Hi guys, hope you can help with this...

A few months ago, after a long drive, I was driving up a hill, the engine light came on, and the engine cut out. After a bit of a wait, got it to restarted and coasted it to garage, diagnostics reported misfiring, I was far from home, but got it back with regular stops.

Mechanics replaced all plugs and coils, and the problem went away for another few hundred Ks, problem reappeared, 'Reduced Engine Performance' message, diagnostics said the fuel regulator was the problem, so had that replaced.

Problem reappeared, but less pronounced, no engine light, but a lack of performance and juddering under acceleration.

I've got a tank full of injector cleaner now, but the problem is still happening. I've been told to replace the fuel pump, but no guarantee it'll fix the issue, I'm reluctant to spend that sort of money if it doesn't resolve it...

Any ideas...

Thanks a lot!

There's so many things on the list "to check" it's a bit hard to know where to start.

It does sound to me that the mechanic has been throwing parts at it without taking the time to really diagnose the problem.

Which codes were being set?

They replaced the fuel pressure regulator, did they change the fuel filter? Has the fuel pressure actually been measured?

What about the air filter? Cleaned the MAF? Checked the intake for obstructions? These are basic things that also need to be crossed off the list.

How many kms on the car?

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Same thing happened on my '08 i6... In warm weather (+30 degrees celcius), after a long drive (500kms), engine began misfiring... Tried changing gears but that didn't do it; revs eventually dropped to the point of the engine stalling. Just like you, I was eventually able to restart the engine and coast to the dealership.

The first time around, the dealership could not isolate the problem; rather than getting anything replaced I opted to run some sea foam (fuel cleaner) just like you. However, the summer after, in similar conditions, the same issue occured. I then got the fuel flow sensor replaced - I'm assuming that is what you mean by "fuel regulator"?

My vehicle has been fine since then...

Seeing as you are still experincing issues, I can only hypothesize. I doubt it would be the fuel pump as I feel as though it would have "failed" and be noticeably struggling at all times now seeing as the problem began occuring a few months ago. So, it it's occuring in warm weather, sounds like some sort of sensor getting hot. On the other hand, if the problem becomes more and more pronounced, I would definitely associate that with a mechanical problem such as the fuel pump, or perhaps the fuel filter. But I'm no mechanic...

Other members may be able to help you better than me on this. As one of the few other i6 owners on here I'm keen to see the follow up on this.

Thank your for your responses.

The car has done about 145000ks.

The weather wasn't especially warm, under 20c, so I don't think it's related to that.

It was the 'fuel pressure regulator sensor' that was replaced.

I don't know the codes unfortunately.

I'm beginning to suspect the fuel filter, as looking back over service receipts (from previous owner), it hasn't been done on the last few services...

Will get the fuel filter checked, and see where we go from there...

Thanks again..

Fingers crossed!

Fingers crossed!