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Did some reading,

 

1. Most causes is fuel pump, namely the left primary pump for obvious reasons. 

2. Wiring rubbing on chassis and caused the cut out. Bad earth also one person reported. 

3. DME dry solder joints, sent to specialist and they found two dry joints. 

4. Hidden under wet fuse box an Aftermarket immobiliser fitted was causing cut out after 10 seconds. 

 

Can't find any other examples......

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Both pumps passed volume and pressure testing, both nipples on the rail (L&R) are measuring between 62-65psi from prime to shutdown and holding after shutdown. DME still throwing a code for fuel relay and cutting spark to engine within 7ish seconds. New relays are in for both, no difference, code still sets.

 

Both pumps had resistance measured and compared to spare pump from Porsche, matched within 0.01. Right within specs.

 

Amperage draw from first pump was 9.7ish, 2nd was 7.x (adds to 15). Scanner shows no spiking, fuses are not blowing.

 

So if something is wrong with the pumps then its not something he can find. Absolutely nothing is off spec. No broken hoses/lines in the tank. No water or trash in the tank.

 

Yes he's using Porsche scanning equipment.

 

I think its a wiring issue, possibly connection to DME or ground, since absolutely nothing else seems off about the car or has been off for quite some time, but I directed he change the two pumps anyway since its good maintenance, and maybe the computer is seeing something the scanner is not.

 

 

 

 

Edited by Charles Bradley

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OK, so let's explore the possibility that the fuel relay fault code was not due to you pulling the fuse but that it is indicating some actual fault. I'm assuming that when you say it is still throwing the fuel relay code that this is after erasing the fault codes (i.e. the fault code is returning on the next start attempt after be cleared.)

 

Things to check:

  • Connectivity check between pin 37 (GRN/BLU wire) on DME connector and terminal 85 on the right fuel pump relay
  • The same between pin 65 (GRN/RED wire) on DME connector and terminal 85 of left fuel pump relay
  • If this checks out then check connectivity between each of these wires and ground (separately of course) with ignition OFF. Should be infinite.
  • Check connectivity between each of these wires and ground after engine is started (you'll have to splice in). In the brief 10 seconds that the engine runs the resistance should be low (less than 5 ohms probably), indicating that the fuel pump relay is being activated. Alternatively you can measure voltage across these wires and +12 during the same conditions.

If all of this checks out then I would look at the DME. It could be that the fuel pump lines are being driven low correctly (this would activate the fuel pumps) but there is a problem inside the DME with the load detection circuitry on one of the two pins. (The DME switches each of these fuel relay pins from a high impedance state to low (ground) and then a separate part of the circuit measures the current running through each pin to determine if the circuit is behaving as expected. This is reported back to the DME microcontroller. All of this is integral to the DME.) If it gets to this point I can give you some pointers but you will probably need someone comfortable with electronics to perform the checks. (Disclosure: In my former life as an engineer I worked extensively with Bosch Motronics electronic hardware as well as software calibration / algorithms.)

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Nice info Brett. 

 

If it helps the guy with 2 dry solder joints on his DME actually was instructed to replace it at cost 3,000 dollars, he opted for a repair instead. The specialist repairer said they doubted the dry joints was the whole issue. His mechanic then found a partially broken wire between the dme and the pump (sorry no more detail given which wire). Concluding that most likely the wire was the real fault, the dry joints where coincidental and maybe not causing the issue. 

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He said he had searched on his own Porsche mechanics forums for examples of actual DME failure, found none, and his buddy who worked at Brumos said he had never encountered one. I'm hopeful its not a DME, since that will add to an already high replacement cost for the pumps and related.

 

Is there a wiring diagram available for your checks Brett, he may have it but I'd like to see it. Where is the chassis ground located for this circuit?

 

 

 

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Follow the wiring of the left pump, under the rear seat. She goes through the car floor, to the far left corner of the car, there is a connection point which will burn in after time and consequently provides too much resistance. If this is the case replace this section.

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3 hours ago, Charles Bradley said:

He said he had searched on his own Porsche mechanics forums for examples of actual DME failure, found none, and his buddy who worked at Brumos said he had never encountered one. I'm hopeful its not a DME, since that will add to an already high replacement cost for the pumps and related.

 

Is there a wiring diagram available for your checks Brett, he may have it but I'd like to see it. Where is the chassis ground located for this circuit?

