Misfire symptoms after filling petrol tank.

[Xanthe]

Vehicle: Renault Laguna 1.6 16v
This symptom occurs when the petrol tank is approximately half full or immediately after filling with petrol. The idle speed drops to roughly 600rpm and has the symptoms of a misfire. At no time has the engine ever stalled. The problem clears itself after a few seconds and does not reappear until the next start up. I initially suspected, dampness around the coils or a similar ignition fault (Coil on Plug type ignition), but now wonder if a partial restriction in the fuel supply (dirty filter) or blockage in the fuel tank breather system. Does anyone have any ideas!!

 

[patprimmer]

A dirty or clogged filter will be most problematic at high fuel usage conditions. It will not be effected by fuel level.

A blocked breather will also be most problematic at high fuel consumption conditions, but a full tank will make it's effect felt sooner as the partial vacuum will build quicker.

The level on the fuel gauge could only effect the engines running if a wiring mismatch has occurred and the fuel gauge signal is being read as an engine management sensor. That seems highly unlikely.

If it is only on cold start, it is most likely something to do with cold start enrichment.

If the fuel pump is above fuel level, the time taken for the pump to prime might have an impact.

Hydraulic tappets may take some time to take up clearance and just might have a very minor effect on idle speed.

Leaky injectors or a dodgy fuel pressure regulator might contribute to poor idle control.



Regards

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[Rob45]

If this problem only occurs after filling the fuel tank, I'd suspect a problem with the evaporative emissions system, if so equipped.

 

[TheBlacksmith]

Second vote for evaporative emmissions system. It may be incorrectly dumping all the collected vapors immediately on startup.

 

[mattsooty]

Quite possibly a problem with the purge valve being stuck open. However you should be getting a MIL illumination for that, pretty much for certain...unless the bulbs been taken out!

Anyway, try hose clamping the purge line off for a few hundred miles - the worst that will happen will be a possible whiff of fuel from the canister - Best will be that you find that the problem has disappeared....

MS