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4 hours ago, DannyHoffman said:

Trickle charger theory is out the window. It said the battery was fully charged this morning but I am still getting an occasional misfire. No fault codes and I monitored the air intake temperature in real time whilst driving. It was giving expected readings with no glitches when the car misfired. My reader's real time monitoring only shows one air intake sensor.

 

As an experiment I've pulled the pipe off the purge valve on the tank side to see how it will run on the way home. My thinking being if the purge valve opens it will just suck in fresh air, not neat petrol

I'm a bit confused by the codes and number of air temp sensors you're seeing. 

I thought there was a built in "intake air temp" sensor on the MAP sensor and one mounted in front of the radiator (ambient temp). 

 

 

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My leaving the tank side of the purge valve open proved nothing. The car still misfired, still no fault codes.

 

I decided to have a bit more of a poke around under the bonnet. I removed and cleaned the contacts for the other two MAF/Intake Air Temp sensors. I also cleaned the contacts for the two other devices near the purge valve that looked like they were attached to vacuum/vent hoses. Not sure what they are?

 

I then had a look at the intake pipework. The right hand (sitting in the car) flexible hose that connects to the Y piece at the front of the engine wasn't pushed fully home at either end. After loosening the clamps it looked like it had been that way since the car was built and there didn't look like there was any chance it had been leaking. I fitted it properly just in case.

 

According to the history I have with the car the air filters were changed about 4,000 miles ago, I thought I would double check. The plastic torx pins on the right hand side air filter box were in the unlocked position, but again I can't see this would cause any issues. I then noticed the small bore hose with a green connector that connects to the right hand side cover wasn't attached. I tried to trace it and it runs across the front of the engine and then disappears low down near the left hand turbo.  Anyone know what this hose does? Could this be the issue?

 

  

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"I'm a bit confused by the codes and number of air temp sensors you're seeing. 

I thought there was a built in "intake air temp" sensor on the MAP sensor and one mounted in front of the radiator (ambient temp)"

 

I'm a bit confused too, I think the two sensors near the air filters are MAF and air temperature, and the one in the centre is turbo boost and air temperature. But I could well be wrong.... 

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To clear up a few things:

They are mafs next to each air box. Pins locked or unlocked don't matter. Green pipe isnt going to cause any issues for running. 

The map sensor is  also temp sensor built in. 

If your standing in front of the car looking at the engine the left side is bank 1 the right side bank 2. Bank 1 cyclinder start 1234 from the front to back, bank 2 is 4567 front to back.

In future this may help avoid confusion. 

 

Interesting about the purge valve disconnected did nothing to change the symptoms. 

 

I think you need to have fuel pressure and flow tested. I got a feeling your left pump is weak. 

Until then try this: open the "wet fuse box" pull out the number 14 fuse for the left pump, cycle ignition off and on which forces the dme to run engine on the right pump. see how it runs. (Need to keep above half tank for this mind). 

 

 

Screenshot_20171025-224051.png

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I drove about 5 miles this morning and it didn't miss but the idle was a little lumpy occasionally. I pulled fuse 14 and it seems smoother but I will have to drive a bit more.

 

Interestingly I found a description of the exact same problem on another forum discussing fuel pump issues. Sadly the poster never said if he found a resolution 

 

https://rennlist.com/forums/porsche-cayenne-forum/590120-cayenne-s-stalling-problems-how-do-i-test-the-fuel-pump-2.html

 

 

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My 04 cayenne turbo had the same issues with intermittent stumbling and it ended up being the left fuel pump. I spent one Saturday replacing both fuel pumps plus the regulator and the filter all at the same time. No issues since. My initial codes were for misfires as well.

 

If you do this job yourself make sure you take notice of how all the hoses inside the tank are connected together and to the fuel pumps and regulator. It’s easy to hook them back up wrong like I did.

 

 

 

Sent from my iPhone using Tapatalk

 

  • Upvote 1

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I found this on line 

 

With the activation of drivers outer door handle - left pump primes fuel rail.

 

starting procedure: left and right pumps on

 

Fuel tank qty >60 L

right pump on

full load: left and right pumps on.

 

Fuel tank qty < 60 L

left pump on.

full load: left and right pumps on.

 

If this is correct the right pump runs when the tank is full, I have pulled fuse 14 so the right pump is always running and at the moment it's running perfectly.

 

It doesn't make any sense

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3 hours ago, DannyHoffman said:

I found this on line 

 

With the activation of drivers outer door handle - left pump primes fuel rail.

 

starting procedure: left and right pumps on

 

Fuel tank qty >60 L

right pump on

full load: left and right pumps on.

 

Fuel tank qty < 60 L

left pump on.

full load: left and right pumps on.

 

If this is correct the right pump runs when the tank is full, I have pulled fuse 14 so the right pump is always running and at the moment it's running perfectly.

 

It doesn't make any sense

This info is incorrect that's why. 

This is from the publication Porsche Service Technik.

Regulation of Fuel Quantity.

As a result of the on-demand regulation of fuel flow capacity, fuel heating in the tank is reduced.

This is achieved by the DME control module switching on fuel pump 2 only as required, while fuel pump 1 is always activated.

With the following switching criteria, fuel pump 2 is additionally switched on to increase flow capacity.

At engine start and then 2 seconds run-on (with a hot start 5 seconds run-on).

With a calculated fuel consumption of > 50 liters/hour the pump is switched on, and at < 45 liters/hour switched off again.

With a fill level of < 10 liters in the tank, it is switched on and with > 15 liters it is switched off again.

Props to Bigbusuki. 

