P0300 Muti CYL Misfire

[HV_handyman]

I have a Chevy 2000, with just over 100,000 miles, a K1500, that misses when the load on the engine is removed at highway speeds (65-85MPH). I have changed plugs, rotor, wires, had it to two Chevy dealers. No help after 8 hours and a $400 bill. Runs fine at idle and is worst when cold. When the RPM is at about 2500 to 3000 is when it's the worst. Easiest way to set the code is drive with the cruise on and go down a hill. (I have thought about driving I over the hill, but can't afford a new one). Any help would be appreciated.

 

Thanks,

 

[ChevyTech007]

Is it missing on cyl. #5 and or #7? What have the dealers done?

[GM-Tech]

The torque converter disengages on decel, so you could be experiencing a TCC problem rather than an engine problem. Next time the problem is occuring, lightly press the brake pedal to electrically disconnect the torque converter.

[HV_handyman]

Is it missing on cyl. #5 and or #7? What have the dealers done?

 

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Thanks for your reply and I will check that, however when cold if I rev the engine between 2-3 thousand RPM, I get a real bad misfire. It's that misfire that I thought I was experienceing on decel. Of course it may have mutiple issues. Thanks again for your rely.

[HV_handyman]

Is it missing on cyl. #5 and or #7? What have the dealers done?

 

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I used a Genesis code reader to read & clear the codes. Seems like I did see an enhanced rate of misfire history codes on the passenger side of the engine. I heard some talk of the recirculation vale near the Gas tank. It does act worse after a rain, but the problem is still there before the rain. The Chevy dealer in Indiana looked at for 6 hours and said it needed a "fuel service". I showed the service manager what it did and how it missed when cold between 2-3 RPM. But still had the problem after the two week period recommended in seeing the problem clear.

 

The second dealer looked at it for 4 hours but I don't remember them having a diagnosis on it.

 

Thanks for your response

.

[ChevyTech007]

If it misses when cold I would suspect a intake gasket leak. The best way to know for sure is to monitor O2 volts on a scan tool. When engine is cold, spray carb cleaner at intake gaskets. If they are leaking your voltage will go high instantly. I have seen it on a few. I think you might have more than one problem.

[HV_handyman]

If it misses when cold I would suspect a intake gasket leak. The best way to know for sure is to monitor O2 volts on a scan tool. When engine is cold, spray carb cleaner at intake gaskets. If they are leaking your voltage will go high instantly. I have seen it on a few. I think you might have more than one problem.

 

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Another guy told me about the potential intake gasket problem. I went to the auto parts store and asked about intake gasket sales for my engine type, a 4.3 V-6. Fellow told me they sold a lot of intake gaskets for V-8 but none for V-6, so I dropped the item as being a potential cause. I tried after that to spray cleaner around the intake; I was told the engine speed would change. I sprayed and could see no noticeable difference, but then it's a bit difficult to do that alone. Thanks for you input, I will try to follow that trail again.

[ChevyTech007]

Whoops, I thought it was a V8. I guess the rotor in your first post should have given it away. I will do some more checking and post back.

[HV_handyman]

Whoops, I thought it was a V8. I guess the rotor in your first post should have given it away. I will do some more checking and post back.

 

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Is there a Engineering section of GM that might be able to deal with these issues on my truck? I would really like to get it fixed if possible.

 

 

thanks,

 

HV

[HV_handyman]

Thanks for your help on my truck repair..

 

 

Leroy

[HV_handyman]

Whoops, I thought it was a V8. I guess the rotor in your first post should have given it away. I will do some more checking and post back.

 

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Hey Chevy Tech,

 

Did you give on me or just tooooooooooo busy?

 

thanks

[ChevyTech007]

The most common cause of missing on one bank is a clogged catalytic converter. I would have a back pressure test done on the right bank. Sorry for the delay.