Sounds like it's misfiring under load. Check for codes in the computer to help you find out which cylinders are doing it. If it's not a misfire, it could be a bad Mass Air Flow sensor.
March, 6, 2011 AT 12:43 AM
I HAVE ALREADY CHANGED THE MASS AIRFLOW SENSOR. THE MISS FIRE IS SPORADIC. IT MISSES ON 1, 4, & 6 MOSTLY BUT THERE IS NO RHYTHM TO IT. IT NEVER FOLLOWS THE SAME SEQUENCE. I HAVE THOUGHT OF A VACUUM LEAK BUT CAN'T FIND ONE. I HAVE CHANGED THE COMPUTER AND ITR DID NOT FIX IT EITHER.
March, 6, 2011 AT 12:45 AM
No, I wouldn't expect the computer to help that. It's usually collective resistance in the secondary ignition components which are the plugs, wires and coils.
March, 6, 2011 AT 12:49 AM
I USED AUTOLITE PLATINUMS TO BEGIN WITH. THEN CHANGED THEM WITH AC DELCO. WHEN I CHANGED TO DELCO I ONLY DID 3 AT A TIME. MY WIFE SAID IT RAN GREAT WITH NO PROBLEMS WHEN IT WAS JUST THE FRONT 3. AFTER I CHANGED THE BACK 3 IT STARTED ALL OVER AGAIN.
March, 6, 2011 AT 12:52 AM
That tells you the problem is in something you did with the plugs and wires. Check your firing order again. You also may have cracked a plug. You didn't mention wire. Make sure they were changed with Motorcrafts.
March, 6, 2011 AT 12:56 AM
WHY WOULD I USE MOTORCRAFT ON A GM. I CHANGED THOSE ALSO WITH DELCO FROM THE DEALER. I ALSO DIDN'T SAY THAT ONE DAY THIS PAST WEEK SHE TEXTED ME TO ASK WHAT I DID TO THE VAN BECAUSE IT RAN PERFECT THAT MORNING. THAT AFTERNOON IT WAS RUNNING BAD AGAIN. I WORK AT AN AUTO BODY SHOP SO I GET GREAT DISCOUNTS, LIKE YOU.
March, 6, 2011 AT 1:14 AM
My bad, I forgot it was a GM.
You're going to have to track down which cylinders are doing it and find out why.
March, 6, 2011 AT 1:15 AM
IT IDLES FINE AND CRUISES FINE AFTER GETTING UP TO SPEED. THE FUEL ECONOMY SEEMS TO BE DOWN THOUGH. I HAVE WONDERED IF IT COULD BE SOMETHING IN FUEL DELIVERY OR SOMETHING WITH THROTTLE POSITION.
March, 6, 2011 AT 1:18 AM
I HAVE HAD IT AT A REPUTABLE REPAIR SHOP IN MY AREA ONLY TO HAVE THEIR MAIN MECHANIC BE JUST AS STUMPED AND SCRATCHING HIS HEAD AS I HAVE BEEN. I KNOW IT IS THE 1 4 6 CYLINDERS IN NO PARTICULAR ORDER. IT JUMPS ALL AROUND WHICH ONE IT MISSES ON WITH NO SEQUENCE TO IT.
March, 6, 2011 AT 1:19 AM
You might want to have the fuel injectors pressure cleaned. They could be all varnished up.