MaxLTV

Need urgent help from someone mechanically minded. My Cayenne Turbo all of the sudden started shaking when I push the throttle pedal further down. It seems to be dependent on the boost or engine load relative to revs rather than throttle position or revs. In fact, I can get a higher boost in higher revs before it happens. Shaking is like stalling for a fraction of a second but maybe even more violent. Drives normally under 4psi of boost at low revs and below 6psi at higher revs.

I once forgot and floored it to pass and it made a series of backfires out of exhaust without going any faster. Check engine light is not coming on. Nothing is leaking. Idle is normal, exhaust has no smoke or color at idle, did not check while driving.

It started about 30 miles after a fill-up - could it be the wrong gas? My wife swears she filled up 94. It's hard to mix up - it's a different nozzle at the gas station. So maybe a coincidence. It's weird that no CEL is coming up - usually it comes up for the tiniest of things. Also, the bost on dash showed 12psi once, but normally it does not go above 8 in non-sport mode.

I have a 4x4 driving event tomorrow, so it's such unfortunate timing. 😡

Any ideas what to try?

marinerbc

sounds like lower octane or bad gas, best and quickest fix is to add Torco or Klotz octane booster. i use Klotz and it is great.
i do add 100 Oz. per a full tank of chevron 94.
Now a days with the gas prices in lower mainland 94 octane stays in the gas station tanks for ages.
good luck.

deilenberger

Or some diesel in the gas tank.. could it have been at a station where the diesel nozzle lives alongside the gas nozzles?

travestyevo

OCNYPORSCHE

deilenberger

Even though the SES/CEL isn't on - there ARE stored codes in the ECU. It can't misfire without storing them.. so you might look into getting a Porsche specific code reader that can read those codes. That might give a clue - if it's misfiring on all cylinders, then likely fuel related. If it's a misfire on only one cylinder, I'd be looking at the coil and plug. Looks as if you have enough P cars to justify having your own scan tool.

MaxLTV

After about an hour of driving, it threw CEL and p1021 code. I did a data log and two things I could see being abnormal when the vibration happened were fuel trim (shooting up to 23%) and sometimes fuel rail pressure dropping. Looks like fuel pump dying or boost leak. I could not get it fixed by myself, so I ended up taking the 911 instead to a snow driving event I almost missed because of this. 911 handled it almost as well, surprisingly, and the Cayenne will go to a real mechanic now.

marinerbc

MaxLTV

Porsche tech diagnosed high-pressure fuel pump going. It's a rather expensive repair - $3K Canadian (2400 USD) for parts and labor. A bummer that it happened less than two months before the car was supposed to be traded in.