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after a recent post about fuel pump tuning and a predictable response of "better take it to a pro mate" I thought I might shed some light on what is often clouded in mystery and myths. I'm by no means an expert but here are my findings. feel free to correct or add, particularly the aussi lads as they are pretty much the experts on this.
first off you really need at least an egt gauge and preferably a boost gauge as well. some of the "pros" will claim they can tell off the amount of black smoke coming out the back, I find this hard to believe as ive had mine running pretty clean on the smoke front but reaching high egts on long uphill drags. I suppose if the main fuel screw is just turned a little and the other adjustments tweaked a little 9 times out of ten it will be fine...
anyway.
strictly speaking its not actually the fuel pump that is being tuned, the only adjuster on the fuel pump is the main fuel screw, this just fire more fuel In there, period. were playing with the boost compensator, some cruisers don't even have this on, but we have a turbo so we do. it sits on top of the fuel pump and its purpose is to increase the amount of fuel In relation to boost. it does this via the pipe that comes off the top that allows the manifold pressure created by the turbo to overcome the spring and push the fuel (aneroid) pin down. the profile of the fuel pin is followed by the, yup, follower pin..
so if you imagine the follower pin sitting against the fuel pin as the boost pressure increases the fuel pin moves down, allowing the follower pin to extend into the recessed section, as the follower pin is extended more into the recesses more fuel is allowed in, until the flat section is reached and then ultimately fuel is cut back when the full diameter of the pin is reached again.
you will notice a section of the profile is more aggressive than the other, as mentioned on other forums when you turn the diaphragm this turns the fuel pin to allow the more aggressive side to face the follower pin, allowing more fuel in, and earlier in the rev range.
the fuel pin inserted back in its housing.
this picture shows the spring and star wheel, at the bottom is the fuel pin attached to the diaphragm.
some suggest cranking the star wheel right down, this reduces the tension on the spring allowing the fuel pin to move with less boost, the problem being you will reach the fuel cut off part of the fuel pin too early, so at say 2700rpm the motor will be starved of fuel, power will drop, boost will drop and egts rise.
bottom left is the cam that the other end of the follower pin sits against, this pushes a lever in the fuel pump that allows in more fuel. a little match mark can be seen where the pin sits.
close up of spring and star wheel, the wheel can be accessed from the right hand side with a flat head screw driver through the hole left once the nut is removed.
the follower pin inserted back into the bush it sits in, there is also a O ring to stop diesel finding its way into the chamber the fuel pin sits in.
here is the cam that we saw before installed. the spring and nut in the foreground screw in and keep the cam against the follower pin, and therefore the follower pin against the fuel pin.
here is the assembly on its side. in the middle is the cam, to the left you can just make out the coiled spring. as said before as the profile of the fuel pin is followed the cam pushes against a lever in the pump adding and reducing fuel. to the right is the main fuel screw with the anti tamper sleeve still intact. again, screw this in or out and it pushes on a lever in the pump increasing or reducing fuel. at the bottom is a idle up cam for iirc the power steering, again this pushes against a lever in the pump.. the hole on the left is where the throttle pivot pops through.
diaphragm and fuel pin back in place, note the marker pen mark so I know the most aggressive profile of the fuel pin is against the follower.
here is the top of the whole unit, the bit that can be seen in the engine bay with a nut on top, when the nut on top is turned it rotates the tapered cam which presses the fuel pin further down its profile. this introduces fuel earlier in the rev range so the turbo spools up sooner, increasing low down response. the match mark can be seen. turn the taper so that the thickest section sits on top of the fuel pin.
again a marker pen to mark the thickest part of the taper before tightening the nut back up.
everything back together.
then bolt the lot to the top of the fuel pump.
so, there are the tweaks to liven up the old girl. all of this can be done without taking the unit off. if you've got a boost gauge and egt gauge fitted, do the adjustments and turn the main fuel screw up an eight of a turn, turn the boost up to 15 psi.
go for a drive. max safe egts are 1250f, higher egts are normally seen towing and on long up hills. so its a compromise of more fuel and drivability, you don't want to fly up to the 1250f mark and constantly be backing off the throttle.
here is the angle I ground on the fuel pin on my truck so that it slots back in, its needs to be as smooth as possible, I finished it off with polishing compound and the dremel. some very fine wet and dry etc would do too. before you attempt to put the pin back in push the follower pin back first as it can over extend once the fuel pin has been removed.
if you want to tweak things to perfection, mark the pin with marker pen, after a bit of driving around you will be able to clearly see the position of the follower pin on the fuel pin.
a view of the follower pin with the fuel pin removed.
something worth doing is taking the sharp edge off the threaded hole top of the picture, it is sharp and could damage the diaphragm when removing and reinstalling it.
that's it really, once you get the hang of it all this can be done in about 15 minutes.
the next step is grinding the side of the fuel pin that is in contact with the follower pin, this will allow more fueling where you choose it to be.
