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bad alternator causing misfire??

This is a discussion on bad alternator causing misfire?? within the Technical / Maintenance forums, part of the General Discussion category; ok after dumping lots of money into trying to fix my p0300 misfire and everythig checks out just fine ! ...

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    bad alternator causing misfire??


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    ok after dumping lots of money into trying to fix my p0300 misfire and everythig checks out just fine ! but coincedently my alt has been squealing alot now....hmmmm.......thinking back my mis fire started out plowing one night and my alt was only reading 10 volts for a few hours then bounced back to 14 ( on the gauge )
    so, can a weak alternator cause lower voltage to coils / injectors/ pcm tha would obscure the real readings for proper combustion ( im getting alot of lean misfires ) i can feel a mis at idle and ses flashes above 2400rpm
    2002 Chevy 2500HD- Flowmaster 40, Walker Hi-Flow cats,K&N filter,Custom dump kit, pvc CAI, sittin 33's on Outlaw II wheels and Cooper ATR tires
    1983 Chevy C-30- Cummins 6bt powered,#10 fuel plate,afc FF,6" dual miter cut stacks,sm465 trans,4bt flywheel

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    FSC Midwest Chapter! Nyle's Avatar
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    Re: bad alternator causing misfire??

    It is very possible, I've seen bad/corroded/missing grounds cause all kinds of driveability issues. So a weak alternator, (or the rectifier going bad causing AC voltage to reach the battery) could cause problems as well. Alternators aren't that expensive, replace it and see what happens.
    Formerly Grey89

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    DD'n an OBS is great... If you don't have to go anywhere, or you can afford a $hit ton of gas.

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    Re: bad alternator causing misfire??

    ya, im going to test it in the morning. how much volts should it be putting ouy under a load? its making a grinding noise now too, i think a bearing is fried...greaaaaat...fml
    2002 Chevy 2500HD- Flowmaster 40, Walker Hi-Flow cats,K&N filter,Custom dump kit, pvc CAI, sittin 33's on Outlaw II wheels and Cooper ATR tires
    1983 Chevy C-30- Cummins 6bt powered,#10 fuel plate,afc FF,6" dual miter cut stacks,sm465 trans,4bt flywheel

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    Re: bad alternator causing misfire??

    Quote Originally Posted by blackcloud83 View Post
    ya, im going to test it in the morning. how much volts should it be putting ouy under a load? its making a grinding noise now too, i think a bearing is fried...greaaaaat...fml
    14.0-14.5V is normal. if it is grinding, just get a new alt. and be done with it..

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    Re: bad alternator causing misfire??

    What are your plug gaps?

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    Re: bad alternator causing misfire??

    ok, heres my test results. everything off battery test 12.8volts , engine on @ idle no load ( warm ) 14.98v , under load 14.1v ( highbeams on, heater on 5 , hazards , radio, wipers etc... i dont have ac either ) my plug gaps are .060 per gm spec seems to me like its ok. i talked to a local shop and tey will fully rebuild and rewind to 200amps for 50$ ( a very reputable shop ive used before ) plus hell replace both bearings with new ones ,cant beat that price !!!!
    2002 Chevy 2500HD- Flowmaster 40, Walker Hi-Flow cats,K&N filter,Custom dump kit, pvc CAI, sittin 33's on Outlaw II wheels and Cooper ATR tires
    1983 Chevy C-30- Cummins 6bt powered,#10 fuel plate,afc FF,6" dual miter cut stacks,sm465 trans,4bt flywheel

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    Re: bad alternator causing misfire??

    Good to hear you are getting the alt issue taken care of, and that is a pretty good deal. I suggest starting another thread for your misfire if you haven't already, tons of people on this site, one of them may have had a similar problem in the past.
    Formerly Grey89

    97 Chevy K3500 CCLB SRW 6.5L, 4" exhaust, 305's, 20% tint, block/cranked
    97 Chevy K1500 Suburban-Sold

    Quote Originally Posted by MSF
    DD'n an OBS is great... If you don't have to go anywhere, or you can afford a $hit ton of gas.

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    Re: bad alternator causing misfire??

    wow 50 bucks for a 200 amp alt


    98 k1500 5.7 Magnaflow exhaust BBK 80 mm throttle body AEM brute force CAI nelson performance tune 93 octane RC 6" 285/70/17 BFG KM2 4 14 bolt sf disk brakes 4l60e fully built

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    Re: bad alternator causing misfire??

    ha ha, ya it is a pretty sweet deal...the guys there at Yankee Electric are awesome, they rebuild anything from alternators, starters, electric motors of any kind etc... really cheap and they do great work too.

    i should have a misfire thread by now, ive posted just about everything else LMAO im down to stick lifters / valves now... i guess the generation III gms had a problem with the bronze valve guides having too tight of tolerences and once they get hot they contract...i have a TSB on it if your interested !!
    2002 Chevy 2500HD- Flowmaster 40, Walker Hi-Flow cats,K&N filter,Custom dump kit, pvc CAI, sittin 33's on Outlaw II wheels and Cooper ATR tires
    1983 Chevy C-30- Cummins 6bt powered,#10 fuel plate,afc FF,6" dual miter cut stacks,sm465 trans,4bt flywheel

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    Re: bad alternator causing misfire??

