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For those of you unfamiliar with the boost compensators found on some 4BD1T and 4BD2T engines, here is a quick run-down.

They are a can fitted to the back of the injection pump with a diaphragm inside connected to the intake piping. Inside they have a rocker with an adjustment screw on the end which pushes a plunger into the injection pump body. This plunger limits rack travel which limits fuel injection quantities and hence torque and power.


The pump shown on the top of the photo has the boost compensator on the back of the pump. Note some pumps also or instead have an altitude compensator, these aren't offset and have no boost line to them.

Inside the compensator can (feel free to open it up, it's about 3 bolts) is a rubber diaphragm that can and does wear out. The first check is to blow down the tube, if you feel it leaking then a new diaphragm is needed or it'll never work properly.
The boost pressure moves the diaphragm and pushes on one end of the rocker, the other end of the rocker lifts away from the plunger, allowing the rack to move and more fuel to be injected.








My boost compensator has a range of around 3psi. Previous settings of mine have had it starting to move at 4psi boost and being open at 7psi. This was checked on the bench with a bike-pump and pressure gauge. I have adjusted it since but not re-checked. It will be possible to change springs to change the operating range.

The adjustment is a screw with a locknut on the inside end (towards the engine block) of the rocker. It is accessed by unscrewing a cap with a socket and requires a thin-wall 10mm socket to loosen the locknut and a flat blade screw-driver to turn the screw inside. I use a combination of a tube spanner and a screwdriver through the spanner for adjustment. Half a turn makes a big difference to engine behaviour.
Screwing it in reduces smoke and power, screwing it out increases smoke and power through the transition.

The other adjustment points are the maximum fuel set with the "more power" screw on the side of your pump. Link here: http://www.4btswaps.com/forum/showthread.php?1035-more-power-from-a-4bt1t-2t&p=10464#post10464
and there is a 6mm screw in the back that can be used to limit the stroke of the compensator. I don't like using this one for two reasons. Firstly it reduces the stroke and effectiveness, secondly it can damage the diaphragm behind. My pump has a short blanking screw in this hole.

I've long considered these boost compensators needed another adjustment point. So I've fitted one.

Stock you have just one adjustment on the rocker arm, which sets how far out the plunger moves for a certain boost and consequently how far the fuel rack can move to increase fuelling.
But, there is no lower stop. Trying to adjust the compensator to stop smoke when just on boost limits the fuel you have off-boost. Making driving awkward when you get caught with no boost.

So I popped my wastegate open (zero boost) and did some tests.

First run, the EGT's would hit 550-600C maximum and it's very sluggish. Confirming what I've thought for a long time, it needs more fuel before boost.
So I pulled the compensator off and measured where the stop sat. It was roughly 24.3mm from the end of the plunger to the back of the fuel pump. Reducing this distance would reduce the fuel available off-boost, increasing this distance increases the fuel available off-boost.

The main modification is simple, I turned up a sleeve that goes over that little spring to provide a lower travel limit. Thus stopping the boost compensator from interfering with my off-boost fuelling.



I also added some 5mm washers for good measure for the first test. The total stack was 27.9mm measured from the head of the pin to the end of the compressed spring, sleeve and washers.

This was smoke propelled, seriously bad. I removed the washers and trimmed down the sleeve over the next four test runs. In the end I had a stack length of 25mm (0.7mm more than my original adjustment) which gives me sustained EGT's of around 750C and minimal smoke under acceleration and no boost. This is about 50% more power off-boost than I had before.

The final dimensions for that sleeve are 10mm OD, 7mm ID and 12.3mm long. Even 0.5mm makes a big difference.

The drivability improvement is great, there is no longer a hole in the fuelling off-boost, it starts pulling well and then the turbo takes over. This also means I can better tune out the smoke when boost comes on.

My fuelling now has three adjustment points.
Fuelling with no boost. (tuning of the spacer length).
Fuelling during the transition when boost arrives.
Fuelling maximum (the fuel screw on the pump).

I highly recommend this mod to anyone with the boost compensator on their pump.
Attached Thumbnails
Boost compensator, how does it work ??-imag0116.jpg
 

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Dougal,
This is fantastic. I have found so much good information on this site and hope that someday I'll be able to return the favor. These are the kind of things that improve our performance and increase our knowledge base to build further. Once again, thank you.

