2005 c6 p0300
Thread Starter
Intermediate
Joined: Mar 2022
Posts: 34
Likes: 4
From: California
2005 c6 p0300
Hi guys, it's been some time and I really need your insight, I was driving back home when suddenly I felt a strong vibration and spurting, no check engine but it's obvious something is wrong, so I pull to the side, turn engine off then back on, very heavy misfire could be heard and felt, it's a hard rattle, at the time no code was given, I called AAA and had it towed to my house, pulled up my scanner again once the check engine light popped and P0300 code came up, no other...
SO, long story short I ordered some Iridium plugs (AC Delco) and AC Delco gold spark plug wires which I changed today... but no joy, same issue, as such I'm stumped, I checked the ignition coil wires in case they were lose and no dice. As for the plugs I had to gap a few to the recommended .040...
Here's a video:
-There's a strong gasoline smell when running.
-Sometimes it runs and dies a couple seconds after.
-Another thing to note, while it's running rough the light on the hood starts flickering as if it's getting drained, at the time battery was at 13+V.
-Another thing I noticed is that if I push the gas pedal it lags and accelerate poorly.
SO, long story short I ordered some Iridium plugs (AC Delco) and AC Delco gold spark plug wires which I changed today... but no joy, same issue, as such I'm stumped, I checked the ignition coil wires in case they were lose and no dice. As for the plugs I had to gap a few to the recommended .040...
Here's a video:
-There's a strong gasoline smell when running.
-Sometimes it runs and dies a couple seconds after.
-Another thing to note, while it's running rough the light on the hood starts flickering as if it's getting drained, at the time battery was at 13+V.
-Another thing I noticed is that if I push the gas pedal it lags and accelerate poorly.
Last edited by ace1987; Aug 4, 2024 at 05:49 PM.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,565
Likes: 4,034
From: Cape Coral, Florida
Video really doesn’t help and trying to figure out what you mean by “the light on the good starts flickering”…what is on the good ??…for a DIY’er diagnosing a misfire can be frustrating…what you can do is if you have a fuel pressure gauge and check that…also with ignition on (green start light on) see what your MAP sensor or BARO is reading…if you have a scan tool and not a cheap code reader I’d be looking at a few data PIDS…MAF, MAP, O2 sensors, fuel trims, ECT, IAT…if you have the P0300 look at “freeze frame data” and take a snap shot of what the ECM was seeing when the trouble code set.
Thread Starter
Intermediate
Joined: Mar 2022
Posts: 34
Likes: 4
From: California
Video really doesn’t help and trying to figure out what you mean by “the light on the good starts flickering”…what is on the good ??…for a DIY’er diagnosing a misfire can be frustrating…what you can do is if you have a fuel pressure gauge and check that…also with ignition on (green start light on) see what your MAP sensor or BARO is reading…if you have a scan tool and not a cheap code reader I’d be looking at a few data PIDS…MAF, MAP, O2 sensors, fuel trims, ECT, IAT…if you have the P0300 look at “freeze frame data” and take a snap shot of what the ECM was seeing when the trouble code set.
Oh and it was the light inside the HOOD, stupid autocorrect on my phone, sorry for the confusion.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,565
Likes: 4,034
From: Cape Coral, Florida
See what cylinder or cylinders were misfiring…I wouldn’t worry about the hood light right now since the car was barely running…you just need to gather some evidence via the scan tool.
Thread Starter
Intermediate
Joined: Mar 2022
Posts: 34
Likes: 4
From: California
Cylinder Misfire History as per scan tool:
Cylinder 1: 3
Cylinder 2: 261
Cylinder 3: 2
Cylinder 4: 14
Cylinder 5: 9
Cylinder 6: 86
Cylinder 7: 0
Cylinder 8: 1
Engine RPM: 315 rpm
Desirable Idle RPM: 800
Now I have a new code "P0506" - Idle Air Control System RPM Lower than Expected
Additional data if it matters:
Crankshaft position: 357rpm
Camshaft position: 26 counts
Mass Air Flow sensor: 0.02 lb/s
Thread Starter
Intermediate
Joined: Mar 2022
Posts: 34
Likes: 4
From: California
Just a quick update, I've been tinkering with the car, so far I've:
-Replaced Spark Plugs (OEM iridium, properly gapped).
-Spark Plug wires.
-Swapped ignition coils (1 to 2, 2 to 1, 3 to 6 and 6 to 3), same cylinders misfiring.
-Changed all fuel injectors (OEM).
O2 sensors checked OK, MAF sensor OK.
It's very likely a head gasket issue, so I'll be running a compression test tomorrow.
I genuinely hate working in the current California heat.
-Replaced Spark Plugs (OEM iridium, properly gapped).
-Spark Plug wires.
-Swapped ignition coils (1 to 2, 2 to 1, 3 to 6 and 6 to 3), same cylinders misfiring.
-Changed all fuel injectors (OEM).
O2 sensors checked OK, MAF sensor OK.
It's very likely a head gasket issue, so I'll be running a compression test tomorrow.
I genuinely hate working in the current California heat.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,565
Likes: 4,034
From: Cape Coral, Florida
I would be checking for a broken valve spring before going down the head gasket rabbit hole…you checked or changed everything except “mechanical”…pull the valve cover and check…have you been losing coolant ??…how did the old plugs look when you changed them ??…usually the spark plug ceramic insulator with the coolant leak will be very clean and white since it is “steam cleaned” by the water in the cylinder when it vaporizes…to do a quick “sound” check for low/no compression put the gas pedal to the floor and keep it there while attempting to start the car so it takes 2 feet to do this…one foot on gas and one on brake pedal…the car will only crank (clear flood crank) so listen to how the cranking cadence of the engine sounds…it should have a even cadence !!…the scope test is normally one of the first tests I do to determine mechanical integrity of the valve train…takes 2 minutes vs 2 hours doing an old school mechanical compression test…spend a summer in southwest Florida and then talk about summer heat.
Last edited by C5 Diag; Aug 11, 2024 at 05:58 AM.
Thread Starter
Intermediate
Joined: Mar 2022
Posts: 34
Likes: 4
From: California
Thanks for that, I'll look into it; No coolant loss so far, spark plugs were not clean at all when pulled out.
Ha! Ive spent most of my life in El Salvador, I know your pain with high humidity + summer heat, but it's pretty brutal here right now too at 43oC in So Cal.
spend a summer in southwest Florida and then talk about summer heat.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Thread Starter
Intermediate
Joined: Mar 2022
Posts: 34
Likes: 4
From: California
Just a quick update, found a cracked valve spring on cylinder 2, so I'll be replacing all of them because of their age anyways.
As for the compression test, on cylinder 2 we had no compression and on cylinder 4 it had low compression (around 60 psi), all others tested fine.
As for the compression test, on cylinder 2 we had no compression and on cylinder 4 it had low compression (around 60 psi), all others tested fine.