Frickin' 460....missfire...

[rusty ol ranger]

97 F250 HD 460

Damn thing is missfireing when hot.

Cold it runs great. I got it warm and started unplugging sensors to no avail. It smells gassy, but have no fuel in the FPR vaccum line. Plugs/wires only have about 4000miles on them. No check engine on.

Its not actually dieing but is running way to rough/nutless to only be missing on one cylinder. It will hit 8 intermittantly. Would a coil cause this? I dont recall ever having a coil cause one to miss, usually they just quit till it cools, same with the TFI.

Im going to go yank a coil from the junkyard to see if it makes a difference before i spend 50 to replace it, just to see if it gets better.

Is there anything else i should look for?

 

[adsm08]

On a distributor system the coil cannot cause a single cylinder misfire. Pretty much has to be cap/wire/plugs or fuel injector(s).

 

[rusty ol ranger]

I know, it seems more like a random cylinder missfire. I say that because ive had single cylinder missfires on many large ford V8s and you didnt really hardly notice, this one shakes the whole truck like theres more then one missing.

 

[adsm08]

Does it improve any if you bring it up off idle with no load?

 

[RonD]

I wouldn't rule out TFI module

Someone here at TRS took a bag if ice in an ice chest with him and then after engine warmed up and started the misfiring he shut it down and put a the bag of ice on the TFI module(you could do same on coil, but only one at a time).
Left it for a few minutes then remove the bag and restarted to see if misfires were gone.
Low tech but free to try

Summer temps bring out the worst in TFI systems

 

[rusty ol ranger]

Does it improve any if you bring it up off idle with no load?

Actually at idle in park it seems fine. As soon as you plunk it i gear it goes to missing. Missing decreases with RPM but still feels pretty weak even at WOT.

Ron, cool idea with the ice, ill try that.

 

[Will]

Seems like low quality fuel to me. How often do you drive it?

 

[rusty ol ranger]

Since rusty #2 has proved to be a good daily, not often. But i had just filled up before the trip and burned 3/4 tank when i started acting up.

It smells gassy as hell. When cold it runs good, but smells gassy, when warm it smells gassy and goes to missin at any hint of a load.

I pulled plug wires, one by one, all made a difference, so its not a single cyl. Shut it off, foot on the floor, crankin for days with no hint of starting, so rules out injectors. Swapped out coil/MAP, still same issue. I nabbed the wrong TFI from the boneyard (mines black, got a grey one), so didnt try that.

No check engine, no fuel in FPR line. Truck smells gassy but has no black smoke out tailpipe and still misses pretty good even at a WOT 35-55 run.

Im pulling my damn hair out here....

 

[Will]

You checked the fuel pressure regulator? Could have a ruptured diaphragm.

 

[bobbywalter]

what is the fuel pressure? what do the plugs look like? what does the vacuum look like?

sounds like dirty injectors if ignition and vacuum leaks have been ruled out. couple hangin open will do that...or its leaning out and you think its rich...

 

[rusty ol ranger]

I gave up on it. After the issues with the ranger and the F250 bein down i took it in. I got so much other shit to fix right now the 200 bucks to get it runnin didnt sound so bad.

I tried fresh fuel. No change. Yanked a couple plugs, its def rich or not getting hot spark. But its not belching smoke. I dont know.