Engine light came on and said 8th cylinder misfire i changed spark plugs and ignition coil but still showing same problem

Chris Weber

• 131 Answers
• Posted on Oct 05, 2010

SOURCE: My 2001 Ford Windstar has

You still need to replace the plugs and wires regardless of the visual appearance. If it persists then a compression test and fuel injector swap is needed. If it persists then more expensive parts and tests are needed to see if it s internal engine issue or lean running issue or clogged EGR port.

SOURCE: Check engine light comes on. p0171 and p0351 codes found

From Lusty Kid:

I know the economy is bad, but change all of the plugs. Check your PCV Valve hose, 150 rottens them out allowing air to be sucked in, thus all kinds of codes.

Depending on mileage. Dismount the EGR valve and clean passages. If you are really good dismount the throtle position sensor body and clean out passages with Choke Cleaner., dismount where the EGR valves connects to the engine, clean out passages. Also check the hose thats behind this mounting to ensure is not clogged. If clogged clean it out. If not replace it. Is about 1.5 ft. long, connects to the PCV Valve Hose.

When is the last time you change your harness. Can't remember??? Replace it. Good Luck

SOURCE: engine code p0307 cylinder #7 misfire

It could be carbon deposits on valve seats keeping valves from totally closing. You can try getting you a can of motorcraft PM3 top end engine cleaner and get engine up to operating temp then remove one of the small vacuum lines from the intake and draw the contents of the can slowly into the engine.After you have drawn in the contents shut engine off and let it soak for about 45 minutes then crank it back up and let it run until it clears. Now it will smoke like a forrest fire while you are doing this so don't be alarmed,just tell the neighbors you are spraying for mosqitos.This may cure the problem. If not you may be looking at a valve job.
This can be verified with a compression test if this is what is causing it.

ZJ Limited

• 17989 Answers
• Posted on May 05, 2010

SOURCE: diagram of spark plug

Check this for 4.6 or 5.4 sizes engine...

2004 Ford Expedition 4.6 liter V-8 VIN "W"




2004 Ford Expedition 5.4 liter SOHC V-8 VIN "L"



Hope this help (remember comment and rated this).

Testimonial: "thanks for the info. I worked like a charm"

SOURCE: vehicle came in for check

A misfire at idle that smooths out at cruise is ALMOST ALWAYS caused by a vacuum leak. Take a hard look at your fuel trims at idle. If the Bank 2 Long Term Fuel Trim is more than + a couple points higher than the Bank 1 trim, your problem is most likely a vacuum leak. If the Fuel Trims even-out while holding the engine at 2000 RPM for about 20 seconds, then a vacuum leak is DEFINITELY your problem. I would suspect a leaking lower intake gasket leak because an upper plenum leak will normally affect all cylinders.