A Hard Shift and A Little Lope

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by chrissytaz, Sep 20, 2012.

  1. chrissytaz

    chrissytaz New Member

    :glasses: Hi guys,

    Well it's been a while since my last post, but I have been under the hood almost every weekend cleaning and changing parts. The stuttering problem seems to have been resolved when I changed out the idler pully. I noticed the old one wasn't sitting in the right spot and kept slipping. Since the new one has been on there haven't been any more "stuttering" issues, but now I have encountered something new.

    Along with the idler pully, I also replaced the tensioner pulley by the water pump. (I think that belt goes from the water pump to the A/C compressor? Am I correct?) I also put a new cover on my after market K&N air filter (it looks like a cone). The cover is completely open on the side where the air flows in, about 4" from the inside of the fender, and has about 1/2" room around the filter itself before it meets the MAF on the other side. I have new plugs and wires and a new fuel filter. I have run numerous bottles of fuel injector cleaner through the tank and a bottle of sludge cleaner mixed in with the oil.

    Now, all that being said, I really don't think that what I have done so far would have created my current problem, but as I have stated before I am new to this and I haven't been under the hood this much in a long time.

    The current problems:
    1) I have a very hard shift from first to second gear when I push the truck to accelerate. If I baby the gas then it shifts normally. If I'm pulling in to traffic and need to accelerate quickly, the truck litterally jumps when it shifts from 1st to second. After that it shifts into higher gears smoothly, but is very sluggish and seems to be over reving to get into 3rd and 4th, shifting around 2000-2500rpm regardless of whether I am trying to accelerate quickly or slowly.
    2) While I'm driving at a constant speed, probably between 40-50 mph, it starts to lope (if that is the correct term). It feels like it is losing power and then recovers very quickly. I think it may be starving for fuel?

    Additional Info:
    I have checked the pressure by pushing the nozzle thing on the engine block and it sprays like it has plenty of pressure. Is there something that I can use to determine what the actual pressure is? What is it supposed to be?

    I look forward to your responses, thanks for the help!
  2. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    You can rent a fuel pressure gauge from autozone for free. They just take your creditcard info incase you do not bring it back. You screw it on the fitting and start the truck. I believe that the pressure should be between 50-60 psi but I could be wrong.
  3. chrissytaz

    chrissytaz New Member

    Thanks! I will have to check that out. What do you think about the problems that I'm having? Do you think it is starving for fuel? Or could it be something else?
  4. bazar01

    bazar01 Epic Member 5+ Years 100 Posts

    This is my take on your second issue. I had the same issue while cruising between 50-55 mph. When I try to accelerate from 55 mph, it jerks back and forth as if it was starving for fuel or missfiring. It will not speed up above 60 mph unless I turn the a/c off.

    I just did a fuel pressure test on my 2001 Suburban. I had to buy the tool from Advance since they do not rent the tool anymore. It took me almost a week of elimination to come to a conclusion that my fuel pressure regulator was the culprit. I was dealing with a fuel pressure below spec issue. I was only getting 44 psi and bleeds off to zero in 2 minutes. There are 3 sources of fuel bleeding off. Injectors, regulator and check valve in the fuel pump. I found out my regulator was bleeding off fuel before I even got into the check valve on the fuel pump.

    As far as your first issue, I don't have any idea.
  5. chrissytaz

    chrissytaz New Member

    Thanks for the help guys! I finally was able to check the pressure and it was at about 48 steady. I let the truck run for about a minute and it didn't change. How long should I leave the truck is running to see if it changes?
  6. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    From what I understand you should shut it off and see how long it holds the pressure
  7. j cat

    j cat Epic Member 5+ Years 1000 Posts

    indicate what engine year and if its e85/regular fuel.

    on a gasoline 87 octane 5.3L engine 1999-2006 the fuel pressure should be 60-65psi key on engine off. if it rapidly drops off then you must check pressure at the fuel pump to see if its the check valve in the pump.

    with the engine running the pressure should be 53-60psi. I find 57 psi normal.

    e85 engines run on lower fuel pressure. 47-53psi .
  8. chrissytaz

    chrissytaz New Member

    How do i determine what the engine year is and whether it is e85?
  9. j cat

    j cat Epic Member 5+ Years 1000 Posts

    what model year is the vehicle ? using the vin # check with the dealership if its e85 capable. look at the gas cap IF OEM see if it says e85 fuel .

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