Another thought, or question that occurred to me the other day as we installed and tested a turbo on a NA 4b1--what implications does the (lack of) boost compensator have for adding a turbo to a normally aspirated engine?
Tim
 

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Tim I think we are far better-off without it. I have generally been happier with the n.a pump and performance than the later, stock turbo system. I'm sure this might not be the case if I were looking for higher performance, but our Scout will go over 85 mph and delivers 30 mpg. I have no doubt Dougal could design a 4bd1t to power the space shuttle, but I am wooed by the simplicity of the earlier design. Do we know the fueling capacity of the early and later pumps?
 

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Discussion Starter #4 (Edited)
Tim, with a non-compensated pump and aftermarket turbo you will get some smoke when under load and off boost (accelerating hard from a stop for example). If you know about it and drive according it's not a problem.
Most of the 4BD1T's in the US appear not to have boost compensators (my engine was imported used from Japan and I'm not in the US), I suspect their fuel plate in the governor is shaped to limit fuel and minimise smoke on an rpm basis rather than boost. Where my engine can deliver enough fuel from idle to smoke out bee hives if I tuned it that way.

Coog, we have a few data points for fuel delivery on these pumps.
Around 70-75cc/1000 shots stock.
Randy (carcrafter22) found 140cc/1000 shots or thereabouts on a US pump with 9 or 9.5mm plungers (can't recall) and the screws wound out.
John (Bush65) found 180cc/1000 shots in his pump on a test-bench. I think 9mm elements, but John will likely confirm or deny.
My pumps (one fitted, one spare) have 9.5mm plungers. I am currently at 24psi max with no intercooling and have never approached the limits of my pump. My best calculations and estimates put my current injection volumes around 100-110cc/1000 shots.

I have only just found a possible location for intercooler pipes (I spent the last two weekends shuffling parts around the engine bay). So time will tell.
 

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IIRC Randy's pump had the 9.5mm plungers, that's what my 4BD2-TC pump has too.

Thank you for posting this mod, mine could certainly stand more fuel off boost (it will allow me to crank more timing into the pump, while still having the turbo spool, maybe ;) ).

Probably still have to do the HX30 but this may help.
 

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Discussion Starter #6
You'll be able to go even richer with IDI than me. One of the good things about IDI is being able to run really rich and hot without the black smoke.
 

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Great info as usual, Dougal. Do you think the relative fuel delivery rates account for the greater fuel economy of the n.a pump equipped engines? I have had both a 4bd1a and a 4bd1t in a Ford E350; the 4bd1a gave me 6 to 8 mpg better economy. I've also been told that the same van fitted with a n.a 6bd1a returned 24-25 mpg, which is more in line with what I read for 4bd1t swaps. Impressive figures when you remember that this was before overdrive automatics were used.
 

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Discussion Starter #8
The better fuel economy of the NA engines isn't a phenomenon I've encountered. I know in the vehicle mine is in (classic rangerover) the only engines getting better fuel economy are the much smaller 200/300tdi's which are 2.5 litres and they are a lot slower.
Perhaps it's more due to the injection timing being retarded on the later turbo engines to reduce NOx emissions? My engine runs quite advanced and has the distinctive "crackle" when pushed.

One problem several Aussies have found is surging on a turbocharged 4BD1 under steady load. Have you experienced that?
 

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I'll have to answer " I don't think so " , as I'm not sure what surging means in this context. RPM surge? We have not touched the pump, and the turbo is hardly over-sized, so maybe our 'low' performance is preventing such a problem?
 

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I've never experienced it, but apparently surging in power. Trying to accelerate and then dropping back when it should be holding a steady speed. The two guys (or was it 3) reporting it are running conservative tunes on formerly non turbo engines.
 

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You'll be able to go even richer with IDI than me. One of the good things about IDI is being able to run really rich and hot without the black smoke.
Have yet to see that, but kinda hard to tell without instrumentation.

I would love an exhaust analyzer of some sort that could give me an accurate number for AFR, I know the magic number for these is somewhere lean of 22:1 but have no idea where I am relative to that as pump timing has something to do with how it smokes, and mine is a ways off the stock settings.

For that matter, I would love the converter to use a timing light (they are a piezo electric what zit that converts the pressure in the line to a sinal for the timing light, $300 ish for the one I want, and that's outside the budget at the moment :( ).
 

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Tim, with a non-compensated pump and aftermarket turbo you will get some smoke when under load and off boost (accelerating hard from a stop for example). If you know about it and drive according it's not a problem.
Most of the 4BD1T's in the US appear not to have boost compensators (my engine was imported used from Japan and I'm not in the US), I suspect their fuel plate in the governor is shaped to limit fuel and minimise smoke on an rpm basis rather than boost. Where my engine can deliver enough fuel from idle to smoke out bee hives if I tuned it that way.

