I'm having a problem with my '91 460 in my Econoline 350. First described in this thread (item #2), the issue is that under a medium load, the engine will miss or something - I'm not even sure how to describe it. I originally thought it was a torque converter or transmission problem, but after what people on here said (as well as the guy at the transmission shop), I'm now thinking it's an engine problem.

I ran a can of SeaFoam through the gas tank, and it didn't help much, if any. Note this vehicle is a motorhome, so it'll sit for weeks without being used, which may be a contributing factor here. I haven't run the premium gas through the engine (I always forget when I'm looking for gasoline and put in 87 octane).

I replaced the plugs, wires, distributor cap, rotor, PCV valve, and belts last June, and it ran fine until November (about 2000 miles), when this problem started. This weekend, I'm planning to check the cap, rotor, plug wires, and spark plugs to see if I can find anything amiss there - I'm hoping it's something simple: perhaps a plug wire is loose, or a spark plug went bad, something like that.

Am I on the right track for things to check? Is there anything else you can think of that I should check until I get the premium gas in there?

Thanks!

 

Well, I've checked the wires, cap, and rotor, and they all appeared fine. I did find that the PCV valve was out of its spot in the valve cover - I guess just simple resistance is supposed to hold them in place?

(Who knows, maybe the out-of-place PCV valve is the answer to my problem!)

 

when was the carb rebuilt last?? have you checked the timing??

 

A PCV out of the hole will lean the hell out of the engine at light and medium loads. It could very well have been your problem.

 

Okay, time for an update (I don't get to work on this regularly):

--The PCV valve was not the problem, unfortunately.
--I checked all but one of the plugs (you can probably guess which one I skipped). All are new (3,000 miles on them), I put them in myself, all seven that I checked were correctly gapped and showed no irregular signs and appeared to be in decent condition. All plugs are Motorcraft and they are the correct plug according to the sticker on the engine.
--I replaced the coil and the electronic ignition module.
--I replaced the plug wires with a new set, except for one wire that I had to use from the old set - Autolite gave me a wire that was too short (at least, I couldn't figure out where I had one that was too long and shouldn't have). I checked the resistance of the "old" wire (actually, it was new as of the same time as the plugs), and it was 6,000 ohms for a wire just over a foot long. According to Chilton's, the maximum is 7,000 ohms per foot, so I think the wire was okay.

The new wires seemed to help the problem the most...I left this morning working around a misfire, not drastic like it was, but noticeable...but then about 45 minutes out, the misfire went away, and the engine ran absolutely fine until the main seal gave out on the transmission (well, it ran fine after that, too, but it's not like I was going anywhere) about 3 hours later.

So, I'm guessing the problem is/was that I've got two spark plug wires that are parallel to each other and causing the misfire...and they moved or something after driving a while. I dunno. Or maybe the computer is doing something weird.

SwOkcOffRoader - it's fuel injected. I have not checked the timing, but it definitely sounds ignition-related, especially with how the problem cleared itself up today. I'll have to wait and see if it comes back or what.

Thanks for everyone's help with this.

 

Just wanted to update this one last time - it was the torque converter causing the problem. I have NO idea why Cottman Transmission didn't catch that. With a new transmission in place, it runs like a champ now!