throttle opening and responds quickly) at other times it feels a bit flat and sluggish, comparatively speaking. Sure, theres still plenty of power when you put your foot down, because you've got 190HP to start with a small loss of power isn't nearly as obvious as it would be on a 125HP 4 cylinder...which combined with the vibration got me wondering about possible cylinder missing. (1 cylinder out of 6 missing is going to be a lot less obvious than 1 out of 4 I assume, as would 1/6th of 190HP missing compared to 1/4 of 125HP missing)

As for the shuddering noise another thing has occurred to me - to do the handbrake cables I had to remove the heat shield around the exhaust which meant a lot of bending it out of shape to extract it and put it back, its possible there is a spot where its touching and the vibration is causing the heat shield to shudder against the body - it does sound a bit like it could be that, so I'll check the heat shield to make sure there isn't a spot where its touching but not anchored. It's possible the vibration from the engine was there all along, but it wasn't triggering something into shuddering/buzzing before.
Simon

1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White

2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive