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  1. 2004 gmc envoy code p0300

    TrailBlazer / Envoy Chat
    I just bought a 2004 gmc envoy from a used dealership. I took it to get the oil changed & to just get an overall look at it to see what all it needs. The mechanic said I need new valve cover gasket & spark plugs. I paid him $700 & soon as I left in my truck it threw code p0300. No check engine...
  2. P0300 Code. Help!

    I have a 2004 Trailblazer 4X4 4.2L. My starter went out. After replacing it, I got a bunch of weird codes like something was unplugged. It also had a misfire in cylinder 2. I replaced the coils and plugs, now I have random misfires. Anybody have a clue where I should start?
  3. HELP! P0300 after engine swap

    Engine Tunes/Mods
    Hello all, I have a problem with my 05 TB 4.2 EXT LT (160,000 miles). Here is the short story: I did an engine swap after the original engine needed a valve job and original block was damaged beyond repair trying to remove broken head bolts. Got an engine from salvage yard. Removed head and...
  4. Continuing Misfire Problems- What's Next?

    OEM Issues
    Hey Everyone, I'm new here and have an issue I'd like to get some better insight on. I have a 2004 Envoy, I6 with a continuing misfire P0300 issue. 150,000+ miles. Several weeks ago, the engine started to misfire (blinking check engine light, running terribly). I put in AC Delco plugs about...
  5. Power Loss/Won't Shift. Need Help.

    OEM Issues
    Haven't been on here in a looong time, but I am having an issue with my 2003 TrailBlazer with the I6 engine. A couple of days ago, it seemed as if it was having some power loss while accelerating. Just to confirm, I floored it and it accelerated kind of slower than normal. The acceleration...
  6. Missfire during cold engine

    OEM Issues
    First, I would like to say hello. I've been a member for several years, but have never posted before. I know there are several forums discussing the P0300 code, but none seem to be similar to my issue. Vehicle: 2007 Envoy SLT with the 4.2l engine. OD: 188,000 About a month ago I decided to do...
  7. P0300 - Can't track the misfire down

    Well it seems I have the dreaded P0300 misfire and I'm having a terrible time tracking it down. I'm in a bit of a tight situation right now and can't throw money at it to see if coils will fix it so I'm hoping to find a few hints and help here. It's a 2004 4.2L 2wd. The back story is that I...

    Engine Tunes/Mods
    My 2003 TB all of the sudden started running bad at a stoplight. Check engine light flashed and then came on steady. Checked code when I arrived home. P0306, misfire cylinder 6. After going through the forum I decided to swap ignition coil 2 and 6 to see if the problem would move to cylinder 2...
  9. Intermittant P0394 Misfire code

    OEM Issues
    So I have a 2007 TB with about 113k miles, it has the I6 engine. I am very familiar with these engines as in the past I already have had an Envoy for many years and put over 175k miles on it. A few months a ago I started to get the cylinder 4 misfire code and I read about every forum on here...
  10. Multiple Codes no luck

    OEM Issues
    Okay, i have been reading these forums for several years and they have been a huge help in diagnosing and fixing the issues that my 02 TB has presented... until now. This is going to take a little bit to explain so bear with me. About a year ago, i had some missfire issues and ended up...
  11. Rough Idel and Exceleration 04 TB

    Ok I have a 04 TB with about 172,000 miles Recently it has started to misfire . I took it had a code p0300 So I replaced the plugs "boots" and found Coil #1 was bad and replaced it. It made it Run better but still shows same code. I have ran a couple bottle of Lucas Fuel Treatment...
  12. It died! I killed it! 4.2 heaven! Fan Clutch - Water Pump - P0304 - P0300- Engine!

    OEM Issues
    Well this is a long drawn out story that is worth writing and I thought I'd take a few minutes to share some experiences worth hearing about. All started a week ago, I was towing my RV back from Indiana and the TB started overheating, Check engine light was on and it turned out to be a bad fan...
  13. Misfire after a number of fixes

    OEM Issues
    Whats up, I am having problems with the 05 Tb. I have changed my spark plugs, cleaned my throttle body and changed 2 coil packs and I am still getting a p0300 error. Also, if I get the rpm's over 2k the ses flashes. I have stopped driving it. It all started when it was pouring down rain and...