HELP!!!! Engine miss in my GMC?

Question

I have a 2004 GMC Sierra 4x4 with a 5.3 engine and auto tranny with 65,000 miles. It has a hesitation or miss when traveling but not at idle. I replaced the mass airflow sensor 2 times, cleaned the throttle body, new spark plugs, plug wires seem ok, only ever used factory air filters, use fuel injector cleaner every oil change and there are no codes coming up at all. I also checked for vacuum leaks but couldn't find anything. I just don't know where else to look next. PLEASE HELP!!!

Answer 1

On my son's Mazda it would idle smooth but when i put in drive it would miss. i thought plugs, but after a little looking discovered 2 bad wires ... maybe same prob??  good luck

Answer 2

Sounds like you spent a lot of money and time guessing on the problem with your truck.

Without a failure code, it's imperative that a scanner be used, preferably a TECH 2, to monitor engine data, to see what's going on with your truck. But a scanner is only as good as the person using it.(or reading it).

My advise is to take your truck to a GMC dealer, for a fee of one hour,

they will diagnose the problem, and give you a price to repair the problem, at that time the choice is yours if you want them to repair it or take it to your mechanic.

A miss fire in the engine will set a code , so will a vacuum leak,or any other faulty sensor.

It's possible that what you perceive as a MISS FIRE might be something else, like lack of fuel volume. (fuel pressure might be good, but volume might not) Pump is not supplying enough fuel volume when needed.

Answer 3

Plug wires SEEM ok. an ohm meter is the best way to check wires for proper resistance. Any plug wire coming close to an engine part (within a 1/4") should be suspect for short to ground. Go in very dark garage at night, open hood and start engine. Look carefully for any sparks that may be seen around wires and parts of ignition syatem.