CJChris Posted October 21, 2021 Share Posted October 21, 2021 Looks like CJ stock steel fuel line is 5/16 inch. 4.0 fuel rail is 3/8 inch connection. Is there any need to install 3/8 fuel supply tube even though the stock tank nipple is probably 5/16? I am going to run external pump. Quote Link to comment Share on other sites More sharing options...
Administrators Moses Ludel Posted October 21, 2021 Administrators Share Posted October 21, 2021 CJChris...So, you're installing a 4.0L in a CJ7? You want to know whether the OEM CJ 5/16" fuel pipe is adequate fuel flow to the fuel rail? 5/16" fuel flow should be adequate for a stock 4.0L engine. The pressure is fuel pump and rail regulator controlled, which compensates for the fuel line size. Your concern would be 5/16" fuel line gph fuel volume flow, and the stock 4.0L will not "starve" with a 5/16" fuel line. The Mopar EFI Conversion Kit for the 4.2L relies on OEM 1980-86 CJ and early (1987-90) YJ 4.2L chassis fuel lines. The 1994 4.0L MPI/EFI system is two-rail with a pressure regulator at the rail. You need a return line, and I am guessing you'll use the OEM Jeep fuel return line to the tank? You do need a return line with two-rail EFI. The CJs with a BBD carburetor and three pipe fuel filter have that return line to the tank. An external pump is not an issue as long as it's close to the 4.0L OEM fuel pump pressure. These are high pressure pumps. Pump pressure specs are in a 1994 YJ Wrangler or XJ Cherokee FSM. Replacement pump catalogs offer these specs as well...Make sure your fuel supply line connections and any hoses can handle EFI/high pressure. (The carbureted CJ was a light pressure mechanical fuel pump.) Any line, hose or fittings between the high pressure fuel pump and rail must handle the pressure. Moses Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.