Jeep 4.0L Fuel System
20 March 2007Fuel System Info
As with any fuel injected motor, it is critical to have a fuel system designed to deliver fuel to the FI system’s needs that is in good condition.
91-96 (Mopar) fuel system
The following information mainly applies to the 1991-1996 HO system.
The ‘91-’96 fuel rail has 2 fuel line connections, one for supply and one for return. The pressure regulator is built into the fuel rail, unlike the later 4.0 systems which are regulated by the in-tank pump. For vehicle swaps, one can either get a tank with an in-tank pump or use an inline pump. With an inline pump you should use a fuel filter before and after. When a pump dies, little parts of it go through. All Jeep vehicles that came with a 4.0L use an in-tank pump. In-tank pumps are more effecient, as it is easier for a pump to push fuel than to pull it.
The regular in the fuel rail regulates fuel pressure down to ~45 psi, so the fuel system should deliver fuel pressure higher than this, 60+ psi is recommended.
In-tank fuel pump
Since all stock applications of the 4.0L use an in-tank fuel pump, I strongly recommend it for reliability. All ‘76-90 CJs and YJs used the same general fuel tank hose locations and sending unit bunghole. This includes the standard steel 15 gal tanks as well as poly 20 gal tanks. ‘87-90 YJ Wranglers had a MPI 4cyl, with an in-tank pump that will deliver the proper fuel pressure and volume for a 6cyl as well. So, a common solution for those swapping a 4.0L into a CJ or early YJ is to retain the stock fuel tank and drop in this ‘87-90 YJ 4cyl in-tank fuel pump.
- ‘87-90 4cyl YJ sending unit: Mopar 83502990
Another option for 4.0L swaps is to retrofit a later model fuel tank. Since the hose locations changed, this will require some modifications.
All ‘91-95 YJs used a 20gal tank. The 15 gal tank was really just a different filler vent hose [source]
‘97 and up (Mopar) fuel system
Starting in 1997, the fuel pressure regular was moved from the fuel rail on the intake manifold to the in-tank fuel pump assembly.
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