06 Cayenne S fueling issue

[Charles Bradley]

Own an 06 Cayenne S since it crossed 98K. Its now at 170K. Has been serviced routinely by the stealership, except for a few things I've figured out myself. This one has me and my mechanic stumped however.

Driving along at 50mph, I had to pass a slower car on the right. I pull out, give it gas, and engine just freaks out. Revs go up, seems to act like it was out of gear or the TC just crapped out immediately. Had just enough power to make the pass. I got a quarter mile further and limped off the road, put it in P, and the engine died.

Car will fire, run 10 seconds, and die. This suggested to me that it was a fuel pump issue. Gauges all read fine, no CEL at the time. I had a small scanner with me.

Since I was 2 hours from home, I researched on my phone and saw that a fuel pump failure happens on these cars and you could pull the fuses and trick it into running on the secondary pump. I tried this, and the same behavior resulted. 10 seconds and dead.

Had it towed to a local mechanic I trust, an import guy who works on a lot of Germans. He looked at the pumps, both put out 65psi. He read the Ohms and compared to a new spare he had handy, checks out fine. He tried replacing relays, same behavior.

Basically you have fuel to start the motor, fuel pressure holds, and then the computer is killing the engine. So we're at a wiring issue now. What would cause the engine computer to let the engine fire and cut it off within 10 seconds? Its not seeing some reading from a sensor or some pin issue. He did look at the crankshaft position and that was correct, and the computer is seeing it correctly.

Has anyone run into this bug before?  

 

As of today, he said the codes it was showing were 907 (load mgmt.), a 1049, a Fuel pump no signal (set when I pulled the fuse we think), and a Check Brake light error (one of my 3rd bulbs is out).

Edited August 17, 2017 by Charles Bradley

[wizard]

Have you physically checked that you have enough fuel in the tank?

[Charles Bradley]

Tank was completely filled up.

[Loren]

I would get both fuel pump outputs tested.

[Charles Bradley]

Output as in the pressure? Both put out 65psi

[JFP in PA]

3 minutes ago, Charles Bradley said:

Output as in the pressure? Both put out 65psi

 

I think he is referring to fuel volume delivery over time.

[Loren]

Sorry yes, fuel volume.

[Charles Bradley]

If they are maintaining 65psi from engine prime until engine shutdown, then how is that not telling me that they are putting out adequate volume

[JFP in PA]

1 hour ago, Charles Bradley said:

If they are maintaining 65psi from engine prime until engine shutdown, then how is that not telling me that they are putting out adequate volume

 

Pressure and volume are not necessarily related, you can have sufficient pressure, but not sufficient volume delivery.  There are separate tests for each.

[Brett968]

The load management error is indicating that non-essential electrical circuits are being shut down because proper battery voltage cannot be maintained. In other words, your battery is likely on the fritz. This isn't an engine ECU fault code, it's coming from the central electronics module (I think Porsche might refer to it as 'Electrical System' module). Anyways, bad battery is a possibility. It kinda sounds like a problem where the immobilizer is activating somehow and shutting off the engine. Perhaps an ECU is resetting due to a brown out. I could see this causing some really weird behavior.

 

Are you sure that your mechanic is interrogating the engine ECU with a Porsche specific diagnostic tester and not a generic OBDII scanner? I find it hard to believe that there are no engine DTCs being stored.

[Charles Bradley]

He's a Porsche owner and works on several, I know he has the Porsche testers.

 

I replaced the battery under the seat myself a couple years ago, voltage has been perfect otherwise.

 

Edited August 18, 2017 by Charles Bradley

[Brett968]

Interesting. Since the 0907 electrical load management DTC is the only potentially relevant fault code being reported, I would be inclined to figure that one out--even if it is not entirely obvious how this would cause the problem you are seeing. It's also possible that the battery is just a bit run down from all the cranking and this is triggering the DTC. If that is case then the DTC has no relevance to your problem.

 

Does your car have the optional secondary battery in the trunk?

 

As for the fuel pumps, I agree with you. If you are seeing 65psi, even with the engine not running at all, then you should have adequate volumetric flow for the engine to idle. If the engine was cutting out during partial or full load then you might want to measure fuel volumetric flow. It sounds like your fuel pumps are fine.

 

I just had another thought. By chance, did this problem begin shortly after getting gas? Water in the tank or bad gas maybe?

Edited August 18, 2017 by Brett968

[lewisweller]

907 DTC is a red herring I seriously doubt it bares any relevance to this engine cutting out issue. It may be an early battery or frequent short journey warning issue. 

For me I would check: 

1. Battery voltage with engine off, less than 12.4 volts is not ideal. Engine running 13.7-14vokts  is perfect. Unlikely cause but best to check anyway first. 

2. Bad fuel possible? Silicon, water,  containment in the tankers is not unheard of. 

3. The fuel filter is blocked? You will see adequate pressure but the flow test will reveal the flow is not correct, 800ml in 15 seconds is the spec. 

