958 Diesel Cayenne vibration

[slackster]

Evening all,

Im after a bit of advice/steer on where to investigate my issue further if possible.

the cayenne 958 3L Diesel has developed an annoying vibration when sat still/on tick over.

its is faultless to actually drive, and the vibration felt mainly through my backside is only present between steady idle ( 650rpm ) to just about 1000rpm.. as soon as I get above that it gone instantly.

if i slow to a stop at a junction it kicks back in again just before im stopping or just before stop/start kicks in.

startup/crank is fine.. rev needle doesnt jump or flutter but the seat/car vibrates until i start moving basically.

since buying the car a few months ago i have on occasion had the odd random lumpy start in the morning/when cold but that has gone pretty quickly and i put that down to it being a diesel and it being a cold/damp day etc however this seems persistent.

never had a dash light, never had any limp mode or loss in perf..

i've driven it for long periods for work as well as pottering to get milk etc.

any ideas? google seems to suggest engine mount failure/fuel supply issues/downpipe failure causing excessive vibration, however all of these sound to me like i'd get variance in the effects - but what im seeing is very precise in how its showing up.

any ideas?

Cheers

Russ

 

[deMort]

A very difficult question to answer im afraid .. my best advice would be to get your local Indy to sit in the car and experience it ..

I know i could probably nail it down after experiencing the fault first hand .

As a guess ..

I'm wondering misfire .. on a petrol that would certainly cause something like this and you can get a single cylinder running rough which is only at idle ..

It should show up on a tester but not as a fault code .. under a section called rough running .

Engine stabiliser bar o/s of the engine .. a possible ..

Air suspension .. compressor is on rubber blocks .. another possible ..

Countless pipes that could be touching the bodywork ..

I could probably go on .. hence a mechanic experiencing it might lead in a direction .

 

[slackster]

cheers for the ideas DeMort, really appreciated.

I'll take these ideas with me and go to my local Indy to see if they can pinpoint it.

its very frustrating that its a very precise but repeatable situation for this shake/vibration to occur, i can't seem to get it to be any worse or better when sat idling..

putting it in gear/turning on AC, changing air suspension height, pressing sport, pressing offroad etc.. all have zero effect apart from just pushing the revs past 1K and suddenly the car is perfectly still again.

I'll report back when i hopefully know more

 

[slackster]

So.. after 2-3 weeks of regular & repeatable symptoms.. it disappeared down to 99.9% clear within the last 7-10 days! ☹️.

I cannot fathom what may have changed things at all, a few more tanks full of fuel, a few long drives for work.. but thats it. The weather has got a bit colder?

Either way.. as of about 5days ago there are now zero vibrations at any rev range and today it went into my local indy whereby the engine mounts were reported as fine, nothing showing on the ecu diags as a misfire etc and nothing else to note on the car otherwise.

So.. i've been sent away to see if it happens again!

 

[golfprorich]

Be interesting to see if it returns when the weather warms up again. The temperatures currently would firm up any rubber that was slightly soft!

 

[deMort]

As per Riches comment .. rubber gets harder in cold weather so see how it goes next week when i belive its a bit warmer .

 

[slackster]

update! - so friday evening after an hrs run.. i noticed on pull up that the vibration under my backside was back.

still no warning lights on dash etc.

saturday.. no issues at all.. back to normal but no long runs

this morning.. set off and within 15mins i had a new symptom.. the coil icon flashing on the dash and nothing under foot.. however its was just about maintaining cruising speeds at 80mph.. as soon as I got to a hill it was clear there was no actual ability to give it any and i rolled onto the hard shoulder where it just felt very un-even revs wise at idle.

turned it off.. turned it back on and all was gone.. set off again and it seemed fine for about a minute before me trying to put a bit of throttle down and again it did the same thing..

did this all the way back home so i had to nurse it at very low revs but i managed to capture the following on my noddy OBD2 dongle :

P2146 Injector, Group A, Supply Voltage - Open Circuit.

i did a screengrab and then cleared the code and instantly it was feeling fine again.

so i dared to go to the supermarket and as per typical bad luck.. upon returning with arms full of shopping.. the car wouldn't start whatsoever but kept trying to kick up.

RAC have been out to the supermarket carpark and also couldn't get it going without some "quickstart" spray down a pipe or something and he believes this is fuel pressure/sensor regulator related as one bank shows 500ish and the other shows 2ish ( pressure? flow? dunno ) .. but clearly one has got an issue.

its been ditched outside my local indy, i gently limped it the 1 mile whilst it made an awful smell as I presume it argued with itself about how to keep running.

Anyone had similar symptoms? i wonder if the vibration under my backside was the start of this showing itself properly, however it could be nothing to do with it and this is just a fresh problem