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Anybody a diesel mechanic ??

Discussion in 'Random Ramblings' started by BigBirdHatcher, Apr 8, 2012.

  1. BigBirdHatcher

    BigBirdHatcher In the Brooder

    Nov 13, 2011
    Purchased a 1998 3/4 dodge with a 12 valve with 5 speed, it is idling real low, around 500 rpm. I know how to fix it but i have a short list of questions.
    1. What is the exact idle rpm supposed to be. Around 900 or so rite ?
    2. How much turn on the idle screw will get the rpms up to where they need to be ?
    3. What does the high idle screw do ?
    4. And how do I plug the waste gate on the turbo to make it spool faster ?

  2. b.hromada

    b.hromada Flock Mistress

    I'm not, but my hubby is!!!
  3. Royd

    Royd Songster

    May 31, 2009
    Middleburg, Fl.
    I have a '91 Ram 350. Same engine and have replaced all injection parts, over the last few years. Yours does have some electronics in the injection system.

    I don't know exact rpm, but if you are setting a stoplight, the truck should not want to take off, on its own, with light pressure on the brake, and it shouldn't want to lug down, like it's fixing to shut off...I'd say around 750-800 rpm.
    My rpm is adjusted with a double ended screwarm. Loosen both locknuts, turn the bolt in or out to achieve the desired rpm and RETIGHTEN the lock nuts. If you don't, there is enough vibration in the engine to make the bolt unscrew by itself...How do I know?

    As for the last question, I don't know...I do have a brother who is a mechanic, and his advice is, Once you start messing with one thing, you start affecting everything else....The engines were designed to operate effeciently, within certain power parameters. Once you start tweeking things, you are throwing the whole system out of wack.
    Last edited: Apr 10, 2012
  4. Chook-A-Holic

    Chook-A-Holic Songster

    Oct 5, 2009
    Central, N.C.
    Heed the above advice. The turbo in and of itself is not a component but part of a system. You want faster spool, you need to take into consideration...injectors and their timing, pump adjustments, and fuel...alot more fuel. You will also need to watch your EGT's(exhaust gas temps). Things can and will melt or grenade. Also keep in mind that turbos only work within their designed parameters. When you add to the bottom you are taking away from the top.

    I get so tickled when I see these pickups take off leaving a cloud of black smoke with an off the shelf tuner. The owners haven't a clue that they could do the same thing(power wise) with less fuel. They are wasting more than they are burning...lol.

    Good Luck!
  5. Don't know a lot about diesels, but I do know about turbos. The waste gate has nothing to do with how quickly the turbo starts boost. That is a function of a couple of things:
    • The size of the turbo.
    • How free flowing the exhaust system is.

    The waste gate simply limits the total amount of boost. Adjusting it without knowing how much internal pressure your engine can tolerate is something you do at your own risk.
    Last edited: Apr 11, 2012
  6. BigBirdHatcher

    BigBirdHatcher In the Brooder

    Nov 13, 2011
    Thanks for the advice folks. And I just realized that I wrote 1998 in the post it is a 97, my bad.
    I got the idle set to where it sounds a lot better then it did, somewheres around 850-900 or so, but i still have to give it a little fuel for it to start up, and if i give it fuel when it is idling it revs up really rough and it sounds like it slams back down into idle when I let off (don't know how to better explain that). The warmer it gets the less noticeable this sound is, I don't know if that is normal since this is my first 12 valve.

    Royd. Thanks for the advice, its getting hard to find unmolested 12 valves these days, and the one I've got has already been messed with by someone I can tell, but it isn't turned up so I am thinking it has had a rebuild. And also what part of the injection system is electronic, I thought it was all mechanical.

    Chook. I agree with you that it waste more fuel then is actually used to make power. But some people just do that because they like for their trucks to black smoke and its cheaper in the short race to get the power with a programmer. Back in high school we used to slide the fuel plates all the way or take them out completely, cheap mod, but wasted lots of diesel.

    Old Guy. Thanks for the info on turbos, I know almost nothing about turbos apart from the basics on how they work. I forgot that bigger exhaust helps the turbo, but I did notice that the stock pip is still on the truck but with no muffler. Bigger pipes are in the works already. [​IMG]
  7. BigBirdHatcher, if yours is a 12 valve it has a Bosch P7100 inline pump and is mechanical. The one Royd is probably thinking of is late model '98 with a VP44 pump, and the engine would be a 24 valve. I have a '90 model 12 valve with the older VE rotary. Go with bigger pipes first.By the way have you checked the lift or fuel supply pump to see if it's output is right? A worn or malfunctioning lift pump can also make it run rough, and damage the injection pump. Just thought I'd ask.

  8. BigBirdHatcher

    BigBirdHatcher In the Brooder

    Nov 13, 2011
    Thanks for the clarification JD, I was pretty sure that mine was all mechanical. It is no doubt a 12 valve.
    How do I check the lift and fuel supply.
    Also I am going to get a set of stack so the only actual pipe I will have to get is a down pipe. What is the biggest / best dp for the stock turbo? And I know diesels can run with almost no back pressure but how much pipe is too much?
    And I noticed that I might have an injector leaking, I didn't look to hard but if that is so then it might possibly be my rough idle problem.

    I have a few new questions.
    Will all of the door mirrors and glass out of the 2nd gens interchange?
    And will the leaf springs off a ford Dana 80 bolt up to my Dana 80 and frame?
  9. Just a thought; Have you checked for contaminated fuel?
  10. BigBirdHatcher

    BigBirdHatcher In the Brooder

    Nov 13, 2011
    No sir, how would I go about doing that.

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