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Discussion Starter #1
Hi all.
So I've decided to put this together because I found it hard to get the info I was looking for regarding fuel adjustment on the factory SD33T fuel pump.

First, I suggest anyone contemplating making adjustments read this thread Mechanical Diesel Engine Tuning - No Chips! - Patrol 4x4 - Nissan Patrol Forum
Whilst this is based around the TD42T boost compensator and is quite different to the unit on our SD33T engines, it will help you understand some of the adjustments that can be made.

Also my disclaimer: don't make any adjustments without a boost and pyro gauge installed. And don't go blowing your engine up. That won't be fun.
Fueling adjustments are best made in coordination with boost adjustments.

It has been fairly well documented in the past that the overall fuel pressure can be increased by turning the screw on the side of the pump seen here


The boost compensator can be seen here at the very rear of the injector pump.


And here I have removed it from the pump.

To remove: There are three short bolts on the back of the compensator (front of vehicle) and one long bolt on the front hidden down close to the engine which has safety wire tired through it.

It is not necessary to remove the compensator to adjust it, I have so I can understand it's workings.

These are the two adjustment points at the back of the compensator.

"Off boost":


"On boost":


The "off boost" adjustment has a 10mm cap (I have already removed the safety wire in this pic) that is unscrewed to reveal a flat head screw held tight by a 10mm lock nut.

The "on boost" adjustment has a 14mm cap (also with safety wire removed) that when undone reveals another 10mm lock nut and screw inside the body of the boost compensator.

Both caps have a copper washer underneath so be careful not too lose it. Or lose them if you please... i don't care!
Shown here with caps removed.



It requires a deep drive socket or something narrow like a 1/4" drive socket to get to the lock nut under the 14mm cap as it is inside the body of the boost compensator.

Here is a pic of the cover of the boost compensator removed revealing the diaphragm. Under the diaphragm is a spring and although i didn't disassemble it this far it's possible there is a way to adjust the spring tension. Adjusting the "off boost" screw changes where the diaphragm comes to rest in zero boost conditions.



Next picture is showing the other side of the same assembly and you can make out a small rocker with "off boost" on the left and "on boost" on the left.



The "on boost" screw pushes directly on a long spring-loaded pin that goes into the injector pump that determines fueling rate along with throttle position.

So you can see that both screws are affecting the rocker position on opposite sides hence having to turn the "on boost" anti clockwise to increase fuel and the "off boost" clockwise to increase fuel.

Also in the above picture you can see another lock nut and screw. I didn't fiddle with this, but as far as I can make out it will have the same effect as turning the "on boost" screw as it is effectively the same adjustment but on the opposite side of the rocker. It is also possible that there is a spring tension adjustment under there that i didn't find. But I doubt it.

The way I interpret it, adjusting the "off boost" screw clockwise gives more fuel any time you are on the throttle but not yet producing boost. By raising the rest position of the diaphragm you are fooling the fuel pump into thinking there is some boost pressure acting on the diaphragm. But when you actually start building boost this setting becomes irrelevant because the diaphragm lifts from its rest position adding fuel corresponding to the current boost pressure. Adjusting this screw for more fuel can help build boost quicker but adjust it too much and it will get a bit smoky.

So the "on boost" screw name is actually slightly misleading as it increases off boost fuel as well as on boost, allowing the spring-loaded pin to travel further (or less) under any on-throttle conditions. So in theory if you only want to increase on boost fueling you would wind up the on boost and take out some off boost to get that back to where it started.

So adjusting the fuel this way is ,in my mind, theoretically safer and more correct than upping the fuel pressure via the screw on the side of the pump, given that this will deliver more fuel under ALL conditions. This includes when not applying throttle. Hence, people who adjust fuel using the fuel pressure screw often adjust the idle screw to return idle to normal. Having said this, I haven't heard of anyone destroying an engine this way so probably no big deal.

Increasing the fuel pressure also likely changes injector spray pattern and atomisation also but I am no expert on this (or any of the above).

After writing all this and putting the boost compensator back together and trying to make some adjustments to the "on boost" screw I realise that it is nearly impossible to adjust while on the vehicle. So I might remove it again and make some more adjustments but in the future I may also use the fuel pressure screw just because it is far more accessible. Also my vehicle is a farm rig so I'm not too concerned if i do some damage.

I hope this helped other people's understanding as much as mine.

