Hello all. Having issues with my 99 tahoe 4x4 2door v8 350. I'm having a P0300 code. cylinders 4,5,6, & 7 are misfiring. changed all spark plugs, spark plug wires, distributor cap and rotor, new coil, new ignition control module, new MAF, new O2 sensors, new Crankshaft position sensor, new fuel filter, and IAC. I have spark on all plugs however can't tell if it's a weak spark or a good spark but nonetheless, spark in all plugs. I get proper voltages in all areas regarding the coil, Ignition control module, camshaft position sensor and crankshaft position sensor. The only thing I can think of is the spider assembly has gone bad. it has the new MPFI system installed a few years ago. New Fuel pump was installed 1 year ago. Any ideas what can still cause this?

 

Was the intake manifold removed during the conversion from central sequential fuel Injection CSFI to MPFI injection system? You may have an atmo intake leak, which can show up on a scan-tool as a code P0300.

 

Hey OilCan,

So, the issue ended up to be a broken valve spring. after all my tests the only thing I could think of was a mechanical failure. upon removing my valve covers cylinder #6 had a broken valve spring. it was just laying there in two pieces along with the keepers and push rod. no damage to the push rod nor the keepers. And since I had to redo all the valve adjustments anyway I double checked each push rod to see if there was any play. they were all loose. all 16 push rods had lash on them. so disappointed in that. I redid all valve adjustments with zero lash and 3/4 turn to button her up. and she puuurrrrrrssssssssss!!!!!!!! got my baby back.