Edited by lewisweller

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Well I have been running with fuse 14 pulled since my last post and it's been running fine. I got down to about a quarter of a tank and filled up today, and it still runs fine.

 

So it looks like a problem with the left pump. I will run it for another day or so to confirm., then pull fuse 13 and refit 14 to see what happens

 

Long shot, but could it be the relay? I'm inclined to try swapping them as it's easier than a new pump. Can anyone tell me which ones they are?

 

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I drove a bit further today, about 15 miles in total since filling up, still running perfectly.

 

So I pulled fuse 13 and refitted 14, and it still runs perfectly.

 

Will carry on driving with just the left pump to see what happens

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12 hours ago, DannyHoffman said:

I drove a bit further today, about 15 miles in total since filling up, still running perfectly.

 

So I pulled fuse 13 and refitted 14, and it still runs perfectly.

 

Will carry on driving with just the left pump to see what happens

Are you using the same fuel station every time or random? Could there be water contamination or something worse at a certain garage you use? Contaminants settles to bottom of tank shortly after refilling and gets sucked through and cause the stuttering? 

You need a fuel pump test. 

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I have always filled with Shell V-Power, but from different garages.

 

I have a fuel pressure tester on order, but the problem feels intermittent. 

 

I generally drive the car very gently so would low fuel pressure cause problems at under 2,000 revs with light throttle opening? It feels like either the electrical supply to the pump has been interrupted, or the pump suddenly is sucking up air, or the plugs have stopped sparking.

 

Would the fuel pump go weak intermittently? 

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1 hour ago, DannyHoffman said:

I have always filled with Shell V-Power, but from different garages.

 

I have a fuel pressure tester on order, but the problem feels intermittent. 

 

I generally drive the car very gently so would low fuel pressure cause problems at under 2,000 revs with light throttle opening? It feels like either the electrical supply to the pump has been interrupted, or the pump suddenly is sucking up air, or the plugs have stopped sparking.

 

Would the fuel pump go weak intermittently? 

You know I struggled with part throttle stutter and hesitation for a year before selling my 06 ctt. And I ran though everything. The only thing I found and didnt fix before selling was the injectors didn't spray clean or properly, which I'm 95% was the real issue, no codes, fuel trims were spot on, never broke down because of that issue anyway. 

I had new coil, plugs, pumps, regulator, filter, no vacuum leaks, new Divertors, new mafs, new lambda sensors. You get the idea anything that could have been showing 11 yrs of age was replaced. Oh I also had alternator failure which replaced with new and several new batteries under warranty until the 3 rd one was a good one. So that ruled out electrical issues for me and I replaced the fuel pump fuses and relays, which didn't resolve the issue. 

 

So I guess what I'm saying is test the fuel pressure and flow on both pumps individually and double test them when tank is full too. Being intermittent is a real b * tch to find as you may well test ok many times but one time you catch it slippin. 

Scanner Dan uses his oscilloscope to monitor the amps the pump pulls and you can see from the wave form each segment of the rotor windings chopping and you can identify if the pump is failing but still seems to work.

Most garages tend to swap both pumps if they suspect / diagnose a fuel pump issue (at your expense of course). 

I think your looking at some head scratching ....

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I’d plug the fuses back in and keep driving/refilling it to see what happens before spending more money. It’s possible that your issue is now solved after you changed the purge valve — the purge value is suspect #1 with post-refueling issues.


Sent from my iPad using Tapatalk

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Fuel pressure tester arrived today. I've just over 1/4 tank full, and both pumps tested perfectly. 

 

I'm still running on the left pump only and will probably fill up tomorrow. If it starts playing up I'll test the pressure again immediately.

Edited by DannyHoffman

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Filled up today, still running on the left pump only and drove about 6 miles, it ran perfectly.

 

Then I tested the pressure and the gauge needle, whilst at 4 bar,  was jumping around a bit constantly. I switched to the right pump and the needle was rock solid. I then swapped the relays and the problem stayed with the left pump.

 

Looking more and more like the left pump.

 

 

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2 hours ago, DannyHoffman said:

Filled up today, still running on the left pump only and drove about 6 miles, it ran perfectly.

 

Then I tested the pressure and the gauge needle, whilst at 4 bar,  was jumping around a bit constantly. I switched to the right pump and the needle was rock solid. I then swapped the relays and the problem stayed with the left pump.

 

Looking more and more like the left pump.

 

 

I'm on the edge of my seat.........

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Well guys, a new hip stopped play for a few weeks. Hope you're not still on the edge of your seats.......

 

Fitted the new left pump today, filled up and drove about 15 miles - without a stutter. So it seems like it's finally fixed.

 

Trying to come up with theories to explain the symptoms:

 

1) Assuming my pump was a touch weak, after a night on the trickle charger maybe the voltage was marginally higher, enough to overcome the weakness?

 

2) Again assuming my pump was a touch weak, does a full tank put more load on the pump maybe because the pressure on the regulator return is greater as there is more fuel to move around?

 

Thanks for all your help and have a great holiday!

 

 

 

 

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Happy for you .... but disappointed that my valiant attempt at diagnosis (octane (doh)) fell so flat on its face at the first hurdle :-).

 

I'll get my coat in future!

 

Enjoy your Christmas.

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10 hours ago, wizard said:

Happy for you .... but disappointed that my valiant attempt at diagnosis (octane (doh)) fell so flat on its face at the first hurdle :-).

 

I'll get my coat in future!

 

Enjoy your Christmas.

Wizard its only been 15 miles you could still be on to something with the Octane ......lol.

I've been so wrong many times .......it's all good. 

 

Merry Christmas guys all the best. 

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