Dazed and Confused
Q. I have a 1-ton two-wheel drive ’86 C10. This truck had a ’91 350 engine installed but had the TBI replaced by an aftermarket intake topped with a Quadrajet four-barrel carb. The engine is not bored to install a mechanical fuel pump so someone put an external electric fuel pump mounted on the left front fenderwell followed by a clear fuel filter (it’s a 12V DC10 to 14 psi). These numbers were on the pump: AU2635, 6f96, E8153, EP88-9, and E8153—a lot of numbers that maybe helpful. The pump hums and has pressure, but sometimes it pumps gas to the carb, yet leaves me stranded as if I ran out of gas, which in reality, the pump just isn’t pumping gas. If I punch to full throttle, the carb runs out of gas and the pump refills the float bowl in the carb, but, as always, the pump stops pumping. It’s on but no gas comes out. I have dropped the gas tank, blown through the lines, and added a new fuel filter—still no gas. My opinion is that the fuel pump needs to be mounted closer to the gas tank or that I need to get a stronger pump. What can you do to help?
Also, what is this engine? It’s an LS9 from a ’71 C10. Stamped on the water pump pad are the numbers V1212TYC, 6847, and C8146970. On the back of the block is 3970010. I have the original sticker on the glovebox that says engine displacement LS9 350. People say they have never heard of an LS9 in carb form from 1971—or ever—that they’re only familiar with the more recent Corvette LS9 ZR-1. Your column has led me through lots of problem solving. Please help!
Corpus Christi, TX
A. You’re right on with moving the pump to the fuel tank. Electric pumps are designed to push fuel, not pull. Whichever pump you currently have, it needs to be at—or very close to—the tank. Another thing you better look at while you’re revising your fuel system is the fuel pressure at the carburetor after you have moved the pump. If the specifications you gave off of the pump are correct, the 14 psi will overwhelm the needle and seat in your Q-jet and flood over. You don’t want more than 6 psi at the carburetor while the engine is running. The float, needle, and seat can work with this level of fuel pressure.
Your engine codes gave us a little runaround. First, the LS9 engine RPO was used in ’69-86 trucks and vans. The engine was always carbureted with either a two- or four-barrel carb. The casting number 3970010 was used in ’69-79 and was equipped with either two- or four-bolt mains. This has been a mainstay of 350 performance small-blocks over the years. Now, down to your specific engine code “TYC.” You said that your truck is a ’71 model year and this is the original engine. Well, the “TYC” engine code was used with the LS9 engine RPO in two model years. First, it was used in 1976 in a C10 pickup with a manual trans and federal emissions. The only other time they were used together was in 1978 in a G-20 van with a TH350 trans and, again, federal emissions. This level of detail on casting numbers and engine codes would be impossible without the help of our friends at MSA-1. Mark Allen of MSA-1 has, over the years, put together a full line of pocket code manuals. These manuals cover engine codes, casting numbers, and part casting numbers for water pump, exhaust manifolds, distributors, and the like. These books are priceless on a restoration project to ensure that you have a correct build. Check with Mark at MSA-1 at 800.600.MSA.1 for more information and to order the books you need.