Dear Ole Mechanic;
I have a 93 Chevy ¾ ton pickup that doesn’t want to start or run. It has a V8 engine with a four-speed overdrive automatic transmission. I consider myself a fair shade-tree mechanic. I do have one of those cheap ‘trouble code readers’ for my car, but the hook up is wrong for this old truck. I did some checking and this truck is one that will flash the codes by flashing the check engine light. It flashes a code 12 which indicates that the electronics are OK. It has good compression--about 90 to 100 PSI--on all eigfht cylinders. While checking the compression, I saw that it had spark at the spark plugs. I also noticed that there wasn't any gas squirting out of the throttle body fuel injectors, so I tried priming the engine by pouring a little gas down through the throttle body. It started and ran briefly but then died as there still was no fuel coming out of the injectors. I used a test light to see if the computer was sending an electrical signal to the injectors. It was. Thinking that the fuel filter was plugged up, I checked for fuel pressure at the fuel inlet of the filter and got less than 2 PSI of pressure. Figuring that the pump was shot, I tried listening at the gas cap. I could hear the pump running. I could also hear splashing ?? What the heck is going on? I haven’t dropped the tank yet ,but I am getting ready to drop it out from under the truck. Do you have any idea what I am going to find?
No Fuel Injection
Dear No Fuel;
I think that you will find a swollen and ruptured rubber hose that goes between the in-tank fuel pump and the tank outlet-line. While Chevy says that their fuel systems can handle up to 10 per cent alcohol in gas, there have been some reports of over 20 per cent alcohol in some gas. That much alcohol slowly swells and weakens the rubber hose until the higher fuel injection pressure ruptures it, and the pressure goes away as the gas sprays out into the tank. It is becoming enough of a problem that I heard another mechanic refer to it as the in-tank ‘waterfall‘.
You are going to need to drop the tank out from under the truck. First, unhook the gas-cap filler and vent lines. You will need to drop the tank about 10 inches to get enough room to disconnect the wiring connector, the supply and return fuel lines and the charcoal canister vent line. With the tank out, the sending unit and fuel pump assembly can be removed. I would strongly suggest replacing the entire assembly, as I have had to pull more than one tank a second time to replace the sending unit after I had replaced just the rubber hose, pump and strainer. Also, I very strongly recommend replacing the pump and not just the rubber hose. The Chevy in-tank fuel pumps are not the most dependable--especially after a number of years and/or a bunch of miles. If you feel lucky and are going to replace just the hose, then be sure to use the special ‘fuel injection’ hose. It is made to take the higher pressure that the fuel injection pumps put out. By the way, the better hose brands--like Gates®--have a special lining to resist the effects of the alcohol. Some of the cheaper imported hose will take the pressure OK, but it may not stand up to the higher alcohol-content gasoline.
Gas weighs seven pounds per gallon, so I suggest that you siphon out as much as possible before you drop the tank. You may need to try the siphon more than once, as there is a nice plastic tub fastened to the bottom of the tank to insure that fuel stays around the fuel-pump pickup. I have found that you can empty the tub and still have more than 10 gallons--that’s 70 pounds--of fuel in the tank. It makes dropping the tank out a real bear. Have fun.
Herr Professor Nuzanbolts