P0302 cylinder #2 misfire

Tech discussions on the L77 6.0L V8.
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NoMoSnow
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P0302 cylinder #2 misfire

Post by NoMoSnow »

Hi folks, new member here, first post. Thanks to posts in the forum, I've been able to diagnose and repair every issue I've had on my 3 previous 9C1 V8 PPV's.

Then I bought 'Buford T' (I name my cars after famous TV/movie lawmen), the car is overall very nice for a 2012 patrol car, 'only' 83,000 mile and no signs of collision/paint work. It has 9400 total hours and 6775 idle hours.

The car is a 6.0 V8 and it's throwing P0302 cylinder #2 misfire codes. There is a noticeable lumpiness at idle but it goes away when you hit the gas, it is not lacking for power. I've researched other L77 threads on NewCaprice.com and because of the information shared I've already:

- changed oil and filter.
- checked the spark plugs and wires (looks like the police motor-pool mechanic tried replacing these to clear the codes before they sold the car, they are practically brand new)
- I switched cylinder #2 and #4 spark plug wires and coil packs to see if the fault code traveled - it didn't.
- used old school timing light to ensure all coil packs were sending a pulse to the spark plugs, they are.
- used a noid light to ensure that #2 fuel injector is getting the electric pulse from the computer, it is.
- removed the fuel rail, checked every fuel injector, cleaned every one and switched injector #2 and #4, the fault code didn't travel.
- removed valve cover and inspected condition of the valve return springs on right/passenger side, all are good.
- tried to move cylinder #2 rockers by hand, they are tight, no play.
- the inside of the valve cover/head is CLEAN, no sludge buildup.
- kept valve cover off and hooked up all of the coil packs/spark plug wires, ran engine. The operation of the rockers looked identical to other rockers in the head at idle and slightly elevated RPM's.

I am able to reset the P0302 code before every startup attempt, and it always returns, and the lumpiness at idle seems to be less pronounced now (perhaps wishful thinking) but it's there.

My goal is to NOT do any performance modifications to this car, I want to get it running 100% in stock form.

I am unsure where to go from here, your insights are welcome...
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Mooseman
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Re: P0302 cylinder #2 misfire

Post by Mooseman »

Did you do a compression test?
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: P0302 cylinder #2 misfire

Post by Sanford »

Might try doing a running compression test or a leak down test. What does the short term and long term fuel trim look like?

David
s/c'd cav
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Re: P0302 cylinder #2 misfire

Post by s/c'd cav »

swap injectors , then check the valve train
GammaFlat
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Re: P0302 cylinder #2 misfire

Post by GammaFlat »

Assuming your testing is all accurate, it seems it can be one of three things.
As mentioned above..
  • #2 injector
  • burnt valve (or not seating well for some reason)
  • low compression from rings/cylinder wall.
I think the third is the least likely and the most troublesome. A wet and dry compression test would be the easiest thing to do next. Do you seem to be consuming oil? Your mileage (including idle hours) is over 300,000. Just about anything could be worn out.

Unless you need to count on the car for a daily driver, consider it an adventure and take it apart. Re-ring it, lap the valves, install bearings. It's actually not a ton of money but a lot of time. Gaskets: 200+, Cam, Rod and Crank Bearings: 300, specialty tools 200-500. If you have a bad cylinder wall (doubt it), you're into a couple hundred in boring and a few hundred more in new pistons. With 300K miles, I'd also change the timing chain and oil pump. Ahhh, once it's apart, the world is your oyster... lighter valves, beehive springs, a more exciting cam... but I digress.

