P0300 code why can we fix it?

Thanks Roy

I am 100% confident the gasket is not leaking at valley, or anywhere. I was concerned oil getting past rings/pistons was not possible unless a problem existed. The intake valves somewhere on a cylinder logically would be open and as you explained it worked its way through to crankcase/oil chambers.

A follow up question?

This started with a P0300 code. I have replaced gaskets, hoses, injectors, fuel regulator (psi 42 idle), fuel line from regulator, vacuum is 19 inhg, replaced cam sensor, map, purge valve, cleaned maf, cleaned valve covers/gaskets, confirmed all valves rocking/moving (not lifter). NOID test on injectors pass, spark test on coils pass except did see it miss on #1 briefly (see video), swapped bank1 / bank2 coil packs so #8 coil moved to #1 and this also tested/moved the coil connector wiring to primary connector. Dry compression testing shows 179 to 186 psi across #2-8 cylinders. #1 tested 160 psi. Wet test on #1 showed 160 also, but if I double crank cycles from 5 to 10 it reached 180 psi. Also after only 2 cycles it reached 151 psi. If I remove coil connector on 2-8 idle gets worse, on #1 it does not change. I sprayed seafoam injector cleaner into throttle but still has rough idle. I never see codes P0301-308, nor any other code. LTFT is 8% on bank 1, 17% on bank 2. STFT are +/- 3% on both banks. I plan to do a pressure check at upstream O2 sensors but think exhaust pressure clogged cat) would effect more cylinders? I am down to the coil wires from primary pack connector to ECU could have intermittent loss of signal for #1 coil? Or a bad ECU? Or is it most likely the lower compression on #1 cylinder indicates enough valve leakage (although 160) to misfire? If the attached video does indicate coil misfires then that would be separate and unrelated to cylinder pressure right?

Please provide ideas or thoughts?

I think it is because it is the E-85 Flex Z engine? Early on I found some blogs and videos with a 2004 5.3L Z Flex fuel and information provided was 48-52 psi. On video this was pump on but not cranked. On video when cranked and idle psi dropped 8 psi to 42. My Tahoe is 50 not cranked and 42 idle. In a blog I cannot locate a person referenced a manual that indicated 55-60 for V6 and others, but for E-85 fuel 5.3 it was 48-52. Can you help me confirm and if I am good what is your next suggestion?

Here is another source. I forgot to mention that when idle and I remove the fuel line from regulator it jumps from 42 to 50. I did replace the fuel filter early on at same time I replaced regulator. It appears my fuel pressure for Z engine is okay. Do you agree? My luck is it is not an obvious and easy fix. On other video a fix was replacing main coil wiring primary connector. Question: Do you think a leak down test on #1 should be performed? Or is 160 psi good regardless of it being 12% lower than other cylinders okay?

Roy I know you are the ASE MASTER EXPERT but that is wrong. The specs for a Flex Fuel 5.3 Z is 42 psi when idle / 48-52 without flow. This video below proves it after this guy put in a brand new fuel pump his new pressure at idle is 42 psi.

Either you are not ASE or you want to get rid of me. Oh well thanks for the dedicated support!

I just joined ALLDAYdiy for $15.00 a year subscription. Under my vehicle specs, fuel pressure, it lists below. Per below it lists Z engine as (48-54 psi). That is for KEY ON, Engine OFF. Thus the idle pressure should be (40-46 psi) with engine running. (Or 8 psi less when running). My readings on my truck are 50psi KEY ON, Engine Off and 42psi running IDLE.

Do you still think I have low fuel pressure? If not can you reread my situation and provide more feedback?

Thanks

Below from ALLDATA:

Your Vehicle: 2004 Chevy Truck Tahoe 2WD V8-5.3L VIN Z Flex Fuel

Specifications

Fuel Pressure (Key ON, Engine OFF) 385-425 kPa (55-62 psi)

Fuel Pressure (vin Z) 335-375 kPa (48-54 psi)

Roy

I installed new injectors during gasket upgrade. All test NOID and I can hear them clicking with stethoscope. Should I still swap them around?

Pictures below are from freeze data. Trims on both banks above 10% with bank 2 being worse.

Since I have new injectors, new MAP, and intake is not leaking would this point to bad O2 sensors? I will get two new sensors in mail tomorrow. Should I replace both upstream, or a full bank?

Were you able to see my video I sent yesterday of the spark test on cylinder #1? Did the spark appear to be missing?

Injectors that I installed below. They were new and supposed to be factory spec tested.

Product description
Specification:
NEW! Performance 8 Pack Fuel Injector 25326903 FOR 2002-07 CHEVY FLEX FUEL 5.3L 12580426 FJ502 FJ737

Interchange Part Number: 50130 832-12114 832-11182 217-1626;
Manufacturer Part Number: 25326903 12580426;
Other Part Number: FJ502 FJ737;

Fitment For:
2007 Chevrolet Silverado 1500 Classic
CHEVROLET AVALANCHE 1500 2005 V8-5.3L Fuel Injector
CHEVROLET EXPRESS 1500 2007 V8-5.3L Fuel Injector
CHEVROLET SILVERADO 1500 2002-2006 V8-5.3L Fuel Injector
CHEVROLET SUBURBAN 1500 2002-2006 V8-5.3L Fuel Injector
CHEVROLET TAHOE 2002-2006 V8-5.3L Fuel Injector
GMC SAVANA 1500 2007 V8-5.3L Fuel Injector
GMC SIERRA 1500 2002-2006 V8-5.3L Fuel Injector
GMC YUKON 2002-2006 V8-5.3L Fuel Injector
GMC YUKON XL 1500 2002-2006 V8-5.3L Fuel Injector

Roy, I am trying to attach the spark test video again (cylinder 1). Hope it works.

It indicated it compressed the video and uploaded it. Hope you can see it.

I read in an article about fuel trims. Would this mean that if my MAF was bad only cleaned it) or there were a slight intake leak (none found) that high trims would not be caused by higher air intake so I got a new MAF that fixe it thank you.

Roy today I swapped the injectors. Again a refresh is I am having misfires on 1 and 8. Vacuum is 19 steady, all plugs and cables replaced, coils moved around with no changes, MAP replaced, CAM sensor replaced, Fuel Regulator replaced, fuel pressure 50 on / 42 idle (Z engine).

I swapped injectors as follows:

Before swapping cylinders 2-7 running good with no misfires. 1 & 8 misfiring.

1&3 swapped
2&4 swapped
5&7 swapped
6&8 swapped

After swapping injectors no change. Cylinders 1&8 still the problem.

Roy attached is freeze data screens from drive this morning where P0300 code set.

Roy

I found an article about restricted exhaust (cats) below. This seems what is happening to my FTs. Thoughts?

Restricted exhaust. (Although no two converters fail exactly the same, if fuel trim goes high under acceleration on only 1 bank, suspect a restriction on the other. The MAF reads complete air intake, and then ECM initially distributes fuel evenly to both sides. If much less air is going through one side, there will be more than enough fuel for that restricted side and not enough fuel for the unrestricted side.)

How do I fix a misfire trouble code p0300