2013 caprice ppv p0303

Tech discussions on the L77 6.0L V8.
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crd
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Joined: Wed Oct 06, 2021 5:36 pm

2013 caprice ppv p0303

Post by crd » Thu Oct 07, 2021 12:14 pm

I recently bought a 2013 caprice ppv 6.0 . it idles rough and has a p303 dtc. Other than that it runs great. No lifter noise. Engine is really quiet.

While idling the check engine light flashes and the trac system is disabled. This happens as goes into close loop and rpms drops. I can bring the rpms up to about 1500 and the check light goes off and the trac system is abled.

I have swapped the spark plug ,coil, plug wire and injector one at a time to see if the code moves to a different cylinder. It stays at cylinder 3. Pull the valve cover off and checked for broken valve Spring. All looked normal.

Next checked the manifold temperature at each cylinder. The temps are consistent across all 8 cylinders.

Next i did a compression test. Number 3 is 148 psi the rest were 150 to 155. Ran a simple leak down test on #3. I could hear air in driver side valve cover. Couldn't tell exactly where. I am thinking maybe a crack valve seat or guide.

Has anyone else had a this issue? I am kinda stuck here.

BluesBro
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Re: 2013 caprice ppv p0303

Post by BluesBro » Fri Oct 08, 2021 3:41 pm

Odd issue. The symptoms kind of lead in two directions. The compression leak into the valve cover could be a simple seal or guide, but I don't think that would give you the misfire issue you are seeing, might be an unrelated symptom.

The fact that it clears up as the RPMs rise kind of lead me to believe it could be lifter/oil pressure related.

Another thing to check thoroughly before tearing into the top end would be wiring. The harsher climates these cars tend to be put into service in, end up corroding grounds and connectors. I myself have a few gremlins that come and go with temperature, run time, and vibration. I am slowly clearing these up as I identify corrosion and clean it up.

What are the fuel trims doing when it misfires and clears up?
2014 Caprice PPV 6.0L - TSP Stage 1 Cam, Solo 3in Mach Cat Back, HP Tuned
2002 Avalanche 5.3L - MBRP Exhaust, RC 6in Lift

crd
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Re: 2013 caprice ppv p0303

Post by crd » Fri Oct 08, 2021 8:20 pm

Thanks for the reply. The fuel trim are negative 3 on the freeze frame on that bank . its negative 5 before I start it. While bank 2 is 0 before its started.

crd
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Re: 2013 caprice ppv p0303

Post by crd » Fri Oct 08, 2021 8:24 pm

After rpms are raised 1600. The fuel trims are negative 1-2 on both banks

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Mooseman
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Re: 2013 caprice ppv p0303

Post by Mooseman » Fri Oct 08, 2021 10:03 pm

Check for a vacuum leak using carb cleaner around the intake manifold.

If you have an actual advanced scanner like a Tech 2 or Snap On, do an injector balance test to see if it's a failing injector. SMA walks through a misfire on an older Silverado but the diagnostic methods are the same. Turned out to be a dead injector. At the same time, check your fuel pressure.



I have a similar issue on my 07 Trailblazer with the 4.2 I6 where it has a slight misfire on Cyl. 4 at idle only. I did every type of diagnostic tests, including the balance test, and was never able to find the cause, and it too has a slightly lower compression on that cylinder. I just don't let it idle for too long but it's not as severe as yours as mine won't trigger the CEL until it has accumulated a lot of misfires.
2011 Caprice PPV, former RCMP test vehicle, never put into service
Build Thread: http://www.newcaprice.com/forum/viewtopic.php?t=2419

Sanford
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Re: 2013 caprice ppv p0303

Post by Sanford » Sat Oct 09, 2021 4:18 am

Try a running compression check to see what results you get. Pull the injector wire so you don’t heat up the cat. You can Google “running compression test” and get some informative info. I have seen a slightly bent valve cause a rough idle that would go away after the engine gets off idle.

crd
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Re: 2013 caprice ppv p0303

Post by crd » Sat Oct 09, 2021 5:47 pm

Thanks everyone for the help. I have sprayed carb cleaner around the intake no apparent vacuum leak. I am going to do a balance test on the injectors then a running compression test.

Also I looking at buying a clone tech 2. Has anyone use one if so what are you thoughts?

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Mooseman
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Re: 2013 caprice ppv p0303

Post by Mooseman » Wed Oct 13, 2021 3:13 pm

I have one and it's a great tool however I have a 2011 and it works with it. Yours being a 2013 is on the edge of not being compatible so it may not work. And it wouldn't be compatible with anything beyond 2013. I'd get a GM MDI instead. It's backwards compatible and you'd be future proofed, at least for now.

Just be careful if ordering from overseas, like from Aliexpress, as the US Customs lately have been seizing them and charging importers of these Chinese clones. Be sure you order from somewhere that's shipping from the US. Had a guy on another forum I'm on have his seized and facing possible heavy fines. Luckily he only lost the Tech 2.
2011 Caprice PPV, former RCMP test vehicle, never put into service
Build Thread: http://www.newcaprice.com/forum/viewtopic.php?t=2419

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