4911 Inner Workings

[6.5L]

A while back somebody had posted about the side advance arm and transfer case pressure on my DB2-4911 MECHANICAL injection pump. I had asked a few times what these were, where they are located, and what they would do if I messed with them and even what I could do to them to improve performance or drive ability, or anything for that matter, and nobody gave me a clear cut answer. Does anybody have an answer to these?

 

[Woody35]

this kind of explains it. ds4 and db2 have very similar parts

http://www.thetruckstop.us/forum/showthread.php?22350-DS4-pump-mods

 

[WarWagon]

Side arm is to roll on timing as you add throttle. The screw for case pressure is in the fuel inlet port. You have to remove the fuel fitting to get to it. The case pressure also controls timing by RPM.

Add more case pressure and the timing advance, like weaker distributor springs, comes on sooner. The extra case pressure also fills the plungers more/faster. I have read if you overdo it the pump locks up and breaks the driveshaft.

The next adjustment is the RPM governor screw above the fuel distributor head. Usually has a plastic tamper cover over it. This controls the top engine RPM and is known to start to cut fuel early costing you top end power.

 

[Acesneights1]

How can you lower the idle ? Does that screw on the linkage do it ? It looks like it does. Mines idling too high. IP probably came off an Auto. Careful removing that fuel inlet cover on the back. That requires a special socket and has to be torqued upon re installation as the torque sets the preload for the transfer pump. That is why it has that little lock setup on it.

 

[iamdave0887]

How can you lower the idle ? Does that screw on the linkage do it ? It looks like it does. Mines idling too high. IP probably came off an Auto. Careful removing that fuel inlet cover on the back. That requires a special socket and has to be torqued upon re installation as the torque sets the preload for the transfer pump. That is why it has that little lock setup on it.

Kenny there's an idle screw on the linkage. Look down at the throttle arm on the IP itself, around where the cable connects. You'll see the idle screw close to the IP case where the throttle shaft goes through the case. Tighten it to bring the idle up, loosen it to bring it down.

 

[WarWagon]

How can you lower the idle ? Does that screw on the linkage do it ? It looks like it does. Mines idling too high. IP probably came off an Auto. Careful removing that fuel inlet cover on the back. That requires a special socket and has to be torqued upon re installation as the torque sets the preload for the transfer pump. That is why it has that little lock setup on it.

Not sure what part you are referring to. DS4 maybe? I took the "pipe" that has 1/4" fuel feed hose off and was able to adjust the housing pressure screw. Is this the pipe that needs the special attention?

 

[6.5L]

So say I wanted more power and such? What adjustments would I need to make? I probably won't mess with the case pressure but what about the others?

 

[midniteplowboyy]

If you got a long enough allen wrench, all you have to take off is the hose to turn up the charge pump pressure. Just turn it 1/4 turn, I wouldn't go no more without checking housing pressure.

 

[6.5L]

What exactly would that do? as far as rev smoother? less smoke? more power? what exactly are we talking about if we crank the case pressure up?

 

[3500GMC]

Post #3.

There is an internal vane pump that pressurizes the fuel inside the case relative to RPM.

By looking at your signature, looks like you've found the other screw.

 

[bigchevy89]

is any body running a truck with the inlet screw turned up and if so what kind of diffrence is there?

 

[midniteplowboyy]

Dont know how much it helped, but didn't hurt. Tweek all three screws and its a different animal, runs more like a late 90's vortec 454.

Hows that Holset running?

 

[Acesneights1]

So the screw on the inlet is not the one you turn up for more fuel is it ? I took a DB2 apart and don't remember seeing a screw on the inlet but I wasn't looking for one either.

 

[bigchevy89]

I love the hx-40 iam running it really open it up plus when i installed it i did a full 4'' down pipe. iwas thinkin about adjusting the other screws but after this mornin i think the ip might be on its way out

 

[3500GMC]

So the screw on the inlet is not the one you turn up for more fuel is it ? I took a DB2 apart and don't remember seeing a screw on the inlet but I wasn't looking for one either.

The two most fiddled with.

 

[bigchevy89]

another question i know where the fuel scew is and now the inlet screw but were is the third screw and what is a safe amount to turn all 3

 

[3500GMC]

There's actually a few others (beyond what's pictured below) but you have to totally disassemble the IP. I don't mess with any of them to tell you the truth.

 

[Koots]

I was curious about this, because i have my 5079 pump in a box near my feet and i'm gonna do a refresh to it.

I don't think i want to mess with them though. I'll probably turn the fuel screw down 1/8th until turbo time though.

 

[6.5L]

So again, since I am in a quest for more power as always, what is a safe adjustment done to all three screws together to create more power or any combination of them to create a better running or more powerful vehicle?

 

[fallout]

So again, since I am in a quest for more power as always, what is a safe adjustment done to all three screws together to create more power or any combination of them to create a better running or more powerful vehicle?

I know this post is three months old but since no one else replied here is my two cents. The only screw that I would mess with is the Fuel Screw. Alot of people feel that messing the inlet screw gives them more power. It can but all it does is advance the timing on the injection pump by increasing the housing pressure. The biggest problem with adjusting this screw as that it moves the timing curve to a different area in the RPM range. If you were placing it on a motor that had a different operating window it may not be a problem. Increased wear and tear are also problems with the higher pressures. Most of the "Gain" people feel when messing with this screw is due to them reclaiming lost advance due to worn engine and pump components. Without a test bench it is anybodies guess as to what is a safe rate to increase this.