1984 FJ60 2F misfire cylinders 1&2 (1 Viewer)

[Spears41]

To those more knowledgeable and experienced,

I’ve got 2f with a misfire on cylinders 1&2. I’ve been daily driving the truck since 2019, done a lot of work including a head rebuild in the last 5 years. I was driving a short distance around town last week and noticed the beginnings of a rough idle and less power than usual. Vacuum on it usually runs at 18-19, but now I’m at 16 with sharp and consistent dips to 14. I searched for vacuum leaks, and when I didn’t see anything I went back with a water mister across both sides of the truck, still nothing. So I pulled the wires and confirmed spark, but noticed that pulling the wires from cylinder 1&2 had no effect on the idle. So I replaced the plugs, rotor and dizzy cap just to be sure. No change. Then I made sure my intake manifold going to cylinder 1&2 was nice and night. It wasn’t loose, and no change.

Biggest question is what can cause 2 adjacent cylinders to fail like this at once? I have no indications of a head gasket leak and had it replaced a few years ago. Hasn’t and isn’t overheating. I’m otherwise pretty stuck.

 

[Spears41]

Plugs 4-5-6 from top to bottom in case it helps

 

[Skreddy]

I’d start with a compression check on those 2 cylinders at least. Fluctuating vacuum like that can signal valve issue and/or a head gasket break between those 2 cylinders.

 

[Mark W]

First thing I would have done... like as soon as I saw that two adjacent cylinders had power issues... would be a compression check. Long before I started looking for vacuum leaks. Long Long before i started replacing ignition components. Replacing those when you had already confirmed that you had spark kinda set the stage for not making any difference.

When you say that you have no indications of a head gasket leak, I disagree. A pair of adjacent cylinders loosing power is kinda like head gasket leak indicator #1 in an F series engine.

The distance between cylinder 1-2, 3-4 and 5-6 is pretty narrow. The span between 2-3 and 4-5 is wider. It is not at all uncommon to burn/blow the gasket on the narrower spans.

Check compression before chasing any wild geese up other trees.


Mark...