Cptsideways
Well-Known Member
Hello all, a newbie here 
but not to LC's I might add, I've owned a couple of 80's & also have a rather large fleet of tuned Toyota's lurking in the garage.
Anyway onto my weekends exlpoits of tweaking the TD
My recently aquired 4.2TD 24 Valve with 200k on the clock until today, went nowhere near as well as my previous 12v, in fact it was like driving an asthmatic milk float lol. Now having read up on the forums there appeared to be some useful info, so I started twiddling - however some of that info is INCORRECT (notably about the top screw) so let me enlighten you....
The 12v & 24v pumps appear to be the same unit just on the 24v there is some additional gumph between it & the engine that is there to downtune it for emissions reasons I would assume. Now what I have been fiddling with is the off boost initial throttle response & boost up fuelling not the main rail or set screw. The difference now is like night & day.
Previously
Flat as a pancake below 2k rpm, almost no boost recorded maybe 0.3 bar just, constantly having to change gear to drive it out of roundabouts etc so always having to keep it above 2k for everything accept cruising along at 40mph. Felt like a 2.0 petrol engine under there until 2k rpm.
Above 2k it would boost to 0.7-0.8 bar eventually & the turbo was laggy even once up in the rev range eg it'd take almost a second to go from cruising boost of about 0.4bar to full boost. So no notable punch when you floored it.
Now
Wow what a difference!!!! It now drives like a modern Tdi engine, with urge from 1k rpm, it'll boost if required from that rpm (but its not wise to load the engine up down there). However 40mph 5th overtakes from 1200/1300rpm can now be made with ease. Its got poke!! Much less lag when in gear, so cruising boost to full boost time is about halved. There is no apparent heaps of black smoke, no more than my old 12v anyway.
So how did we do it, well I actually took the top half of the pump assembly apart to see how it worked
I 'm not suggesting you do this, but it allowed me to understand whats going on & start adjusting accordingly.
It's a really simple system once you get your head round it.
1) There is an internal plunger-pin that operates an overfuelling part of the pump, in = less, out = more
2) There is a profiled plunger that operates part 1, this is what the diaphram is connected to
3) There is a spring below the diaphram that acts against the boost pressure
4) There is a toothed wheel that adjusts the springs tension against the diaphram
4) On top of the diaphram/plunger is an offset spring preloader (the 3mm allen key bit on top of the pump unit is it)
Part 2) Is the all important diaphram & plunger unit: This moves up & down vertically, the cut away section touches on the internal plunger/pin, so when it goes down with boost it allows the other plunger pin to move outwards adding fuel. This is the part that has the offset in the cutout, so rotating it you can see the profile is offset to one side. Notice the profile is double sided, this is an overboost protection system I think. The bottom 45deg champfer is not standard! If you pull the plunger & diaphram out of the pump you cant get it back in again!! so to get it back you'll need to champfer the bottom of it to move the internal plunger in & get this plunger part to drop in.
The top spring preloader: This is simply a fat disk with a chamfer cut across it at about 20degrees, so rotating it 360 degrees brings it back where it was, not as described in other places! You can see the top of this from outside the pump, its the bit with the 3mm allen key & locknut at the very top of the pump unit.
Part 4: This is the spring pretensioner/adjustment on, raising it anticlockwise will increase the spring tension & reduces fuel input under boost. Lowering it clockwise adds fuel under boost.
It looks exactly like this (I did'nt take a pic so nicked a pic off the net)
On the 12v & 24v there is a boost input to the top of the diaphram, as boost increases it pushes on the diaphram & spring pushing the plunger downwards supplying more fuel. On the 24v there is also a vacuum/boost supply to the base of the spring to keep things balanced out (for emissions I guess) This acts like an external wastegate on a turbo'd car by the way
If you remove the top of the pump/actuator part (4x4mm allen key bolts) you can see the diapram, if you carefully lift the diapram you see the plunger & spring preloader DO NOT lift the plunger part with diaphram more than a few mm!! Or you'll have to modify it to get it back in. However you can run the engine with the diaphram part open/exposed so you can have a play with settings.
So what did I do?
1) Dialed the toothed wheel down clockwise till it bottomed out - for minimal preload on the spring tension, theres about 3-4mm of adjustment on it. It was near the bottom anyway.
2) Rotated the diaphram so it presented the least amount of profile to the internal punger - this can be felt as minimal tension as you rotate it - or with it running at say a fixed 1200rpm the rpm increases/decreases slightly as you rotate it (with no downward pressure on it) I noticed that there was a wear mark from where it had been set previously which was at about 60% of max profile.
3) Dialed the top preload on the spring top to max by rotating it to give max spring pressure down.
So what I have done is give this part of the pump its maximum possible settings but within design limits, from here is can be downtuned it if need be. However it now goes like stink compared to previously & as well if not a bit better than my old 12v cruiser, which always went well compared to others I had driven. So much less gearchanging & general ability to get up & go when required.
