86LT1C10

Now, I have a question about the EVAP system. I have a 86 C-10 with the 93 LT1. I have experienced the vapor lock that 95 TA The Beast has posted about. It doesn't help that the fuel filter sits 2" from one of the cats due to a inline fuel pump being used and having a saddlebag fuel tank. I don't have the EVAP installed in the truck at this time but I am about to be putting it back in. I am putting in a rear mounted fuel tank (Omitting the saddle bag style) and going to run the fuel lines away from any exhaust. The fuel tank I am using will only have 3 tubes off of the sender. One from the pump. One return from the regulator. One for the EVAP. How do I hook up the WHITE vacuum/pressure relief valve in the system? I see that the F body tanks have a 4th tube for it. Tee it between the tank and the EVAP canister? Or is it just required on the plastic tanks, not the steel tank I will be using, and the 'vented' fuel cap do the job instead by letting air into the tank? I am pretty sure all the fuel vapors normally exit into the EVAP canister and the only purpose of the pressure relief function of the 'white' valve is for whenever the EVAP system gets plugged. I just don't know if it is essential for normal operation.

Fatdog2

Since nobody chimed in I will tell you what I know.The reason cars don't get vapor lock anymore is because of the evap system is returning unburned gas back to the tank.I don't think placement of the gas filter would be a issue,but I dunno.For pics and wiring stuff you might try Shoebox.s site.Hope this helps.Hope I don't get slammed too hard on this one.My02.(GaryDoug has some pics to I think)

Injuneer

The EVAP system does not return unburned gas back to the tank. It collects fuel vapor exiting the tank, vapor is stored in the charcoal canister, and then the vapor is purged by engine vacuum, dumped into the intake manifold and burned as part of the normal combustion process. This has nothing to do with preventing vapor lock, which is the flashing of liquid fuel to vapor before it reaches the injectors. Unusual in a high pressure EFI system. The more likely problem is excessive pressure drop on the suction side of the pump, or very warm fuel, which flashes to vapor before it enters the pump.

Locating the fuel filter (or any other system component) near the exhaust, where it picks up excessive heat, can cause vapor lock. Would be easy to insulate the filter.



The white plastic valve is a SAFETY valve, to prevent the tank from rupturing from high pressure, or collapsing from vacuum. GM used it with all tanks, metal or plastic. It needs to be installed. It can only be teed into the vapor vent line if there is no possible obstruction in that line. Stock F-Body sender has a rollover valve that blocks off the vent line in case of a roll over. Tank would not be protected from pressure rupture with the car upside down.

Fatdog2

Thanks again Injuneer.You are tops.