 

 

 

No doubt that failure of an unmolested DME is a rare event. It can and does happen though. Has the DME ever been opened for any reason (e.g. chip tuning)? If it came down to it, there is an inexpensive way to replace the DME; just buy a used DME off ebay and copy the immobilizer data from your original DME to the replacement. The only issue is finding someone with the equipment to copy the immobilizer data off of the diagnostic EEPROM.

 

As for the wiring diagram, I don't believe I am allowed to post that here as it is copyrighted material. If you look around you can probably find the full factory manuals for a very reasonable price.

 

@Lewis- Yeah, LOL, I thought the 2 dry solder joints story sounded fishy.

 

 

 

 

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I feel the same way about my cars.

 

Hopefully it's just a wiring issue somewhere. BTW, the ground for the control side of the relay is the ground for the DME (pins 1&2). The other relevant ground point is the ground for the fuel pumps themselves. The manual isn't very good at spelling out exactly where this is. According to the wiring diagram, the point is MB33 and it is located at the "top left of "C" pillar". However, in the "grounds location" section of the manual it says MB33 is "near center of vehicle". I think RFM's post describes where the actual location is.

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its the jet suction(venturi pipe) hoses are broken and brittle.  though your pumps are working its not sucking any fuel from the venturi pipes.  Its the one connected to each of the pumps

Edited by Kikokiko1976

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5 hours ago, Charles Bradley said:

Dealership diagnosed it as DME failure, no spares in Atlanta and I have to wait a week for it from Germany.

Remove and send to specialist for repairs. 400dollars approx. Reprogramming may not be required after repair but you'll have to ask them. 

https://www.bosch-repair-service.com/UK_en/Engine_Control_Unit-ME7_1_1-0261207696-Porsche

I removed mine to check inside for dry joints and failed components, don't be afraid to have a look inside it took me 30 mins. 

Replacement and programming will be bloody expensive. What you got to loose by exploring other fixes first. ? 

Edited by lewisweller

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So the car is running again, the faulty DME was causing the FP#1 to not run, but it won't stay running now because one MAF is bad. So did the MAF kill the DME or the DME failure kill the MAF? Since it happened at the same time and there were zero issues with performance beforehand.

 

So I get to add 1 new MAF to the bill to drive it out of the dealership. I'm getting the 2nd one aftermarket. Recommendations?

 

This sounds very fishy to me.

 

 

 

Edited by Charles Bradley

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1 hour ago, Charles Bradley said:

So the car is running again, the faulty DME was causing the FP#1 to not run, but it won't stay running now because one MAF is bad. So did the MAF kill the DME or the DME failure kill the MAF? Since it happened at the same time and there were zero issues with performance beforehand.

 

So I get to add 1 new MAF to the bill to drive it out of the dealership. I'm getting the 2nd one aftermarket. Recommendations?

 

This sounds very fishy to me.

 

 

 

Sounds like bull**** to me. You just got a new dme for nothing quite possibly. Misdiagnosis and most garages won't fess up. 

Is the bad maf sending an erroronous signal?? Maf isn't required to start car or idle. Unplugged it should start and idle. 

 

Get only Bosch original MAF. Others aftermarket are problematic from experience. The Bosch isn't all that expensive either. Buy online or from Bosch distributor. 

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Oh I'm going to ask them to swap the old DME back in there and prove that it does not run with the old one and a new MAF.

 

Question is, would a MAF failure exhibit the symptoms I was having before with the fueling? Would it make the car run 5-7 seconds and die repeatedly?

 

On my other vehicles, it would not, it would cause stumbling/hesitation and possibly some rough running, but I don't know enough of the Porsche electronics to say for sure.

Edited by Charles Bradley

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10 minutes ago, Charles Bradley said:

Oh I'm going to ask them to swap the old DME back in there and prove that it does not run with the old one and a new MAF.

 

Question is, would a MAF failure exhibit the symptoms I was having before with the fueling? Would it make the car run 5-7 seconds and die repeatedly?

 

On my other vehicles, it would not, it would cause stumbling/hesitation and possibly some rough running, but I don't know enough of the Porsche electronics to say for sure.

I can't say for sure what the result would be from a signal that may be faulty but my educated guess would be it wouldn't make the dme fudged and need complete replacement! Could be doing the garage a disservice here but swapping in the old dme takes just 3 mins and hook up the battery again, then you'll know for sure if you just got sold a new dme for no good reason. 

