P300, P301, P303, P306 Codes.. Random misfires


Asked by Dec 14, 2014 at 03:59 PM about the 1999 Chevrolet Blazer 4 Door LS 4WD

Question type: Maintenance & Repair

Any input would be appreciated. 4.3L 168,000mi. Scanner is pulling up the infamous P300 code. Just within the past few days CEL is blinking, lack of power. Ignition is good providing good spark. Compression test was in the range of 130 -140 on 1-6 cylinders so I know the valve seats are good. I also ran the truck without the O2 sensor installed to see if I had a back pressure problem, but didn't make any difference.

I do not have a fuel pressure gauge to test fuel pressure, but I'm leaning towards a fuel delivery problem. I'm thinking that I'm having a problem with the fuel spider assembly and\or fuel regulator. At this mileage I would like to replace the entire assembly. At around $300, I would like to think that this is the problem as I've seen a lot of these as the problem on other message boards.

Any insight before I take the plunge and dump the money into this 14 year old truck? Is there anything else that I might look at that I'm not thinking of.


6 Answers


You may have it figured out mark,the only other thing would be ,crank sensor,or distributor.

1 out of 1 people think this is helpful.

This could be caused by a bad dist. cap and/or wires or spark plugs.I change plugs when this happens because it's the cheapest solution.If the plugs show spark they can still be bad.Then I test the wires to ground and if there's spark,my next step is to remove the upper intake.Leave spider injector hooked up.Disconnect all electrical supply to the distributor, and coil wire too, and pull all poppet nozzles from heads.Put paint can caps under all six poppet nozzle injectors.You can have someone turn vehicle over and watch for fuel to fill caps.It will show immediately if injectors are filing with fuel. My guess is it's the injectors.A pressure regulator is a long shot. If you have a manual shift veh. make sure it's in neutral and parking brake is on.I have purchased injector sets from ebay and rebuilt with known working injectors to replace bad ones.

1 out of 1 people think this is helpful.

A fuel pressure gauge does help to determine fuel pressure after pressurized and when key is off. For 60 bucks, It is a good investment.I.M.O. Good luck.


Harbor Freight has a fuel pressure tester on sale right now for $20.00. Go to: http://www.harborfreight.com/automotive-motorcycle/diagnostics/fuel- injection-pump-tester-92699.html

1 out of 1 people think this is helpful.

Thanks guys, I appreciate the input. I'm moving forward with the project this week. Hope this works..


Good news! I replaced the fuel spider with the newer designed injectors and the truck runs great! no misfires. Cleared the codes and nothing came back. Only other things I replaced were a new PCV valve and gaskets. Runs like new! Fantastic!

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