How do you fix a cylinder 5 misfire on a 2000 Ford Taurus?

Answer 1

Several systems can lead to an issue the computer interprets as a Cylinder 5 misfire. In no particular order:

First listen to engine to determine if misfire is audible or can be felt. Listen at exhaust pipe for un-even or hard miss.

Spark Plug (Fouled, Broken insulator, Gap incorrect or otherwise damaged)

Fix: Replace plug, reset code and see if fault returns

Spark Plug Wire (Broken insulation or otherwise damaged allowing spark to ground before plug gap)

Fix: Replace plug wires, reset code and see if fault returns

Note: Plug and wires can be tested to determine if faulty (swap plugs between cylinders, etc...) however these are relatively low cost items and depending on mileage, probably need it anyway.

Fuel Injector (clogged, not pulsing, etc...)

Fix: Swap injectors between 5 and 6 (or 4) and see if fault code "follows" the injector. In other words, if moving injector 5 to 6, after clearing code, does code fault again, except on 6. If moves to 6, then you found your culprit. If fault remains on 5, then proceed onward.

You'll need a noid light for this, however test #5 injector signal to ensure #5 is receiving the injector pulse. If not, then trace the wires looking for breaks, etc...

Fuel Pressure:

Check fuel pressure to test integrity of fuel delivery system (pump, filter, etc...)

Intake Gasket:

Rare cases can be air leak past intake gasket. Check torque on upper intake bolts. Spray WD40 around gasket (front and rear) to see if it makes an audible difference in vehicle engine noise. If not, probably good.

Compression (low or leak down)

Test compression while at TDC on compression stroke. Should be 100 PSI minimum with no more than 15% leak down. Squirt a little oil into cylinder prior to test to eliminate incidental blow by the rings. If all good, then OK. If below 100 PSI, then proceed onward.

Valve Sticking:

If less than 100 PSI or in excess of 15% leak down, then potentials are stuck valve, burnt or cracked valve (intake or exhaust), cracked head or blown head gasket.

Fix: All of these require removal of heads. The job is not that bad on this vehicle, but is time consuming. As a last resort, remove the valve cover and loosen both rocker arms for #5 and perform compression test and leak down again. If still fail, then it is time to remove heads and have them checked.