asilverblazer

What is the actual problem?

Pressure on the low pressure side is questionable... like the other 'questionable' items though with no way of corelating it to the miss firing cylinders I would not focus heavily on it. If you had a data log that had all PID's when the miss fire was occurring so that you could see if the MAP, MAF, O2 sensors or fuel pressure was out of spec during the miss fire then I would rule them out because a malfunction of those items would not be cylinder 2 and 5 specific.

If memory serves... that circuit will power an assortment of sensors. gmupfitter has wiring diagrams that I would look at to trace that circuit looking for faults. Without looking to see what all is on that circuit, I suspect one of them has cut fuel delivery.

The compression seems fine to me. While I am also suspect of some sensors, the MAP out of spec, the MAF getting hosed with brake cleaner and the non factory O2 sensor. The open loop miss fires rules out a lot of things, and to me points back at injectors. My next step would be the injector balance test.

All the comments about how much fuel the gasser is going to be drinking... the diesel will too when towing. Empty though it should do better than a gasser.

I'd use a test light at the starter solenoid if its getting power when ignition switch is used. If it doesn't light, I'd consider the ignition switch.

I thought this snippet from the P0300 code was interesting: "When a catalyst damaging level of misfire is present, the ECM may disable the fuel injectors for up to 2 misfiring cylinders and will flash the malfunction indicator lamp (MIL)."

Action Taken When the DTC Sets DTCs P0300–P0308 are Type B DTCs. When a catalyst damaging level of misfire is present, the ECM may disable the fuel injectors for up to 2 misfiring cylinders and will flash the malfunction indicator lamp (MIL). Conditions for Clearing the DTC DTCs P0300–P0308 are Type B DTCs. Diagnostic Aids A misfire DTC could be caused by an excessive vibration from sources other than the engine. Inspect for the conditions listed below: A tire or wheel that is out of round or out of balance Variable thickness brake rotors An unbalanced drive shaft Certain rough road conditions Transmission operation A damaged or defective accessory drive component or belt High resistance in the circuits of the injectors may set a misfire DTC without setting an injector DTC. Test the injector circuits of the affected cylinder(s) for a high resistance if you suspect a condition. If the condition is intermittent, observing the scan tool IC Circuit Test and Fuel Injector Circuit Test Status parameters may help isolate the condition. The circuit test status parameters will change from OK or Not Run to Fault/Malfunction if a condition exists. A condition in the heated O2 sensor (HO2S) heater control circuits may set a DTC P0300. Reference Information Description and Operation Electronic Ignition System Description Fuel System Description DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference Control Module References for scan tool information Special Tools EL26792 - HEI Spark Tester For equivalent regional tools, refer to Special Tools. Circuit/System Verification Note: Before starting the engine, review the freeze frame failure records data to determine if the misfire sets during a cold start or at operating temperature. If there is a cold start condition and the engine is started, the engine will need to be cooled down before the next attempt to start the engine within the fail conditions. Engine Running at normal operating temperature. Verify there is no abnormal engine noise. If abnormal engine noise is present Refer to Symptoms - Engine Mechanical. If abnormal engine noise is not present Perform the scan tool Crankshaft Position Variation Learn procedure. Verify no DTCs are set. If any DTCs other than P0300–P0308 are set Refer to Diagnostic Trouble Code (DTC) List - Vehicle. If DTC P0300–P0308 is set Refer to Circuit/System Testing. If no DTCs are set Verify the scan tool Cylinder 1–8 Current Misfire Counter parameters do not increment. If increments Refer to Circuit/System Testing. If does not increment Engine Running, perform the Cylinder Power Balance Test with a scan tool. Verify the engine speed changes when each injector is disabled and then enabled. If engine speed does not change Refer to Circuit/System Testing. If engine speed does change Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. Verify the DTC does not set. If the DTC sets Refer to Circuit/System Testing. If the DTC does not set All OK. Circuit/System Testing Note: An erratic or weak spark is considered a no spark condition. Verify none of the following conditions listed below exist: Damage, carbon tracking, or fluid intrusion of the spark plug boots and/or spark plugs Vacuum hose splits, kinks, and incorrect connections Engine vacuum leaks Crankcase ventilation system for vacuum leaks Fuel pressure that is too low or too high. Refer to Fuel System Diagnosis. Contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis. Exhaust system restrictions If a condition exists Repair or replace as necessary. If no conditions exist Ignition OFF, connect the EL 26792 - HEI Spark Tester to the appropriate spark plug wire, engine Cranking. Verify the spark output. If no output or the output is weak Refer to Electronic Ignition System Diagnosis. If the output is good Ignition OFF. Verify the conditions listed below. Refer to Ignition System Specifications. The correct spark plug type The correct spark plug gap The correct spark plug torque If a condition exists Repair or replace as necessary. If no conditions exist Exchange the suspect spark plug with another cylinder that is operating correctly. Engine Running. Verify the scan tool Cylinder 1–8 Current Misfire Counter does not increment for the cylinder where the suspect spark plug was installed. If increments Replace the spark plug. If does not increment Test or inspect for the conditions listed below: A lean or rich Q17 Fuel Injector—Refer to Fuel Injector Balance Test. An engine mechanical condition—Refer to Symptoms - Engine Mechanical. Repair Instructions Gas Engine Ignition Spark Plug Replacement Repair Verification Install any components or connectors that have been removed or replaced during diagnosis. Perform any adjustment, programming or setup procedures that are required when a component or module is removed or replaced. Clear the DTCs. Turn OFF the ignition for 60 s. If the repair was related to a DTC, duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to the Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure. Engine Running, verify the scan tool Cylinder 1–8 Current Misfire Counter parameters do not increment. If the misfire counter parameters increment, a misfire condition still exists. To verify that the performance of the catalytic converter has not been affected by the condition that set this DTC, perform the Repair Verification for DTC P0420 or DTC P0430. Refer to DTC P0420 or P0430.

