4.3 p0300 code help

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4.3 p0300 code help

Postby Blazer Bob » Tue Jan 24, 2012 5:52 pm

1999 blazer 4.3 has been skipping bad lately. Autozone says (code p0300 random missfire detected.) Truck runs o k if you run it wide open from a stop but if you take off normal it skipps real bad. I am going to replace fuelpump this weekend because mine is getting really loud and whinney. Allready have done new plugs and wires and cap and rotor button. Also new fuel filter .If new fuel pump does not solve problem what should be next? I am thinking maybe new distributor? Does the fuel regulator need to be changed when i do the fuel pump? I hope not.
Yah, Yah i know its time to just pull the v6 out and do the v8 swap!!! Soon i hope.
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Re: 4.3 p0300 code help

Postby Rickracer » Tue Jan 24, 2012 7:05 pm

What did the plugs look like? If they aren't/weren't black, or very white, I doubt it's fuel, but still could be. The regulator is under the intake, it's part of the "spider" injector assembly. What does the coil look like? Usually, by the time you need a cap, rotor and wires, the coil is done too, look for white deposits inside the metal frame of it, if you see them, the coil is fubar. :wink: 8)
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Re: 4.3 p0300 code help

Postby FirstGenThree » Tue Jan 24, 2012 7:39 pm

I doubt it's the fuel pump if it runs well under full throttle- that would need more fuel than part throttle driving. Since you've done the other tune up stuff is this not a prime candidate for new spider injection unit? I suppose that's more of an idle quality thing on the ones I've seen. They usually still run decent at part throttle but don't idle well.
Don't get an airtex pump, or any cheap unit for that matter. Get Delco or Delphi, otherwise you may still have the same problem and won't know if it's the new cheap pump or something else.
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Re: 4.3 p0300 code help

Postby superbee » Tue Jan 24, 2012 8:22 pm

Ignition breaking down, it probably does it around 40 mph too. Low rpm heavy throttle really strains the ignition.

If its not from cheap or faulty ignition components (that cap is very critical on these) then I'm betting rick is right with the coil suggestion.

Check the coil for traces of spark carbon tracking down the side even.
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Re: 4.3 p0300 code help

Postby Blazer Bob » Tue Jan 24, 2012 8:29 pm

Spark plugs looked really good . Probablly didnot even need changing. Truck starts right up after sitting allnight with no problems at all and will idle great, but once you drive it and get motor warmed up it is very hard to start. I will look at my coil tomorrow and check for the white spots. Heck i probablly will just go get a new coil tomorrow. I guess i thought a coil iether worked or didnt work , i didnt think that they slowly went bad. Thanks guys.
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Re: 4.3 p0300 code help

Postby superbee » Tue Jan 24, 2012 8:53 pm

can break down under load, and can also act up when hot...
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Re: 4.3 p0300 code help

Postby 83S10V8 » Tue Jan 24, 2012 11:21 pm

huh, thats really weird, my daily drive was doing the exact same thing, with the exact same code... found out my cold air intake had a leak behind the MAF sensor.. fixed most of the problem.. now sometimes when i floor it, it kinda skips. its not missing, but like your hitting a small icy spot in the road ever 10 feet.
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Re: 4.3 p0300 code help

Postby 99s10327 » Wed Jan 25, 2012 8:39 am

I don't like the spider injection ... LOL Its caused me allot of issues running wise .. Spray starting fluid in it when warm see if it starts easy
Didnt GM spec .060 gap on these motors for the plugs , thats hard on the coils cap ect...
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Re: 4.3 p0300 code help

Postby Blazer Bob » Thu Jan 26, 2012 6:21 pm

Well lastnight i put a new coil on and it seemed to help when motor was warm, but this morning when i took off for work it had the same miss but smooths out after the motor is warmed up. So after work today i also put a new ignition control module on it. It is located right next to the coil on the same bracket, but still have a missfire at part throttle but not at wide open throttle. Wide open it runs great! Just skips at part throttle while taking off from a red light. So whats next? I am thinking new distributor or what about the crankshaft sensor, could that be the problem maybe?
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Re: 4.3 p0300 code help

Postby Rickracer » Fri Jan 27, 2012 6:21 am

Take the EGR valve out, make sure it's closing all the way, and fire it up for just a couple seconds while the valve is out, to blow out anything in the passage, sometimes carbon will hold it off the seat just a bit and make it stumble and miss at idle. I've seen this a number of times. 8)
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76 Chevy Vega Drag Car, TWIN TURBO 355, P/G trans w/ brake and JW 4000 stall vert, 4 link back half, narrowed 9", 3.50 gears, 29.5x10.5W ET Drags. Best time9.669 @ 139.79, Latest video: https://www.youtube.com/watch?v=S59riYn ... ata_player
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Re: 4.3 p0300 code help

Postby Blazer Bob » Sun Jan 29, 2012 9:31 am

Just got done putting a rebuilt cardone distributor from autozone in, only cost $89.00 dollars. That seemed to fix my skipping!! The truck runs great now or as good as it can for a 4.3 v6 HA, HA. So between a new coil, ignition control module, and new distributor my problems are fixed. Thanks for all the advise guys, i know its almost impossible to trouble shoot a motor problem on a internet forum , but atleast i did not have to take it to a real shop and pay big dollars to get it running right!!
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Re: 4.3 p0300 code help

Postby sYc427 » Thu May 03, 2012 2:09 pm

I had the same problem in a 1996 Astro 4.3 and after 167k, the dist. drive to oil pump gear was badly worn....also these dist. bodies on the late models I find are plastic..after trying to replace just the gear everything else checked good..so much for not breaking the body...we live and learn..
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