Pulled codes

P0300
P0304
P0303

I'll try cleaners and report back.

Nobody thinks it could be a cam or crank position sensor?

 

Those sensors will affect all cylinders, not just two.

 

So what affects only cyc 3 and 4?

 

^Did you check the Intake plenum pan for leakage?

 

Ok finally got around to fixing the plenum issue. Water pump bearing let go so I pulled it and replaced the WP, Radiator, fan clutch, intake plenum gasket and lower intake gaskets. Started it up and it cleared codes and it seemed a little smoother went for a drive and got P0303 again!


So just to review and save you from 3 pages:

Originally got P0300 and P0303

removed and cleaned the IAC
replaced oil, oil filter
air filter
wires, plugs, cap, rotor
flushed cooling system
cleaned the PCV
replaced ignition coil
Checked compression on #3, #5 for comparison, both are around 120psi.
moved #3 injector to #5 spot did not change anything
Clean all grounds
Tried fuel injection cleaners

So any other ideas beside a gallon of gas and a match?

 

What type plugs did you use and what how did you gap them? .040??

 

Autolite coppers .035

 

The Autolites would not be my first choice in plugs. I've tried those before and now running 4291 NGK and like them a lot better. The .035 is too close of a gap and may be your problem. A stock 3.9 engine should be no less than .040 gap.

 

I'm reaching here so I'll try anything. NGK here I come.

PS: I do run Autolite cop in every other car I own (including 700whp SC stang) and there great, but you are right some motors are finicky.

Thanks

 

I'm not saying the Autolites are not good plugs because some people swear by them in these Magnum engines. Just voicing my personal choice. The choice to change them is your decision but the .035 gap is what I believe to be the problem and should be increased to .040.