deilenberger

This is sort of a repost to RENNTECH, but since it has gathered no replies there, I thought it worth posting here. Sorry if you read it in both places.. I have expanded on it a bit after thinking about it overnight.

Cayenne S (V8) 2006, 56,700 miles. Newish to me.

It's back. It seemed to go away after cleaning the throttle-body.

Symptom is:

1 - Cold start (hasn't been run in hours, cold or cool outside): Starts flawlessly. Turn key, it's running.

2 - Not entirely cold start (was run, got to normal temps, stop, park for 30-90 minutes) but fairly cool environmental conditions (below 50F): Turn key, it tries to start, and sort of stumbles to a start. I usually have to give it a bit of gas via the pedal to get the RPMs up to where the starter disengages. Once started it runs fine. No other symptoms, no SES, no stalling.

I've done:

1 - Air filters - (not that I suspected these as a cause - mostly 'cause it has 56k on it and the 60k service is coming up..)

2 - Plugs - (put in the correct Bosch 4-prong jobbies - great price at Amazon for them, and again done because the service is coming up.) There was a slight stumble coming off low RPMs in A6th - the plugs made this go away.

3 - FI Cleaner - Ran a dose of Techron (FI cleaner - very good stuff) with a tank of fuel. Made no difference I could detect.

4 - Cleaned the MAF's - with CRC MAF cleaner. No difference.

5 - Cleaned the throttle-body - using solvent on a rag (rather then spraying). It seemed to clear up after cleaning the TB, but now (after several days) has started reoccuring.

Things I've found out:

1 - The goofy auto-crank on first start attempt isn't the best thing in the world when this happens. The starter tends to stay engaged and then be over-run by the engine. If I could, I'd disable this. If it wasn't for this, I could pretty much simply ignore it.

2 - Looks as if other people have experienced this - and fuel pumps and engine temp sensors have been mentioned as possibilities, but I can't find any posting where these actually were the solution. Most threads start out with these, and the owners are getting them done, then they never come back to report the results.

3 - It has been intimated here that the fuel pumps DO "charge" the system if the door handle is pulled when the car is COLD. I can't find confirmation on this, except people reporting when doing the coolant pipes that they feared someone opening the door while the fuel injection system is open since it would spray gas all over. That could explain the perfect starting when absolutely cold if there was a bad check valve in the fuel system allowing it to depressurize, and the time that it sits and doesn't start OK is due to the engine not being cold enough to trigger the system pressure charging. (This makes me think this could be fixed by programming by Porsche so the pumps charge whenever the car is cranked like normal vehicles do.)

4 - According to a friendly Porsche tech I chat with - he felt the TB needed recalibration, and there may be a flash for the DME to address this issue. Anyone KNOW about the flash for sure? He's in California, and I'm in NJ, so I can't ask him to run the car on the diagnostics tool until July when I'm out there.

What I'm looking for:

- Anyone have the fuel injection pressure leak-down spec's? I could invest in a fuel pressure gage and check how long it takes to have the system bleed down pressure.

- Anyone else experiencing this? (In the BMW world where I came from - there is a very common problem every spring where certain models start becoming 2nd-crank starters for the first start of the day. It seems related to the seasonal change in fuel formulation from winter to summer fuel. It has been posited by BMW that bad check valves in the fuel pumps cause this - but on my now departed '02 M3 - it continued doing this seasonally for several years after having the pump replaced under warranty. Then it stopped doing it. Go figure.)

- Anyone with firsthand knowledge/experience with the same problem, who has managed to resolve it, and how it was resolved.

I also am considering R&R of the throttle-body so I can REALLY clean it (I'm ordering the "Gasket" for it to the intake manifold), and I seem to recall hearing someplace that there is a check valve in the intake (perhaps for PVC?) that can cause these sort of symptoms. Comments are welcome.

I'm giving strong consideration to buying a DuraMetric so I can watch what is going on as far as fuel-pump activation, and temperature sensors, and see if there are any non-OBD-II codes stashed away in any of the engine management modules.

Anyone - Buhler?

TIA!

cordsig79

way above my paygrade D

v10rick

2004CS with 55K mi.

I have experienced this and it happened this week, the day after driving in the rain and parking in a damp garage. It sounded like the bendix was not engaging but after tapping the gas a few times the engine stumbled as if it were running on a few cylinders.
The exhaust oder was very stong for a few min.

