jcaprice

I have a 96 Chevy Caprice (LT1), under a load I have a constant misfire on cylinder 4, I've swapped the injector from cylinder 2 to cylinder 4, yet the misfire remains on cylinder 4. I've changed the plug and wire on 4 (and all other cylinders a couple of months prior). And the distributor cap was also changed a few months prior to that. At a loss of what it could be, any help is much appreciated. Thank you.

WyrTwister

Does it set a code ?

How many miles ?

So , it has a distributor ? Not a coil pack or coil over plug ?

Are you getting fire to that plug .

Was both the distributor cap and rotor changed at the same time ?

If high mileage , do a compression test ?

God bless
Wyr

jcaprice

Sets P0304, GENISYS shows misfire on 4 only (but only under a load), otherwise no miss.
~277k miles, It has a distributor (Opti-Spark), plug is getting fire
Cap and rotor were changed at the same time.
Compression test was performed ~2 months ago (all was well).

WyrTwister

Can you hear any spark jumping ( in places it should not ) at idle ?

Old school test , wait until night , good and dark . Raise the hood . Start the car . Look under hood for " fire jumping " .

Just for grins , swap # $ plug with another one .

God bless
Wyr

jcaprice

There aren't any signs of spark jumping, but there is no misfire at idle, only under a load (shortly after driving) it shows #4 misfiring repeatedly. Right before changing the wire (a couple of days ago) the plug on #4 was changed.

WyrTwister

I am running out of ideas / suggestions .

Anything metal closer to # 4 plug than it should be ?

Gap on # 4 plug verified ?

Visually inspect plug # 4 , especially the porcelain ?

Are any of the other plug wires close enough in length to # 4 wire , to swap ?

God bless
Wyr

jcaprice

#4 plug is clear of any metal, plug has been visually inspected (and changed recently), problem remains, gap has been verified. Yesterday evening I purchased a new set of plug wires and placed a new wire on #4 and the problem remains.

WyrTwister

Stab in the dark . Check all the sensors . Check wiring & connectors . Check all vacuum devices & tubing . Look into the underside of the distributor cap for carbon tracking .

Swap plugs .

God bless
Wyr

jcaprice

All checked so far (sensors, wiring connectors), the cap I will check, thank you. It may be a few days before I get back to you. Cap is quite difficult to get to.

WyrTwister

You say it misfires under load ?

It is my impression that the greater the load , the greater the demand in the ignition system , to produce a good , effective , reliable spark .

I do not know if this means the resistance at the gap increases as load goes up ? Perhaps requiring higher voltage , to make the spark jump ?

If so , then perhaps the higher voltage gives those little electrons an opportunity to jump at locations they are not suppose to ?

Best of luck . :-)

God bless
Wyr