1HD-FT Performance Adjustments
The '95 - '98 multi valve factory turbo diesel motor (1HD-FT)
is a great motor with gobs of go and gobs of torque. Because
however it has a larger turbo housing and is tuned for tight
emissions, the off boost response is light. This can be alleviated
with simple injector pump adjustment. It's not a difficult task
and the results are impressive indeed.
Adjustments are required to three components of the injector
pump and does not affect the factory seal on the maximum
injection volume screw. Adjustments are required to the boost
compensator characteristic tendency and to the maximum off
boost injection volume screw.
Boost compensator characteristic tendency
The stock boost compensator characteristic tendency on the
injector pump is set very conservatively on this motor. This can
result in lack lustre performance until you get the boost wound
up. It varies quite widely from car to car and I've driven a
couple that were quite bad down low.
The boost compensator is the diaphragm that sits on top of the
fuel pump. On the rear face (towards the rear of the car), just
under the diaphragm is a 12 mm bolt (from memory) with a rubber
drain cover/tube covering it (Aussie spec only. The European
models have that BACS tube in there). Pull the rubber cover off
and undo the bolt. Depending on which tools you use, you may have
to remove the fuel inlet pipe first. It's tight in there....
Inside the hole is a toothed wheel sitting on the horizontal
plane. You can see it if you grow a 3rd hand, shine a light in
there and hold an inspection mirror just right. You don't need to
see it though.....
Insert a smallish blade screw driver (holding the blade in the
vertical plane) and get it on the teeth of the toothed wheel. Now
push the end of the screw driver away from the motor (to turn the
wheel clockwise when viewed from above). As the wheel turns,
you'll hear a faint click as each tooth pushes against a detent
spring. You need to turn it 2 or 3 clicks.
Re-install everything being careful not to over tighten the
bolts. They screw into soft aluminium.
What this tweak does is to allow the pump to inject more fuel
at low to moderate boost pressure. It doesn't affect the maximum
injection volume, so you're not over stressing the motor. Another
benefit is that it'll pull harder as it approaches red line.
There's no noticeable difference in smoke and the net effect is
better economy. You'll end up shifting sooner and not having to
rev the motor to get going quickly.
Don't be greedy however by screwing it down much further. The
gotcha is that it does inject more as the boost drops close to red
line and you can get alarmingly high combustion temperatures when
revving hard for any length of time.
Maximum off boost injection volume
This adjustment determines how much fuel is injected when there is
no boost. Once boost begins increasing, the boost compensator
characteristic tendency described above takes over. By increasing
the volume of fuel injected, there is more torque available under
no boost conditions with the added bonus that with more fuel, more
exhaust energy is available to spin the turbo up quicker.
The adjustment screw is found on top of the boost compensator
diaphragm and usually has a dab of yellow inspection paint over it
(it may however have flaked off with engine washing ;-)
Make a note of its stock position for reference. To adjust, loosen
the lock nut and screw the adjustment screw in. Initially, turn it
in half a turn and tighten the lock nut.
Now it's a matter of trial and error. Warm the engine up and
test the adjustment by looking for a light puff of black smoke as
you hit the accelerator from idle. You can repeat the procedure
and keep increasing the adjustment half a turn at a time until you
do see an increase in smoke.
Try to keep the smoke to a minimum when you do finally find a
screw setting that suits your engine.
This will have a noticeable effect in the off idle response and
can have the turbo spinning up and boosting right down from 1,000
A word of caution however. With all this new-found torque at
low boost, don't be tempted to lug it up long hills simply because
it now can. Bearings don't like being hammered.
I did this mod to mine 6 or so months ago and jumping into a
stock TD now it's noticeable just how different it is.
Boost Compensator Profile
For those a bit more adventurous, there is one more adjustment
(other than the main set screw :-) that can have a significant
affect on low to mid RPM torque.
The boost compensator is essentially a diaphragm that pushes a
pin down as the boost pressure increases. The above two operations
alter the pin's off boost position and the spring's preload.
The pin itself is tapered and the taper angle changes depending
on the angle the pin is on. This pin is bolted onto the diaphragm
itself so rotating the diaphragm also rotates the pin and presents
a different profile to the pump.
Access to the diaphragm is fairly simple - remove the 4 allen
key bolts on top of the boost compensator.
Mark the position of the diaphragm in relation to the housing
it sits in. This gives you a reference point of the original
position. Rotating the diaphragm clockwise as you view from the
top increases the amount of fuel delivered from idle to close to
maximum RPM. Max fuel is determined by the main set screw.
You can rotate the diaphragm past the max point. This now
begins to reduce the fuel delivery. There are no markings to show
where the maximum point is however you can feel where this point
Rotate the diaphragm with your eyes closed (this is important)
and feel the point where the tension is the least. Mark that point
and perform that operation again to confirm the position. The
diaphragm should be in the same position.
I have seen one pump where the diaphragm was set to the maximum
position from the factory - leaving no further adjustment. This is
The week before last, I visited Dave Webster at Cooma
Diesel in Fyshwick (in Canberra) to discuss our vehicle and
some rather sluggish behaviour in low-end acceleration. They test
drove it for me and said that it was indeed sluggish and that it
definitely needed attention in the fuel-pump. They said that
whilst in factory-spec, the spec was wide in its tolerance and
mine was in the very very lower end of "acceptable".
They arranged for me to contact Toyota (which I did) and review
the vehicle for work to be carried out under warranty. This I duly
was granted, and did without my truck for three days whilst they
(Cooma diesel) worked on the fuel pump on behalf of Toyota.
The results? Unbelievable. There is heaps more
power/acceleration from 1,000 rpm to 2,500 rpm and there's more
top-end power too. Before nothing so much would happen over 3,500
rpm; now... much more acceleration and power. It's a different
What Cooma Diesel did was to re-calibrate the fuel pump and run
it up on the dyno to make sure it was at its optimum. They didn't
touch the injectors, or spray patterns or anything like that, just
re-calibrated the pump. And all done under warranty - the cheapest
upgrade I have ever had.
For those who own the 1HD-FT (esp. if it is still in warranty),
try what I did - it could give you a huge boost...
BTW, great service from Cooma
Diesel - extremely knowledgeable and very helpful.