DB2 Tuning Guide

pelky350

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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.
 

Thewespaul

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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.
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.
 

pelky350

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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
 

Thewespaul

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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.
 

jetfly12

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The only thing I did not touch is the fuel screw and I know I have 2-3 flats left from max because I backed it off last time I adjusted it. I know the fuel screw greatly effects top end fueling and egt's. Right now I have my wastegate shut and hovers around 15-16psi and 800 egts going up hills so I got plently of egts to spare. I do not have headstuds, so I am comfortable staying at 15psi. I haven't decided if I will experiment the maxed out fuel screw and take it out for a test drive or wait until I get my ford 6.0 intercooler installed and hooked up, see what the pressure drop is and adjust/tune accordingly.
Thanks again for sharing the guide!

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!
 

hce

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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.
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.
 

Thewespaul

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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!
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.
 

jetfly12

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In a diesel the wastegate is really there to prevent turbo overspeed.

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.

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.

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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Thewespaul

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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
 

ifrythings

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So if one was wanting to remove the leaf spring for the rollers is there anything special you have to do after? Do you need to plug the screw hole? I’m guessing the plungers can’t push the rollers too far out and bind?
 

Thewespaul

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So if one was wanting to remove the leaf spring for the rollers is there anything special you have to do after? Do you need to plug the screw hole? I’m guessing the plungers can’t push the rollers too far out and bind?
Nope, just leave it out. Only thing that needs to be done is the pump will need to be calibrated on a stand, your idle fuel will increase so much you won’t be able to get it to idle below 1700 rpms.
 

ifrythings

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Nope, just leave it out. Only thing that needs to be done is the pump will need to be calibrated on a stand, your idle fuel will increase so much you won’t be able to get it to idle below 1700 rpms.

Interesting, why would removing the leaf spring mess up the idle so bad? I thought it only effected max fuel. Is it just a matter of turning the idle down or does the governor need to be adjusted?
 

Thewespaul

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It’s going to increase fueling a lot across the board, it’s not like the fuel screw which is changing the stroke of the plungers by fractions of a millimeter, it’s almost doubling the stroke of the plungers. These pumps were not designed to idle with that amount of fuel, and with no leaf spring you would be looking at anywhere from 110-130cc of fuel, depending on the condition of the pump so I’d really recommend an intercooler and larger than stock turbo along with studs for running that much fuel. But back to the idling issue, these pumps aren’t meant to idle with that much fuel delivery, the idle is controlled by the minimax governor, which controls the position of the metering valve, which controls how much transfer pressure gets to the plungers. The plungers displace the same amount of volume no matter what, so it’s up to the metering valve’s setting to control the flow to the plungers so you can get that 5cc to idle correctly. The problem you run into on these larger db2s is you can run out of adjustment quickly and you have to adjust the regulator for the transfer pressure pump to bring down idle transfer pressure as a way to cheat the flow down to the metering valve, as a way to get more fine adjustment to get a crisp idle and good droop setting. Issue with that, is transfer pressure affects your hydraulic advance, so you have to have a stand to be able to check your hydraulic advance and adjust the advance piston setting accordingly to get it back into spec, 6-7.5* locked at idle is what you want. Another issue you can run into with doing this without a stand is your return fuel volume, one of the bigger wear spots on these pumps is the advance piston bore to piston tolerance. This tolerance controls your return fuel volume, and when you increase your total fuel volume you also increase your return fuel volume. These bores wear out really quick because it’s a steel piston sliding in a aluminum bore. These bores need to be re-reamed after your main fuel is set to get your return fuel into spec, there are several oversized pistons available to account for wear but lots of pumps already have the largest piston in them already, I put a ceramic sleeve in them to go back to the standard bore size, and to eliminate the quick wear issues.
 

ocnorb

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Thanks for this great write up!

Does it mean anything if you take the minmax screw all the way in and the idle rpm stays the same?
 
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