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'97 5.7 hesitation ??

Discussion in 'Chevy Trucks' started by scottL, Nov 20, 2004.

  1. scottL

    scottL PlowSite.com Addict
    Messages: 1,600

    '97 5.7 k3500 with 81k on the motor. In the last few weeks it has slowly grown to have a hesitation, slight lack of power when accelerating. Almost a bit jerkey like it was mis-firing. This would be true while in park and reving the motor too.

    I had the fuel injectors and pump replaced new about 12 months ago. Spark plugs, wires and cap too. Exhaust doesn't smell bad. Any thoughts?

    Thanks in advance,
  2. redhenny16

    redhenny16 Senior Member
    Messages: 134

    Check your fuel filter, if it's plugged it could easily cause a hesitation problem. If you compare a new filter to your old one by blowing through them, you should be able to tell if your filter is plugged. Hold a clean shop rag over the inlet side unless you like the taste of gas.
  3. Low fuel pressure could be causing the problem. You can pick up a cheap fuel pressure guage and parts house(or maybe rent one). You will have a schraeder valve on your fuel line next to carb. I'm not sure what recommended fuel pressure is, but a dealership should be able to tell you.

    I also use Alldatadiy.com very often, it has saved me money on numerous occassions, check them out, its a good deal for $25. You can access any info that a repair shop can, but only for 1 vehicle.
  4. scottL

    scottL PlowSite.com Addict
    Messages: 1,600

    the alldatadiy.com site looks cool.

    I'll check the fuel pressure - I would assume it to be good as it was only 10 months ago the replaced a new pump and filter.
  5. lawnmedic

    lawnmedic Senior Member
    Messages: 703

    My first check would be the throttle position sensor. use an analog VOM to see if there are any spikes as you go from closed to full open. It can be quickly done by disconnecting the plug the sensor attaching the VOM with alligator clips then slowly opening, then releasing the throttle. If it is not perfectly smooth it needs replaced...

  6. I don't know if you used aftermarket or OEM part. But if there is one part that I always buy OEM is the fuel pump. Hopefully that's what yours is, because I've heard nightmare stories about them.
  7. Tarkus

    Tarkus PlowSite.com Addict
    Messages: 1,113

    Check knock sensor and fuel quality because with GM trucks when the hear knock thay can ****** timing aggressively and suddenly without warning and cause engine to lack power and feel "funny" at times
  8. scottL

    scottL PlowSite.com Addict
    Messages: 1,600

    The fuel pump was from GM and installed by them when they put all new injectors and fuel filter. Based on the observations I suspected the MAP sensor. Although, the motor is smoother I still have the problem.

    The issues comes into play after the engine is fully warmed up. Then I will notice the hesitation, jerkness when loading the motor ( accelerating at any speed or pushing on the throttle up a hill ). I did run to autozone and there were no codes in the computer.
  9. Tarkus

    Tarkus PlowSite.com Addict
    Messages: 1,113

    I still say check knock sensor and timing as well as fuel quality because all your problem times are in that possible operations envelope. When it adjusts timing a lot dynamically from knock (and you will not usually here it either) it can make engine feel funny and weak suddenly. Also for "grins" try a full tank of high octane fuel.
  10. JMR

    JMR Senior Member
    Messages: 567

    Short of throwing parts at the vehicle and hoping you find the fix (roulette method of repair), take the vehicle to a competent professional repair facility that has the ability to properly read and interpret scanner data (not just codes) and check fuel pressure. If I were to GUESS, MAYBE a fuel pressure regulator. Remember there is no substitute for proper diagnostic procedures. Good luck.
  11. scottL

    scottL PlowSite.com Addict
    Messages: 1,600

    I appreciate all of the help! Although, one of my favorite types of repair is roulette method of repair :)

    It turns out that the original issue was the MAP sensor. The ride got better immediately however, there was still a nagging similair issue. So, I had searched and found the unfortunate thing was I went and did the spark plugs too. When doing the plugs I must have nicked the jacket and caused an arc. Dugh! The arc only appeared when I was placing load, accelerating moderate to hard. I corrected the arc and now the truck runs great!

    Thanks again,

  12. Tarkus

    Tarkus PlowSite.com Addict
    Messages: 1,113

    It is not that hard to fix a GM FI system when you understand how it works. If it was a fuel pressure problem it would likely be even worse when cold because engine uses more fuel before it is warmed up fully. This is a "management" issue for sure and I have seen truck go to "dealers" for prefessional help and come back with big bill and no fixes. A over active knck sensor and/or poor octan fuel will not throw codes generally either.