Rough engine, P0300 code
Thread Starter
Instructor
Joined: Nov 2011
Posts: 137
Likes: 8
From: Dallas Tx
Rough engine, P0300 code
Hi everyone,
Driving 15 miles home in my 2004 C5 Corvette, suddenly the engine starts shaking and the engine light comes on. I drive the last 3 miles at 35mph and make it home. Since then, it miss fires all the time - immediately on start up.
Pull the codes (using option and fuel button) and only the P0300 code shows. I get a code reader and get the same code.
I've replaced the spark plugs and wires - no change. Old spark plugs looked (gap ok) except one side of the the insulator is black (all plugs). Pulled a new plug after a 1/4 mile drive - same pattern.
Cleaned the air filter (it is 6 months old). Checked the fuel pressure at the fuel rail (54psi on turning on the key, 62 psi when engine is running). Battery is charged up.
Following the service manual, I removed the drive belt and checked all the accessories and pulleys turn freely. I replaced the belt anyway.
Corvette is stock and has run perfectly every day for 7 years.
Any ideas?
Driving 15 miles home in my 2004 C5 Corvette, suddenly the engine starts shaking and the engine light comes on. I drive the last 3 miles at 35mph and make it home. Since then, it miss fires all the time - immediately on start up.
Pull the codes (using option and fuel button) and only the P0300 code shows. I get a code reader and get the same code.
I've replaced the spark plugs and wires - no change. Old spark plugs looked (gap ok) except one side of the the insulator is black (all plugs). Pulled a new plug after a 1/4 mile drive - same pattern.
Cleaned the air filter (it is 6 months old). Checked the fuel pressure at the fuel rail (54psi on turning on the key, 62 psi when engine is running). Battery is charged up.
Following the service manual, I removed the drive belt and checked all the accessories and pulleys turn freely. I replaced the belt anyway.
Corvette is stock and has run perfectly every day for 7 years.
Any ideas?
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 29
From: Van Buren Arkansas
Wounded Warrior Escort '11
If you don't get a specific code for a specific cylinder as mentioned already, one item to check is the ground on the rear of the driver's side head. The bolt there, grounding the wires, seems to come lose from time to time on some cars. If there's a specific cylinder, then check the plug wire and insure its plugged onto the plug all the way.
Thread Starter
Instructor
Joined: Nov 2011
Posts: 137
Likes: 8
From: Dallas Tx
Thread Starter
Instructor
Joined: Nov 2011
Posts: 137
Likes: 8
From: Dallas Tx
Thanks for the suggestions.
Safety Car
Joined: Jun 2005
Posts: 4,977
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From: St. Louis Missouri
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Thread Starter
Instructor
Joined: Nov 2011
Posts: 137
Likes: 8
From: Dallas Tx
This thread may be of some help...
http://forums.corvetteforum.com/c5-t...ont-start.html
http://forums.corvetteforum.com/c5-t...ont-start.html
Running the engine for a few minutes, I noticed more exhaust on the driver's side tail pipe. Using a digital temperature laser gun, these exhaust pipes were 106 dF and 94 dF. The passenger side exhaust pipes were both around 74 dF. Both are pushing air, but it seems the driver side exhaust is stronger.
Le Mans Master
Joined: Nov 2005
Posts: 6,993
Likes: 25
Checked the ground A on the two spark plug harness connectors. Both are 00.2 ohms to battery ground.
Running the engine for a few minutes, I noticed more exhaust on the driver's side tail pipe. Using a digital temperature laser gun, these exhaust pipes were 106 dF and 94 dF. The passenger side exhaust pipes were both around 74 dF. Both are pushing air, but it seems the driver side exhaust is stronger.
Running the engine for a few minutes, I noticed more exhaust on the driver's side tail pipe. Using a digital temperature laser gun, these exhaust pipes were 106 dF and 94 dF. The passenger side exhaust pipes were both around 74 dF. Both are pushing air, but it seems the driver side exhaust is stronger.
