Talk Morgan Forums Community The Malvern Arms Missfire on bumpy roads

Hi, I wonder if anyone else has suffered this problem:
My 1999 4/4 Zetec 1850 misfires when driven on a bumpy road. The problem is particularly bad when engine is cold and accelerating away from a standstill, and the driver of a following car reported a puff of black smoke from the exhaust when the fault happens. On the assumption that it is caused by a loose wire, I have pulled and tugged at every exposed wire with the engine running to no avail. I did notice that the anti-tramp rubber bushes were worn and replaced them in case rear axle-tramp was causing load and unload of the engine, but no success.
The car runs perfectly and accelerates strongly on smooth roads.
Any ideas or similar experiences please?

An OBD reader will confirm, but the first place I would look would be the coil pack.

Check fuel filter, it may be the vibration is dislodging crud and reducing the flow of fuel temporarily

Arwyn

try resetting the inertia switch

Budster - thanks I'll have a poke around
Arwyn - the effect is immediate and feels more ignition-related because I feel that a fuel problem would be delayed, but I'll do as you suggest
Smudger - first thing I did was bypass the inertia switch :-(
Thanks fellows, something to be going on
Cheers

You probably have already done this, but make sure all your spark plug wires are tight and none are rubbing or burned.

I had a similar problem in that the 4/4 would run fine, except when one of the wires shorted being too close to something hot (I don't remember what at the moment?) and had its insulation burned away.

Then the car ran lumpy on only 3 cylinders, until the wire was away from what ever it was touching and sparked the 4th cylinder fine.

Cheers,

Thanks Mark, worth a look

A silly idea - but does it happen in low gears and could it be your foot jumping on & off the accellerator pedal?

This is a good suggestion. If the contacts are not clean it could become intermittent when bumped.You could temporarily by-pass the switch with a length of wire and some clips.

I had an intermittent cough from my previous Plus 4 over bumps, and it turned out to be a loose electrical connection on the engine. And it took a long time to track down!

It is surprising how tenuous earth connections can be, it's always worth checking them. My non-starting Guzzi Le Mans eventually turned out to only have an earth via the frayed throttle cable outer where it touched the cylinder head fins.