Loss of power due to misfiring but only under heavy load conditions, typically on motorways?
Here is the situation:

On the flat, the car sails beautifully along the motorway and then there's an uphill section - as usual with a 2CV, your right foot goes down to the metal and stays there until its time to slickly change down into third - only today, things work out different!
After half a mile or so, there's suddenly a terrible crackling in the exhaust and a dreadful sinking feeling in your stomach as the power ebbs away. You dive downward through the gears before coming to an ignominious halt on the hard shoulder but find that the engine doesn't actually die completely. So you wait for a few seconds gingerly revving the engine and then set off to find all is now apparently well. You carefully rejoin the traffic and accelerate normally and then, just when you are fervently hoping you imagined it all, the whole scenario repeats. Much frustration but not a total conk-out and you eventually reach your destination, perhaps after several such episodes. Around town, the problem doesn't even appear and the engine ticks over as normal.
Like me, having made it back to the garage, you could then spend many happy hours checking valve clearances, manifold tightness, exchanging ignition coils, and blowing out and retuning the carburettor. But your test-drive reveals that it's all been to no avail and your car still has the problem.
But before spending hours doing all that stuff, ask yourself - how old is the fuel pump? If you don't know, or the answer is 'getting on a bit' (say more than a decade, mine was 18!) try changing it (don't forget the spacer!). You will more than likely find that that was your problem - a weak fuel pump!

This is the 2CV's equivalent of a heart attack. As the fuel pump ages, the diaphragm material stiffens and resists the spring which should cause it to drive fuel up to the carburettor with more-or-less constant pressure. The result is a gradual drop in feed pressure until one day it reaches a point where, under heavy load, the engine's demand for fuel exceeds the pumps ability to supply it. Hence, fuel starvation and everything comes to a spluttering halt. Your fuel pump has reached the end of the road.
When replacing the fuel pump on the crankcase, don't forget the spacer.
Technical pages
Close this window