C5 misfire and power loss after Covid, no codes

[sjc204]

C5 2.0 HDI 2006 95000 miles

Hi all,

For various reasons my C5 was left standing through the Covid lockdown, from the end of March to July. No previous engine problems.
It was parked with half a tank of diesel.
Back in use, before I did any long trips, I had a full service including fuel filter. It started and ran fine.
Then, on the motorway, a couple of hesitations.
Then sometimes it wouldn't accelerate, like when you hit the speed limiter (which was not set), but dipping the clutch it would rev freely, just not pull.
I topped up with fresh fuel.
Another time after a long 50 mph section, I tried to accelerate and there was nothing. I could drop a gear and it was willing to keep going, but little power, and at one point I was down to 20mph in second gear to keep rolling. But it got better and seemed to clear. I sailed past a truck that I had previously held up! (sorry mate) Seeming to use a lot of fuel, but the problem is intermittent. Got home fine. Filled up again. Now it sometimes loses power / misfires, once it stalled at idle and I may have heard a clanking sound on restarting.

Local reliable garage, Citroen specialist - it won't do it when he drives it! There are no codes coming up except for one about fuel cap off (it had lost one of the magnets in the cap) He said this could make it misbehave / not regenerate etc. After more trips I had it back to him again, insisted he check the fuel for contamination/water, he says it is fine, plus the filter was recently changed, and no fault codes. He suggests a diesel expert has a look.

The speed limiting thing made me wonder about TPS, but in neutral the accelerator controls it nicely.
The power loss thing made me think about MAF, but would that cause an intermittent fault? - it is sometimes fine - and no codes coming up at all.
I also wondered about condensation in the fuel tank (after sitting for 3 months) but the garage saw nothing.

Puzzled, very grateful for any wisdom out there. Thanks.

[GiveMeABreak]

First thing I suggest you do is use a suitable diesel fuel system cleaner (make sure it is suitable for use with DPF equipped engines) next few times you top the fuel tank up. Leaving it standing without operating the engine periodically may be the cause. There may of been some gunge picked up in the fuel circuit.

Try that for the next few tankfuls and then afterwards, I would suggest using a premium diesel fuel for a while that should contain enhanced additives and fuel improvers. That may help. Unless you are getting any specific fault codes after a diagnostic, I wouldn't be replacing parts.

This may just help clean the fuel system.

[sjc204]

Thanks Marc, I'll give that a try.
Steve

[sjc204]

Hi Marc,

I put in a bottle of Diesel Advanced Fuel System Cleaner and after 200 miles of mixed driving it seems to be fine again, no stutters or anything, mileage back to 42+mpg.
Completely different to when I was running at 20mph in the slow lane with hazard flashers on.

Great advice, many thanks.
Steve

[GiveMeABreak]

No worries pleased it's seems to be running ok again. Just treat her to some premium diesel for the next few fill ups and maybe every third fill up out of 4 after that to make sure she's happy!