Diagnose rough running chevy R10

Discussion in '1973-1987' started by MikeH, May 22, 2017.

  1. MikeH

    MikeH Member

    Joined:
    May 22, 2017
    Messages:
    3
    Good morning all - I am new to the forums and to Chevy trucks

    I just acquired a 1987 Chevy R10 5.7 litre with TBI for $1 from my neighbor who bought it new in 87 and no longer wanted it. The truck is in pretty good condition for 30 years old, but does have some issues and no rust at all - AZ truck :)

    So here is the issue and I am hopeful someone can help -

    The truck starts fine and idles pretty well, but when you drive it it is very rough and sputters quite a bit. When going from park to drive it sometimes almost dies and when idling it does surge a bit.

    So I have done the following -

    1) Replaced all plugs, plug wires, cap and rotor
    2) Replaced MAP
    3) Replaced PCV valve

    I have a fuel filter which I have not replaced yet because I was unsure if I had to disable the fuel etc. or just get under there and replace it.

    I read on this forum that there are two (2) pumps - 1 for each tank. When I have the dash tank selector positioned to the RH tank and turn on the key I hear a pump run, but when I switch to the LH tank and do the same thing I hear nothing - is that normal or should I hear the pump run?

    I appreciate any help anyone can give and hopefully I have given all of you enough information to help out.

    Thanks!

    Mike
     
  2. nerfherder78

    nerfherder78 Member

    Joined:
    Aug 15, 2003
    Messages:
    318
    Location:
    Fairfield, CA
    You can replace the fuel filter without disabling the fuel pump, most often you just remove the gas cap to relieve any pressure in the tank.
    Typically you disable the pump then run the engine till it stalls to bleed off most of the fuel in the lines so you get less of a mess when undoing the lines. You can disable the pump by disconnecting the fuel pump relay on the passenger side firewall.

    If you cant hear the pump working from inside the truck it may still be working fine, in fact fuel pumps can get louder as they get weaker. Does it run from either tank? The best way to check the condition of the fuel pumps would be to hook up a fuel pressure gauge. I dont know if there's a factory port you can hook it up too, but it should be around 11 - 13 psi.
     
  3. MikeH

    MikeH Member

    Joined:
    May 22, 2017
    Messages:
    3
    Thanks nerfherder - I was able to swap out the fuel filter and the truck still runs rough on either tank. The dash tank selector switch does not work well - it is very old and I am not certain it is actually switching. I fiddled with it and it broke apart and the truck stopped running :) thank goodness I was in the driveway!

    So I need to replace the tank selector, but I wonder if that could be causing some of the issue as well - maybe it was not switching properly - who knows.

    I saw some articles on how to check the fuel pressure so maybe I need to go down that path as well.

    Question - there are fuel pumps in the tanks, but is there also a mechanical fuel pump on the engine block?

    Thanks for your help - much appreciated.
     
  4. MikeH

    MikeH Member

    Joined:
    May 22, 2017
    Messages:
    3
    Oh and to answer your question about running from either tank - yes it does. The left hand tank seems to run more rough than the right, but that just could be me thinking that is the case.
     

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