So, finally got round to fitting my intercooler.
power was great above about 2400 rpm. Below this it felt a little lean, so I ground the fuel pin on the lower tapered section of the profile, adding more fuel lower down in the rev range.
What a difference.
I'm reaching max boost, 15 psi, at 1800 rpm. Pulls much better now below 2400rpm.
I'll keep playing..
first off you really need at least an egt gauge and preferably a boost gauge as well. some of the "pros" will claim they can tell off the amount of black smoke coming out the back, I find this hard to believe as ive had mine running pretty clean on the smoke front but reaching high egts on long uphill drags. I suppose if the main fuel screw is just turned a little and the other adjustments tweaked a little 9 times out of ten it will be fine...
anyway.
strictly speaking its not actually the fuel pump that is being tuned, the only adjuster on the fuel pump is the main fuel screw, this just fire more fuel In there, period. were playing with the boost compensator, some cruisers don't even have this on, but we have a turbo so we do. it sits on top of the fuel pump and its purpose is to increase the amount of fuel In relation to boost. it does this via the pipe that comes off the top that allows the manifold pressure created by the turbo to overcome the spring and push the fuel (aneroid) pin down. the profile of the fuel pin is followed by the, yup, follower pin..
you will notice a section of the profile is more aggressive than the other, as mentioned on other forums when you turn the diaphragm this turns the fuel pin to allow the more aggressive side to face the follower pin, allowing more fuel in, and earlier in the rev range.
some suggest cranking the star wheel right down, this reduces the tension on the spring allowing the fuel pin to move with less boost, the problem being you will reach the fuel cut off part of the fuel pin too early, so at say 2700rpm the motor will be starved of fuel, power will drop, boost will drop and egts rise.
bottom left is the cam that the other end of the follower pin sits against, this pushes a lever in the fuel pump that allows in more fuel. a little match mark can be seen where the pin sits.
close up of spring and star wheel, the wheel can be accessed from the right hand side with a flat head screw driver through the hole left once the nut is removed.
the follower pin inserted back into the bush it sits in, there is also a O ring to stop diesel finding its way into the chamber the fuel pin sits in.
here is the cam that we saw before installed. the spring and nut in the foreground screw in and keep the cam against the follower pin, and therefore the follower pin against the fuel pin.
here is the assembly on its side. in the middle is the cam, to the left you can just make out the coiled spring. as said before as the profile of the fuel pin is followed the cam pushes against a lever in the pump adding and reducing fuel. to the right is the main fuel screw with the anti tamper sleeve still intact. again, screw this in or out and it pushes on a lever in the pump increasing or reducing fuel. at the bottom is a idle up cam for iirc the power steering, again this pushes against a lever in the pump.. the hole on the left is where the throttle pivot pops through.
diaphragm and fuel pin back in place, note the marker pen mark so I know the most aggressive profile of the fuel pin is against the follower.
here is the top of the whole unit, the bit that can be seen in the engine bay with a nut on top, when the nut on top is turned it rotates the tapered cam which presses the fuel pin further down its profile. this introduces fuel earlier in the rev range so the turbo spools up sooner, increasing low down response. the match mark can be seen. turn the taper so that the thickest section sits on top of the fuel pin.
again a marker pen to mark the thickest part of the taper before tightening the nut back up.
everything back together.
then bolt the lot to the top of the fuel pump.
so, there are the tweaks to liven up the old girl. all of this can be done without taking the unit off. if you've got a boost gauge and egt gauge fitted, do the adjustments and turn the main fuel screw up an eight of a turn, turn the boost up to 15 psi.
go for a drive. max safe egts are 1250f, higher egts are normally seen towing and on long up hills. so its a compromise of more fuel and drivability, you don't want to fly up to the 1250f mark and constantly be backing off the throttle.
here is the angle I ground on the fuel pin on my truck so that it slots back in, its needs to be as smooth as possible, I finished it off with polishing compound and the dremel. some very fine wet and dry etc would do too. before you attempt to put the pin back in push the follower pin back first as it can over extend once the fuel pin has been removed.
if you want to tweak things to perfection, mark the pin with marker pen, after a bit of driving around you will be able to clearly see the position of the follower pin on the fuel pin.
a view of the follower pin with the fuel pin removed.
something worth doing is taking the sharp edge off the threaded hole top of the picture, it is sharp and could damage the diaphragm when removing and reinstalling it.
that's it really, once you get the hang of it all this can be done in about 15 minutes.
the next step is grinding the side of the fuel pin that is in contact with the follower pin, this will allow more fueling where you choose it to be.
So, finally got round to fitting my intercooler.
power was great above about 2400 rpm. Below this it felt a little lean, so I ground the fuel pin on the lower tapered section of the profile, adding more fuel lower down in the rev range.
What a difference.
I'm reaching max boost, 15 psi, at 1800 rpm. Pulls much better now below 2400rpm.
I'll keep playing..
Last edited:
I was fishing to find a tuner and i even rang a few rolling road places .... I fear that tuning non computerised engines is become a dying art :-(
