cummins fuel problem

Discussion in 'Mechanic and Repair' started by ManleyLawn, Oct 20, 2003.

  1. ManleyLawn

    ManleyLawn LawnSite Member
    Messages: 107

    i have a 96 dodge ram 3500 with th cummins 12 valve diesel. i have been getting very poor fuel mileage. it has 137,000 miles on it. it has progressivly gotten worse. ive tried additives and cleaning the air filter and checked fuel linesfor cracks etc. would you guys give me your thoughts and opinions on this. thanks
    oh yeah it gets a bout 250 miles to a tank (29)gallons...
  2. Grassmechanic

    Grassmechanic LawnSite Silver Member
    Messages: 2,697

    Is it blowing black smoke? Did you have the valve lash adjusted every 48,000 mi? Is someone siphoning fuel from your tank? More info, please.
  3. sdwally

    sdwally LawnSite Senior Member
    Messages: 386

    Valve train probably needs adjusting, especially if the injectors are unit injectors(no diesel injector pump with steel injector lines running to injectors on the exterior of the engine.) You may also have some injectors with bad spray patterns, ie. pull the injectors and have them rebuilt.
  4. ManleyLawn

    ManleyLawn LawnSite Member
    Messages: 107

    yes it is blowing black smoke and no no one is siphoning gas from my tank and i haven't put 48000 miles on the truck but i'm sure the valves could be adjusted is that something that i can do or should i take it to a diesel tech?
  5. ManleyLawn

    ManleyLawn LawnSite Member
    Messages: 107

    thanks for the info
  6. Randy J

    Randy J LawnSite Bronze Member
    Messages: 1,124

    i'm trying to remember, I think the valves need adjustment on the old 12 valves about every 30,000 miles. It's not hard to do, if you're at all mechanically inclined. If not, than any diesel shop should be able to do it.

  7. Grassmechanic

    Grassmechanic LawnSite Silver Member
    Messages: 2,697

    Initial valve adjustment is at 24,000, then every 48,000 afterwards. It sounds like injector pump may need adjusting.
  8. ManleyLawn

    ManleyLawn LawnSite Member
    Messages: 107

    ok i talked to 2 diesel mechanics and they both said that it sounds like the injetors may need cleaned or replaced. the one also said that they have had cummins motors come in with over 200,000 miles on them and never have the valves touched i dunno i think i will give this lucas additive a full tank and see if it helps clean the injectors. thanks for the input
  9. floridalawncare

    floridalawncare LawnSite Member
    Messages: 98

    manley has the right idea. my uncle has one with over 500,000 and never a wrench on the engine. also be sure your air filter is in top notch shape. this is very important on any diesel. if these things don't work, your injection pump timing is adjustable. sometimes wear on your cam drive components can cause it to get a little out of time. it'll still run if it's not to far out, but not that good. i'd let a qualified tech perform this procedure.

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