Engine/Transmission (1994 - 1998) Control Rack Adjustment

[bubba_PA]

Besides sliding the AFC forward and the spring kit and moving the fuel plate forward and adjusting the governor arm, are there any other ways to adjust the control rack for further travel? Also, how do you measure the travel? Older posts have talked about 18mm being the optimal distance. I'm looking for a little extra juice if possible.



Paul

 

[JGK]

I was talking to a local Bosch tech the other day about our P7100 pumps. He said the upper screw at the back of the pump behind the cover (as seen in Piers's tech page for adjusting the governor arm) sets the rack travel. He also said fiddling with it can screw up the pump. It is set to get optimum fueling relative to how the governor works. Changing it can mess things up. Beyond adjusting the AFC, plate, GSK kit and maybe delivery valves, you'd probably be better off to have the pump bench tuned by a certified tech who will tweak it up for you rather than going it alone.



JMHO,

-Jay

 

[bubba_PA]

I've been looking at that adjustment screw also but too chicken to change it. A pump manual I have shows it linked directly to the control rack. Seems like it is almost too simple so would probably REALLY mess things up. Any one out there ever mess with it?

 

[chrleb1]

There is a rack stop in front of the pump that can be spaced. If you take off the plug that is in front and add another washer you can make sure the rack won't hit that stop.

 

[JAmos]

more info please

This is an interesting topic. Could someone elaborate more on how the pump would be messed up by messing with the other screw, instead of just saying it will be messed up? Also can someone throw out some specifics on how and what changing the rack travel does and how to do it? Thanks for any help, I absorb this stuff like a sponge. Jordan

 

[chrleb1]

Not sure on the screw, but rack travel is related to how much fuel you are delivering. Your pump is made up of pistons and cylinders. Each piston is connected to this rack and when you moce the throttle the rack will cause the piston to rotate. On the pistons, there are groove cut in each side to allow fuel to travel to the top of the piston. These grooves are cut in a spiral kinda sorta. They only go down a 1/2 inch or so. So what happens when you install a different cam plate is that the rack moves on a different "fuel curve". That is why if you move your plate forward, you get more fuel. Now different pumps have different cuts in the pistons, different cams (dictates how much fill time there is), and different governor weights. Now a 215 pump has the most fill time out of the P-pumps, most advance, and the lightest governor weights. Some people put different pistons and cylinders in there pumps ( 12mm to 13mm, even 14mm), and also people put different cams in also. Governors can be modified by just changing the springs. Hope this helps a little, pm me if you have more questions. Also there are a lot more people out there that could explain more things.

 

[bubba_PA]

Chrleb1 -

I follow you on your explanation (good descriptions by-the-way) as I've been reading the Bosch in-line pump book. I still have the questions of:



1. How to most accurately measure rack travel? I've read that 18 mm is best and 21-23 mm takes it to the start position of fueling for the plunger helix.



2. As was also asked - what happens when you adjust the upper screw to the control rack? Will it mess up a pump like the above Bosch tech said? And if so, how?



The reason I ask #2 is that I had a Cummins Certified Mechanic thinking I was completely nuts for wanting to change the timing. Oh those of little faith and only knowledge from the EPA and books. Any help with above could really enlighten many of us.



Paul

 

[JGK]

Paul, Jordan,



I hear ya callin' but I can't really elaborate. I mean, I chatted with this guy for about 15 minutes while he was taking a break from working on a truck and between answering phone calls. I would have loved to pry more specifics out of him but I wasn't a paying customer.



Even if he'd done a brain dump on me about all the details I'm not sure I could begin to explain it here in writing since I haven't gotten inside these pumps on a bench to work with them and get a better understanding.



And yeah, its true, some of these guys won't think beyond factory spec settings (where's the fun in that?!).



I'd suggest you contact a Bosch guru directly. Is there a shop anywhere near you? I'm sure someone like Piers or Joe Donnelly, or Mark Chapple or the other performance folks would know what you can get away with fiddling with that screw. The trick is finding one that will explain it all to you. For me, all I can do is take this guy at his word for now. But I, like you, would love to know more. I just don't have the time or the inclination to figure it out on my own. There are a number of mods available to these pumps to get more fuel out of them. But no one has suggested adjusting that screw as one of them. Maybe that's the proprietary secret they hold close to their chests!



Let us all know if you learn any details. Sorry I couldn't provide more info.



-Jay

 

[Jim Fulmer]

I'm sure someone like Piers or Joe Donnelly, or Mark Chapple or the other performance folks would know what you can get away with fiddling with that screw. The trick is finding one that will explain it all to you. For me, all I can do is take this guy at his word for now. But I, like you, would love to know more. I just don't have the time or the inclination to figure it out on my own. There are a number of mods available to these pumps to get more fuel out of them. But no one has suggested adjusting that screw as one of them. Maybe that's the proprietary secret they hold close to their chests!



That screw is like turning the barrels, you can do it if your on a test stand and tuning the pump.



Jim

 

[Forrest Nearing]

or you can do what I did and accidently advance the rack when you're trying to adjust the lever arm



oh well, only repurcussion is 900rpm idle and instant starts



I'm assuming I didn't throw it too far out of whack :-laf

 

[hsmith]

Don't think I hurt mine either, but did have to go back in and readjust after a trial run. It would lay a cloud that would hang till tomorrow. Dropped it back to the tip, and love the instant starts, and response is great!

 

[Highfinance97]

Besides sliding the AFC forward and the spring kit and moving the fuel plate forward and adjusting the governor arm, are there any other ways to adjust the control rack for further travel? Also, how do you measure the travel? Older posts have talked about 18mm being the optimal distance. I'm looking for a little extra juice if possible. Paul

Mack plug!!!



Michael

 

[Matthug]

or you can do what I did and accidently advance the rack when you're trying to adjust the lever arm



oh well, only repurcussion is 900rpm idle and instant starts



I'm assuming I didn't throw it too far out of whack :-laf

Did you have more power though?

Also how does this screw adjust for more advance? in, out, up, down?

 

[hsmith]

Definitely more!

 

[Forrest Nearing]

I didn't notice any more power... just seems like I turned the idle up