What Could This Be?

[Johndouglas]

I had a worrying five minutes when I was out driving this afternoon. I'd just run down a long hill in 3rd gear and as I continued along the road in a line of traffic, I found the running of the engine had become very lumpy. Tickover was OK, it was just that the accelerator had no response at certain spots, so the car felt jerky. After five minutes or so I needed to stop and didn't restart for about 10 minutes. After the restart and on the journey back, all was fine. But 'd like to know what was wrong. I've got the car in Spain for a while.

[paul.h]

In the C5 I had something similar when in about a 1 hour crawling pace queue but once going again and presumably the engine/underbonnet temperature falling it was then ok. The engine fan was cutting in /out. Suspected a fuel fault (maybe temperature/ water contam) but once flushed through as the car got going it cleared and did not happen again.

 

On petrol cars similar has occurred, usually related to fuel mixture includes: a faulty open thermostat and rain suddenly cooling the radiator, a faulty spark plug as the engine heated up, a loose needle valve in a SU carburettor allowing flooding/rich mixture, an Astra which sometimes seemed to turn into a kangaroo - never sorted this but suspected the ignition module, a faulty temperature sensor giving too rich a mixture, badly adjusted manual choke, C3 wear in the accelerator pedal electrics giving uneven acceleration from low revs.

 

One thought, running down hill, would this let any sediment/water in the fuel tank go to the fuel pump ?

Edited November 29, 2012 by paul.h

[Johndouglas]

Thanks for your reply Paul. Before I came away I changed oil & filter, air filter, fuel filter & pollen filter - although I appreciate that none of that would clean any sediment from the tank. You mention the accelerator electrics. It was the position sensor that I first thought about. Maybe if Steve comes along, he will give an opinion. But been out in the car today and all was back to normal.

[coastline taxis]

weve encountered this on a few ocasssions normally going up or down a local hill. when it happens most seem to have a quarter tank or under. we think ( just think mind) thats it down to the quantity of fuel in the tank because when there full they dont do it on the same hill. Years ago a tank had a swirl pot built into it now the intank pumps have them built into the housing. if you ever take one out youl see that to keep the pump lubricated and running then by what weve seen it needs more thatn quarter of a tank or youl start and suck air into the pump which will allow the engine to idle but not rev. then the car goes onto flat ground and fuel restored and power back to normal.. cant prove none of this other than it dosnt happen with a full tank

[Johndouglas]

Thanks for that Steve. The hill I'd travelled down was a steep one. Over a 100 metres of fall down a fairly bendy road. Then back to almost the same height on the next section of road. When I made my stop, it was at the hypermarket where I filled up, but only with 32 litres, so the tank was half-full. Anyway, the fault hasn't happened again, so until it does, I'll go along with your theory.