old school db2 tricks
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Lead Driver
Joined: May 2007
Posts: 8,608
Likes: 13
From: Belair md
old school db2 tricks
ok guys, forgive my lack of memory but its been quite a while since i played with your pumps. i am helping out a friend with his and i remember about the fuel allen behind the plate, but isnt there another allen when you remove the center fuel line on the rear of the pump as well? and to advance the pump do you have to rotate the whole pump or can you adjust a trim screw for the cam on them?
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
The rear screw sets internal pump pressure.
Internal pump pressure affects timing and advance, so it is best left where it is.
If the pump is a 92.5 or newer, there is an external screw on the rear top, but not the earlier ones.
Internal pump pressure affects timing and advance, so it is best left where it is.
If the pump is a 92.5 or newer, there is an external screw on the rear top, but not the earlier ones.
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
In my limited understanding of the DB2......
There are primary and secondary fuel pressure circuits inside the pump.
The primary circuit pushes fuel in and through the pump between 5 and 8 psi and this pressure will infuence the timing and fuel delivery map.
The secondary circuit is a high pressure flow that is raised by the pumping plungers to deliver to the injectors.
I don't think the low pressure has a direct influence on high pressure above 8 psi, but I remember reading that its not recommended to go above 8 psi. Couldn't get a direct answer as to why, but I would guess it has to do with throwing the timing map off.
Unfortunately, DB2 tech is a bit of a black magic topic where anyone that knows anything tends to keep it to themselves. Not easy to glean info.
There are primary and secondary fuel pressure circuits inside the pump.
The primary circuit pushes fuel in and through the pump between 5 and 8 psi and this pressure will infuence the timing and fuel delivery map.
The secondary circuit is a high pressure flow that is raised by the pumping plungers to deliver to the injectors.
I don't think the low pressure has a direct influence on high pressure above 8 psi, but I remember reading that its not recommended to go above 8 psi. Couldn't get a direct answer as to why, but I would guess it has to do with throwing the timing map off.
Unfortunately, DB2 tech is a bit of a black magic topic where anyone that knows anything tends to keep it to themselves. Not easy to glean info.
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Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
The internal screw changes the max pressure.
The external screw changes how much fuel is injected at what RPM, sometimes refered to as the torque screw.
The screw is only present on 1992.5 and later engines, 4 different pumps that are all in the DB2-50xx series.
Drivers side rear of the pump, right below the fuel shut off cover on the top of the IP and leans up at a 45 degree angle.
Losen the lock nut, turn the screw out to lower the point fuel rate increases.
Just like the internal screw, say 1/4 turn at a time.
Also a pyrometer should be installed before adjusting the IP.
The external screw changes how much fuel is injected at what RPM, sometimes refered to as the torque screw.
The screw is only present on 1992.5 and later engines, 4 different pumps that are all in the DB2-50xx series.
Drivers side rear of the pump, right below the fuel shut off cover on the top of the IP and leans up at a 45 degree angle.
Losen the lock nut, turn the screw out to lower the point fuel rate increases.
Just like the internal screw, say 1/4 turn at a time.
Also a pyrometer should be installed before adjusting the IP.
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Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
I wish I had a picture of the screw in question.
If the red cap is on a screw that lays flat right above the rotary head, that is not it.
The 92.5 and newer IP works better with a turbo, simply because you can adjust the fueling curve externally.
I would compare the external fuel screw to the aneroid valve on a Big Cam 400 Cummins.
You can adjust how much fuel goes to the engine at lower RPM's which limits the smoke until the turbo spools up.
The screw is only on 4 IP's.
DB2-5013 on the auto tranny 92.5 to 94 NA
DB2-5028 on the manual tranny 92.5 to 94 NA
DB2-5069 on the auto tranny 93 and 94 turbo motor
DB2-5070 on the manual tranny 93 and 94 turbo motor
So if the truck is 91 or older and even the first of the 92 model trucks, the screw is not there on the IP.
All IP's that start with numbers below the DB2-50xx do not have it.
DB2-41xx, DB2-45xx, DB2-47xx and DB2-48xx are the numbers without the external screw.
If the red cap is on a screw that lays flat right above the rotary head, that is not it.
The 92.5 and newer IP works better with a turbo, simply because you can adjust the fueling curve externally.
I would compare the external fuel screw to the aneroid valve on a Big Cam 400 Cummins.
You can adjust how much fuel goes to the engine at lower RPM's which limits the smoke until the turbo spools up.
The screw is only on 4 IP's.
DB2-5013 on the auto tranny 92.5 to 94 NA
DB2-5028 on the manual tranny 92.5 to 94 NA
DB2-5069 on the auto tranny 93 and 94 turbo motor
DB2-5070 on the manual tranny 93 and 94 turbo motor
So if the truck is 91 or older and even the first of the 92 model trucks, the screw is not there on the IP.
All IP's that start with numbers below the DB2-50xx do not have it.
DB2-41xx, DB2-45xx, DB2-47xx and DB2-48xx are the numbers without the external screw.
