DB2 Tuning Guide

[Black dawg]

A few things from my messing with these pumps:
As far as the guide stud adjustment, at least half of the db2s I have had apart don't have the spring that rides up against the end of the guide stud, so I am not sure that adusting it in will do anything at all on some pumps.
On knocking the guts out of the return valve, I haven't seen one that behaves correctly with no housing pressure.....does the same thing as if you have the cold advance wired on. Maybe I have just have been dealing with crappy pumps?? Maybe this is where your note of electric pump needed comes in??

And just a note on bottoming the fuel screw, be careful trying to bottom it out, you can actually tighten it to the point that it distorts the rotor to where the pungers wont move, causing a no start/ no fuel issue.

 

[Thewespaul]

Black dog, can you post a picture of the spring you are referring to and a pump that is missing it? I’m not sure I follow what you are referring to. All db2s have an upper and lower governor spring, if they were missing one they would either never return to idle or they wouldn’t come past idle

For the housing pressure, every db2 gets the “rough adjustment” done with the top cover off to get the idle fueling about where it needs to be, then the cover is installed to dial it in on the test bench, so the pump can run fine with no pressure at all in the top of the housing. Theres a few videos floating around of pumps running on trucks with no cover. There’s still pressure in the housing, remember pressure is a measurement of restriction, and if you follow how the bypass works, there’s much smaller passages in the housing than the fitting on the top cover, like you said it’s effectively like running with the cold advance on all the time, which isn’t going to hurt anything. I’ve got this done on all of my own pumps and several customer’s pumps, and had no issues, Ive been testing these things for years now, I wanted to be positive they were safe for posting them on here.

For the fuel screw, yes you need to be very gentle with the adjustment, when you feel it start to tighten just stop, don’t try and force it. I’ve seen these screws stripped, broken and bent in pump cores, and that gets expensive.

 

[Macrobb]

I want to point out a test case of the 'torque screw' - it affects high RPM fueling a lot more than lower RPM - exactly the opposite of what you want with a turbo.

Last year, I took my '92 with Banks to Hunting 4 horsepower. i'd maxed out the fuel screw, and it'd smoke down low, but didn't have much high end. Dyno said 150HP(rear wheel, so probably 210 crank).

I Backed out the torque screw and ran again, a few hours later... 200RWHP(so 260-270 crank). BIG difference.

That was at 7 psi of boost, due to a 1" hole leaking boost from the intake.

 

[Thewespaul]

That’s interesting you had that result, I wonder if it was because the turbo was getting spooled sooner in the rpm range so you were able to match the amount of air you needed up top. The screw in my experimenting on the test bench netted about four times more fuel down low than it did up top

 

[Runningaford]

Interesting thread, good write up OP.

 

[68f2506.9]

Awesome, thank you for the writeup! I had been wondering about adjusting the pump. I can always use more fuel.

 

[BlackNoma]

It has now occurred to me that I need to start tinkering with my pump...

Thanks!

 

[Thewespaul]

It has now occurred to me that I need to start tinkering with my pump...

Thanks!

I offered to time and tune the truck when I was at Matt’s place, but they wanted to invest as little money as they could into the truck. From the sound of it I would reckon it could use a good bit more fuel.

 

[BlackNoma]

I offered to time and tune the truck when I was at Matt’s place, but they wanted to invest as little money as they could into the truck. From the sound of it I would reckon it could use a good bit more fuel.

I plan to come visit you as soon as I can. This truck deserves someone who knows what they are doing. Haha

 

[Steven Donald]

Great write up! Very well written explanation of everything we went over on the phone a few months back.

I know the spring he is talking about. Blacknoma had that spring fall out and get eaten inside his IP (my fault!). It's the spring that the rear adjustment guide pushes against inside of the fuel/throttle assembly. The IP will run without it completely, I've done it for a long while. And yeah, if that small interior spring isn't in there, the rear fueling adjustment won't do anything.

 

[Thewespaul]

Great write up! Very well written explanation of everything we went over on the phone a few months back.

I know the spring he is talking about. Blacknoma had that spring fall out and get eaten inside his IP (my fault!). It's the spring that the rear adjustment guide pushes against inside of the fuel/throttle assembly. The IP will run without it completely, I've done it for a long while. And yeah, if that small interior spring isn't in there, the rear fueling adjustment won't do anything.

Thanks Steven, hope you and the truck are still doing well! That’s interesting about the spring, I’ve got a late model case in the parts bin I’m gonna have to take a look at. I’ll post some pictures when I get a chance to tear into it

 

[Goose_ss4]

Great info

 

[Agnem]

Just to caution some folks, there is a lot of truth, but also a bit of vapor to what has been stated here. Hot start issues have nothing to do with fuel pressure in the case. It's simply a matter of the fuel in the nose cone getting superheated by the radiant heat from the engine, and thinning it out. If you want to invent something to fix that, make yourself a radiator for the nose cone. The amount of starting fuel is affected by pop pressure. But then all the fuel, starting or not, is affected by pop pressure. 1700 PSI is the spec the pumps are calibrated to. Making it much lower then that will result in poor chatter. Huff was playing around with keeping his cold advance solenoid energized to get the extra 2 degrees of advance 15 years ago. Busting up the return check valve is going to impact your core value. Just wire your cold advance to your fuel shutoff to achieve the same thing without damaging anything. A custom cam for the throttle shaft is only going to affect lower RPM's. Above a certain point, the cam and arm have little bearing on what is going on with the advance because hydraulics and not mechanical spring pressure will be the dominant force. keep up the good work Wes, but do caution people that they could end up with enough tweaks on their pump that they will end up very unhappy. Every adjustment affects another, and you cannot know for certain how many turns of X will be needed to compensate for turns of Y, andwhile power changes may be obvious, MPG changes wont be.

 

[sjwelds]

Thanks for chiming in on this one Mel.

 

[Thewespaul]

Thanks Mel, your knowledge is definitely missed here, it’s good to see you check in from time to time! I agree housing pressure has nothing to do with hot starting, my goal with the return fitting mod was to get more fuel flowing through the return, pulling heat out of the pump. I am also working on a fuel cooler, but that is in another thread and is mid project, but I’d love to hear your thoughts on that as well. With no cooler I am seeing up to 175* fuel coming out of the return of the injection pump, I am working on trying to bring that temperature down but like you said a lot of the heat is coming from the pumps connection to the engine, and there’s not much that can be done about that