Adapter plates for Woodward 8404-2006 to FGC25K mixer/intake
I fixed the problem by replacing the ECM and throttle body actuator with a Woodward L-Series throttle controller. Not knowing which one was causing the problem and both costing more than the Woodward system I figured it would be cheaper to replace them. The Woodward controller needs to be programmed to work, but I had previous experience in doing that from some other projects. I also had an adapter plate made for the mixer and some gaskets cut. It has worked very well. Only problem I have had is that if it sits at an idle for a long period of time sometimes it will just turn off. I think the engine speed signals gets weak and the Woodward controller no longer senses it running and closes the throttle valve.
12/30/2025 - Added some photos
Used Woodward 8404-2006
A couple of things to try , first check diaphragm in mixer it may be dirty and sticking causing too much fuel to enter chamber
Next look at the air intake system make sure it doesn't disrupt air flow to mixer
Is there a flashing light on dash ?
Is the triangle light on on the dash if so that is why it will not throttle up if the computer seen a fault it would cut the throttle to half speed at the throttle body L believe you could count the flashes on the light to tell what the code is to repair the problem. I believe the computer is no longer sold also the map was built into the computer the computer was potted so you can not have it repaired there were some adjustments on the throttle body L might have some paper work on that system at work and will post it when L get to the office. The throttle body had to 12volt coils inside that controlled the plate and if there was a problem it would cut the voltage to the coils in the barb Coleman. Throttle body. That system was the beginnings of emissions.
Hey Eaugie, did you ever find a fix?? I have one exact same problem. Thanks.
Did you ever get this problem resolved? I have the same truck with the same problem and having a hard time getting anywhere with it. Was hoping you may have gotten it figured out and could shed some light on your resolution for me.
Thank You
So the problem went away for a while but is now back and more consistent. It seems to run fine on start up in the morning but once it gets a warm and you try to restart it the engine will start but not idle up. I've done the following. It has a S15G-2-N039-002 (91165-15800) ECM. I have tracked down all the I/O wires and they have tracked out fine. The engine intake manifold temp sensor, throttle position sensor, fuel lock off, FCSV and throttle body controller all are connected to the ECM.
What I have found is the throttle body valve gets about a 50% duty cycle PWM at 180HZ (about 4.6 - 5 VDC read on a DMM) as the engine cranks and then runs at a very low idle. Foot pedal input will not change this PWM nor is the FCSV chattering. I can hear a slight hum over the throttle body. If I remove the connector going to the throttle valve the hum goes away and the engine speed drops a little bit more. I have applied a variable DC power supply to the throttle valve and once I get over 4 volts the engine picks up speed and I can control the engine speed in the 4 to 5 Volts DC range. Higher the voltage equals higher engine speed. Once the engine speed gets high enough I can see a change in voltage from the ECM wires that should be going to the throttle valve. If I press the foot pedal it will increase the PWM signal as well. You can also feel a vibration in the FCSV valve too. It seems to me that the input voltage to the throttle valve is not high enough on start up to open the throttle enough to increase the engine speed high enough to think it is running. I looked at the PWM signal to the throttle valve while the valve was connected and I was getting a good 14.2V pk output which would lead me to believe the ECM is in good condition.
Is the throttle valve actuator going out? Are they repairable or can you open them up and clean/lube them back up? The throttle valve is a Barber Colmen 91165-05400
Thank you for any input.