2001 Chevy Express 2500 5.7L Check Engine Light P0300 & U1301

[Jacob Martinez]

Hi everyone, new here but seeking help because this problem feels so illusive and my mechanic skills are pretty basic to intermediate at best. 

 

This code started back in May 2022 and I put new AC Delco pre gapped spark plugs. I put new cap and rotor that were aftermarket parts.  Problem went away for about a year but check engine light would come up intermittently and seemed to be after filling the van up with a full tank of gas.  Light would go away and the van would run good, sometimes going gas fill ups coming up maybe once a month.

 

So the check engine light started coming on a lot more consistently and I pulled out a cheap scan tool which gave an EGR code, I don't remember exact code and P0302. I replaced the EGR valve but that did not help.   Started researching and found these possible causes: I also bought what I thought is a better scan tool off amazon and attached is the freeze frame of what's going on during the P0300 

 

• Damaged or worn-out spark plugs   THINKING ABOUT REPLACING AGAIN
• Rusted or damaged spark plug wires and coils  THINKING ABOUT REPLACING AGAIN WITH HIGHER QUALITY PART WIRES  I replaced Ignition Coil 
• Defective fuel injectors   REALLY DON'T WANT TO HAVE TO REMOVE INTAKE MANIFOLD AND CHECK OHMS ON EACH INJECTOR. WAS WONDERING IF SPIDER IS SIMILAR TO INDIVIDUAL INJECTORS AND THIS COULD BE THE PROBLEM
• Improper ignition timing 
• Blockage on EGR valves or tubes REPLACED EGR VALVE
• Vacuum leakage HAVEN'T LOOKED INTO THIS
• Low fuel pressure THINKING OF GETTING FUEL PRESSURE TESTING GAUGE NEXT  I REPLACED FUEL FILTER. THINKING OF REPLACING PRESSURE REGULATOR
• Leaking head gaskets   HAVEN'T NOTICED ANY WHITE SMOKE OR MILKY LOOK AROUND OIL CAP
• A cracked distributor cap   THINKING OF REPLACING WITH NEW ACDELCO
• A faulty camshaft sensor   DIAGNOSTIC TOOL CHECKED OUT GOOD
• A faulty crankshaft sensor  DIAGNOSTIC TOOL CHECKED OUT GOOD
• A malfunctioning mass airflow sensor DIAGNOSTIC TOOL CHECKED OUT GOOD
• A malfunctioning oxygen sensor DIAGNOSTIC TOOL CHECKED OUT GOOD
• A broken throttle position sensor DIAGNOSTIC TOOL CHECKED OUT GOOD
• A defective catalytic converter   THINKING ABOUT DISCONNECTING CAT
• Has a faulty PCM   WONDERING IF POSSIBLE BECAUSE OF THE U1301 CODE BUT I THINK THAT CODES MORE RELATED TO AN ABS ON DASHBOARD
• Damaged or worn-out distributor cap (only if applicable to the vehicle) 

 

ANY ADDITIONAL THOUGHTS ON WHAT COULD BE GOING ON HERE WOULD BE APPRECIATED.  My next steps seem to be getting fuel pressure gauge to test line pressure. Replacing  cap and rotor, then taking off CAT and seeing if there is an improvement.

 

My thoughts on this from the diagnostic data is I don't understand how it could be a fuel pressure problem or vacuum leak because BANK 1 looks good within spec and BANK 2 seems off with that cheap scan tool bringing up P0302 cylinder 2 / bank 2.  So leaning towards bad distributor cap. I ALSO have replaced the spark plug on cylinder 2 with a new ACDelco and no improvement.  The van idles great and doesn't do the check engine light at idle, just under load. Runs good and then when the light comes on feel a slight shaking / misfire  THANKS to everyone and all help is appreciated. 

• Damaged or worn-out rotor button (only if applicable to the vehicle)