gleasone

Hello,
I'm new to the forum, so please be gentle...

I own a 1999 Silverado Z-71(5.3L) with 94,000 miles. I'm having a problem with the engine hesitating when I accelerate - almost to the point that it stops running. It tends to be worse after I've put gas in it, on warmer or hotter days. There seem to be different degrees to the "hesitation". It's not the "either runs great, or it hesitates" It doesn't get better when the engine warms up or if it's driven for a length of time, if anything it tends to get worse (meaning the hesistating gets worse and more often). The only code it pulls is the famous P0440 code, which what I've been told and what I've researched, shouldn't have anything to do with the hesitation. I have replaced the fuel filter, and the air filter. As far as the idle goes, it seems to idle fine in my opinion. It doesn't seem to hesitate any worse if it's under any type of resistance (hauling, driving up a hill, etc.).
Also, it does seem like my gas mileage has dropped dramatically.

Sorry for the long post, but if anyone has any ideas to what my problem might be, I would really appreciate the input and the help! This issue is driving me up a wall!!

Thanks for your help...

ffmed6134

The P0440 code is a trouble code for the powertrain management EVAP SYSTEM
lots of stuff can be wrong w/ it or just one simple thing, my advice is to go to a trusted mechanic and have them do a vacuum test to the purge connection on the Evap purge Solenoid valve if the vacuum is low then its an evap / issue

bacano

i am experiencing the EXACT same problem with my truck. it is driving me crazy. at first i thought mabey it was the transmission but that was ruled out. then i thought it was mabey a bad ignition coil but im not too sure about that either. Did you ever figure out what the problem was?

loosebearing

Try cleaning maf sensor/ mass air flow. And check all downstream of maf for leaks
any un metered air will cause your problem.
Maybe coolant temp sensor... if it is reading -22 will cause you too use more fuel.

bacano

i figured it out. back when i changed my plugs a year ago they tell you to not gap them because they are pre-gapped. well i always check just to be sure and the "pre-gap" was .04 when it is supposed to be .06 so i changed it. well i decided to redo my plugs yesterday and bought new ones, i contacted NGK to find out why the gap is wrong and they told me that the way these plug spark (they are the NGK GP Platinums) they need a smaller gap, so when i made the gap to .06 last time i was actually making it too big. so i just replaced them without changing this time. also cleaned the MAF sensor, throttle body and put a new fuel filter in-- the result....truck runs like a champ again. no hesitation issues.