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ragpicker
Reims


Joined: 14 Apr 2013
Posts: 4030
Location: North East England


PostPosted: Wed Feb 27, 2019 8:52 pm    Post subject: 955 Cayenne Turbo hesitation at partial throttle Reply with quote

Miss Piggy is misbehaving.

Its not a big problem but there's definitely a hesitation at partial throttle at low speed.

I've read lots about coil packs and spark plugs causing an issue but I've done those.

At one point I had a valve timing fault code which I cleared (wasn't sure if it had been there since the PO had the car) which hasn't returned.

Do the variocam solenoids play up on these? Will this cause the symptoms. Anyone got any ideas?

Cheers
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deMort
Dijon


Joined: 21 Mar 2015
Posts: 7477
Location: Brighton


PostPosted: Thu Feb 28, 2019 9:08 pm    Post subject: Reply with quote

Ok .. overall i would need fault codes or actual values .. cam shaft deviation .. more than 11 degrees would indiate a streatched chain .. these can be reset .. in other words adjusted in situe .. not an easy job though ..

You adjust the camshafts .. chain still has stretch but you basically put it back to where it should be .

A tester is needed to check these values .

Misfire the more likely option , again a tester will tell you what cyl .

Gen 1 and the coils cracking was common ... not so much after that .

Gen 1 and sometimes .. rarely they can get bore score due to a blocked oil jet at the base of the piston... gen 1 only and a borescope check to see if it has has hapened .

Turbo .. it can fail to a degree . it will dump oil ... this can coat the maf sensor on one side .. incorrect air flow reading will alter the mixture giveing rough running .

Pull off the Y shaped intake pipe to the throttle houseing and have a look .

Basically i need more info .. solinoids can fail .. but ive not seen any yet .. its a possible atm .
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ragpicker
Reims


Joined: 14 Apr 2013
Posts: 4030
Location: North East England


PostPosted: Fri Mar 01, 2019 5:27 pm    Post subject: Reply with quote

Thanks pal!

Bit more info for you -

No misfires ever recorded since I've had it. The code I was referring to was P1372 - valve lift control, bank 1.

Since I've cleared the code it hasn't ever come back although every now and again I get a rough idle for 20s or so and a hesitation at part throttle, usually when cold. After a good run it almost never does it.

Coil packs and plugs changed with no difference.

No smoke whatsoever but the car does like a drink - 1.5l oil in 1500 miles. Still within factory spec of 1l per 600 miles I hasten to add..

Borescore - christ I hope not! I've heard lots of cars with piston slap but mine sounds fine, although one morning when just fired up I heard something similar which lasted 30-40s before disappearing completely. I was hoping it was just a chain tensioner (or cam actuator solenoid) being sticky when cold.

You're right though, I need to get my borescope down and see what I can see...

Thumb

PS: I've also had a CEL for lambda values at idle suggesting there is an air leak. I can hear a feint whistle when accelerating from the near side. Would a vac leak cause hesitation, I know it can cause an unsteady idle... Also, where are the common places for vac leaks to occur?

Sorry for all the Q's!
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deMort
Dijon


Joined: 21 Mar 2015
Posts: 7477
Location: Brighton


PostPosted: Fri Mar 01, 2019 8:17 pm    Post subject: Reply with quote

Sorry young man .. im afraid i treat you like the mechanics i work with and just bang on about what problems there can be .. not realiseing this is your car.

I hold you in High esteem though to do this .

In truth the bad things are pretty dam rare but im the worst person to ask .. as i see the bad ones.

you have changed the plugs .. we all look at them .. if you had issues you would have seen it so you have pretty much covered the engine is ok .

Drinking oil .. hmm .. pull off the throttle intake .. the Y shaped piece .. look for oil resiue either side .. oil from a tired turbo can get onto the maf sensors .. its a pretty quick check .. if dry both sides then thats ok .. you have ruled out any Turbo problem .. i also dont think its this now but its worth checking .... also thats a fair amount of oil going somewere .

Valve lift code .. pretty common .. if it hasnt come back then its a spurious code .. in other words as its oil based it blocked for a bit then cleared .. oil change usually clears this.

Its only a fault when it comes back .. its for the vario cam adjustment .. it moves the inlet cam to different positions that the engine req.s etc etc .

Your problem is going to be the lambda fault .. was the code to say rich at idle or lean at idle ?

Problems like this are always at idle .. RKAT is the figure you are looking at on the fuel trims .

Air leaks .. were to start ..

Really you need to smoke test the inlet tract .. there will be many leaks if its anything like the last one i did but none of them are really a problem .. the pipes from the turbos will leak , there are vacuum pipes at the back end of the inlet mainifold ..

If the inlet mainifold has been off recently then the gasket can get caught when reinstalling it and cause an air leak .. i know .. ive done it .

For now .. if it was me ..

Check cam deviations .. you want less than 11 degrees ..

Check the Y piece inlet pipe ...

Smoke test the inlet tract .. this is the quickest way of finding an air leak .. trust me .


Also just to add .. whistle from n/s .. turbo pipe leak when under boost im guessing .. i doubt that will cause the hesitation but if you can hear something one side then there is a fault there .

BTW .. clean out the throttle houseing when you have the Y pipe off .

Second BTW .. i keep reading your post and thinking .. probably tappet or tensioner as its kinda a one off for the noise .
_________________
.

My Daughter's Crowdfunding has hit the target .

Thank you all so Very much .

She's not going until july 2020 though .



Mechanic

7pm - 9pm

Now At An Indy.
 
  
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ragpicker
Reims


Joined: 14 Apr 2013
Posts: 4030
Location: North East England


PostPosted: Sat Mar 02, 2019 8:57 am    Post subject: Reply with quote

Thank you my friend. I'll have a gander and get back to you with whatever crops up!

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