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98 Vortec 350 NO POWER

Discussion in 'Chevy Trucks' started by jb1390, Sep 30, 2009.

  1. jb1390

    jb1390 Senior Member
    Messages: 710

    Hello all, I have a 1998 chevy 2500 8 lug. Seems to have no power at all, especially on hills. Runs ok flat. If you mash the pedal down it goes better, at higher rpms as expected. I tow with it-with 4000 pounds behind it, on some back roads in Connecticut, it couldn't hold 2nd gear! I think with the power ithas now, I would have to do some of my driveways in 4Low to even get up them. Last year I don't remember having this problem at all. Here is stuff I have replaced

    Plugs, wires, cap, rotor
    Fuel filter
    New injection system
    cleaned MAF sensor
    New Map sensor
    Compression is good the whole way around

    I did a fuel pressure check a few months ago, and it seemed to read fine (60 psi). The truck seems to have less power now than it did then, and the fuel pump is making more noise, and fluctuating in noise. Also have a little bit of a rough idle. Truck starts right up, even when it has sat for a few days. Do fuel pumps go bad slowly-causing a lack of power and it will eventually die? I am nervous to just toss one in for the heck of it, cuz they are upwards of $300.

    Any ideas are welcome-I'd love to be able to beat my mom's minivan in a drag race sometime soon - yes it is that bad.
     
  2. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

  3. jb1390

    jb1390 Senior Member
    Messages: 710

    Plugs are correctly gapped ac delcos (I think .060") Did the seafoam thing, and I cleaned out the intake when I was in there doing the injectors.
     
  4. jb1390

    jb1390 Senior Member
    Messages: 710

    One other symptom i can think of that has gotten worse recently-
    I hold the accelerator pedal steady climbing a hill-the truck will pull, maybe it loses speed some, but then all of a sudden with no change to the pedal, it will have significantly more power for 5-10 seconds, then go back to being slow.
     
  5. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    Tighten your gaps down to .040". Made a tremendous difference for me.
     
  6. jb1390

    jb1390 Senior Member
    Messages: 710

    I'll try the gaps and see if it helps-any chance the fuel pump is weak when warm or something? It (the pump) has been sounding differently lately, but is 300 for a new one so if it's a gamble I'd like to at least hear of someone that has had one act similarly.
     
  7. 70monte

    70monte Senior Member
    Messages: 468

    check your coil. I've had a lot of problems with my coil body arcing to the square metal piece that surrounds the coil body. Look for white burn marks on the coil body. My 98 K1500 with the 5.7L shows the same kind of symptoms when my coil starts arcing. I don't know why mine does this but I've probably had around five sets of ignition components in this truck since new. This all started after my first intake manifold gasket replacement by the dealer at around 25,000 miles and I've been fighting it ever since.

    Wayne
     
  8. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    JB - get yourself a fuel pressure gauge. About $40 at AutoZone. Get one with a long enough hose so you can drive down the road with it connected.

    Wayne - do you have your gaps down to .040"? The big gaps put a much greater load on the ignition components.
     
  9. 70monte

    70monte Senior Member
    Messages: 468

    No, I don't have my gaps down to .40 They are still at the factory .60 I'll try the lower gap and see what happens. Thanks.

    Wayne
     
  10. jb1390

    jb1390 Senior Member
    Messages: 710

    I have a friend that has a fuel pressure gage-I am heading to his house with a trailer on Saturday morning to see how it does. I will post back after that is done.
     
  11. brad96z28

    brad96z28 PlowSite.com Addict
    Messages: 1,526

    Make sure to ck fuel VOLUME its equally as important as pressure. U can have plenty of pressure and little volume.It often goes unchecked and unmentioned for some reason.
     
  12. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    What's the procedure?
     
  13. brad96z28

    brad96z28 PlowSite.com Addict
    Messages: 1,526

    Open the valve on ur fp gauge while engine running Insert hose into clear container Should have a few ounces in about 5 to 10 sec. Should have good steady flow.

    I would also be looking into a possible restricted cat converter. I doubt ur gona have a back pressure gauge .So u could also try a test drive with the exhaust disconnected before the cat just to see if it helps.
     
    Last edited: Oct 1, 2009
  14. augerandblade

    augerandblade PlowSite.com Addict
    Messages: 1,054

    Check for plugged exhaust. Catalytic converter may be plugged
     
  15. T-Trim

    T-Trim Senior Member
    from NE OH
    Messages: 207

    I agree. What goes in must come out.
     
  16. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    Good tip, thanks.
     
  17. jb1390

    jb1390 Senior Member
    Messages: 710

    I think it is the cats

    Fuel pressure is fine. TPS and other sensors are fine on the computer (but maybe we didn't look close enough at the MAP, and here is why)
    I just did a vacuum test while driving. I had done one before at idle, and revved it up to 2500 rpm-all showed fine. That is how I thought you tested cats. I thought to test it today while driving, so I set up my gauge so I could see it. I put it in gear-vacuum went from 20 down to 15. I then pulled out onto the road, gave it 15-20 percent throttle-and the vacuum went completely to ZERO!!!
    So the cats are coming out. I will post later on whether this definitively solves it. Thanks for your help.