Diagnostic Aids The fuel trim cylinder balance diagnostic is very sensitive to heated oxygen sensor (HO2S) design. A non-OE sensor or an incorrect part number may cause a DTC to set. Monitoring the misfire current counters, or misfire graph, may help to isolate the cylinder that is causing the condition. Certain aftermarket air filters may cause a DTC to set. Certain aftermarket air induction systems or modifications to the air induction system may cause a DTC to set. Certain aftermarket exhaust system components may cause a DTC to set. Reference Information Schematic Reference Engine Controls Schematics Connector End View Reference Component Connector End Views Component View Reference Powertrain Component Views Electrical Information Reference Circuit Testing Troubleshooting with a Test Lamp Testing for Intermittent Conditions and Poor Connections Wiring Repairs Connector Repairs DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference Control Module References for scan tool information Circuit/System Verification Ignition ON. Verify no other DTCs are set. If any other DTCs are set Refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis. If no other DTCs are set Verify DTC P219A or P219B is not set. If a DTC is set Refer to Circuit/System Testing. If no DTC is set Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed in the Freeze Frame/Failure Records data. Verify DTC P219A or P219B is not set. If a DTC is set Refer to Circuit/System Testing. If no DTC is set All OK. Circuit/System Testing Engine idling, transmission in Park or Neutral, verify the manifold absolute pressure (MAP) sensor parameter is between 19–42 kPa (2.7–6 PSI). If not within the specified range. Refer to DTC P0106. If within the specified range, inspect for the conditions listed below: Modified, damaged, leaking, or restricted air induction system components. Improper operation of the crankcase ventilation system. Refer to Crankcase Ventilation System Inspection/Diagnosis. Split, kinked, or improperly connected vacuum hoses. Restricted, damaged, leaking, or modified exhaust system from the catalytic converter forward. Refer to Symptoms - Engine Exhaust. Malfunctioning fuel injectors. Refer to Fuel Injector Diagnosis. Fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis. Excessive fuel in the crankcase due to leaking injectors. Change engine oil as necessary. Malfunctioning ignition system. Refer to Electronic Ignition System Diagnosis. If a condition is found Repair as necessary. If no condition is found Test the engine for any mechanical conditions such as sticking valves, lifters, etc., which could alter the flow into the combustion chamber. Refer to Symptoms - Engine Mechanical.

Perhaps its the opposite then - all the others cylinders are getting too much fuel, then the O2 sensors are picking it up and leaning them all out. Essentially an injector balance issue. Because 2 and 5 are flowing the least amount of fuel, when their respective bank gets leaned out because all the other injectors on the bank are flowing too much it causes a miss fire in the leanest of the injectors. What would happen if injector for 2 was swapped with 3 so that the two miss firing injectors are on the same bank? I would expect the two banks to have significantly different fuel trims then. This would also confirm it is in fact a fueling issue. It could also be a different type of valve train issue not associated with a collapsed lifter. Has a compression check been performed?

