I decided to take some time and go through my whole tuning process so far, for my own record keeping and hopefully it will contribute to others who are coming down the same path.
First I take delivery of the HDJ from it's previous owner in SD, he bought it from land cruisers direct. The PO told me he hadn't touched the pump settings. Driving home I was shocked at how well the engine performed, I had read that when stock they are pretty slow compared to a 1FZE but this thing felt almost as fast off the line and WAY faster when pulling at highway speeds. I was keeping an eye on the EGT gauge and keeping it below 1000F since it was a post-turbo probe.
My first Mod was to move the EGT probe to the Exhaust manifold, On my first drive I realized that this tune was super weird, my EGTs would climb like crazy when the turbo was spooling, the somewhat stabilize at full boost. Just cruising down a flat road at 50 mph could get the EGTs above 1200. I turned the Fuel screw down almost a half a turn and it helped keep things under control while I waited on my boost controller.
Once I installed my boost controller and started trying to adjust it to 15psi it became clear what was going on. The truck would pull like crazy while spooling, then once the boost got above 10psi it would flatline, my EGTs would stop rising and I had no acceleration. Pulling the fuel rod showed my why.
As you can see (hopefully the pic above worked) the wear mark on the fuel rod shows that this thing was regularly going into over-boost cut-off, even at stock boost levels. My theory is that someone wanted more power and just cranked the main fuel screw up so far that it would keep accelerating even with the fuel rod pushed way down into cut-off. This means the engine was getting the most fuel during spooling, which was causing my erratic and hard to control EGTs.
I adjusted the star-wheel over 2 turns counter-clockwise until I was getting this wear mark at 15psi:
As you can see, the pin is traveling just to the cut-off slope at 15psi but no further. Driving now had much more predictable and linear EGTs, but it would still get hot fast if I was accelerating onto the highway or up a big hill. I wanted to de-tune it until it took several seconds of WOT up a hill before I'd pass 1200 EGTs.
First I put the fuel rod on it's deepest cut and started turning down the main fuel screw until EGTs were safe. This worked but it took all of the bottom end acceleration out of it. Pulling away from a dead stop was almost dangerously slow. I set the screw on the top of the diaphragm to it's most aggressive spot, so the fuel rod starts at a lower position. This didn't seem to make a difference.
I started turning the diaphragm towards a more conservative cut to control top end EGTs and turning the fuel screw up at the same time to increase pre-boost and spooling fuel. This seems to be the right approach. Right now I have good drive-ability and stable EGTs. Unfortunately it's not as fast as it was when I first got it, but the goal here is longevity.
I can very clearly see why people add inter-coolers and big exhausts to these engines. They really make great power when you add fuel, the only limit is EGTs.
