Aneroid Pushrod Removal

Aneroid on the back of my fuel injection pump.

This is the aneroid that I chose to disable.

A few days ago I removed the aneroid pushrod from my injection pump.  The 4BD1T in my Suburban is a direct, mechanically-injected system that requires no electronics.  Combined with the NV4500 5-speed manual transmission, this makes for a drivetrain that requires no electronics to function.  In an encounter with an electromagnetic pulse (EMP) or high power microwaves (HPM), most vehicles will be completely unusable.  The Suburban might lose the dash instrumentation, the radio, and the ability to shift in/out of 4wd because all of these things use solid state electronics, but it would still be drivable.  Chances are that this will never matter.  The real benefit of mechanical injection is that it’s simple and somewhat adjustable without expensive tuning equipment or programs.

After I replaced the stock turbo with a Garrett GT2259, the engine can produce much more boost than the fueling justifies.  Recall that, on a diesel, fueling dictates power while boost keeps the exhaust gas temperatures in check.  So, a turbo is a safety feature to protect the engine from high-temperature damage.  So, with the wastegate set the way it was for a Hino truck, I get a maximum of 14 psi and I get it by around 1800 rpm.  I have an EGT gauge on the A-pillar, and I know that my temperatures are never at dangerous levels.  So, I know I can get away with more fueling without damaging anything.  Provided that my foot isn’t heavy all the time, it shouldn’t hurt my fuel economy in normal driving, either.

Many who have transplanted the 4BD1T into other vehicles have pursued larger injectors and a modified injection pump to increase their fueling.  Reworking the injectors could easily cost $500 and the injection pump modifications start at twice as much.  I’m not ready to pay for these increases, but I would like a little more fueling for better performance and driveability.

Removing the aneroid

I removed the aneroid with a 27mm wrench.

The aneroid is a barrel shaped device with a nipple on the back of it hanging on my injection pump.  This device contains a diaphragm that senses ambient air pressure and adjusts fueling appropriately.  At high altitude, this limits fueling to ensure that the engine won’t be hurt by high EGTs.  This pump doesn’t have a boost compensator that would increase fueling when boost pressures increases, so this injection pump has no clue that this engine has a lot more turbo than it originally had.  Stock fueling curves — even with the fueling screw backed out all the way — is a little weak.

Because this device limits fueling, it turns out that it may even be limiting fueling at sea level.  Several people on the 4BTswaps boards have said they got better performance with the aneroid pushrod removed.  I’ve been meaning to do this for awhile, but I finally had a chance to do it.

aneroid removed

This is the aneroid removed from the injection pump.

I got out my 27mm wrench and loosened the locknut on the aneroid.  Then, I was able to twist the aneroid to unscrew it from the back of the injection pump.  When it was out, I mistakenly thought that the the pushrod to be removed was the one that extends from the inside end of the device.  After starting disassembly of the aneroid, I realized that there wasn’t an easy way to get rid of it, though I could take the caps and locknut off the outside end and adjust the aneroid to back it out as much as possible.  Removing the pushrod was still the objective — in order to assure that this device doesn’t limit my fueling.  After doing some more reading, I realized that the pushrod others have removed must still be in the injection pump.

pushrod & aneroid

Here’s a shot of the pushrod laying next to a partially-disassembled aneroid.

I put my finger into the cavity where the aneroid attaches and found a button that felt like there was a spring on the other side of it when I applied pressure.  I realized that this must be the pushrod, but I couldn’t get my fingers onto it to pull it out, so I withdrew it with a magnet.  I reassembled the aneroid and reinstalled it in the back of the injection pump.  I set the pushrod aside in case I decide to reinstall it at a later date.

I drove the Suburban to work on Friday morning and noticed faster rises in turbo pressure and a little more responsive torque from the additional fueling.  Exhaust gas temperatures are still extremely safe, so I’m not worried about damaging the engine with this modification.  I can certainly do more to increase fueling, but this sure was a cheap and easy way to get a noticeable difference!

–Putting the “engine” back in engineering!

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