2004 Sierra 1500 4.3l V6 0300 Code Random Misfire

mendomike420 · April 26, 2011

Hey there everyone, I have a 2004 GMC Sierra 1500 4.3L V6 5 Speed manual. I just replaced the fuel pump about a month ago, Just got a tune up and service done about a week ago. Before the tune up it would misfire, the check engine light would come on. I took it into a local shop and they couldn't connect with the computer to see the code. I took it in to get tune 150,000 mile service and they recommended a tune up. I replaced spark plugs and wires. New Distributor cap and rotor as well. The truck has 167,000 Miles, and is receiving a 0300 code now when hooked up to a code reader. I lose power when accelerating and when in motion it misfires when i let off gas to resume speed. Mainly noticeable in third and 4th gear I have disconnected the pre-cat and post-cat Oxygen sensors, no difference. Cleaned the Throttle plate sensor. Cleaning the Air filter to see if that will make a difference. K&N air filter by the way. Please help if possible. Thanks!

generalmotor · May 10, 2011

I am curious to if anyone has any suggestions to this dilemna. My father has a 2002 gmc sierra with the 4.3 it has roughly 150k on the odometer we just did a tuneup and replacement of the fuel filter thinking maybe this would rectify the problem. It has just gotten a little better I am almost at the end of the rope with throwin parts at it. Next thing I will do will change both the oxygen sensors. It has the same symptoms and codes popped up as mendomike has. Also last year my mother ran it out of gas we had a new delco pump installed and ran fine till about 3 days ago so I dont believe the pump is failing but I will throw a pressure gauge on there so I can eliminate that. If any one has a suggestion please chime in....

wrench19703 · May 12, 2011

I am curious to if anyone has any suggestions to this dilemna. My father has a 2002 gmc sierra with the 4.3 it has roughly 150k on the odometer we just did a tuneup and replacement of the fuel filter thinking maybe this would rectify the problem. It has just gotten a little better I am almost at the end of the rope with throwin parts at it. Next thing I will do will change both the oxygen sensors. It has the same symptoms and codes popped up as mendomike has. Also last year my mother ran it out of gas we had a new delco pump installed and ran fine till about 3 days ago so I dont believe the pump is failing but I will throw a pressure gauge on there so I can eliminate that. If any one has a suggestion please chime in....

My 99 4.3 had the same issues; I dropped in a replacement distributor base. So called Dist gear wear; i did not see that much wear but it fixed the issue.

generalmotor · May 12, 2011

maybe the gear is throwin the fit, I am willing to try anything right now

Stevens03 · May 12, 2011

When was the last time you cleaned the MAF sensor?

generalmotor · May 12, 2011

The sensor was cleaned when this first happened and was also replaced with a used known to be good one and it didnt help at all. Replaced both oxygen sensors no help still the same. Ran a datalog while driving it around everything is checking okay sensor wise also changed the gear on the distributor a few minutes ago. I am taking a break right now. After the truck cools for a bit I am goin to check the valve timing. If I see or find anything out I will post it up hopefully the bad luck I am having can benefit someone once I find out the diagnosis

generalmotor · May 15, 2011

I am officially at my wits end. I checked the valve timing alls good. new distributor now, fuel pressure is within limits, pressure regulator functioning correctly, and the oxygen sensors all read correctly. Here is the kicker it runs good cold but once it warms it starts going haywire. Well it doesnt run perfect but a hell of alot better than it does warm there is one last thing I am goin to check tomorrow then it goes to a advanced diagnostic specialist aka.."Dealer"

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asc08 · May 16, 2011

I would check the catalytic converter.

Harv1 · May 18, 2011

I am officially at my wits end. I checked the valve timing alls good. new distributor now, fuel pressure is within limits, pressure regulator functioning correctly, and the oxygen sensors all read correctly. Here is the kicker it runs good cold but once it warms it starts going haywire. Well it doesnt run perfect but a hell of alot better than it does warm there is one last thing I am goin to check tomorrow then it goes to a advanced diagnostic specialist aka.."Dealer"
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This may help......I had the P0300 code on my '05 Sierra 5.3L V-8. I pulled the sparkplugs and the right bank (sitting in the drivers seat) and all four plugs were sooty. With the help of this forum, I replaced the o2 sensor for that bank ( infront of the cat) and so far, everything is good. May be worth a look. here is the thread : www.gm-trucks.com/forums/index.php?showtopic=130536&hl=5\.3L+02+sensor

TommyGun07 · May 23, 2011

I was having the same issues with my 2001 4.3 V-6. The truck would misfire while at speed and ran really rough while accelerating and decelerating. I changed all of the items you mentioned such as the distributor and fuel pump. I ended up replacing both the camshaft and crankshaft positioning sensors. Once this was done the truck ran like it was brand new and I haven't had any problems since then. The sensors are about $75 a piece and are pretty easy to replace yourself. Good luck and I hope this helps!

generalmotor · May 27, 2011

I found the problem it was a stopped up cat. I ended up buying a new pipe from a outfit called wundercarparts.com got a magnaflow cat pipe cheaper than I could of ever fabbed one up never had this problem before so I hope this helps someone in the future. I am sure glad i got this thing fixed.