having an issue on 1998 f150 4.6l, showing misfire fairly consistently on number 4 cylinder, periodically showing multiple misfires on random cylinders, am preparing to siphon last 2-3 gallons from tank to check for water. having read about potential causes i see cam phaser would create sound that would indicate the issue, i hear no unusual sound. was looking at re-manufactured ecms at parts store and i imagine they may be re-programed for various years and vin number ranges, any one have any knowledge on these?

 

Have you done the basics like examining the #4 spark plug? You should have the dual coil packs so spark plug and plug wire would be the first place I'd look. Then injector.

Water in the tank, phaser, and PCM are far down the list of potential causes.

It will help future advice-givers to know how long you've had it, how many miles, and when it last ran correctly for you. Good luck.

 

thanks 180,000 miles 22 years, yes looking at mentioned items but trying to see where someone would put pcm and phaser on the list, plug wires are good, not sure about plugs or coil packs

 

Smoke testing the intake manifold or a conventional intake leak test is where ai would start
Phasers and the rest are about tenth on the list after coils and injector replacement
Spark plugs are first
You say the wires are good, does that mean new, or you ohmed them out or what exactly?
Plugs and wires are first, both coils are second, injector in #4, third
Good luck

 

I would start with pulling that #4 plug wire partially out of the coil terminal and verify the strong spark with the engine running (those coils crap out after years and years)
Followed by the same thing at the plug end, pull it up and out some and listen for the spark jumping
Followed by a noid light test in the #4 injector connector
Followed by testing the injector itself manually, with a fuel pressure gauge on the vehicle and manually firing the injector with an extra connector and some jumper leads
Clear codes and retest a few times along the way
Good luck

 

You can eliminate phasers since you don’t have those on a 2V 4.6.

I know the heater core hose that runs back towards the firewall likes to leak on #4(?) coil. Could have KO’d that coil.

Otherwise, it’s a 26-year old engine if it’s factory installed. Gotta pull out the compression tester if the spark plugs reads that it is warranted. May just comp test all cylinders, anyway.

Fuel, spark, compression…one of those goes sideways, you have misfire.

 

Just a follow-up based on your first thoughts - is there any reason to suspect water in the fuel? Has it been sitting a long time with the gas cap off or something? Or do you have bad gas in your area?

If I thought that I had water in my fuel but the engine still ran I'd run some fuel treatment through the system. They suck up the water so that it can pass through the system.

HEET is a common old brand name. Probably not your problem but it's cheap and might let you focus on other causes.

https://www.autozone.com/fuel-and-en...2oz/136368_0_0

 

thanks for the responses, makes it easier to get focused, we live in an area where humidity is high all year, condensation builds up under the hood as well as on truck body.

 

High humidity climates like that, i would pull a few plug wires out and inspect for water droplets on the boots myself
Get the vehicle to operating temp each time you run it
Those 4.6 plug boots are supposed to seal but also have a vent
Inspect those boots closely

 

thanks, ive gotten in there and discovered at least one cracked wire so will replace all wires as well

 

It's hard to did, with all the wire separators and such but replace the wires one at a time, and or take a few good pictures
Pretty damn easy to get those wires messed up on a 4.6 with dual coils