Misfire under load

[Blackntan90]

Well last Sunday I took 1987SupraComp Baby and his wife out barefooting with my new prop and new boom. Things were going good for a minute or two, and then we lost power- found loose spark plugs from winterizing that I forgot to torque. We went back to the dock and took care of the plugs, went back out for round two but still a misfire under loads more than idle. Any simple checks or ideas at all, I do have pertronix ingnition, everything seems OK there. I have NEVER had any problems like this before. Any suggestions?


-Rich '90 Supra Mariah 351 PCM 1.23:1 PCM trans

[Cusefan78]

Few things to check. Bad gas will cause this sometime. Also check to make sure your plug wires are on in the right order. If the plugs where loose I'm guessing you rushed the winterization process and maybe put the wires on the wrong plug. I'm not sure you're firing order but I bet someone can chime in on that. If none of that works check the distributor. Make sure everything is tight and the timing is correct. Lastly if its none of those things you may have a bad valve.

[2500HD]

Few things to check. Bad gas will cause this sometime. Also check to make sure your plug wires are on in the right order. If the plugs where loose I'm guessing you rushed the winterization process and maybe put the wires on the wrong plug. I'm not sure you're firing order but I bet someone can chime in on that. If none of that works check the distributor. Make sure everything is tight and the timing is correct. Lastly if its none of those things you may have a bad valve.

Ditto, also check cap, rotor and wires

[Cusefan78]

Yeah make sure the rotor is seated properly and that the cap is in the groves.

[Blackntan90]

Thanks for the replys. I did rush the de-winterization, and that was due to an impending storm. Well live and learn. The plug wires are numbered so I do not think that is the problem, cap and rotor are ok looking. I will try new plugs cap and rotor, add some gas line dryer and see where it goes from there. thanks again!

[DKJBama92Mariah]

Sounds like fuel starvation to me. Have you changed the fuel filter recently? There is also a screen on the carb inlet that can collect debris and the fuel pickup in the tank can get clogged as well.

[mlaosa]

If you were running with "loose"plugs there's a good chance that you could have some hairline cracks in the plug(s). I'd pull them and check for carbon tracks on the porcelain part of each plug. If there is then that means your not getting full spark to the combustion chamber causing misfire issues especially under a load. Seen it many times on vehicles.

[cadunkle]

It's either ignition cutting out or a lean misfire. Could be incorrect firing order. If you switch two that fire sequentially it won't be as noticeable at idle and low load (though is still noticeable. At what MPH/RPM does the misfire occur? Misfire only while barefooting sounds more like fuel starvation. Check your filters. Also verify your timing is advancing, though if stuck and not fully advancing that would cause a loss of power at higher RPM but not a misfire.