Half an engine

Hello all, I was driving my 1999 Ford F150 with the v6 engine when suddenly cylinders 4 5 and 6 started misfiring. Any ideas as to why? Thanks, Patrick

Just some extra info. The truck has 107,000 miles and was running great before. Has new plugs and wires and has been well maintained.

Coil Failure? Fuel injectors bad? Head gasket bad? Cheap wires failed? Improper routing of the wires? intake manifold gasket failed? Too many possibilities.

First thing to check is the ignition wires to the passenger side. maybe they were damaged because of how they were routed around.

“Has new plugs and wires and has been well maintained” Wires??? Doesn’t this engine use COPS, coil-over-plug ignition? Have you washed the engine recently or otherwise flooded the top of the engine with water or anti-freeze?

It has a single coil pack on top of the intake that all the wires go to. As far as water or anti-freeze…no. I am getting spark to the plugs but the timing is totally off on 4 5 and 6. I’m suspecting a bad coil pack but don’t know enough to ascertain if this is so.

I’ve checked the wires and all appears well. I wish to “work” my way into the engine, eliminating the easier and more obvious items first. Can half a coil pack go bad? And still send spark?

The ignition coil is the chief suspect. Sometimes resistance checks on the coil will reveal a defect; and, sometimes, they won’t. You’ll never know unless you follow the instructions in the repair manual, and use a voltmeter (multimeter) to do so. You MIGHT save the $75 for a new coil, if you do the tests.

I was unable to find a schematic online, but even though the coil pack is a single cylinder, I believe it contains two coils. Parts lists allude to the plural “cores” rather than the singular “core” and call it a “coil pack” rather than a “coil”.

It I’m correct, then a bad coil in the coil pack would make sense.

Perhaps someone with a subscription to Mitchels or Alldata could clarify.

This engine uses a wasted spark system, meaning the coil fires two spark plugs at once, with one plug on the negative side of the secondary coil and the other on the positive side of the secondary coil. One spark is wasted every time the coil fires. On these engines, the passenger side of the engine in on the negative side of the coil, and the driver’s side is on the positive side of the coil.

I’m relucant to call the coil pack bad, because it is firing the driver’s side cylinders OK. That’s why I mentioned the other possibilities.

First, check the wires with a ohmmeter. Resistor wires should give you about 1000 ohms per foot. Check the spark plugs for fouling, then time to get serious with the other possibilities.

I suggest that you start with a compression test. You may find that a timing chain has jumped on that side due to guide or tensioner failure.

Another good point. This engine, the SOHC 4.0L, has a timing chain to the passenger side bank of cylinders that is on the backside of the engine. Failure of this chain is not unheard of.

The engine is a 4.2. I don’t know if this makes a difference

My wife will be bringing my meter home with her, I’ll let you know. I live in the middle of the woods in Michigan so without a running vehicle on hand accessing parts and tools that I don’t have here is difficult

UPDATE…Tested the coil and couldn’t get any readings from the secondary’s. Will be buying a new pack in the morning. I’ll let you know if it works.

Alas, twas not meant to be.The coil pack tests out fine. Turns out my meter lacked the sensitivity needed for the job. Sounds like my first marriage. So… back to the drawing board. I’ll continue testing my way in and let you know. If anyone has any new ideas please let me know. Thanks, Trout.

BTW, testing the resistance (primary and secondary) of ignition coils will only detect gross failures. In any event, your problem is not consistent with coil or ignition failure. It is consistent with timing chain failure. How’s that compression test coming along?