Nutsy
 

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Discussion Starter #2
Also as a side note, the body of my boost compensator was completely full of dirty black engine oil. I don't know how or why but I assume that is not supposed to happen.
 

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Great post nutzy, very informative!, would be good if some others chipped in with a bit of info on the compensator mod that I've heard off, softer spring or something?

Sent From The Seventh Floor Of Hell
 

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Great post nutsy!

Hmm, my car idles high and blows plenty of smoke under acceleration... wonder if it's had a dodgey compensator adjustment.
 

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Nice post nutsy. Ive got 5 pumps at home (3 turbo and 2 non-turbo) was thinking about sacrificing one and dissecting it for research purposes to see how it works and maybe learn how to rebuild it.
 

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Good write up , might just put this in the bible not to loose it .

Hey James , funny I have my white patrol that just does it thing and my red one that does a big puff off black smoke when you get on it , all still with factory ties on the pump . Go figure .


Sent from Alf Stewart's rape dungeon .
 

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Discussion Starter #8
Thanks for the feedback blokes. I hope it wasn't too hard to follow what I was trying to explain. I'm happy for others to add info to this, as i certainly don't know everything about these things.
I should add that the boost compensator isn't terribly difficult to remove and there isn't really any parts that will fall out and get lost. But there is a paper gasket that will possibly rip when you take it apart. And it will be quite time consuming to remove and make repeated adjustments if you don't get it right the first time.
 

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The Prodigal Child Has Returned
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The other thing you can do is replace the spring in the compensator with a lighter spring and get full fuel earlier or something like that .


Sent from Alf Stewart's rape dungeon .
 

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The real gains in fuelling goes from modification in boost compensator stroke.
This can be achieved with lighter spring sourced from thermostat and making new adjustment screws.
And there is no fuel pressure screw! Bolt at side of the pump is simply rack limiter screw.
Anyway, you need to mod boost compensator stroke, to achieve more fuel and no smoke(rack stroke is limited by boost compensator before side screw).
Remove factory off boost screw and replace it with bolt, so you can use full stroke - it can be done to around 10mm, and factory is something like 2mm.
 

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Discussion Starter #11
Yes I was unconvinced that it was actually a fuel pressure screw. But that was what others had referred to it as. Thanks for clearing that up. So what exactly does the rack limiter screw do then?
 

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Any chance you could do a bit of a small write up on the compensator mod Azotec? With pictures and such so anyone reading could have a go at it? if it's not too much trouble! :)

Sent From The Seventh Floor Of Hell
 

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Rack limiter screw limits maximum fueling when boost compensator is at maximum stroke(max boost).
Taking pictures with black oiled hands is not easy. Tear it apart, and you will see how it works. I have enough work with my diesel range rover now - changing engine, modding IP and turbo.
Done it few years ago, may not remember everything. Boost response with modded compensator is much better even on stock turbo. Stock clutch starts smelling when booted. Also it's worth replacing turbo rubber intake elbow with something stiffer(may be silicone, 60mm diameter if i remember correctly)
:D
 

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Hey guys

Has anyone here apart from the WA boys modded their own boost compensator ?

I'm keen to give it a go but not really sure where to start

Soft spring from thermostat and I need to make longer bolts I know that much

Any help would be appreciated

Marc
 

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Didn't Cody give It a crack at one stage ??? How's the best going. Loving life or what.


Sent from my iPhone using Tapatalk
 

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Hey mate

Yeah Codys done quite a few now but he is very busy with work and his family so don't want to bother him if I can help it

He has offered to help though I just wanted to see if I could do it off my own back

It really makes the biggest difference
Turns them into a monster haha

And yes you have no idea how happy I am
Just the smell on a cold morning :):)
 

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Rack limiter screw limits maximum fueling when boost compensator is at maximum stroke(max boost).
Taking pictures with black oiled hands is not easy. Tear it apart, and you will see how it works. I have enough work with my diesel range rover now - changing engine, modding IP and turbo.
Done it few years ago, may not remember everything. Boost response with modded compensator is much better even on stock turbo. Stock clutch starts smelling when booted. Also it's worth replacing turbo rubber intake elbow with something stiffer(may be silicone, 60mm diameter if i remember correctly)
:D
How many turns of these screws is the right ball park mate?
 

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Registered
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Hi all.
So I've decided to put this together because I found it hard to get the info I was looking for regarding fuel adjustment on the factory SD33T fuel pump.

