Mercury Mountaineer

1998 Mercury Mountaineer, 78K miles, 5-litre V-8, started misfiring several months ago but did not trip check engine or throw error code. Problem varies from mild shaking/rough idle to severe 'bucking' backfire, etc. Gets worse pulling grade/under load. First garage gave me new plug wires, fuel filter, 1 coil pack, checked compression - Ok, all plugs checked-ok, valve springs checked-ok, timing checked-ok. I've tried several rounds of injector cleaner through the tank. Seemed to help for little while. Second garage put cleaner directly in injectors and checked fuel pressure-ok. Also put in new fuel pump (sounded like it may be going out). No signs of spark problems. Fuel consumption up dramatically (less than 10 mpg). Any help greatly appreciated. Thanks.
April 19, 2007.

Fuel mileage, check 02 and temp sensors. Backfires?
Check camshaft position sensor. Or worn lobes on cam.

Apr 21, 2007.
Hi, I have a same truck, same year, same engine, same mile and same problem. I'm trying to solve month now. Seem to me nobody knows what it is.
I Change the O2 sensors, nothing change. Clean MAF sensor, nothing. Mechanics can't see no code on OBD computer. I'm thinking to just junk it. What happen your problem. Did you solve it. Can you please update it.
Thanx John
Bespecter@msn. Com

Jun 26, 2007.