1998 Ford F-150 • V8 2WD Automatic • 200,000 miles

My check engine light was on and my diagnostic tool said misfire so I changed the coil packs (both) and the plugs and wires. Now the light is out but its backfireing and hesitating at takeoff. During driving there is an extreme loss of power. What should I try now?
May 10, 2011.

Engine running rough or misfiring can be cause by the following:

1.Defective spark plugs
2.Inadequate spark/coil,defective spark plug wire.
3.Lack of compression
4.False air leakage.
5.Faulty fuel injectors.
6.Insufficient fuel pressure.
7.Contaminated fuel.
8.EGR valve that is leaking.
9.Oxygen sensors.
10.Throttle position sensor.
11.Manifold absolute pressure sensor
12.Mass Airflow Sensor
13.Idle air control valve

Note: If it doesn't apply disregard it-

May 10, 2011.
Its not misfireing as much as its loss of power. It was misfiring but now its loosing power and hesitating.

May 10, 2011.
Misfiring, backfires, and loss of power tell me there's a timing issue. Check the timing. It should be between 8-10 degrees BTDC. It's a 98 with over 200K miles, so when was the last time the timing chain was changed? While checking the timing, watch for timing stability, as well as proper setting. If the timing bounces around, change the timing set. For best results over the long run, specify a double roller chain and gear set.

Also, perform vacuum leak checks using a can of carburetor cleaner. Spray all vacuum lines and fittings, as well as the intake manifold mating areas. Also spray the air intake after any air measuring sensors, to see if maybe un-metered air is being introduced into the combustion system.

Find a retailer that loans tools and check the fuel pressure at the regulator and after the regulator if you can. Decreased fuel pump output can give a good idle, but starve the engine of fuel at speeds and under load.

Loss of power could also be related to a plugged catalytic. If you can, disconnect it temporarily and see if that makes any difference in the power output.

Jun 15, 2011.