99 350 Vortec Need Help Misfiring

     1999 C1500 Suburban 350 Vortec - 86K - Started misfiring - Code P0300 - Engine misses throughout driving speed range
It first started with code P0307 misfire and went away. Next time
engine started code P0301 misfire and went away. The next time the engine was started code P0300 multiple engine misfire and is always there now. Checked plugs ( AC 41-932 ) the gap was about .056 . We have only put 3K on the car and have had it for about 2yrs. The car always ran supper. I have not done anything to the car except change the oil. I have and AUTOXRAY EZ-SCAN 5000 that I read the codes with.
Thanks Warren
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The gap is not necessarily the issue with a plug misfire, if they are original at 86k I would consider plugs and wires here, other issues can cause this such as dirty injectors but at 86k the tune up is the first place to start.

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Shep's advice is good, Warren. Just FYI, I just bought a '97 Tahoe with 350 vortec. It had a slight miss at all speed ranges. Replaced plugs only--they really looked too good to discard, IF their replacement did not fix the miss. It continued to miss, still just slightly at all speeds as before. I replaced the fuel filter and that made it run like new. Has 99000 miles. Those are nice engines. My mechanic-friend has one in a king-cab with 180,000 miles that runs equally as well as mine. HTH, s
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I do not know when the plugs - wires - filter - have last been changed, but it sure sounds like a good place to start. I think the fuel filter will be first. Thanks - I will keep you updated.
The reason we purchesed the car was because of the very dependable Vortec engine. We had a 1964 Suburban and we really liked it.
The newer Vortec engines have changed. Do the new Vortec engines have the same reliability.
Warren
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warrenry wrote:

You must be kidding! The old style Vortec's were not what I'd consider "dependable". The new style GEN III chev small block (new Vortec) engines are far more reliable then the old one's.
If you change everything and still have problems, you may want to check the intake manifold gasket.....I've seen and repaired many of these for warpage, causing a vacuum leak.
Ian
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PROBLEM SOLVED
Changed the fuel filter and it still ran bad. Started checking for loose connection, had my hand around in back of the throttle body and suddenly the engine started running better. Removed the air tubes and found that the electrical connector to ( I think it is for the injectors ) but not 100% sure, was loose. The 2 seals were jamed all the way into the cover so that it would not clip together. Cleaned both seals and positioned them in the right places, clipped it back together and it runs great.
The fuel filter really needed to be replaced, I could barely blow air through it.
Thank you for the help.
Warren
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