Coog, we have a few data points for fuel delivery on these pumps.
Around 70-75cc/1000 shots stock.
Randy (carcrafter22) found 140cc/1000 shots or thereabouts on a US pump with 9 or 9.5mm plungers (can't recall) and the screws wound out.
John (Bush65) found 180cc/1000 shots in his pump on a test-bench. I think 9mm elements, but John will likely confirm or deny.
My pumps (one fitted, one spare) have 10mm plungers. It appears they will produce more fuel than I can ever burn. I am currently at 24psi max with no intercooling and have never approached the limits of my pump. My best calculations and estimates put my current injection volumes around 100-110cc/1000 shots.

I have only just found a possible location for intercooler pipes (I spent the last two weekends shuffling parts around the engine bay). So time will tell.
My pump has 9.5 mm elements. On a test bench it delivered 180 cc/1000 when the rack was pushed to the stop bt hand (governor removed). With the governor controlling, it could deliver something like 170 - 175 cc/1000 - that is with a modified torque cam.
 

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I have a 4BD1na in a 110 with a 200TDI turbo off a discovery and it surges at high rpm low load ( not sure exactly on rpm no tacho). The fuel screw is all the way out and doesnt blow any black smoke from about 14psi. Boost peaks at 20psi but drops off at top end. Turbo is very small and has boost when free revving (around 5psi holding steady). The previous owner ran straight vegie oil through it for quite a while does anyone think this could have damaged the internals of the pump?
I rebuilt engine at 470,000 before turbo charging and found completely coating the inlet and port exhaust ports a thick jelly like substancce about 5mm thick. IT was from the Vegie oil! It was also all around the piston rings.
My fuel economy is around 15L per 100km. Witch doesnt really change with the way i drive.
 

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I have a 4BD1na in a 110 with a 200TDI turbo off a discovery and it surges at high rpm low load ( not sure exactly on rpm no tacho). The fuel screw is all the way out and doesnt blow any black smoke from about 14psi. Boost peaks at 20psi but drops off at top end. Turbo is very small and has boost when free revving (around 5psi holding steady). The previous owner ran straight vegie oil through it for quite a while does anyone think this could have damaged the internals of the pump?
I rebuilt engine at 470,000 before turbo charging and found completely coating the inlet and port exhaust ports a thick jelly like substancce about 5mm thick. IT was from the Vegie oil! It was also all around the piston rings.
My fuel economy is around 15L per 100km. Witch doesnt really change with the way i drive.
On these pumps I would expect it would have more to do with how well a job of pre filtering he did to know if it damaged the pump or not.

How did he start it, diesel or some other fuel for startup, and just before shutdown, or was he starting it with clogged arteries?
 

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My pump has 9.5 mm elements. On a test bench it delivered 180 cc/1000 when the rack was pushed to the stop bt hand (governor removed). With the governor controlling, it could deliver something like 170 - 175 cc/1000 - that is with a modified torque cam.
Do tell, I seem to recall you mentioning that before, but I don't recall the mods in question.
 

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On these pumps I would expect it would have more to do with how well a job of pre filtering he did to know if it damaged the pump or not.

How did he start it, diesel or some other fuel for startup, and just before shutdown, or was he starting it with clogged arteries?
Im pretty sure he was starting with the oil and shutting down with it. When i purchased vehicle it had electric fuel pump that had bypassed mechanical one. When i pulled mechanical pump off it was clogged with a gooey sticky mess that had stopped plunger. Once i cleaned gunk of and put seals through it worked fine.
Would the lubericative qualities be adequate for them injecton pump, and injectors for that matter?
 

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Great info and write up Dougal! I checked out the IP on my 4HE1 and it also has a boost compensator but configured a bit differently than the one from the 4BDx series. Maybe I'll get brave and open up the one on my "parts" 4HE1 to compare.
 

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Im pretty sure he was starting with the oil and shutting down with it. When i purchased vehicle it had electric fuel pump that had bypassed mechanical one. When i pulled mechanical pump off it was clogged with a gooey sticky mess that had stopped plunger. Once i cleaned gunk of and put seals through it worked fine.
Would the lubericative qualities be adequate for them injecton pump, and injectors for that matter?
If the particulates were filtered out and the water was removed (heat, centrifuge maybe) it could.

I have to wonder if the lift pump was clogged how well filtered it could be though. :confused:
 
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