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

Mark Grignon

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.
Mark Grignon

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

Mark Grignon

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!

Your Answer

Add photo

Related Questions

  • 2000 4.3 vortec bazer changed plugs wires cap roter spider runs rough if i pull plug wire it runs better 3 answers

    Random misfire

    2000 Chevrolet Blazer 4 Door LS


    Maintenance & Repair

  • Why do I have a P0300 code? 4 answers

    New engine installed last week. This is the second new engine in 18 months. The first one failed and thankfully was under warrenty. I picked it up Thursday and it runs better than it has in years. Pro...

    2001 Chevrolet Blazer 4 Door LS


    Maintenance & Repair

  • Codes 3 answers

    I did a code scan on my 99 blazer and each time I do i clear them abd when the check engine liye come on it gives me a misfire in the next cylinder. I've changed plugs wires cap rotar ignition pic...

    1999 Chevrolet Blazer 4 Door LS 4WD


    Maintenance & Repair

  • my service engin light keeps throughn codes 1 answer

    will be driven an the light will start flashen

    2003 Chevrolet Blazer 4 Door LS 4WD


    Maintenance & Repair

  • random misfire 4 answers

    I have a 2000 s10 4.3 that has a bad miss and i changed the plugs and distributor and distributor cap and rotary button and it syill is missing so i ran a diagnostic test and it said random misfi...

    2000 Chevrolet S-10 2 Dr LS Xtreme Standard Cab SB


    Maintenance & Repair


Looking for a Used Blazer in your area?

CarGurus has 1,632 nationwide Blazer listings starting at $1,595.


Search Chevrolet Blazer Questions

Chevrolet Blazer Experts

#1 Andrew Olsen
Andrew Olsen
Reputation 1,680
#2 yetilikesbeer
Reputation 1,010
#3 dandyoun
Reputation 630
View All

Related Models For Sale

Used Chevrolet Tahoe"
1,126 Great Deals out of 36,602 listings starting at $1,695
Used Chevrolet S-10"
9 Great Deals out of 1,813 listings starting at $1,749
Used GMC Jimmy"
371 listings starting at $1,900
Used Chevrolet Silverado 1500"
2,453 Great Deals out of 144,268 listings starting at $1,995
Used Ford Explorer"
1,380 Great Deals out of 71,748 listings starting at $300
Used Jeep Grand Cherokee"
1,225 Great Deals out of 74,255 listings starting at $1,500
Used Jeep Wrangler"
447 Great Deals out of 16,356 listings starting at $2,395
Used Chevrolet C/K 1500"
1,140 listings starting at $2,400
Used Chevrolet Camaro"
839 Great Deals out of 39,073 listings starting at $2,650
Used Ford F-150"
3,239 Great Deals out of 216,692 listings starting at $1,000
Used Chevrolet Impala"
947 Great Deals out of 35,735 listings starting at $700
Used Chevrolet Suburban"
666 Great Deals out of 24,293 listings starting at $2,000