Thread Starter
Instructor
Joined: Nov 2011
Posts: 137
Likes: 8
From: Dallas Tx
I'm ready to remove the valve rocker arm covers to look for a broken valve spring.
Is there anyway it could be a bad sensor causing the misfiring?
Thread Starter
Instructor
Joined: Nov 2011
Posts: 137
Likes: 8
From: Dallas Tx
Hi everyone,
Driving 15 miles home in my 2004 C5 Corvette, suddenly the engine starts shaking and the engine light comes on. I drive the last 3 miles at 35mph and make it home. Since then, it miss fires all the time - immediately on start up.
Pull the codes (using option and fuel button) and only the P0300 code shows. I get a code reader and get the same code.
I've replaced the spark plugs and wires - no change. Old spark plugs looked (gap ok) except one side of the the insulator is black (all plugs). Pulled a new plug after a 1/4 mile drive - same pattern.
Cleaned the air filter (it is 6 months old). Checked the fuel pressure at the fuel rail (54psi on turning on the key, 62 psi when engine is running). Battery is charged up.
Driving 15 miles home in my 2004 C5 Corvette, suddenly the engine starts shaking and the engine light comes on. I drive the last 3 miles at 35mph and make it home. Since then, it miss fires all the time - immediately on start up.
Pull the codes (using option and fuel button) and only the P0300 code shows. I get a code reader and get the same code.
I've replaced the spark plugs and wires - no change. Old spark plugs looked (gap ok) except one side of the the insulator is black (all plugs). Pulled a new plug after a 1/4 mile drive - same pattern.
Cleaned the air filter (it is 6 months old). Checked the fuel pressure at the fuel rail (54psi on turning on the key, 62 psi when engine is running). Battery is charged up.
What to look for now?
Tech Contributor
Joined: Apr 2007
Posts: 10,924
Likes: 78
From: Forney Texas
Doing more testing - found that there is no manifold vacuum at all (while idling). I hooked vacuum gauge to a tee between the manifold valve rocker cover and the throttle body. Pulled the gauge off and could not feel any suction. Double checked the vacuum gauge with a vacuum pump and it checks out.
What to look for now?
What to look for now?
Tech Contributor
Joined: Jan 2007
Posts: 19,360
Likes: 1,127
From: Dyer, IN
Doing more testing - found that there is no manifold vacuum at all (while idling). I hooked vacuum gauge to a tee between the manifold valve rocker cover and the throttle body. Pulled the gauge off and could not feel any suction. Double checked the vacuum gauge with a vacuum pump and it checks out.
What to look for now?
What to look for now?
Thread Starter
Instructor
Joined: Nov 2011
Posts: 137
Likes: 8
From: Dallas Tx
Here is a picture of what looks like a broken spring - just took off the passenger side manifold valve cover.
And another view of the same spring (center).
Thanks for the help! Now what to do?
Thread Starter
Instructor
Joined: Nov 2011
Posts: 137
Likes: 8
From: Dallas Tx
If you have a stock setup, and connected the vacuum gauge between the forward rocker cover nipple(passenger side) and the throttle body, I would expect the exact same result, as that is the fresh air intake for the crankcase. If you want to test manifold vacuum, that should be tested at the back of the intake, or at the reservoir.
Drifting
Joined: Jul 2005
Posts: 1,484
Likes: 27
From: Torrance Calif
Do the trunion upgrade also since you have to remove them as well. IMO
Also, go buy yourself a lottery ticket.
You are so lucky you didn't drop the valve into the cylinder.
You could/would be looking at major $.
Also, go buy yourself a lottery ticket.
You are so lucky you didn't drop the valve into the cylinder.
You could/would be looking at major $.
Last edited by heavymetals; Dec 4, 2011 at 02:34 PM.
Tech Contributor
Joined: Jan 2007
Posts: 19,360
Likes: 1,127
From: Dyer, IN