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P0300 code

4K views 12 replies 11 participants last post by  carlbush 
#1 ·
I made a New Years Resolution to get to the bottom of the P0300 (Random Intermittent Misfire) code in my R.

After exhausting every fix on the R site and any ideas my shadetree fiends came up with with no fix I took it to the local GM dealer service department.

Two weeks and a lot of money later they saw my performance torque converter and blamed it on that. (complete BS) They offered to take more of my money with no guarantee of a fix and I declined.

I called Greg in weatherford and had him check out the torque converter. He also did a lot of troubleshooting and replaced all the usual sensors, cleaned and checked all the grounds, and did all the things his mechanic buddies recommended....still have the code. Greg did not charge me for this, Shows you what a stand up man he is.

So here I am back at square one although with new pugs, wires, sensors, cleaned injectors, etc..

Anyone out there have any ideas??????

I want to keep the R (love it) but I am in mental turmoil over this.

Any help would be appreciated.:confused:confused
 
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#3 ·
A complete detailed list of what has been checked and replaced would sure help. Not having all the date will just end up having people posting a ton of stuff that has already been done. Have an aftermarket tune?

There are many causes for this OBD code. Since it is a "random misfire" or "multiple misfire" this means that the misfire is on different cylinders and not just one all the time.

==Causes?
Low Fuel Pressure
Vacuum Leak
EGR system malfunction
Internal Engine Problems (such as low compression)

-- Less Common Causes
Faulty Coil
Faulty Spark Plugs and/or Wires
Camshaft or Crankshaft sensors
Ignition module
Computer

I wonder if it is a faulty ECM? Seems quite a few people have had issues with them lately...... Might try buying one on EBay to try it and flip it if it does not work.
 
#4 ·
My "R" had an Performance tune.
After I had the "R" for 1 year, the "R" started to misfire, but I could not read the misfire with the Tech 2.
The local Chevy dealership reset the ECM to "Factory" and the Tech 2 could now read the # 7 plug misfiring.
(cracked spark plug)
You may want to restore the ECM to "Factory" settings
 
#6 ·
Thanks Dragon.

They checked everything listed on your post and sent the ecm to gm who removed my performance tune (at my ok) and reprogrammed to the latest Chevy tune.

I may try the ECM to see what happens.
 
#7 · (Edited)
John
You say they checked everything on Dragon2U list - but did they check anything else?
What if any parts were replaced?
Something else that might help is the freeze frame information.
Whenever a code is set the computer should store data concerning operating parameters when the code was set.
Be sure to check serpentine belts and tensioners (two belts = two tensioners) and all pulley driven accessories for proper operation - problems here could cause a crankshaft vibration that ECM will think is a missfire.
 
#9 ·
One of the things that have puzzled me about the coil packs on the LS motor is the grounding path of the coils. The coil packs are well grounded to the mounting bracket and in turn to the cover, but the rocker cover itself appears to be mounted with rubber.

I'm not suggesting a change in design is required, or even that I know what's causing the problem....... Just offering a question that could lead you to a solution for a random misfire.

Regards,

Mike
 
#10 ·
A recap of what we did here at the shop:

Replaced cam position sensor, crank position sensor, had custom tune removed and updated factory tune installed, checked fuel pressure, checked pcv system(replaced one torn hose), performed compression check, clean grounds for coil packs, check injector harnesses and connections, replace bank 2 sensor one, O2 sensor, installed fuel injector cleaner into system, checked and cleaned battery and body grounds.
 
#11 ·
Cracked or defective spark plug. Replace them all and don't over torque them.

If the spark plug wires were not changed I would also do that.

Time and time again we have a guy that adds a turbo or blower or Nitros and they have tried everything and even if the spark plugs and wires were changed and have less then 200 miles on them. We change the plugs only and problem goes away. With a cracked plug the engine will run fine and idle fine until it is under load. For less than $100 bucks have the plugs changed and treat them like glass. If you drop one don't use it put in another new one they are less then 6 bucks each.

Let us know what you find. Jerry
 
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