Thinking back I did run my ctt 06 with one maf disconnected. It will start and will run. The idle would rise ok and then fall slower I remember, idle was alittle high with maf disconnected. 

 

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2 hours ago, Charles Bradley said:

Is this the correct part that I need for the Bosch sensor, and is this a fair price?

 

 

Part should be right but its quiet expensive .

here they are available for half

Edited by ekstroemtj

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3 hours ago, Charles Bradley said:

Oh I'm going to ask them to swap the old DME back in there and prove that it does not run with the old one and a new MAF.

 

Question is, would a MAF failure exhibit the symptoms I was having before with the fueling? Would it make the car run 5-7 seconds and die repeatedly?

 

On my other vehicles, it would not, it would cause stumbling/hesitation and possibly some rough running, but I don't know enough of the Porsche electronics to say for sure.

 

I agree with the others. It sounds like they are parts slinging at your expense instead of performing a proper diagnosis.

 

The Motronics version used in these cars has sophisticated algorithms for detecting faults in components such as the MAF and provides "limp-home" modes that should keep the engine running, albeit not optimally. So to answer your question, a bad MAF would not normally exhibit the symptoms you described at all.

 

It is highly unlikely that a bad MAF would kill a DME or that a bad DME would kill a MAF.

 

You should be able to pull the electrical connectors to both MAFs and the engine should start and run.

 

 

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Car was fine since returning to me, And here we go again today.

 

Had 1/4 tank this morning, no issues and filled up. Few hours later, I am driving through the mountains of NC, tank down to about 1/4, and I have to pass a slower 18 wheeler. 

 

No power to make the pass, had to get back on right, then power surges back. Few miles later, same. On a hunch I pull off to get gas, engine dies as i pull up, but I fill up and she gets me to my destination without a hiccup. That's a fuel pump. Must have sucked one side dry and the other is basically dead. This after both the shop and the Dealer said both sides are good.

 

So after I chew out the Service manager for giving me a huge bill, a pump problem that remains and a car that's still likely to strand me, he says they're paying to fix it right, and I guarantee they will.

 

But I still have to get back to Alabama, can the only pump get me 5-6 hours back home so long as I keep it over 1/4 tank?

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 I don't know how to link to another page but if you do a search for '08 Cayenne S Vapor Lock, it may provide a useful pointer to have checked out i.e. if this occurs when the vehicle is on an incline but not when on the flat with the same amount of fuel in the tank.

Edited by wizard

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11 hours ago, Charles Bradley said:

Car was fine since returning to me, And here we go again today.

 

Had 1/4 tank this morning, no issues and filled up. Few hours later, I am driving through the mountains of NC, tank down to about 1/4, and I have to pass a slower 18 wheeler. 

 

No power to make the pass, had to get back on right, then power surges back. Few miles later, same. On a hunch I pull off to get gas, engine dies as i pull up, but I fill up and she gets me to my destination without a hiccup. That's a fuel pump. Must have sucked one side dry and the other is basically dead. This after both the shop and the Dealer said both sides are good.

 

So after I chew out the Service manager for giving me a huge bill, a pump problem that remains and a car that's still likely to strand me, he says they're paying to fix it right, and I guarantee they will.

 

But I still have to get back to Alabama, can the only pump get me 5-6 hours back home so long as I keep it over 1/4 tank?

This is number 1 Bull****. Search YouTube for that inside joke. 

In your previous post you said about changing both pumps but you didn't go ahead with it I'm assuming? Unfortunate, it's probably the only Fix you needed. It was also the #1 Likely problem I posted in my reply, left fuel pump. Anyhow we are all wise after the fact. 

The pumps can have a tenancy to test ok and still fail, a real b*tch to diagnose and a brave punt to replace even when the testing shows otherwise, so don't beat yourself or the mechanic up too much. The reason behind this is to do with fuel heating, (its also the reason why Porsche doesn't run both pumps all the time and only if required) the pumps get hot and the fuel is quiet warm as well as a result and from external sources also, when the tank level drops the heat increases and an intermittent pump fault can expose itself briefly. When you fill up, more fuel equals cooler temps and the pump might seem ok. 

I would be not be keeping the new DME, swap in your original dme and return new unnecessary dme to the stealership with a big middle finger and let it linger.

After all hope your fixed and back on the road albeit a bit lighter in the wallet.  

 

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