Well that explains why Fromage and my trucks both don't even have input from VSS-2 to the TCM. Thanks Astr!
I am still unsure if I get lockup in second, I haven't really tried to figure it out to be honest with you. I get lockup in 3rd and OD, but it will only occur when traveling faster than 48MPH. It will remain locked when decreasing speed down to 43ish MPH, but won't relock until 48MPH is achieved again. Honestly, transmission behavior is no longer a concern of mine. Once I added a quart of ATF and got more miles on the trans (bedding in the clutches I assume), it performs beatifully. The ONLY thing I'd like to change about it is the speed at which the converter will lock. 40MPH would be nice. I have yet to connect my "Power" button to the TCU, but I plan on doing that this weekend if I get the opportunity.
On the topic of power... I replaced my lift pump with a new OEM Zexel pump, I ran 1/2" hard line from the tank to the water separator, and I now have 3/8 from the separator to the lift pump. I put clear line on the return side and confirmed I have no air in the system. The new lift pump came with a new gauze filter. No difference in power output.
I then bumped the timing back up, which definitely improved the throttle response and low end, but minimal difference in top end power. EGTs are very low now, they never get over 1000 degrees regardless of engine load/vehicle speed/gear selection.
20.25 MPG US on the last tank!!! 500+ miles and the light never even came on. Gotta love the 38 gallon tank...
I have a theory about the apparent drop in power. This is 100% a theory, but it's all I've got at this point.
When the truck lost all its power, it wasn't a gradual change. It was litterally one day it felt mediocre, the next day it felt like it lost 30HP and could no longer go faster than 68MPH. It was as if a switch was flipped, not something wore out. Yes, it coincided with the injector R&R, but the low end feels better since the injectors were changed and the truck idles better.
The truck feels the same as it always did between 0% and 50% throttle. Now, there is litterally no difference between 50% and 100% throttle. I can just slap the accelerator pedal between 50% and 100% repeatedly and nothing changes. No change in boost, EGT, nothing. And yes, I checked the TPS output and it is functioning exactly as the FSM states it should.
Remember a few weeks ago when I was playing with the fuel rate resistor? I tried the highest setting and lowest setting with no effect? I thought maybe the throttle response was a little better at the lowest setting, but no concrete evidence of it. Placebo effect probably.
Well, I had left the potentiometer in at the lowest setting without thinking about it again.
Side note:
GM 1994-2000-something 6.5L diesels also have a fuel rate adjustment resistor. By changing it they can raise and lower power, by a small amount, but it works. However, the GM ECU only references that resistor on every 50th start. So the effects aren't necessarily immediate. Depending on where you are in the reference cycle, it could be weeks before the change is noticed.
IF, and this is a BIG IF, the Zexel ECU treats its fuel rate resistor in the same way, only referencing it under certain conditions, it may have finally looked at my potentiometer which was currently set at ZERO ohms (which is LOWER than a #1 resistor), and pulled a whole heck of a lot of fuel out.
It is the only explanation I have besides a failure within the injection pump that has caused a sudden loss of fuel flow. Needless to say I now turned the potentiometer up to a high end of the spectrum (#7 setting). I am going to drive the truck as it is for a few weeks and see if the power all of a sudden comes back. If it does, I know the resistor does actually do something. If it doesn't, I'll start shopping for a new injection pump.
If the power does come back, it will be a very simple way to add power to these trucks. The problem will be in how long it takes to realize any changes. If the high resistance adds too much fuel, I will have to drive very carefully until it relearns the next setting I try.
On the GM vehicles a scan tool can be used to force a re-learn (disconnecting the battery does not work). There is no 12V constant to the Zexel ECU, so disconnecting the battery also does nothing. I tried using the "memory clear" wire for the DTCs when I was first playing with the resistor, and that had no effect then and no effect now either. I asked the technician at my local Fuso dealer and he didn't even know what the fuel rate resistor was, let alone any re-learn function. He's worked on these trucks for 30 years... never even knew the resistor existed. When the part number on my stock #3 resistor was put in their system, it didn't even show up.
So, now it's just a wait and see game. I can deal with the piss-poor performance now that it is getting 20MPG. I am literally going to change nothing for the next two-three weeks to see if the resistor changes anything. Stay tuned...