First, I suggest anyone contemplating making adjustments read this thread Mechanical Diesel Engine Tuning - No Chips! - Patrol 4x4 - Nissan Patrol Forum
Whilst this is based around the TD42T boost compensator and is quite different to the unit on our SD33T engines, it will help you understand some of the adjustments that can be made.

Also my disclaimer: don't make any adjustments without a boost and pyro gauge installed. And don't go blowing your engine up. That won't be fun.
Fueling adjustments are best made in coordination with boost adjustments.

It has been fairly well documented in the past that the overall fuel pressure can be increased by turning the screw on the side of the pump seen here


The boost compensator can be seen here at the very rear of the injector pump.


And here I have removed it from the pump.

To remove: There are three short bolts on the back of the compensator (front of vehicle) and one long bolt on the front hidden down close to the engine which has safety wire tired through it.

It is not necessary to remove the compensator to adjust it, I have so I can understand it's workings.

These are the two adjustment points at the back of the compensator.

"Off boost":


"On boost":


The "off boost" adjustment has a 10mm cap (I have already removed the safety wire in this pic) that is unscrewed to reveal a flat head screw held tight by a 10mm lock nut.

The "on boost" adjustment has a 14mm cap (also with safety wire removed) that when undone reveals another 10mm lock nut and screw inside the body of the boost compensator.

Both caps have a copper washer underneath so be careful not too lose it. Or lose them if you please... i don't care!
Shown here with caps removed.



It requires a deep drive socket or something narrow like a 1/4" drive socket to get to the lock nut under the 14mm cap as it is inside the body of the boost compensator.

Here is a pic of the cover of the boost compensator removed revealing the diaphragm. Under the diaphragm is a spring and although i didn't disassemble it this far it's possible there is a way to adjust the spring tension. Adjusting the "off boost" screw changes where the diaphragm comes to rest in zero boost conditions.



Next picture is showing the other side of the same assembly and you can make out a small rocker with "off boost" on the left and "on boost" on the left.



The "on boost" screw pushes directly on a long spring-loaded pin that goes into the injector pump that determines fueling rate along with throttle position.

So you can see that both screws are affecting the rocker position on opposite sides hence having to turn the "on boost" anti clockwise to increase fuel and the "off boost" clockwise to increase fuel.

Also in the above picture you can see another lock nut and screw. I didn't fiddle with this, but as far as I can make out it will have the same effect as turning the "on boost" screw as it is effectively the same adjustment but on the opposite side of the rocker. It is also possible that there is a spring tension adjustment under there that i didn't find. But I doubt it.

The way I interpret it, adjusting the "off boost" screw clockwise gives more fuel any time you are on the throttle but not yet producing boost. By raising the rest position of the diaphragm you are fooling the fuel pump into thinking there is some boost pressure acting on the diaphragm. But when you actually start building boost this setting becomes irrelevant because the diaphragm lifts from its rest position adding fuel corresponding to the current boost pressure. Adjusting this screw for more fuel can help build boost quicker but adjust it too much and it will get a bit smoky.

So the "on boost" screw name is actually slightly misleading as it increases off boost fuel as well as on boost, allowing the spring-loaded pin to travel further (or less) under any on-throttle conditions. So in theory if you only want to increase on boost fueling you would wind up the on boost and take out some off boost to get that back to where it started.

So adjusting the fuel this way is ,in my mind, theoretically safer and more correct than upping the fuel pressure via the screw on the side of the pump, given that this will deliver more fuel under ALL conditions. This includes when not applying throttle. Hence, people who adjust fuel using the fuel pressure screw often adjust the idle screw to return idle to normal. Having said this, I haven't heard of anyone destroying an engine this way so probably no big deal.

Increasing the fuel pressure also likely changes injector spray pattern and atomisation also but I am no expert on this (or any of the above).

After writing all this and putting the boost compensator back together and trying to make some adjustments to the "on boost" screw I realise that it is nearly impossible to adjust while on the vehicle. So I might remove it again and make some more adjustments but in the future I may also use the fuel pressure screw just because it is far more accessible. Also my vehicle is a farm rig so I'm not too concerned if i do some damage.

I hope this helped other people's understanding as much as mine.

Nutsy
How many turns of the off boost and on boost did you do nutsy? And how was the outcome of the mod?
 
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