ed h.
I suggest to check very carefully the ignition spark.many times technicians confuse about problems in the fuel system but the problem is in the ignition. Gas or starter liquid or inyector cleaner ignits easily than l.p.

"teir 1" Cat trucks did use a Cobra vaporizer. I do not remember the mixer but I know for a fact it was not the Impco 100 like the 90s likfts.

this is a "teir 1" 2003 truck, and so has an pretty normal mixer, (slightly different spacer [+.05" thicker] under the "bullet") but the throttle body itself and the ECM is a barber/colemen (who no longer exist). I am pretty sure it takes a ca60 impco mixer, and a cobra LPG regulator.

Carb/Mixer is a FT60M series

Impco Cobra is correct but the carb is marked Model 60. The sticker on the side of the carb is scratched uo and can not be made out.

Ed;
Am I reading this discussion incorrectly? The serial number along with the model number and the year is telling me that this fuel system is an Impco Cobra (vaporizer-regulator) with a CA100 carburator. Would please confirm this for all concerned so we may assist you better.

You are correct Ed that you most likely need to calibrate the throttle pot with the new ECU, I have been able to in the past to get a new ECU to work without calibrating. The ECU does not use the throttle pot during cranking or base idle. Initial start up RPM command from the ECU is 1000 RPM. The ECU should be commanding 1000 RPM during cranking even if the pot was completely out of whack. 1000 RPM equates to like 3.5 volts at the throttle body. The only exception is if the throttle pot was open. If you turn the key on after 45 seconds the MIL will flash a four code indicating an open throttle pot. Or go to the green wire at the ECU. You would see.7 volts with the accelerator pedal at rest, and around 3.9 with the accelerator pedal fully depressed.

if you replace the ecu, you will still need to hook up a laptop and "learn" the accelerator pedal position sensor, wouldn't you?
And failing to learn the pedal will still give these same symptoms, wouldn't it? So then there may be some wisdom in bitting the bullet and getting someone to hook up a laptop and check the pedal position sensor before you spend the money on the new ecu?

yes, replace the ECU

thats what I was thinking but its not. Any more ideas?

If the fuel lock-off is energizing then the ECU knows the engine is cranking and should be powering the throttle.

Yes, fuel lock has power

I have had many ecu go bad causing a no start condition. In all cases the fuel lock would not open. Are you getting voltage to the fuel lock?

The 2 Black wires on the sensor have not been put together and are still on the lug/sensor. Throttle pot has not been moved but i have accuated the throtle linkage with the floor pan removed.

I just checked and I do have voltage going to the ECU from the coil but no voltage going to the throttle body. I am thinking the ecu is bad but not sure. Is there a way to test it or any thing else I should check?

The electronic throttle should see about 5 volts at WOT. If the throttle plate is not opening during cranking the ECU may not know the engine is cranking. Verify the wiring harness at the coil to the distributor is good. The ECU receives its tach signal via the red wire on this harness. No tach signal equals no cranking according to the ECU. If you have some voltage to the throttle plate make sure that the coil inside the throttle plate is not open. I think the coil resistance is around 10 ohms

I would also suggest as a test to remove (and do NOT plug) the vac line that attaches with a small black plastic elbow on the part of the air intake hoses that is mounted to the valve cover and make sure the air can get through the hose

Make sure the vacuum lines are good and in the correct locations, second check the FCVS for voltage, Its the solenoid by the converter. This controls the fuel.

edward t,
Sorry but I didn't know the answer but I looked into my Dewey Decimal System Cards for Cat/Mitsu technical experts & voila' your name was at the top of the list.
As you may recall I am (or was) just a simple technically oriented, well traveled, sales/marketing lift truck guy for 41+ years. Then I hung up the spurs & turned it over to those that have not had that much chance to gain experiences - like surviving another recession.
But I do wish to thank all that are gamely employed and pay into Social Security as 1/30,000,000 of you weekly, monthly or bi monthly contribution goes to me. That might or might not make you feel any better - either way thanks.

I know its not the cap, either the ECU or spark module