Strange intermittent issue

[MarkyD1977]

I have a problem with my Peugeot 5008 1.6hdi. It's a 2013 model with a DV6 engine. Well looked after and regularly serviced.

It developed a problem whereby it would turn over but not start or would sometimes start after manual priming or sometimes if it was left for a few minutes, no rhyme or reason.

It had a small, unrelated oil leak so I changed the rocker cover gasket as a precaution and at the same time, changed the fuel filter and housing as the o ring on the drain valve was a bit perished and it occurred to me that it might be drawing air into the filter. Anyway, the filter is full of diesel and there are no fuel leaks that I can see.

After replacing these bits the car wouldn't even turn over, just a single brief lurch of the engine then dead, like an immobiliser type symptom. Battery fine and no faults on Pug computer except for occasional "inconsistency between crank shaft sensor and cam shaft sensor"...perhaps I'd disturbed something?

Changed both sensors, no improvement.

With a direct 12v feed to the starter motor it would turn and turn and eventually fire, occasionally it would work with the key too.

So got it going and took to garage, Citroën garage actually, not Peugeot as they couldn't fit it in....but potato potarto.

They diagnosed BSM unit. I had it changed.

Now it starts on maybe every second or third try. Sometimes first try...

Anyway, they're stumped. They suggested change timing belt.... Was done about 6 months ago. I had it checked by a trusted mate who inspected it, the holes all line up and it runs fine, not lumpy or clattery and it's been running fine....

So I've lived a couple of weeks with it starting 2nd go but now the fuel supply issue is back, 2 or 3 goes to crank over then lots of threat to start, prime it, wait a few minutes, try again and eventually it will fire.

I'm not a mechanic but I'm not stupid. My mate isn't a Peugeot fitter but he is a diesel engineer by trade and is also stumped.

I can't see that it's timing belt related. One problem feels like a fuel supply issue, the other an electronic issue.

I can't understand why a new BSM unit would sort of half fix the problem, surely it would cure it or not, and I can't see that the issues are related.

Am I or a garage missing something obvious?

Anyone with similar experience, I'd be extremely grateful for a response, even if just to point a garage in the right direction.

[white exec]

Sounds like air in the fuel.