I have a hesitation problem where when u accelerate it hesitates while u r driving..As well there is a loud buzzing(humming) sound that is constant.. The idle seems weak and feels like the vehicle is about to stall...This is what I have done so far: had fuel injectors cleaned, tried premium gas, had it scanned and it gave a code for faulty gas cap/fuel problem-vacuum...Had all my spark plugs changed, Tranny has been prev serviced and all my fluids are topped up... The fuel pump was tested for pressure and it is fine...Distributor cap and rotor are new, as is fuel filter and air filter... It stalled one day and would turn over but wouldnt catch.. eventually it did and I was able to drive a half block and it stalled again.....I have tried everything I can think of short of changing the fuel pump... I could really use some help/input from you guys......
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Ya got a tough one there.....where do you hear the buzzing, near the center of the dash?

 

I'd recommend that you remove the MAF sensor and give it a good cleaning (search 'MAF cleaning) as well as remove the EGR valve and clean all of the carbon out. Use a sensor safe cleaner on both the MAF and the EGR. You'll need a new EGR gasket so buy one ahead of time.

 

About 8 months ago I heard a humming noise coming from under the hood and the idle was a little rough and I had serging problems not hesitation but it turned out to be the vacuum lines were all cracked. One had a slit in it and that was the humming noise. I replaced all the rubber vacuum lines and it did the trick.
Just a thought.

 

Also check the PCV valve, I have seen them go bad and produce the humming noise, and it also allows too much vacuum to pass like a vacuum leak and cause problems that way. Just pull the PCV out of the valve cover, and plug the hole at the bottom. If the noise goes away, then replace the PCV valve. Korey.

 

thanks, I will try a couple more things before replacing the fuel pump.. Trust me,I wouldnt wish this on anyone and when i find the solution, u guys will be the first to know.. I just wish the truck would break down completely as it would be easier to fix a direct fix as opposed to an intermittent issue... stay tuned......
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That gas cap/vacuum fuel code could also mean that the evaporative emissions system needs attention, there is a vacuum module at the rear of the intake on the passenger side. It uses vacuum to check the fuel vapors in the tank. If you overfill your tank a lot this system gets fuel logged and fails....it is located near the fuel pump at the rear of the truck...

 

You really have all the symptoms of a vacuum leak somewhere. That is what I would be focusing on.

 

If a vacuum gauge were to be placed into the system, what would a good reading be if the system is leak free? I was thinking that a small gauge coyld be placed into line at some point and that would be a source to monitor the vacuum whenever you wanted to check it. Is tat feasible?

 

Still no luck.. I found that if driving in "drive" as opposed to "overdrive" the hesitation is there for the 1st ten minutes and then goes away... Idle still is weak and feels like vehicle will stall while sitting at a red light.... I just wish this damn thing would break down so I could find out what the problem is