1HD-FT /1HD-T pump

[cmjtaco]

Looking for knowledge on BACS and SICS. Currently cleaning up and simplifying my engine bay.

If I understand it correctly, I'd like to

1. Remove the solenoid for SICS and connect that directly to vacuum, for constant vacuum.

2. Remove the solenoid for BACS and either connect that to vacuum or run to atmosphere.

Questions:

- My 1HDFT JDM spec with EGR has no manual diaphragm for BACS. How does it sense the altitude? Is there a pressure switch inside the orange solenoid?

- I live at about 6000' and mostly travel/wheel from 4000 - 10000'. Would it be beneficial to hook up BACS to constant vacuum so that it's always "on"?

- OR am i overthinking it and should I just leave the stock setup? I'd love to simplify if possible.

Thanks

Did you ever figure out how the JDM EGR-Equipped 1HD-FT handles altitude compensation?

I just went through the EGR delete and vacuum simplification. I have vacuum routed to the BACS port on the fuel pump, constantly pulling the aneroid pin down. I thought about retrofitting the High Altitude Compensator diaphragm (25709-17030) but it's NLA. Alternatively, I could rig a manual VSV switch or yank the vacuum line if I am over fueled at higher altitudes, but I want this to be a passive system not needing to be fussed with.

If the EGR computer was handling it, it won't work anymore after I pulled the pins and disabled it. Now IF the EGR computer handles altitude compensation, I would consider reconnecting it and figuring a way to keep the error codes from constantly triggering the dash light.

 

[ikarus]

Did you ever figure out how the JDM EGR-Equipped 1HD-FT handles altitude compensation?

I just went through the EGR delete and vacuum simplification. I have vacuum routed to the BACS port on the fuel pump, constantly pulling the aneroid pin down. I thought about retrofitting the High Altitude Compensator diaphragm (25709-17030) but it's NLA. Alternatively, I could rig a manual VSV switch or yank the vacuum line if I am over fueled at higher altitudes, but I want this to be a passive system not needing to be fussed with.

If the EGR computer was handling it, it won't work anymore after I pulled the pins and disabled it. Now IF the EGR computer handles altitude compensation, I would consider reconnecting it and figuring a way to keep the error codes from constantly triggering the dash light.

Never did find out much. I don't think there's much adjustment to be had just in terms of altitude and I don't think the EGR computer would do anything. I just did exactly what you did - constant vacuum on BACS - and simplified all the vacuum hoses. It's so simple now and I haven't had to tune anything, runs well enough at 6K ft where I live. I think the best thing to do is just tune your pump to the altitude you spend the most time in.

 

[96TrailSurfer]

Did you ever figure out how the JDM EGR-Equipped 1HD-FT handles altitude compensation?

I just went through the EGR delete and vacuum simplification. I have vacuum routed to the BACS port on the fuel pump, constantly pulling the aneroid pin down. I thought about retrofitting the High Altitude Compensator diaphragm (25709-17030) but it's NLA. Alternatively, I could rig a manual VSV switch or yank the vacuum line if I am over fueled at higher altitudes, but I want this to be a passive system not needing to be fussed with.

If the EGR computer was handling it, it won't work anymore after I pulled the pins and disabled it. Now IF the EGR computer handles altitude compensation, I would consider reconnecting it and figuring a way to keep the error codes from constantly triggering the dash light.

I went through the exactly same process. You should now have a lot more low-end power that the EGR system was killing, but your boost compensator spring will likely be completely out of wack now - with the vacuum pulling the diaphragm down, you'll likely be starting about mid-way on the fuel profile on the fuel pin. Great for low end power, but crappy as you get the boost up you quickly hit max fuel. Paint the pin and reduce the preload on the BC spring to get the diaphragm higher until you get it where you want it.

One side effect of this is that, at rest/idle/zero boost, the diaphragm will bulge up - if your diaphragm is old and its edges are dried up (as mine was), this may cause some pressure leakage, to the point thay may max out where additional applied pressure is the same as the pressure loss. Fortunately, it's pretty easy to get a new diaphragm.

 

[96TrailSurfer]

By the way, in case anyone is interested, here are some before and after diagrams.

 

[syche]

Hi all, Diagram 2 is the way to go, all you need is to bypass the BACS VSV , and you will be all good with a permanently regulated vaccum under the boost compensator.
Regulation is done by EVRV and VSV TP, plugging the vaccum pump directly as on diagram 3 isn't correct and will apply way too much vaccum. If VSV TP isn't connected you will have the pre heat light on the dash.

 

[96TrailSurfer]

Why do you want that vacuum regulated?

