Question about Ford Thunderbird
#7 cylinder only misfiring. Have changed the plugs, wires and the coil packs. Also changed the #7 injector. Any ideas?
Misfire problems have 3 possible reasons: gas, spark, or a mechanical problem. You have tried to address the gas and ignition problem. If you now do have spark on #7, and the injector is putting gas into the cylinder-you should make sure of this before proceeding-then you may have a valve or cam lobe problem in that cylinder, or even a head gasket leak. A leak-down test will confirm that and indicate the problem. Alternatively, you could have an engine compression test done. Low compression in #7 will confirm the problem, but won't give you any indication of what or which valve may be not sealing.
Posted on Jul 30, 2013
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Posted on Jan 02, 2017
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.
Posted on Feb 05, 2009
SOURCE: 2003 Chevy Venture misfiring
The injector is a good possibility, although you should check for spark in the wire first, as the electrical is the weakest link in the system. Put a spare plug in the end of the wire with the plug resting on metal, then have someone crank the van to see if you have spark that far, test and replace spark plug, (do not get shocked!) then look into a new injector or a good cleaning.
Posted on Jul 17, 2009
check the injectors with a noid light you may find a bad one. if not check the compression.
Posted on Aug 03, 2012
SOURCE: #7 misfire
Had same problem with 1999 ford ranger i worked on and it was a cracked valve. Might want to preform a compression test on that cylinder. hope this helps and if so Please leave rating on this post and good luck.
Posted on Aug 15, 2012
SOURCE: 1997 ford f150 cyliner 7 misfire
After replacing the coil, plug and wire. The injector is working properly so I would say that you have a burnt exhaust valve. Get a cylinder leak down test or compression test to confirm this at a reputable mechanic.
Posted on Mar 04, 2013
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