2002 f150 misfire in Cyl 1 AFTER replacing all the usual suspects

2002 5.4 L f150. Getting a misfire in a cyl. Code says Cyl 1. Run truck and disconnect/reconnect coil connectors 1 at a time just to make sure it’s right. It is. It’s due for new plugs anyway, so I replace all plugs. still misfiring. Replace all coils because I have extras laying around, still misfire. so I replace the injector for cyl 1 because I don’t have extras and injectors are expensive. Cyl 1 still misfiring. I’m out of ideas, as this is as far as my knowledge goes on the matter. What, other than coils, plugs and injector, could cause a misfire?

A burned valve could do it. I’d do a compression test and hook up a vacuum gauge.


Low compression, valves, injector wiring. Using a mechanics stethoscope or a screwdriver to your ear can you hear the injector firing?

Do a compression test. If #1 is lower than the others, squirt some 30 wt oil in the cylinder and repeat the compression test. If the compression come up to normal, it is the rings. If not look at the valves.

Bad cam lobe… broken rocker arm…

With the plugs out a compression check should always be run. If a cylinder is dropping compression then the test will save a lot of money and the aggravation of beating your head on a wall.

As mentioned, a vacuum gauge is a cheap, fast way of determining whether or not there’s a compression issue. A compression test could be used as a follow-up test.

You need to make sure you have good spark at #1 . . . just because you replaced the coil doesn’t mean much

You use this to determine good spark . Should be an extremely bright blue spark. no ifs ands or buts


You also need to make sure the injector(s) are getting pulsed correctly. This is how you do it


Now if you’ve got no spark on #1 or the injector isn’t being pulsed, you need to take a good look at the wiring. It wouldn’t surprise me if the wiring is brittle, given the age of the truck.

And use the vacuum gauge and compression tester, as the other guys have already mentioned

none of those tools are very expensive. Probably less to buy the tools and use them, versus paying several hours diagnostic charges at a decent shop

Please don’t get offended at the next question . . .

You didn’t drop any of the spark plugs before installing them?

Or you didn’t happen to tap them with a tool before installing them?

It might seem like nothing, but the porcelain can get damaged so minutely, that you didn’t hear the crack, and can’t see it, either . . .

I’m assuming the new plugs were pre-gapped. None of them had an obvious problem, such as a gap a mile wide?

the spark plug . . . you were able to thread it all the way in?

it never blew out, it’s never had a time-sert or heli-coil or something along those lines installed?

I’m asking, because sometimes if a plug blows out and a guy does a lousy job installing an insert, it’s possible the plug isn’t properly located, cross-threaded, not in all the way and so forth

Please elaborate . . .

New coils of good quality?

Old coils with a ton of miles?

The plugs were reputable quality?

Okay. I’m back. My coils are from carparts.com they are new, I bought an 8 pack instead of just 1 because coils in fords go bad fairly regularly. But i switched it with another new one just to be sure. I also re- replaced the new spark plug with another new one, just to be sure. I ordered the noid lights and spark tester from this post and found that the fuel injector IS being pulsed properly, and the coil is happily sparking away as well. However, after closing it all up, it’s still misfiring… oh and yes the plugs are gapped correctly, and as far as I know it’s never had a blow out

Take off the valve cover and inspect the cam lobes and followers and bits.

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Is this the three valve engine? Not sure how they work because I left the cylinder head business but I do know that with the two and four valve heads, the rocker is a bit tenuous. It is suspended at one end by the lifter and the other by the valve stem. The cam pushes down on the middle.

I’d check those rockers first, then do a leak down test of the rockers look good.

Would it not have been easier, faster, and much cheaper to verify compression on at least the No. 1 cylinder before spending more money? Which is kind of what I mumbled back on July 9.

If compression is dropping then a trainload of spare parts will not fix anything.

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Nope . . . that was a few years later

A 2002 F-150 is going to have a 2-valve Triton