Hey all I'm workin on my 99 f-150. I replaced all my spark plugs and coils after I got a misfire on cylinder 3 reading on the scanner. The truck was running ok but two weeks later it started to ride rough again I checked the scanner and got the same reading for a misfire on cylinder 3. Any ideas why its giving me the same misfire again? Could my injector cause that missfire? What about the egr valve?

 

Which engine? What plugs and coils were used?

It might be the injector, the COP, the plug, water in the hole, or some other mechanical problem (valve, gasket, etc) related to that cylinder.

Inspect for water or coolant in the hole. Check the COP and injector connectors and harness. Swap #3 Cop and plug to another cylinder to see if the problem moves or stays put. Just because parts are new doesn't necessarily mean they are good - I've learned that lesson the hard way over the years....

It's unlikely to be EGR-related.

 

I have the 5.4 v8. I used aftermarket COP's that I bought on ebay and motorcraft sparkplugs. Is there a way I can test the COP ? If there was coolant in it how long will it take to evaporate?

 

Just do a visual exam of # 3 hole to see if coolant is in there. If it is, it might take forever to evaporate, so clean it out and do what is necessary to prevent it from happening again.

Test the COP by swapping it and its plug to another cylinder that is easiest to reach. Otherwise, you'd need very expensive test equipment to bench-test it.

 

Thanks.I will clean out cylinder 3 and see how that works out. Should I reset the computer by taking the battery off.

 

Yes. Disconnect the negative cable while you're doing your work.

 

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I'm cleaning out cylinder 3 and sure enough it has coolant in it. I don't see signs of leakage on the outside, could it be internal? Like the manifold gasket?

 

Check for a leaking coolant hose above it. A clamp most likely has rusted away and slowly leaking. It was a $1800 mistake for a simple bad clamp.