Ok, truck is in my sig. 180K miles. Plenum is done, cap/rotor/wires replaced at that time, and all appear to be in good condition. Plugs have been changed a couple times since then as well.... (oil fouled) O2 sensor is about a year old. (Denso) Problem I am having is.... when the engine gets up to temp, sometimes sooner..... it will start missing on random cylinders. (every one except 8 it would appear from the codes....) Trouble is, it's intermittent.... I have noticed it more now that the weather has warmed some..... Today, I replaced the crank sensor.... (bwd unit, that's all they had..... they have a delphi they can order if the consensus suggests it....) Along with the miss, I get popping in the exhaust.... step on the gas harder, pops louder, and more often... (I suppose that seems reasonable...) Given the symptoms, I was pretty sure the crank sensor would fix it, well, no.... It DOES seem to run a bit smoother... but, the problem I was going after is still there.

I am open to suggestions.

 

Lotsa views, no clues....

Just for giggles, disconnected the front O2 sensor, and went for a drive. Still the same problem. It DOES idle much smoother than it did before though....

Engine seems to miss a bit while just cruising, put it under a load though, and it pops out the exhaust while missing really bad..... Real curious what's goin' on here.....

 

i had that issue when i first got my truck. switched gas stations, and it fixed it. nothing else i did would solve the problem. went from using which ever gas was cheapest to using mobil(where i worked) and by by misfiring issues.

just a thought to consider...

 

Maybe I should take a fuel sample......

I get gas at two different stations, a BP, and a speedway.... Think I got gas at BP last time.... I am going to need to get gas tomorrow.... maybe I will toss in some 89 from a good station.

 

just for shlts and giggles, throw in some dry gas, see if that helps. could be part of the problem. BP had a problem with their gas a while back. it was gelling up in peoples tanks and lines, destroying the engine in the process.

 

Low fuel psi from injector problems (dirty or pcm/electrical problem), weak pump, etc. would cause lean condition, random misfire, afterfire and the like. Fuel pressure test to confirm.

If your plugs are still getting fouled I suppose the plenum fix may have come unfixed, causing vacuum leak and your symptoms. Or other intake leak... Intake vacuum test to confirm, I think spec is like 14-16in. hg? I might have just made that up, I dont remember lol

Couldn't hurt to check compression either.

That's all I got.

 

Sticky valves, flat cam, bad hyld lifters, worn out dizzy bearings, worn out intermediate shaft cam to oil pump to dizzy, idk just ideas.

 

I'll take stab in the dark...although rare, a failing camshaft positioning sensor might produce intermittent random misfires. I've had plug wires from O'R***lys that only lasted a year before they looked like glow worms,but didn't have your symptoms. How old is the coil? I put a new coil on last spring that caused really bad part throttle predetonation. The vacuum test for blown plenum w
ill only find large leaks. I thought maybe it was a trick thread at first.

 

have you confermed the problem to be either spark or fuel sounds like its not powering the injectors like chafed wiring?

 

It pops when missing, so, might be fuel related. (insufficient mixture to burn?) But, I should think if it were a pressure problem, and I was running lean enough to miss, it would set an O2 code.... but, test is easy enough, probably shoulda done it while I was at the shop today..... Nah, that woulda been too easy.

Check wires, wires are good, plenum is still nice and squeaky clean. My valve seals are pretty much shot, and I am not sure I really want to know what my compression numbers are...... makin' me wish I had bought that motor for 250 from the member down in Jasper when I had the chance...... Damn.

I don't think it's anything 'really' damaged.... as there are times when the engine runs just fine. Smooth as glass. (especially when it is colder out.) This has been a problem in the past, but, it has gotten MUCH more prevalent. Was VERY intermittent before, not it is getting pretty consistent... Makes me wish I had an O-scope to hook it to as well.....

Do a bit more poking and prodding, and see what I can come up with. But, not tonight.