"Sorry, I don't want any adventures today. Thank you." - Bilbo Baggens

An unrelated side note: I used 1 quart of oil in < 1000 miles while I had a broken motor mount (meaning that spirited driving was very limited). After changing to "Dexos" oil (and replacing the motor mount) I used less than a quart in 3500-ish miles while dealing with a pent up demand for spirited driving. The previous owner had the oil done at a quick change with an unrecognizable brand of oil filter and (I'm assuming) non-dexos oil. The engine sounded happier as well - the valve train was much quieter. I thought it was a good deal at 24.99 / 10 qts in store. You can also get (4) 5qt bottles for 46.99 online (2.35 / qt before tax - shipping included)
Costco Oil.png
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Current: 2013 9C3, deeper trans pan, 12VoltSolutions Remote, Class III hitch, Android Auto capable radio
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NoMoSnow
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Re: P0302 cylinder #2 misfire

Post by NoMoSnow »

Thanks for the suggestions. I just bought a compression tester, should be able to get a reading for all cylinders in the next few days and I'll report back.

Honestly I had to Google 'wet compression test', I'll do that if there is a noticeable drop in compression in cylinder #2 vs. other cylinders.

I'll have to research more about the leak-down test. I (believe) I am mechanically inclined, however y'all have shared some new, next level ideas. I'm appreciating the knowledge.

Just to share my thoughts on the car, I was laid-off a few months ago due to covid related business slowdowns and have been buying a few vehicles (Caprice's, and non-running XJ Cherokee's and full size pickups) to fix and resell for a few dollars till I find another gig. As fun as an engine tear-down/buildup would be, I just want to fix the car so I can resell it with confidence that it's a solid car repaired correctly. I'm hoping I don't have to dig into the short block.

Thanks again and I'll report back this week.
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NoMoSnow
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Re: P0302 cylinder #2 misfire

Post by NoMoSnow »

so I completed a compression check of cylinders 2 & 4, thought I'd start there (#2 is throwing the code).

'Dry' crank-over test showed #2 @ 130psi
#4 @ 145psi

I kept #2 connected to the gauge and started engine, #2 increased slightly to 135psi.

Reading other threads it seems like the PSI should be much lower (I saw 90psi range) for mechanical issues.

Suggestions on what to investigate next?

Thanks!
Sanford
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Re: P0302 cylinder #2 misfire

Post by Sanford »

Did you relieve the pressure on the gauge when you fired it up to do the running compression?

Here is a link that pretty well explains the running compression test.
https://diag.net/msg/m20h4tundft1e0712c21vwxwl6

David
GammaFlat
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Re: P0302 cylinder #2 misfire

Post by GammaFlat »

Switch plugs. I have heard (not seen myself) that a plug can look okay but fail.
Current: 2013 9C3, deeper trans pan, 12VoltSolutions Remote, Class III hitch, Android Auto capable radio
mburrus
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Re: P0302 cylinder #2 misfire

Post by mburrus »

this is a copy paste from another similar thread about a p0303... this one seems to fit also, and im looking to see if you ever resolved this issue?

i have this IDENTICAL issue, ive had this car for 2 weeks. ive thrown new injectors, plugs and wires at it... issue seems to be while idling, especially while cold. while driving normally, its fine.

ive run a quickie graph on the ignition timing, and its all over the place at idle, however if i hold the accel at 1500 rpm, the timing sits very steady at 30 degrees. from what ive read, the ecu seems to use spark timing to quickly correct for any discrepancies in engine speed... and it appears that its oscillating trying to find the proper advance... but this isnt the "issue", rather a side effect

its always cyl 3 giving the misfire. i pulled the valve cover, and found one of the valves actuated while the car was stopped, but when i ran it witht he cover off, it seemed to move normally with the others, and came to rest at closed when turned off again.

ive noticed some valvetrain noise, so im wondering if this is just a lifter thats sh*t the bed. this car has AFM turned off by tune by the agency that owned it before, though a true delete was never done. car has about 8500 hours total, 5k of which are idle.

did you ever resolve this issue? and if so, what was the magic bullet?
2013 9C1 (former city of Ft. Lauderdale FL), L77
2014 Silverado 2500HD L96, 6L90e, 4.10
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