I’m experiencing some engine shutter. It seems to happen after a deceleration like going down a hill or around a curve. The engine will shutter a little bit when accelerating again. The problem will occasionally happen during normal driving at cruising speed. Engine light came on a few months ago and we had a coil and plug replaced. Tried cleaning off all 8 plugs since then and the problem didn’t go away. Light came on again yesterday and the local mechanic told us it was another plug. After replacing it the light is off again but the shuttering still remains. We have also replaced the fuel filter and used HEAT in the gas. Any clues what to try next?
Have you considered replacing all 8 plugs? I have never liked the idea of replacing just one bad spark plug. Spark plug wires are also a possibility. Why the HEAT? Do you suspect water in the gas tank? Have you had the fuel pump pressure checked? If the pump is on the low end of it’s range it may be starving the fuel system. I would have it checked.
When it comes to spark plugs they should be replaced in sets and cleaning plugs is pretty much pointless anymore. Piecemealing something like this is ill advised.
In the old days of copper core plugs and carbureted vehicles you could sometimes get away with cleaning plugs. Now it’s a waste of time and a plug that may look fine to the eye may be horribly bad.
You did not state how many miles are on this vehicle and I’m not certain if your vehicles falls under the following or not, but some Fords of this era had an extended warranty for COPs. (coil on plugs)
This means the possibility of free at the dealer.
A stumble on deceleration can often be caused by a poor contact in the secondary ignition; in this case, the end of the COP where it snaps onto the spark plug.