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Chugging under acceleration. no SES light

Discussion in 'Chevy C/K Truck Forum' started by milisd, Nov 14, 2011.

  1. milisd

    milisd New Member

    heres the deal, i got a 98 GMC sierra with a 5.7 vortec. its starts and idles just fine and as long as you accelerate lightly it is also fine. if i accelerate hard it will just pick up RPM's a little and then sit there and chug and hesitiate. if im at a higher speed and i try to accelerate hard enough to cause a downshift it will not downshift and it will sit there and hessitate and chugg. it up shifts perfectly also. if i stop and put the truck in park or nuetral and i slowly build up RPM i can get it to redline. but if i just hammer on the accelerator in park or nuetral it will get up to about 2500 rpm and sit there and chug and hesitate(same thing it does in drive). there also is no service engine light on. it just randomly started doing this today when i was out for a drive. i turned the truck off and let it sit for 5 hours and then drove it again and it still doing the same thing. Im wondering it anyone has had the same problem and gotten to the bottom of it? or could point me on a good direction to start looking. thanks in advance
  2. RebelChevy

    RebelChevy New Member

    same problem on my 2001 a few years back. bad fuel pump- the pressure on the rail was normal but the volume was way low, couldnt supply enough gas to the injectors
  3. milisd

    milisd New Member

    Thanks for the response. Thats kinda what i was thinking, i was gunna run a test pressure test on it today as soon as i got home. the fuel pump thats in there was replaced about 30k miles ago, so that kinda makes me wonder if it is the fuel pump or maybe a sensor like a TPS or MAP sensor. is there anyway to test the fuel pump with a multi- meter?. i know i would rather replace a TPS sensor then a stupid fuel pump.
  4. silveradotrailblazer

    silveradotrailblazer New Member 1000 Posts

    Welcome to the club. Has your truck thrown any codes,SES light??
  5. milisd

    milisd New Member

    it threw a service engine light this morning. and when i got it scaned it said TPS low voltage and some Torque converter code which are prolly caused because it wouldnt downshift and i was kinda beating on it to see if it would or not, because the tranny shifts fine. im gunna run a test on the TPS tomorrow and see what types of voltage reading i get. and when i started my truck after work the SES light was gone and i didnt not clear it
  6. milisd

    milisd New Member


    so i pulled my front o2 sensors and ran the trucka nd its still runs the same, so i think i can eliminate the cat as one of the problems. i also put new plugs and wire in it because they looked horrible and were cracking, still running the same. then i tested the TPS and it checked out fine. im starting to think it might be the fuel filter, but im gunna dance around that issue until im sure about it, so fuel filter first then pump. thanks for your input
  7. milisd

    milisd New Member

    just put the new fuel filter in and its still doing the same thing. i did a presssure test and i got about 55 when key is on and not running, 48 when running at idle. when you step on it the pressure spikes to 55 maybe 60 and then drops to 48 again........ WTF is this things problem?????
  8. RebelChevy

    RebelChevy New Member

    pressure can be fine on a bad pump

    theres 3 different fuel pump tests. pressure, voltage and volume. the pressure may be fine but it might not be putting out enough fuel you gotta get liters/hour specs on that pump, pull off a fuel line and check that the output is sufficient

    ---------- Post added at 12:37 PM ---------- Previous post was at 12:31 PM ----------

    theres 3 different fuel pump tests. pressure, voltage and volume. the pressure may be fine but it might not be putting out enough fuel you gotta get liters/hour specs on that pump, pull off a fuel line and check that the output is sufficient

    also try brake stalling the converter. should be around 2500 RPMs less could mean the converter is bad
  9. milisd

    milisd New Member

    i just bought a new fuel pump, but im gunna try this brake stall thing your talking about first. but it does it in nuetral and drive....thats why i think its the fuel pump, and the mechanic when i went to get my fuel pump said that 48 psi is low, should be around 65.
  10. milisd

    milisd New Member

    it was the fuel pump. i was 48psi before and now i running 54psi and it runs like its brand new. the guy before me replace it with an airtec and all ive heard is that those are junk. ive heard that the bosch is the way to go. just so everyone knows...and its got a lifetime warranty
    :)

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