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2015 Cayenne Diesel Loss of Power at Highway Speeds No CEL
Today driving to NC I experienced several episodes of loss of power on highway in my 2015 CD. The car would barely get above 50 MPH, transmission would not shift out of 5th gear. After about four episodes of power loss it behaved itself the rest of the trip up a 4000 foot mountain. No CEL. 31K miles, all service done at Porsche, Use Exxon diesel exclusively. Fuel level 3/4 of a tank.
Any thoughts? I wonder if the feed pump in the tank had a hiccup.
That the RPMs didn't change seems to rule out the turbo charger.
If you were getting air but no fuel, I can't see how you wouldn't get a CEL. That would make me think that fuel delivery is OK.
The only obvious thing I can see left, since the entire system is electronic, is that the ECU was acting up and effectively not acting on your accelerator input.
If that is the case and since there was no CEL, that means that it thought all was right in the world. Given that the ECU acts and reacts on many inputs, there would have to be a number of sensors at fault for it to believe that the engine is correctly responding to full throttle input.
I think the two most likely scenarios here would be a communication issue between the accelerator and ECU or a fault in the ECU itself.
I would be careful on the rest of your trip to avoid getting in a situation where a repeat could put you in danger. When you get home, get it in to have it looked at.
Ideally talk directly with the Tech rather than the SA. I have found too much information can get lost in that grapevine which will cause them to go down the wrong path (and give it back to you with "no issue found"). I've also had success with cases like this writing as much detail as possible down and including it with the drop off paperwork (even had one Tech call me and thank me for the note as he never would have found the issue as described by the SA).
Thanks Gnat, that is my plan when I get home. I found one other post on RL where a CD developed a cracked boost hose that caused a CEL. Without a CEL I theorized it might be fuel delivery. My fuel filter was changed at 20K. ( comedy of errors at that service where they changed the cabin air filter instead of the fuel filter which I caught by examining the part numbers on the receipt. The parts guy was on vacation, after pointing out the error they replaced the fuel filter )
Agree that much is lost between SA and tech working on the car. One copy of my service notes go to the SA and a second copy is left on the passenger's seat.
Frighteningly my SA wasn't aware the CD uses C30 oil, luckily the techs & parts dept know.
Could have been a bit of water in the fuel. Or dirty fuel. I'd start with the fuel filter... and get it done immediately.
Even using good brand fuel, if you filled up shortly after the station tanks were filled, it could have stirred up some crud that got pumped into your tank. If that's the case, your filter probably caught it and is now flowing OK, more or less, but if that's the case, that filter needs to be replaced right away.
I've done roadside filter swaps on my diesel pickup for this very reason and it has fixed the problem.
If not the filter, it gets complicated. Fuel pump, lines, injectors, etc etc all need to be checked.
OK I'll try that. I found a dealer open until 4 Today in Asheville and he has one filter in stock. I'll be carrying a spare filter on the next trip....
I'll be doing most regular maintenance from now on since the PSMP is done.
Could have been a bit of water in the fuel. Or dirty fuel. I'd start with the fuel filter... and get it done immediately.
A bad fill was my first guess, but what he described doesn't sound right for what I've experienced.
If water got through the filter (it's whole point) or air got into the system either the whole thing would have shutdown due to lack of fuel or it gets really rough. Neither fit his description as I read it.
He also mentions that he only uses Exxon. While it's not 100% proof against bad fuel, it's not like he's trekking out to Joe's Discount Truck Stop that sees a customer once a month.
I've done roadside filter swaps on my diesel pickup for this very reason and it has fixed the problem.
While completely doable, messing with the CD's filter on the side of the road isn't something I want to do. You have to pull panels, need a hex driver, and lots of rags to keep from slopping fuel on hoses that it will compromise. Then you have to know the purge processes since there is no physical way to drain/purge the system. It's a badly design/placed system they used
I do have the filter drain/replace process detailed in a DIY over on 6spd for those interested. Not hard, just annoying.
If not the filter, it gets complicated. Fuel pump, lines, injectors, etc etc all need to be checked.
His description makes it sound as if the delivery system is functioning fine and delivering an even flow of fuel, just not in the amounts requested. Those are certainly things to look into. To me, however, it just doesn't sound like he is seeing the typical signs of such problem areas.
OK I'll try that. I found a dealer open until 4 Today in Asheville and he has one filter in stock.
Hah! I had a feeling that was where you were headed. Enjoy your time there. Beautiful place! Those mountain roads are the perfect environment for a Porsche too!
A bad fill was my first guess, but what he described doesn't sound right for what I've experienced.
If water got through the filter (it's whole point) or air got into the system either the whole thing would have shutdown due to lack of fuel or it gets really rough. Neither fit his description as I read it.
He also mentions that he only uses Exxon. While it's not 100% proof against bad fuel, it's not like he's trekking out to Joe's Discount Truck Stop that sees a customer once a month.
While completely doable, messing with the CD's filter on the side of the road isn't something I want to do. You have to pull panels, need a hex driver, and lots of rags to keep from slopping fuel on hoses that it will compromise. Then you have to know the purge processes since there is no physical way to drain/purge the system. It's a badly design/placed system they used
I do have the filter drain/replace process detailed in a DIY over on 6spd for those interested. Not hard, just annoying.
His description makes it sound as if the delivery system is functioning fine and delivering an even flow of fuel, just not in the amounts requested. Those are certainly things to look into. To me, however, it just doesn't sound like he is seeing the typical signs of such problem areas.
I was just using my truck side of the road repair (rest area, actually) as an example. It's easy in the Cummins, with no purge process necessary. There's a water drain valve built in, so that'll take any water out. The filter just lifts out and a couple of bumps of the starter refill the system and then you start and are on your way.
I've not attempted this on the CD. We, too, bought a service plan, and have a year and a half left on it. I suppose I shouldn't be lazy, since we do road trip with it and a service plan won't do squat for a fouled filter in the middle of nowhere....
Yeah the Cummings is easy and follows the same basic plan diesels have used for years. Even the T-Reg apparently has something similar. But no, not Porsche
Ok I did the scenic drive along RTE 64, etc to Asheville and got the filter. Car is running fine but tomorrow I'll change it out and report back. I needed to buy more fuel and there was no upset. My carry along tool bag has the torx bits and I now possess two Ingles turkey basters.
I may have found my problem. When they did the 30K service one fuel filter screw was left out. Aargh.
missing fuel filter screw courtesy of PSMP 30K service
I didn't think to buy an extra screw when I got the new filter.
Given the chance of Murphy's law on the mountain top versus the karma of having a new filter on board I'm going with karma and a new screw on Wednesday.
06-29-2017, 11:33 PM
2015 Cayenne Diesel Loss of Power at Highway Speeds No CEL
