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Discussion Starter · #1 ·
Hi all,

I have an annoying fault on a 2008 S5

Whilst driving along at a sedate pace in 6th gear, if I press down on the accellerator to accellerate, I get a small hiccup at 4000 rpm and the EPC licht comes on resulting in reduction to 50% power.

I pull over at the earliest opportunity and switch off the engine and immediately restart and the EPC light clears and I can go on without any problems.

The EPC light may not come back on again for a few weeks or it could be days - totally random, but always @ 4000 rpm and only in 5th or 6th gear.

Can anyone shed any light on this as the dealer says they cannot find any fault codes and my warranty is about to run out. :hissyfit:

Regards

Simon
 

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Discussion Starter · #5 ·
It happens on motorways and dual carriageways when the road ahead clears and I can put my foot down.

I don't drive on unmade roads - it is my pride and joy after all !!

I have taken it to an approved Audi dealership in Oxford

On other forums other owners have found split vacuum hoses or faulty air mass meter (sensor) may be the culprit

It is just typical, whenever you take your car into a dealer their apprentice mechanics seem incapable of diagnosing a problem !!!
 

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Discussion Starter · #6 ·
Just done an experiment on a 300 mile drive today

It appears that the EPC light only comes on if when I am in 6th gear driving along steadily at around 3000 rpm and then flooring the accelerator at which point when I reach 4200 rpm there is the charactistic hiccup and the EPC light comes on and power reduced by 50%

If I gradually press the throttle (i.e. not floor it) the EPC light does not come on.

It feels like it could be something to do with the throttle

Any ideas ?

Regards

Simon
 

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Discussion Starter · #9 · (Edited)
Just got back from Audi Dealer and managed to demonstrate the EPC fault to their master technician - they then got a fault code relating to a low pressure fault on the fuel rail.

The DTC code is as follows:

00135 P0087 fuel rail/system pressure too low

Possible causes


- Fuel pressure sensor harness is open or shorted
- Fuel pressure sensor electrical circuit poor connection
- Faulty fuel pump
- Blocked fuel filter
- Fuel line restricted
- Faulty fuel pressure regulator
- Faulty fuel pressure sensor

Now since it ONLY happens when I am on full throttle in 6th gear at 4200 rpm and does not happen in any other gear or when I apply half throttle in 6th gear at 4200 rpm

Which of the above possible faults is most realistic ?

Regards

Simon
 

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Discussion Starter · #10 · (Edited)
EPC fault caused by supermarket petrol - shot spark plugs & damaged HP fuel pumps

I took the car to Revo Tecknik in Daventry and they immediately found that all spark plugs were shot and badly damaged and the retard was running at over 15 degrees. They fitted new spark plugs and drained the fuel tank and refilled with Shell V-Power - they claim the car is running a million times better now.

On further investigation they road tested the car connected to a laptop and subjected the engine to maximum torque in 6th gear - they have found that the one or both high pressure fuel pumps are under performing thereby starving the engine of fuel at maximum load, which subsequently triggers the EPC light.

The problem in their view is caused by prolonged usage of supermarket 95 RON unleaded petrol. Apparently Tesco Momentum 99 RON is even worse due to the crap they put in it. What I didn't know was that you should only use 95 RON as a last resort - No-body told me that !!

In Germany they don't have the crap grade fuel that is sold by UK supermarkets and as a result, Audi are now reducing the compression ratios on all UK spec cars due to the widespread usage of supermarket fuel.

Revo Technik recommend only using Shell V-Power, BP Optimax or Total Excellium.

The car is in with the main dealer on Tuesday and hopefully they will replace the fuel pumps under warranty. Also, the spark plugs were damaged by the excessive retardation caused by low grade fuel - they should last 40,000 miles which probably explains why the master technician at Oxford Audi did not even look at them - the car has only done 22,000 miles so I will be asking for these to be covered under warranty too.

I just goes to show that the calibre of mechanic at Audi Main Dealers is not that great and unless the on-board computer gives them an exact fault code, they are incapable of diagnosing a fault and fixing it - this fault has been happening since August 2010 and Oxford Audi have had my car several times to unsuccessfully diagnose & fix the fault - Revo Technik diagnosed it in 45 minutes !!

Guess where I am getting my car serviced in future !!

Regards

Simon
 

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Discussion Starter · #12 · (Edited)
I am scheduled to go back to Oxford Audi on Wednesday 30th for expensive diagnostics which they wanted to charge me for.

I have a friend at Revo Technik who did the work for free !!

I just don't have any faith in Oxford Audi to find the fault - remember my car has been in and out of their workshops several times since last August and they could not find the fault let alone fix it.

At least now have a solution to what needs doing - replace both fuel pumps under warranty.

Also since having the new plugs fitted and running with Shell V-Power, the car runs loads better and the EPC fault is now coming on in 5th gear much more readily - the HP fuel pumps cannot cope with keeping up the pressure running 8 bar below what they should run at.

Regards

Simon
 
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