Yes the pump runs when the door is opened but not always.

This is the first event in 1.5 years of ownership.
?
Please post updates.

User 4221

Does this happen after filling the tank?

These are symptoms of tank vent check valve. Do a search and you will find a recent thread on the subject.

When my check valve failed, it would have an extremely hard start (similar to vapor locking). The auto start would time out once or twice.

deilenberger

Scott - no, it's not necessarily tank fill related. It can happen with 1/4 tank of fuel. Or a full tank. I read up on the check valve - but one other thing makes me think it's not that.. I think if that fails you'll get an OBD-II Check-engine-light (could be wrong on that..)

V10Rick:

It happened last night right in front of a friend who happens to be a very good high-end car mechanic.

When I saw him today (I was checking on a parts delivery for my wife's BMW 5-Touring's brakes..) he immediately said "check valve" - as in the one in the fuel system that keeps it pressurized when the pumps aren't running so it can start quickly. He said it sounded like no fuel.

So.. gotta get a fuel pressure gage and hook it up and see what the bleed-down rate is on the fuel-rail. Unfortunately the check valve appears to be part of the fuel pressure regulator which is part of the passenger's side fuel pump access panel assembly - the part that fastens into the opening in the tank.

Part isn't silly awful money (around $125 or so) - but replacement looks like a smelly PITA job. And to do it right requires buying (or renting/borrowing) a special tool used by Porsche, Audi and VW for the locking ring for the assembly into the fuel tank. Or - a hammer and an old screwdriver.. (BTDT in the past, trying to avoid McGuiver's as I get older..) Best price I've found on the tool is a bit over $40.

The DuraMetric showed up tonight. It very happily found absolutely no codes at all in any module it could read in the truck. It only managed to read some of them after an instrument cluster reset (accomplished by pulling the cluster fuse - left-door/dash fusebox.) Apparently the cluster also serves as the computer buss "gateway" for the diagnostics, and if it gets confused (which apparently it can rather easily) it won't let any codes sneak out to the OBD-II port.

Interesting stuff this. Next - find a fuel gage.

v10rick

Thanks for the update deilenberger.

No repeat of this at my end. I have not heard the pump run when opening the door either but this was always sporadic.

My CS is not driven daily so it may take longer for this to happen.

Please let us know the outcome of the fuel pressure measurements.

Slow Guy

My '06 S has a couple K mi. more than yours but I've not had any starting problems. Transmission issues yes, starting no.

Best of luck resolving it.

deilenberger

Gonna try to get on it this week, first week of retirement, seems I'm awfully busy already..

deilenberger

Found Harbor Freight has a fuel pressure guage. After I finish putting brakes and summer tires on SWMBO's BMW 5-touring I might wander down and pick one up.

Stopped at the friendly local Porsche dealer today (who will go unnamed..) They'd offered to print out the service history for the truck. Imagine my suprise (not!) to find that everything I've spotted as a problem - including the balky starting was submitted to their service department by the former owner. The note says "Check DME for faults, None. Could not verify stalling or rough running" (he'd reported problems starting, and running rough after starting.)

So - it got the sunshine treatment. No pressure test - if the DME doesn't say somethings wrong, apparently nothing is wrong. I sort of think this is why so many people on this and other Cayenne forums report problems with their trucks.. Other items I've noted (not biggies - but stuff I noticed) had been repeatedly submitted to the dealer for repair, and went unrepaired.

This is a great opportunity for independent mechanics eh?

v10rick

Your P dealer report is no surprise if the service was covered by the warranty.

Previous owner of my CS supplied the service records from day one. Of the 12 dealer visits 6 were repeats for the same issue.

agustin guevara

Deilenberger, I had a similar problem with a Cayenne S, take your SUV to a official dealer and request a test, if the computer doesn`t show anything... you could have a mechanical problem and it could be with the Oil pump. Porsche has a NHTSA Campaign Number 08V076000 for oil pumps. The dealer I visit had already 15 Cayenne S call back`s, and I`m in a backorder list for the pumps... also for the Bose System radio`s and the Airbags software.

wirunner

I think that recall was related to MY08 V6 fuel lines. If you search that number, the recall issued in 2008 comes up.

deilenberger

Update - also posted to the thead on RENNTECH..

