Possible mis-fire

[johnsiddle]

I have recently aquired what I believe is a mis-fire.

Starting and acceleration are all fine but when the car gets into top/overdrive and hits 50 and with the throttle open just enough to keep the speed constant I find the car feels as though I am running over a very bumpy road.

If I accelerate the bumping along fades, if it were a petrol car I would immediately change the spark plugs.

Apart from this the car is running perfectly I am running homemade B100 with a twin tank system (same fault when running Dino) Fuel heater in the bio tank, a heater wrapped around the fuel filter and a stainless steel coax type heater just before the pump.

Any idea's guys, do you think it could be the injectors????

Regards John

[davemaxx]

i had a car that did simular to this, when the engin was warmed up and i was calling for any kind of power, it responded as if it had a miss-fire or choked kind of thing, it turned out that the egr valve was jamed open, had to take it off and make a blank plate with a pop tin and then refit it...

just blocking off the vac pipe wont cure it if the valves jamed open.

you can connect a tube to the little pipe where the vac tube fits and gently blow or suck and see if the valve opens and closes,,,

[BUSHWHACKER]

Could be the throttle position sensor.
The contact tracks in them burn out over time causing a 'dead' spot at the usual cruising position of the throttle, and the fuel delivery intermittantly cuts out causing the jerking.

[johnsiddle]

Thanks Guy's will check both today, although I ball bearinged the vac pipe to the EGR over a year ago.
John

[johnsiddle]

Found the reason for the mis-fire, rather it found me. The car stopped altogether.

Pump out again and found it really gummed up including the Spill Valve.
A good strip down and clean fixed that.
I decided to change the Bio filter and found that the filter had got blocked during the cold weather with dregs of glycerol and the fuel pump had sucked the paper roll down into the water trap area so breaking the paper roll and a load of crap then flooded into the pump.

I have now fitted a cartridge filter at the back where the fuel leaves the bio tank, its easier to change and I figure if this one fails the one up near the engine will catch the crap.
Regards John