To me it sounds like cylinders the truck is leaning out some cylinders too much. When you "floor it" the miss fires go away. The ECM doing a 'power enrichment' dumping extra fuel in. That makes me think those cylinders aren't getting the amount of fuel they should. Either the O2 sensors are seeing too much unburnt fuel and leaning it out too much or the injectors aren't shooting enough in. I don't think it is an O2 sensor issue because that would cause a problem on all cylinders. Conversely, the amount of air entering the cylinders could be unexpected and the fuel trims are trying to correct it. For it to only be on a couple cylinders it would have to be intake gaskets or valves.

How fast is the engine spinning? If it is turning fast and strong then the starter is fine. Could be. Maybe. Nope.

I doubt it, probably going to be around 9 MPG regardless of engine choice.

To me it comes down to exactly one thing... how much do you like hearing a gas engine rev for hours on end? I went from a 1/2 ton 5.3 to a 1 ton diesel, the 1 ton feels a little more secure towing our travel trailer but the ride is punishing so that was a wash. Fuel mileage is the same towing, though unloaded I can get slightly better mpgs out of the 1 ton (until it does a regen). Practically speaking the gas engine would be fine, but in the back of your mind the the diesel will be calling out.

Thats what makes me think they got messed up some how.

Intake manifold gasket?

No engine codes related to the oil pressure?

Anywhere raw metal on the engine to the negative battery terminal.

Naw... the best scenario is to take the regulator and throw it in the trash.

I guess I missed where the oil pressure spike is setting the engine light. What code specific to that is there? What is "higher than normal"?

Make sure the engine (everything for that matter) is well grounded. Test by using a jumper cable from the engine to the battery negative.

Wonder what level of scan tool would be able to take over control of (or at least monitor) the oil pump solenoid... turn it off and see if the miss fire clears up. The only way oil pressure could affect engine performance would be through the DFM lifters. Maybe the oil pump and pressure are as intended (no codes) and the lifter is the problem. In other words, so what if the oil pressure spikes - none of the other cylinders have a problem with it.

You can use the regulator... but it isn't helping anything and sounds like it is causing problems. Bypassing or removing it will fill the tires faster and easier. A nail gun isn't using the volume that filling a tire is. Generally speaking and some what in line with Richards comment, a consumer grade compressor isn't going to develop so much pressure that it needs to be regulated to properly run (protect) consumer grade tools. That being the case I'd say that most uses for compressed air are the more volume and pressure the better. Putting the regulator on is just inviting more issues. The reason its in the manual and it suggests to use it the way they have is to prevent someone from blowing up something like putting 110PSI in a lawnmower tire rated for 15PSI.

I wonder if the incorrect oil pressure is causing a weak DFM lifter to act up?

So there was 110 PSI in the tank, about 30 PSI over the regulator setting and 40 PSI over the tire. The first 'burst' engaged the regulator, now only 80 PSI at the chuck, only 10 PSI over what the tire is. A small pressure differential will fill slowly. Sounds like a problem with the regulator. The compressor won't come on because pressure in the tank never fell below the pressure switch setting. The tank still had air pressure in it. Yes and no, that behavior is accurate except that your regulator is in the way. Like noted above, bypassing the regulator will let you inflate the tires using 110 PSI instead of what the regulator is set at (Its 'set' at 80 but I bet its closer to 70). The pressure switch is set at 110 PSI max, below the tanks max so as not to blow it up... safety factor. The regulator is the root cause of the issue describe, I'd remove it. Then the compressor will cycle, fill the tank to 110 PSI and shut off. Once the air has been bled off to the pressure switch minimum (60 PSI?) it will come back on. If there is more air in the tire than what the minimum PSI is on the compressor switch you could have a situation where the tire has 65 PSI, the tank has 65 PSI and the compressor won't come on until it goes lower than 60 PSI(?), meaning no rise in tire pressure. You would have to manually bleed off more air in the tank to get below the switch setting to fill the tank (and tire) back up. I don't know what the minimum on your pressure switch is though.