The "new" Go faster cruiser with 200k on it
but not to LC's I might add, I've owned a couple of 80's & also have a rather large fleet of tuned Toyota's lurking in the garage. Anyway onto my weekends exlpoits of tweaking the TD
My recently aquired 4.2TD 24 Valve with 200k on the clock until today, went nowhere near as well as my previous 12v, in fact it was like driving an asthmatic milk float lol. Now having read up on the forums there appeared to be some useful info, so I started twiddling - however some of that info is INCORRECT (notably about the top screw) so let me enlighten you....
The 12v & 24v pumps appear to be the same unit just on the 24v there is some additional gumph between it & the engine that is there to downtune it for emissions reasons I would assume. Now what I have been fiddling with is the off boost initial throttle response & boost up fuelling not the main rail or set screw. The difference now is like night & day.
Previously
Flat as a pancake below 2k rpm, almost no boost recorded maybe 0.3 bar just, constantly having to change gear to drive it out of roundabouts etc so always having to keep it above 2k for everything accept cruising along at 40mph. Felt like a 2.0 petrol engine under there until 2k rpm.
Above 2k it would boost to 0.7-0.8 bar eventually & the turbo was laggy even once up in the rev range eg it'd take almost a second to go from cruising boost of about 0.4bar to full boost. So no notable punch when you floored it.
Now
Wow what a difference!!!! It now drives like a modern Tdi engine, with urge from 1k rpm, it'll boost if required from that rpm (but its not wise to load the engine up down there). However 40mph 5th overtakes from 1200/1300rpm can now be made with ease. Its got poke!! Much less lag when in gear, so cruising boost to full boost time is about halved. There is no apparent heaps of black smoke, no more than my old 12v anyway.
So how did we do it, well I actually took the top half of the pump assembly apart to see how it worked
I 'm not suggesting you do this, but it allowed me to understand whats going on & start adjusting accordingly.It's a really simple system once you get your head round it.
1) There is an internal plunger-pin that operates an overfuelling part of the pump, in = less, out = more
2) There is a profiled plunger that operates part 1, this is what the diaphram is connected to
3) There is a spring below the diaphram that acts against the boost pressure
4) There is a toothed wheel that adjusts the springs tension against the diaphram
4) On top of the diaphram/plunger is an offset spring preloader (the 3mm allen key bit on top of the pump unit is it)
Part 2) Is the all important diaphram & plunger unit: This moves up & down vertically, the cut away section touches on the internal plunger/pin, so when it goes down with boost it allows the other plunger pin to move outwards adding fuel. This is the part that has the offset in the cutout, so rotating it you can see the profile is offset to one side. Notice the profile is double sided, this is an overboost protection system I think. The bottom 45deg champfer is not standard! If you pull the plunger & diaphram out of the pump you cant get it back in again!! so to get it back you'll need to champfer the bottom of it to move the internal plunger in & get this plunger part to drop in.
The top spring preloader: This is simply a fat disk with a chamfer cut across it at about 20degrees, so rotating it 360 degrees brings it back where it was, not as described in other places! You can see the top of this from outside the pump, its the bit with the 3mm allen key & locknut at the very top of the pump unit.
Part 4: This is the spring pretensioner/adjustment on, raising it anticlockwise will increase the spring tension & reduces fuel input under boost. Lowering it clockwise adds fuel under boost.
It looks exactly like this (I did'nt take a pic so nicked a pic off the net)
On the 12v & 24v there is a boost input to the top of the diaphram, as boost increases it pushes on the diaphram & spring pushing the plunger downwards supplying more fuel. On the 24v there is also a vacuum/boost supply to the base of the spring to keep things balanced out (for emissions I guess) This acts like an external wastegate on a turbo'd car by the way
If you remove the top of the pump/actuator part (4x4mm allen key bolts) you can see the diapram, if you carefully lift the diapram you see the plunger & spring preloader DO NOT lift the plunger part with diaphram more than a few mm!! Or you'll have to modify it to get it back in. However you can run the engine with the diaphram part open/exposed so you can have a play with settings.
So what did I do?
1) Dialed the toothed wheel down clockwise till it bottomed out - for minimal preload on the spring tension, theres about 3-4mm of adjustment on it. It was near the bottom anyway.
2) Rotated the diaphram so it presented the least amount of profile to the internal punger - this can be felt as minimal tension as you rotate it - or with it running at say a fixed 1200rpm the rpm increases/decreases slightly as you rotate it (with no downward pressure on it) I noticed that there was a wear mark from where it had been set previously which was at about 60% of max profile.
3) Dialed the top preload on the spring top to max by rotating it to give max spring pressure down.
So what I have done is give this part of the pump its maximum possible settings but within design limits, from here is can be downtuned it if need be. However it now goes like stink compared to previously & as well if not a bit better than my old 12v cruiser, which always went well compared to others I had driven. So much less gearchanging & general ability to get up & go when required.
The "new" Go faster cruiser with 200k on it