Finally got to Harbor Freight today.. and of course the $25 (-20% coupon) fuel pressure gauge I was buying turned into a $150 bill (this just seems to happen at HF..)

Got home, put it together (nice kit - comes with all sorts of adaptors..) Pulled fuses 13 & 14 (do NOT drop a fuse in the underhood fuse box - it's a PITA to diassemble to get to the bottom, I could have left it there - nothing to short, but just couldn't bring myself to.. but I digress..) Pulled the fuel pump fuses then cranked the car to relieve any residual pressure, and hooked up the gauge.

I actually needn't have bothered pulling the fuses. I replaced the fuses, and tried starting the truck. On starting - it did it's usual bumbling start - and the fuel pressure gauge read a nice solid 4-Bar. I tried pulling fuse 13 - no change - solid 4 bar. Put it back in, pulled fuse 14 - engine died as fuel pressure dropped to 0. Tried restarting - another bumbling start - and then I had 4-Bar again - so the fuel pump switchover that others have described worked as expected, and both pumps were capable of 4 bar.

I replaced both fuses - then shut the truck off. Pressure immediately started dropping - reaching 0 Bar in about 15 seconds. Tried this several times, start it (starts lean) check pressure - 4 bar, shut it off - pressure immediately drops. Manual leakdown spec is - 3-bar 10 minutes after shutdown. Mine fails this miserably.

So - I'm guessing the check valve isn't checking. Or I have a really badly leaking injector. I really feel it's probably the check valve since once the truck does start, it smooths out quite quickly - no indication of a rich mixture, and when I replaced the plugs - they all looked the same. If one injector was dribbling fuel, I'd expect to see it in the plug.

Anyone know where the check valve is?

I'm going to approach the dealer with the info - since they hadn't bothered doing a pressure test (or ANY testing) when it was in before for this problem.

Oh - what else did I buy at Harbor Freight? They have a neat boroscope tool - usually $130 - on sale for $79 - couldn't pass it up. Has a flexible probe about 2' long with a camera on the end with two LEDs for illumination (the brightness of these can be varied.) Color LCD - about 3"x2.5" - battery operated. I figured I could try to see if the heater pipes had been replaced in my truck. I can now authoratively say they haven't. By wiggling it around behind the engine, with the tip bent to point forward a bit - I was able to see the pipes where they pass through the clamp at the rear of the block - and they're black plastic. I also picked up a set of storage bins, and some small toys (aluminum valve caps, 1/2" deburring tool - free with a coupon!) It's not easy getting out of HF for less then $100. I've proven that many times.

deilenberger

Thought I'd update this.

The truck now starts correctly.

It spent the past week at Princeton Porsche in Lawrenceville NJ puzzling their techs and Porsche-Germany.

The initial thought (and diagnostics via the manuals) was fuel pumps having a bad check valve. So - it got two new pumps. No joy. Next thought was the fuel-pressure-regulator, since it's supposed to work as a check valve. New FPR - no joy. Finally Porsche Germany had them looking at the spaghetti nest of plumbing inside the tank for a leak in a hose. In order to check it out, they removed everything from the tank, setup a test with the pumps in gasoline, and wired it up. No leaks. Finally - since the only component they hadn't tried was the fuel filter - they borrowed one and put it in. JOY! They ordered a new one and installed it this AM - and the truck now starts perfectly. Apparently there is an undocumented check valve inside the fuel pump that even Porsche Germany is unaware of.

I give Princeton Porsche's service department 5 stars on what is an ugly job well done (mucking about inside a fuel tank with gas in it is not a pleasant job at all.. BTDT and don't want to do it again.) They persisted, when other dealers had given up. They kept me well informed on what they were doing, and I had use of a loaner Audi for the duration (2.0T - it isn't a Porsche for sure.. but at one point they felt bad it was taking that long and they offered me a Panamera loaner. Not wanting to get spoiled, I stuck with the Audi..)

If you need GOOD service in NJ - I can recommend them without reservations. Good friendly people, who didn't mind me bothering them with my ideas on what it could be (and I was wrong - but no one had thought of a check valve in the fuel filter.)

hk_usp9f

I'm glad there was a happy ending in your story.

Just to clarify, was the undocumented check valve in the pump or the filter?

My impression from reading your narrative is that it was in the filter.