Swoop,
Were having a similar issue.
cat GC30K s/n: AT83C000805
fuel system is tier 1
ECM with vacuum line
no check valve in line with vacuum hose
replaced ecu 90401-06396
we have the ecu setup instruction for the S15G tier 1 fuel system
but not exact to ours system. we have no oxygen sensor and the wires are not the same colors.
we did try to calibrating by using vom but not accelerating.
any additonal ideas? what other parts should we id t get the correct setup

Where can I get that program ?

I tried a few things and even cheeked the pressure and I am getting 4lbs from the regulator so I don't think its the regulator. I will have to look up the program and see if I get any better results. Thanks for the help.

luis,
do you have the MCFA Tier 1 diagnostic program?
you will have better luck diagnosing the truck and fixing it with this.
These Tier 1 trucks with that ECM with the vacum hose (MAF Sensor) were difficult to troubleshoot without the program.
There are many service bulletins on this system about this very issue with this setup. MCFA made many changes to the system after it first came out so you will have to verify exactly what components are on it and then get the correct diagnostic and repair guide to troubleshoot it and repair it.

There is a check valve inline with a vacuum hose that plugs into the air inlet hose that can clog up, make sure its clear and working properly.
Also the engine dwell setting can affect how the truck runs and only can be set using the program.
Plus calibrating the PPS to the TPS can be only done effectively using this program. It can be done by using a VOM but is alot more difficult.
Also make sure the mixer is clean and the diaphragm is seating properly inside the mixer. Pay close attention to the little bullet and seat in the center of the diaphragm. The dwell adjusting screw is behind a small expansion plug on the side of the mixer and uses a small Allen wrench to adjust.
You will need the proper documentation to check it out and verify the settings and adjust it as needed to get it set correctly.

good luck with this

Hey Kevin ,
It's a GP30K its stamped on the plate & serial number AT13L30849
I believe it's a Mitsubishi engine most parts have the Mitsubishi logo on them.
I was working on it today, and this is what i did. I started the forklift , disconnected the cables that come from a black box that also has a vacuum hose, anyways I disconnected the cables that come from the black box to the carburetor , but once I connected the cables again it wont run anymore, I had to depress the diaphragm on the valve regulator to get it to start. please help.

P.S the black box has the wires coming from the TPS and distributing them to the carburetor and the distributor.

Is this a GP30N? What is the model and serial number of the truck,does it have the Nissan K21/K25 Engine?......are there any codes showing up in the display????