It used to be intermittent, but now it's pretty constant. It idles fine, but taking off it misfires. It goes away if you're cruising or accelerating at light throttle (10%), but happens at medium+ throttle from about 2k RPM to 4k RPM (guessing, I don't have a tach). Past 4k it runs fine, which is why I'm confused. Plugs, wires, cap, and rotor all look fine and a weak spark wouldn't preform better at higher RPM anyway. Same with low fuel pressure. I shook the AFM and it didn't change, so I don't think it's the problem either. Not a clogged cat because there is no cat. Not sure what else to look at

 

First check your timing (or at least make sure the adjustment bolt is snug and distributor didn't rotate) to make sure the adjustment bolt wasn't loose and that got out of whack. Could be a failing ignition coil. If you've ruled out the plugs and wires, then go up stream and test the ignition coil and ignitor. Do you suspect it's running rich when it's missing? Can you see black smoke pouring out of the exhaust when this happens? Seems to make sense that the truck would run the richest in the 2k-4k range and could be overwhelming a weak/failing ignition.

 

I'll test the coil and check the timing. Also could be the O2 sensor. No codes though. It doesn't make black smoke. It's got a turn down tip so if I park in a spot and rev it for a few minutes there will be a sooty area where the tip was aimed so perhaps a little rich, but no more than it has been. Haven't driven it enough like this to say how mileage is, and I don't intend to

*edit* the coil was out of spec so I'll go ahead and replace it. Even if it doesn't cure the misfire it won't make it worse. I'm probably gonna spend the extra $6 for the Accel Super Stock coil over the BWD. My only question there is the stock coil spec is .5-.7 ohms primary, and 11k-16k ohms secondary. The Accel Super Stock is 1.2k primary and 8.9k secondary. Will that make a difference?

 

I wouldn't suspect the O2 causing what sounds like an ignition problem. Doesn't sound like you are experiencing an extremely rich condition either, so I'm more suspicious of the ignition components at this point.

Certainly can't rule out the fuel pump either. It seems like whenever the system (fuel and fire) are called upon in heavier doses that some component is falling short.

 

Plug wires? Broken distributor cap?

 

Changed the coil out and it feels spunkier, but after about 15 minutes the misfire came back, same as before. I'll play with it some more tomorrow

 

Bizarre... Did you change the wire out that runs from the coil to the distributor (can't recall the technical term)?

Just an idea- if you have a timing gun and you say when you rev it up it misses, try hooking the light to multiple plug wires (and even the primary wire that runs to the coil pack) to see if you can see a change in light flashes when the missing occurs. Might help you narrow down the miss to a cylinder or even narrow it down to more of a fuel issue than an ignition problem.

 

Try checking the resistance of the signal coil in the distrib, and the air gap. Clean up the connector on the igniter, and the igniter ground (mounting bolts). Could possibly be a bad igniter.

 

Check your air induction hose,vac lines... I had the same problem about a year ago, but mine was when the air temp outside was around freezing. Just a suggestion.

 

Beg, borrow or steal a vacuum gauge and let me know the results at idle.

I had a horrible idle problem I couldn't figure out for a long time and only 11" of vacuum. After much exploration it turned out to be the wrong throttle body gasket, I have the '93 throttle body on my 86 and they use a different gasket. Changed it out and now she purrs like a kitten at 18" of vacuum.

I know yours is an off idle problem but un-metered air will still affect the operation of the engine.

 

Check your fuel injectors. My 22RE ran similar to what you are describing and it turned out to be a bad fuel injector. The injector would work most of the time (especially at high RPM), but there would be a miss. Checking them is very easy and will rule out the rest of your injection system (since you have gone after the rotor cap, bottom, wires, and plugs): just put 12V across them and listen for the click. 13.4-14.2 Ohms across each injector is in spec.

 

So what happened?? Haha did you fix it? I'd really like too know. I'm having the exact same problem and am exactly where this forum started and would love to just start where you ended haha

 

It's an old thread, and most of them seem to end with no fix. Like its a big secret. Or folks just forget. Or sell it. Here's what I had goin on, and what appears to have fixed it.
https://www.yotatech.com/forums/show...916&styleid=51

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