12.7 questions

Maybe I’m wrong, but until you rule out a lost prime, you’ll be wasting effort time and money. Here goes. Go to Wal Mart or harbor freight, spend $20 on a portable air compressor. Cut end off compressor hose, take vent hose ( near fuel cap) off Drivers side tank. Attach cut off hose end to vent nipple tighten up with 1/4” hose clamp. Take passenger side vent tube and bend it and tape it, so it’s crimped off. Plug compressor into a cigarette lighter,/acc outlet. Turn it on and wait, the less fuel in tanks the longer it will take. Maybe 20-30 minutes. When gauge shows 5 lb or more, try to start it. Use a little ether if you like. Any compressor set up will work, but this way you can keep the portable one for any time you lose prime in the future, when you may not have access to compressed air. Changing ecm is self explanatory by looking at it . Un plug, un bolt . Reverse procedure with same type ecm.

 

I’ve never changed one, but would either disconnect battery or just remove ecm fuse, in battery box, just in case. To avoid any damage. It may be unnecessary but easy enough to do.

 

Could be, Mine went bad, no codes. Good Luck, I wish I could help more. You can blow all the fuel you want through it, but until you pressurize a closed system, it won’t flow. It needs to have a siphoning effect. Same principle as siphoning fuel from a tank. Because of the newer top side draw . It works different than the old bottom draw gravity fed type. Gotta get working myself, good luck

 

Ha Wanna: Been busy chasing my own rabbits. You did not find a check valve because it never had one. I bought these books when we bought White GMC,s with S 60.s. Ours had Davco fuel water separaters. They had a check valve on the inlet.
I saw a fuel can made like a Cheetah tank. Put fuel in it and connect it to the fuel supply prefilter. Crack the outlet valve and prime the system. Cats meow when you hit the starter.
Would expect the sensors to throw a code. Look at power and ground to ECM and install a test ECM. As long as it is the same DDEC series and a 6 cylinder it will run. That is just my thoughts. Let us know what you find.

 

I am not real sure about all of that. Those pumps are not positive displacement pumps. If it is air locked you can roll the truck off the top of a mountain and it is not going to start. If you have fuel through the system it should pump.
Does the air compressor output shaft spin with the engine? Is the drive coupling there and correct for your new pump?
A check valve in the back of the head would probably be a good update.