2006 f150 5.4 missing on 5 cylinders

I purchased a Ford F-150 truck that had caught on fire. Just give me your best guess. The truck had an aftermarket electric fan added at some point and appears that's what started fire. Fire partially burnt washer wiper tank, battery box, battery and battery wiring to starter.

Fire did melt some of the computer wires in front of battery ( 5 wires) that I spliced and replaced. Computer was heated up but did not melt any wires coming directly out of computer. It looks like no damage was done to engine wire harness. After replacing battery starter wires and fixing the 5 bare wires I started truck. Surprisingly it started although missing bad. By removing injected wires one at a time 5 of the 8 cylinders are not firing. A strong gas smell leads me to think its a non fire or spark issue. The truck is a 2006 4x4 Ford F-150 with 5.4. I tend to guess that if it were computer related it wouldn't fire at all, yes/no ? What else my I be overlooking. Thanks.

Answer: The problem could be computer related. The computer is what controls each injector firing. If a wire is grounded, it would keep that (those) injectors ON all the time. This would result in dumping fuel continuously instead of small shots of fuel every cycle. That much fuel would flood a cylinder, cause it to misfire and smell like raw gas from exhaust.

Remove the spark plugs on those cylinders and check to see if plug is saturated with fuel. If so, you need to trace wiring and look for one or more that are grounded or melted to something metal or even to each other. If wiring ok, then i would suspect the computer is bad.

You could also have those cylinders spark plug not firing. Remove a plug wire from effected cylinder, place it near metal and see if spark is jumping when engine running or cranking. If not, you have an ignition problem.

Comment: With so many cylinders not firing i would think you still have a wiring problem on your Ford. Trace all the wires for the ignition coil of the cylinders that are not firing. With smelling gas, yes, you are right, you are missing spark and the fuel injectors are firing just fine. You should also use an ohm meter to check the continuity of the coil wiring. Sometimes a broken wire is not easy to see and can have broken copper inside the colored wire insulation.

Just for the heck of it, check all of the fuses. This is a very overlooked check that most people don't do and you can easily get screwed trying to diagnose a car without doing this basic check.

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  • There is no spark in those 5 cylinders.Doesn't the computer also control the spark ?swapping the coils didnt change anything.

  • In reply to: richard

    Yes, the computer also controls the spark.