4. The regulator works when pump is primed bit maybe it's failing as the engine runs? You would need a test kit that can measure pressure whilst the engine is running and also at different loads and rpm, tape gauge to windscreen and go for a drive. 

5. If none of the above highlight anything tangible or sensible I would be getting inside the tank and looking for a pipe split or broken! And at 170k replace both pumps, filter and regulator regardless. They don't last forever. 

 

If you switched between pumps it's unlikely that both pump failed simultaneously. 

If crank sensor or coolant sensor etc the car won't start. And no codes is a big clue to something less than obvious like a pipe split in the tank for example. 

 

 

[Charles Bradley]

Well we can't drive the car, the engine won't stay running more than 10 seconds before the computer cuts the spark and kills it. He's been pushing it in and out of his shop as he has had other cars prescheduled for service dropoffs.

 

It will fire and run 10 seconds ad infinitum, I tried it at least 15 times as I was trying to figure out on the side of the road what it was doing. He has seen the same. It always fired right up immediately, and didn't drag any as I kept going, but I did stop just to ensure no further wear to the battery.

 

I do not know if mine has a battery in the trunk, I thought they all did, but I know I have not replaced that battery.

 

I did have the problem after getting gas, but 1.5 hours after getting gas. I had filled the tank up before heading out of town. No sputtering or other symptoms of water/trash in gas.

[Brett968]

Highly unlikely it is a fuel regulator / filter / or inadequate fuel issue as it makes pressure unloaded and very little flow is required for engine idling (he says it only idles for 10 seconds and maintains pressure throughout). A split hose in the tank is feasible, causing some air to be pulled in, but he indicated his tank was full so the break would have to be near the top of the tank to cause an issue.

 

My money is on bad gas (e.g. water contamination).

[Brett968]

(my last post was a cross-post with Charles)

 

Charles, you said you had the problem 1.5 hours after getting gas. Was that 1.5 hours of driving time? I'm confused because you said the tank was completely full but if you drove on it for 1.5 hours after filling up then surely it couldn't be.

Edited August 18, 2017 by Brett968

[Charles Bradley]

The tank is about 3/4 full actually, I had filled up before getting on the road. As I recall it was a little above 3/4 when I was on the side of the road.

Edited August 18, 2017 by Charles Bradley

[Brett968]

OK, that totally changes things. Much less likely to be a problem with fuel quality if you drove on it for 1.5 hours without issue. I like Lewis's idea of looking at the plumbing inside the tank.You could be pulling in air with the fuel.

 

BTW, as I understand it the secondary battery was standard up to MY2004 and then optional from that point forwards.

[lewisweller]

06 is optional battery in boot and most do not have one. That said the boot battery is only for stating the engine and I'm struggling to hypothesise how that would chase this issue. 

 

As a sanity check can you do one thing, pull out fuse number 14 and start the car. What happens?

You mentioned pulling out fuel pump relay but was it the right one? 

Fuse 14 is the left side primary pump, when you start the car it runs both pumps for about 5-10 seconds then if fuel level is above say 1/4 tank it only runs the primary. So this is consistent with your symptoms. 

If the car runs with the fuse 14 removed then bingo, it the primary pump, or its piping or its electrical feed somewhere. 

[Charles Bradley]

As stated in the first post, I tried the fuses. Same behavior.

 

This is actually the thread I was using as reference for the diagrams as to which to pull.

 

 

Edited August 18, 2017 by Charles Bradley

[Brett968]

That thread doesn't say anything about which fuses to pull. You said you pulled fuses but are you sure you pulled the correct ones? Left fuel pump is fuse 14 in water box and right is 13. Both are 15A.

 

Are you 100% certain that the fuel pressure is still being maintained when the engine dies after 10 secs?

[Charles Bradley]

It identifies relays 19 and 1/6, as well as Fuse 14, I found 13 was the other one by pulling off other diagrams.

 

He told me both pumps hold 65psi throughout

[lewisweller]

9 minutes ago, Charles Bradley said:

It identifies relays 19 and 1/6, as well as Fuse 14, I found 13 was the other one by pulling off other diagrams.

 

He told me both pumps hold 65psi throughout

Flow volume test to rule out fuel issue and move on with the search. 

 

[Brett968]

Charles,

 

OK, but did you follow the procedure that Lewis stated exactly? (only pulling fuse 14)

 

I'm still not at all convinced that the diagnostic data is correct. After the engine dies what does the fuel pressure gauge read? When he checked each pump did he relieve the system pressure between the tests?

[Charles Bradley]

2 minutes ago, Brett968 said:

 

OK, but did you follow the procedure that Lewis stated exactly? (only pulling fuse 14

 

 

YES

I do not know if he relieved pressure, all I know is that he said it read 65 psi during prime, run, and after failure.