Hesitating at full throttle ?

[tolsen]

I shall cut a fuel filter open soon to inspect its guts.

[marcjero]

We never thought it could be a fuelling issue. Because filter was quite new and fuel pump looked fine. There were few chances having an issue here... except if a maintenance mistake happened. Had a long drive today, no problem any more.

[tolsen]

I thought you had checked your fuel supply for both flow and pressure. That is usually my first check when fault finding fuel issues on diesel engines.

[marcjero]

Larger filtering area in the inlet side I read. Maybe capability to handle pressure too. Depending on design I guess.

[Thrumbleux]

I'm struggling though, to imagine what exactly makes a filter 'directional'.

[marcjero]

Yes he didn't drive a lot during all this time for obvious reasons.

[Thrumbleux]

The sad story is the previous owner looked for this problem during 18 months. .

Very slightly at odds with info in post#3 ('' a few thousand miles old''). Good it's fixed now though.

[Thrumbleux]

I wonder why we did not think of that!

I did....

As I recall fuel filter has an arrow on it indicating direction of flow..

.....but didn't mention it due to the above.

[marcjero]

Aftermarket filters can be slightly larger or smaller according to the brand.Probably smaller one would fit in both directions easily. The sad story is the previous owner looked for this problem during 18 months. Mercedes even said him the engine was dead. So he bought the car new, spent money at Mercedes for maintenance, they did this stupid mistake and didn't find where the problem was so they suggested to replace an healthy engine. He gave up and sold the car.

[tolsen]

We are all human and screw up from time to time. Most likely fuel filter support cradle was broken. Not uncommon on Smarts serviced by dealer and garages. That’’s why I service all my own vehicles including sewing machines and garden machinery. Got an incredibly high reliability rate. Never any need to check the cars over before MOT except lights and check for broken springs.

[marcjero]

Fuel filter looks exactly the same on both ends. So it can be fitted the wrong way definitely. And it was !

[EmilysDad]

It's supposed to be impossible to fit stop/tail lamp bulbs wrong ..... but people do (I cant think what the fuel filter looks like)

[tolsen]

I can’t see how it is possible to fit fuel filter wrong way as it only goes one way into its support cradle.

[marcjero]

I don't care about the return line. At the filter area one fuel line is coming from the pump and another is going to the injectors rail. We found that the upper fuel line is the one coming from the pump. So the arrow on the filter should be top down. The old filter was fitted bottom up !

[tolsen]

I wonder why we did not think of that! As I recall fuel filter has an arrow on it indicating direction of flow. Why do you need to know which fuel line is which? Impossible to fit filter on return line as no quick connectors.