You can simply close off the BACS port on the pump, or apply vacuum to it like I did, in which case you will need to adjust the boost compensator spring to match vacuum preload. But if you are deleting the EGR, there is no reason to leave vacuum the EGR vacuum regulation there

 

[syche]

On the HD-FT, at least in europe, the spring is so stiff you need this vacuum, and regulated one to get the correct ratio during boost ramp up. The 12 and 24v 80 are very different in the upper part of the pump, i had both and have to use a different setup approach for the 24V. At factory boost the vacuum represent a force equivalent to 60% of the boost force on the membrane.

I tried all, vacuum full on, vacuum regulated, and no vacuum, , the regulated vacuum is the way to go.>> because of the factory spring.

I am now trying to get custom made boost compensator but i need a spring from a none BACS equipped lc 80, basically a 12v, but i can't find any. I tried bosch springs from iveco and landrover defender 300TDI pumps but they are way too soft and too long.

Currently i have 20PSI boost, 2.5mm boost compensator cover spacer, and 1mm preload on the spring, fuel screw maxed out to keep idle at 700rpm with idle screw backed all the way, totally smoke free. i need a new boost pin to get a bit more fuel, i may get 10/15% more, to be tested.

 

[HDJ80L]

Interesting discussion. In regards to BACS, after reading through various forums and manuals, it seems to me that there are three different configurations the 1HD-FT came in:

1) with BACS, VSV contolled through emissions ECU (w/EGR)
2) with BACS, mechanical diaphragm (w/o EGR)
3) without BACS (w/o EGR)

Based on parts cross reference, the mechanical diaphragm 25709-17030 posted above was only used in JDM versions (w/o EGR). The Australian version (for example) must have been without BACS then. The vacuum diagram in the EPC also only shows two hoses to the injector pump instead of three.

According to the engine manual, the version without BACS has an overflow screw with a rubber cap on it. Might be a small vent or fully capped of, any FT owners who have this configuration or know and could confirm? Looks like this would be the obvious configuration to run if one wants to convert to no BACS.

As for what BACS does in the VSV controlled EGR variant, all the inspection test in ERM111E shows is that there should be vacuum on the BACS port when the throttle lever is pushed quickly.

I was speculating that the emissions ECU might have an inbuilt baro sensor like many ECUs in order to control the VSV based on altitude changes. The troubleshoot section of the emissions ECU however simply says that the output for the BACS solenoid (VBAC-E1) is on with ignition on, doesn't mention any switching conditions or pulse width control. Some people in other threads have speculated that it is always on but turns off above a certain altitude.

 

[syche]

Bacs is activated when engine is warm and above 2000rpm, it was to kind of made to fuel starve the engine at low rpm for emissions.

It is described on the schematics with the vaccum valves for egr system.

I unpined the comtrol wire from the ecu plug behind the gloves box and wired it to a dash switch, i now have 2 fuel maps on mechanical IP , the eco full smoke free setting giving me 1 bar at 1800/1900rpm and the very light smoke with 1 bar at 1500/1600rpm.

I reworked the stroke limit spacers under the boost rod, to make 100% use of the full factory ramp ( the longest one) set my spring preload to have a kick in just right, and the fuel screw to be good all the way up, took some time and a lot of tests to get is all right but it is now a pleasure to drive

 

[HDJ80L]

Bacs is activated when engine is warm and above 2000rpm, it was to kind of made to fuel starve the engine at low rpm for emissions.

It is described on the schematics with the vaccum valves for egr system.

Interesting, if that is the case. Doesn't have much to do with altitude compensation but it might be dual/multi purpose. Can you cite the document/page or post a screenshot of the source? I checked the EGR diagrams in ERM111E but no mention of how BACS is operating.

 

[syche]

The BACS integrated to the pump as we have in europe is not for altitude compensation, it is for emission control, the outboard BACS as on some japan vehicles and maybe others, i don't know i did not study thoses.

You can easilly test the 2000rpm thershold, just unplug the bacs hose downstream of the brown vaccum valve and blank the port with a blanked piece of tube, and let the BACS hose free in the air. Drive and you will not feel the kick in the ass at 2000rpm.

it is extremely obvious.

 

[HDJ80L]

The BACS integrated to the pump as we have in europe is not for altitude compensation, it is for emission control, the outboard BACS as on some japan vehicles and maybe others, i don't know i did not study thoses.

You can easilly test the 2000rpm thershold, just unplug the bacs hose downstream of the brown vaccum valve and blank the port with a blanked piece of tube, and let the BACS hose free in the air. Drive and you will not feel the kick in the ass at 2000rpm.

it is extremely obvious.

Thanks for the reply. I don't doubt your observations, I already had a feeling that they repurposed or extended that system for emissions since there has to be a good reason why it is VSV controlled only in the EGR version. Still, it could have multiple purposes, they still call it BACS in all the manuals. Unfortunately there doesn't seem to be any official information on how it is controlled exactly.