Question about DB2 pump

[caterpillar]

so on the pump there is the "advance lever" that changes the timing internally, its on the drivers side of the pump and is directly linked to the throttle, my question is does this actually advance the timing, or retard it, I was playing with it today and it seems as though it retards the timing, can someone explain this lever to me?

Also if it does retard the timing, could we just move the "adjuster" back so the lever doesn't get pushed in until at higher rpms?

 

[Headerpower]

The arm pushs a spring that rotates the plunger cam, advanceing the injection just like the advance on a gas engine. http://www.oliverdiesel.com/tech/howdb2pumpworks.htm has a good description on the pump operation.

 

[Agnem]

The low speed advance (which is what your talking about) retards the timing as the throttle is opened. It controls timing when internal fuel presure is too low to perform this task. After you reach a certain RPM (I'm going to guess around 1200), internal fuel presure takes over, and the arm does nothing.

 

[Mr_Roboto]

If you look at how the arm and the cam ramping works, it works similarly to vacuum advance on a distributor. It retards timing more at full throttle, and less at mid throttle.

The retard cam and arm are both adjustable, however you need to be careful. Just because some timing advance is good does not mean that more is better. The retard arm is there because the centrifugal advance is directly proportional to RPM, and the retard arm keeps the timing in the proper parameters.

You are best off adjusting the base timing by turning the IP so that you do not change the factory timing curve. The retard cam and arm should only be adjusted if the existing timing curve is not correct.

 

[subway]

do we have any idea what the factory timing curve looks like?

 

[Agnem]

That's one of those top secret pump rebuilder things.

 

[subway]

guess i will have to figure out my own excell spreadsheet then.

 

[typ4]

Pump stuff

Here is a tidbit I found out. My pump was off of an auto truck and when I had it done I put big red ink letters to build it to stick specs, so the tech in back removes the tag, goes by the number and builds it to auto specs + 10% like I asked.
I asked them after some performance issues comparing to my buddys truck and lo and behold there is a whole lot of difference in timing curves between the two.
The pump shop will redo it for free but the issue is downtime and labor.
Moral, be very adamant about how you want your pump calibrated.

 

[6xCrew]

Here is a tidbit I found out. My pump was off of an auto truck and when I had it done I put big red ink letters to build it to stick specs, so the tech in back removes the tag, goes by the number and builds it to auto specs + 10% like I asked.
I asked them after some performance issues comparing to my buddys truck and lo and behold there is a whole lot of difference in timing curves between the two.
The pump shop will redo it for free but the issue is downtime and labor.
Moral, be very adamant about how you want your pump calibrated.

Ok this is very interesting. So I take it the stick pump has a little more go? Do we have data on this? What do we look for on the pump to tell us what it is? What performance differances do you see?

Calivn

 

[Michael Fowler]

Interesting,
Some years ago, I bought a rebuilt pump from Diesel Injection Service ( former sponsor at Ford-Diesel, nie The DieselStop.com). I discussed this with the tech on the phone, and he was adamant that there was NO difference between a pump for an automatic and one for a manual tranny. The only difference was the extra arm on the linkage for the kickdown to the C6 auto.

 

[Agnem]

That's correct. No difference.

 

[TLBREWER]

Now I'm confused.

Tom

 

[Michael Fowler]

Maybe some clarification----
From an OEM point of view, there is no difference.
But that doesn't mean that a particular rebuilder ( with the proper facilities) could not alter the advance curve to make it more suitable for a particular application ( manual/ stick).

 

[typ4]

They showed me a chart from stanadyne with different pump numbers and advance and fuel values on it. They wouldnt let me run out the door with it though. I will see if I can get a copy,I have been spending lots of money there for work lately.

 

[Agnem]

Advance is a function of RPM. I'm at a loss as to see any benefit in advancing or retarding the timing because of road speed, when the objective is to make the cylinder fire at the optimum angle of the crankshaft for a given piston volocity.