DB2 Tuning Guide

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Thewespaul, Sep 17, 2018.

  1. pelky350

    pelky350 Full Access Member

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    @Thewespaul how are you getting your truck up to 3500 in 5th gear? Mine just won’t do it even in 4th it just wants to be over with at like 2900? Pulls strong until above like 2500. And if I shift it will climb really fast in 4th and 5th till then and then it just seems to sign off. 1-2-3rd can climb till redline and then some though. With a r and d 90cc and stage 1’s/ upgraded factory turbo/ intercooler and carter 4070 lift.
     
  2. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Sounds like your governor is kicking in prematurely. You should at least have full fueling till 3000. I stretched my gov spring an inch and a half and I can rev to 4K now with the minimax bottomed out. I would make sure the screw on the throttle arm isn’t limiting your travel. Then check your throttle cable and take any slack out of it by holding the pedal up and putting zip ties around the end of the cable. You don’t want the pedal to be touching the floor when it’s all the way down. If all that is good and you are still having issues, I’d bottom out the minimax. This will bring the fuel curve up higher in the rpm range, making it a bit less Smokey and hopefully giving you some more rpm.
     
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  3. pelky350

    pelky350 Full Access Member

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    @Thewespaul it will rev to over 3500 in 3rd and below still, cable checks out I did the zip tie thing also. I was hoping not to mess with the pump too much because it still isn’t that old yet but maybe it’s been a while I just hope it doesn’t void the warrantee idk if that would or not it’s justins r and d pump
     
  4. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    So here’s what I think is happening, when you’re in 4th and 5th the pump is under the most load and the governor will put out the most fuel in those gears. When you are at high load and high rpm, you are at the most fuel demand and it sounds like your lift pump isn’t keeping up. When you are in third you can rev no problem because you have less load.

    I’m having the same issue with the shop truck, plenty of fuel pressure until I get past 110 mph, then I start to loose power as fuel pressure drops. The truck still makes good power since the lift pump is still putting out a decent amount of fuel, but the injection pump could be doing more if it was getting steady fuel pressure.
     
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  5. jetfly12

    jetfly12 Registered User

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    Had tons of free time today, so I went ahead and tinkered with the fuel screw. It is easy enough for me to do in 20 minutes and went for a drive. The result was the pedal was less sensitive and it makes sense because now the governor has more upper end fuel range to work with. MAN it sure pours black smoke before the turbo lights up so more $$$ out of the tail pipe. going up a hill I saw 20 psi in 4th gear, so I got my satisfaction there and better just set the wastegate now before I lift a cylinder head off the block. Went ahead and did a 35-70mph test again, and it shave off another two seconds to my time. If anybody wants a video of that I will post it up. I wish I would of done that in the first place to show that it went from 14 down to 9 seconds!
     
  6. hce

    hce So can i.... Supporting Member

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    This is where the math gets blurry, fuel combusting makes the pressure that will lift heads not boost. More air, more fuel can be burned, more fuel burned more combustion pressure. More air same fuel, very little change in combustion pressure, but lower egt and cleaner exhuast. Obviously turning down the boost via a wastegate will not affect fuel delivery, if combustion pressure are lowering boost then there is more fuel then air to burn. The fuel delivery should be adjusted to attain a safe level of boost or keep the foot of the pedal if the rest of the driving experience is improved. In a diesel the wastegate is really there to prevent turbo overspeed.
     
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  7. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    9 seconds is getting into new truck territory;burnout

    You’re right about the governor, because the fuel screw gives more room to the throttle it makes it less touchy, which is totally normal.

    As far as where to go from here, I would be tempted to leave the fuel screw where it’s at, adjust the wastegate where you’re happy with the boost, then dial back the smoke with the torque screw until it’s acceptable when you’re getting the turbo to light. If you have smoke at wot when you have the wastegate adjusted down then I would play with the timing a bit, it may like a bit more retarded timing now.
     
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  8. jetfly12

    jetfly12 Registered User

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    I agree with you, and I don't have enough fuel to overspeed the stage 1 (upward to 65lb/min) and I think it takes 120cc of fuel to get there and no where near to that with a stock IP. I worry I will have too much cyclinder pressure having no studs, certainly don't want to blow the gaskets and get stranded going over i70 with 13k loaded, trailer with trail rig. I will see where it is at egt wise with an intercooler and adjust from there, also could just keep the foot out lol.

    Yes, does that mean its a 9 second car now?!
    If I grind down the locking nut, would it be more sensitive again? I kinda liked it that way, although the lurching issue has been mitigated.
    To be honest every time i adjusted the torque screw, nothing happens. But that was only before doing all these other adjustments and maybe itll do something now. Maybe next time I get back around to it.
    Timing is retarded as far I can tell, sounds like a gasser, if i have time I will try more retard.
    Notice in the video on the boost gauge on the top right, while in 3rd gear it steadies out at 15psi, going into 4th it spikes to 17-18psi. I thought that was interesting.
     
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  9. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    I turn the nuts down on a lathe to get them perfectly flat, the nut does seal the back of the housing. If you are careful to get it really flat on a grinder or belt sander go for it, or I can have another batch of modified nuts made.

    If you feel the timing is really retarded, maybe give it some more advance and see what happens. Every fuel adjustment on the pump will affect your overall timing to an extent, so it’s best to readjust after you get the fuel we’re you like it.

    You will get more boost in higher gears because there’s more load on the engine. More load brings the flywheights out further which brings more fuel out of the pump, this sensitivity by load is related to the minimaxx adjustment and housing pressure.

    The torque screw has to be screwed in pretty far before it touches anything, you will see how far it needs to go if you take the top cover off, it’s effectively doing what the hypermax smoke puff limitor does
     
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