I have a 97 4.6 4x4 with 155k miles that started missing and check engine light came. I had the code read at advanced auto and it was cylinder 4 misfire. The plugs and wires were changed by dealer at 142k so I took a chance and replaced the coil packs and reset the computer. I still have a miss and now don't have a check engine light on. Why would the check engine light not come back on if it's still missing? Should I let the dealer change #4 plug and wire or wait for the check engine light to come back on?
First off,I would not let the dealer do anything just yet....With that being said,I personally would wait until the CEL (check engine light) came back on,and read the code.You might also want to consider purchasing an OBDII reader,and keep it handy. These will work on almost all makes/models,and are pretty much a "must" for todays newer vehicles..............................Now back to the issue...Since the plugs,and wires have been changed recently,I have doubts that its either causing the issue.There is of course the possibility that either the plug on #4 is bad,or the wire.Wires can be damaged during installation,or removal.Plugs can get a bit of "garbage" on them,and misfire.....anythings possible.
Number 4 is the hardest to work on for that year. Plus it sits right below the heater hose and also water from the cowl area can leak right down into #4 hole. I would pull the wire and blow the hole out (as has been mentioned), make sure the plug is tight, put some dielectric grease down inside the boot, and snap it back on. If it still misses and you still get a CEL, misfire #4, I would pull the plug and check to see if the porcelein cracked, which would allow it to arc out. This plug is kind of hard to access and they may have cracked it putting it in. If all this checks out, make sure the connector on the fuel injector is snapped on tight. Many times these are taken off when they do plugs. One of mine came off shortly after I changed plugs, and I have to assume I didn't snap it on tight.
The advice on buying a OBD 11 scanner is a must these days. Mine cost $90.00 bucks, really is slick. Will pinpoint a miss right away. But... if the miss is light enough it will not trip a CEL. Computers have a threshold for a problem that delays tossing a CEL until "it" is convinced there is a true problem. Let us know what you find.
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