    Quote Originally Posted by blackcloud83 View Post
    my plug gaps are .060 per gm spec seems to me like its ok
    Crank those gaps down to .040". You will be amazed at the difference. The energy required to jump a .060 gap is at least five times the energy to jump .040. GM issued notes to dealers to crank the gaps down on all 96 and newer trucks to cure random misfires and driveability issues. Your ignition components will last much longer too.

    And make sure you are using AC plugs. Either Iridium, which come pre-gapped at .040, or platinums which can be adjusted down to .040.

    These engines run so clean there's no need for the big gap anyway.

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    FSC Midwest Chapter! Nyle's Avatar
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    Re: bad alternator causing misfire??

    Don't get ahead of yourself thinking its a valve issue causing your misfire just because there is a TSB on it. I'm in about the same boat chasing a miss in my 97 Suburban. It started with just a single cylinder misfire at idle, I end up throwing about $1000 into it between distributor cap and rotor, spark plugs and wires, new MPFI fuel injector spider, and a few other shot in the dark solutions that didn't work. I was pretty well decided that it has to be a sticking lifter, burnt valve, bent pushrod, etc.

    Now it's no longer a single cylinder miss, it's a multiple and random misfire, turns out the distributor($75 part) is going out. It just wasn't bad enough yet to show that it was bad.

    A TSB doesn't mean it's always your problem, not saying it isn't because it very well could be, but don't be surprised if it's something else.
    ShamelessTR likes this.
    Formerly Grey89

    97 Chevy K3500 CCLB SRW 6.5L, 4" exhaust, 305's, 20% tint, block/cranked
    97 Chevy K1500 Suburban-Sold

    Quote Originally Posted by MSF
    DD'n an OBS is great... If you don't have to go anywhere, or you can afford a $hit ton of gas.

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    Re: bad alternator causing misfire??

    Quote Originally Posted by 2COR517 View Post
    Crank those gaps down to .040". You will be amazed at the difference. The energy required to jump a .060 gap is at least five times the energy to jump .040. GM issued notes to dealers to crank the gaps down on all 96 and newer trucks to cure random misfires and driveability issues. Your ignition components will last much longer too.

    And make sure you are using AC plugs. Either Iridium, which come pre-gapped at .040, or platinums which can be adjusted down to .040.

    These engines run so clean there's no need for the big gap anyway.
    there is a TSB on this, but i can't find it right now..all new AC plugs should come per gaped to the new standards right out of the box..

    good luck

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    Re: bad alternator causing misfire??

    ya, im right up there about 1200$ now ( alot of the parts i was due to replace anyways ) but huh...plug gaps, ill try that im using iridium ac delco's i took a video today of my problem and as soon as youtube stops being stupid i will up load and post it. problem is that when it gets hot the mis gets worse ( im thinking the valve guid tolerences are way to tight ) but i have overheated this engine many times out plowing..that was before electric fan swap ;)
    2002 Chevy 2500HD- Flowmaster 40, Walker Hi-Flow cats,K&N filter,Custom dump kit, pvc CAI, sittin 33's on Outlaw II wheels and Cooper ATR tires
    1983 Chevy C-30- Cummins 6bt powered,#10 fuel plate,afc FF,6" dual miter cut stacks,sm465 trans,4bt flywheel

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    Re: bad alternator causing misfire??

    Any updates on this? Im experiencing the same misfires as well and was also wondering if its alternator related. I just put in AC Delco Iridiums and MSD wires in it last week. Didnt have any issues til a couple of days ago. I didnt gap the plugs because I was told not to. Never misfired before I changed them. And didnt start til a few days after I changed them.

    No check engine light either.

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    Last edited by JonnyBlaze; 03-08-2013 at 08:48 PM.

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    Re: bad alternator causing misfire??

    i never trust anything out of the box, I have yet to see a set of iridiums actually gapped properly out of the box.

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    Re: bad alternator causing misfire??

    If it was the gap then why would it take a few days to misfire? It doesnt do it all the time. Its random. Like yesturday it didnt misfire at all.

    2003 Silverado 2500HD LS CCSB 4x4
    6.0L V8, 6" RCX Lift, 35" Kumho Tires on 16" Moto Metal Wheels, True Dual Exhaust w/ Flowmaster 50 Series, Nerf Bars. Extang Tonn. Cover.

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    Re: bad alternator causing misfire??

    It seems to only do it when Im stopped with my foot on the brake and my trans in gear.

    2003 Silverado 2500HD LS CCSB 4x4
    6.0L V8, 6" RCX Lift, 35" Kumho Tires on 16" Moto Metal Wheels, True Dual Exhaust w/ Flowmaster 50 Series, Nerf Bars. Extang Tonn. Cover.

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