i have 92 astro van 4.3.recently started missing under a load.replaced cap rotor plugs wires fuel filter and coil and module and pick up coil to still missing.pulled each wire off seperatly and all cyl firing good.whats next?
If all your work was done right I would go next with a through under hood search for something shorting out or knocked off, the inspect that TBI (is it falling off?)I discount EGR problems (mainly idle or NOX related) but get a fuel pressure reading somewhere in this lineup,probably should have done a compression check number one item,get a manifold vacuum reading,if all is good you are into mechanical engine problems(perhaps broken valve spring)
You know a good old fashion secondary ignition scope would be of great value,any codes popping up?
checked tbi already and its tight.checked all vacum hoses visualy and looked ok.does nock a little on accelaration but barley hear it.pulled ech wire off and all firing good other wise wouldnt bad cyl would of show thenno check eng light on so dont think comp related but will run a code check anyway.will cancel each cly again to check for good fire.done t6hat 3 times but will do it again to make sure
My experience has lead me to learn that misfires under load usually end up somewhere in the secondary ignition system. If I read you correctly, don’t conclude the lack of a check engine light eliminates the possibility of a engine mechanical defect,that is the very last thing ODB1 systems will even slightly catch on to,OBD systems are not designed to help you with mechanical engine problems they are there to tell you when you are polluting.
That being said I don’t really believe you have a engine mechanical problem but it should be eliminated.
Do the compression check (another chance to look at the plugs,perhaps you will come across a clue) do the manifold vacuum check,again perhaps a clue,do the fuel pressure chek,perhaps a clue. One thing you have not mentioned checking is how much your coil can put out and if the coil and ignition module has correct primairy voltage. I do see you replaced the coil but is it getting correct primairy voltage?