Fuel Pressure: Testing and Inspection

Fig. 13 Modified fuel pump cut-off relay:

1986 - 87 V6-183 & LATE 1986 & 1987 AEROSTAR 4-140 EFI

1. Check for adequate fuel supply. Also check fuel lines and fittings for leakage.
2. Disconnect electrical connector from inertia switch. The inertia switch is located on the toe board to the right of the transmission tunnel on models with 4-140 engines. On models with V6-183 engine, the inertia switch is located in the engine compartment.
3. Connect a suitable ohmmeter between ground and each of the inertia switch electrical connector terminals. Continuity between ground and one of the connector terminals should be indicated. If no continuity exist, proceed to step 4.
4. Remove fuel tank and check continuity between wiring harness and switch leads. If no continuity exist, check circuit between inertia switch and fuel pump. If continuity exist proceed to step. 5.
5. Check for continuity across fuel pump terminals. If no continuity exist, replace fuel pump and sender assembly. If continuity exist, check fuel pump ground circuit and electrical connections.
6. Connect electrical connector to inertia switch.
7. Connect a suitable voltmeter to fuel pump side of inertia switch wiring harness. The fuel pump side of the wiring harness is the side that showed continuity in step 3.
8. Place ignition switch in the On or Run position. Voltmeter should indicate 10 or more volts for approximately 1 second, then return zero. If voltage is not as described, check to ensure inertia switch is not open, then check fuel pump electrical circuit and repair as necessary.
9. Disconnect inertia switch wire connector and crank engine for at least 15 seconds to relieve fuel pressure in system.
10. Using care to avoid fuel; spillage, disconnect fuel return line from throttle body.
11. Connect a suitable piece of fuel hose from fuel return line fitting to a calibrated container of at least one quart capacity.
12. Disconnect fuel hose located between throttle body and fuel filter and attach a suitable fuel pressure gauge between throttle body and filter.
13. Locate fuel pump control relay and replace with modified relay, Fig. 13.
14. Energize pump, by grounding the ground lead from the modified pump relay, for approximately 10 seconds. Fuel pump should operate as follows:
a. Fuel pressure should reach 35 to 45 psi.
b. Fuel pressure should remain at a minimum of 30 psi. immediately after engine shut down.
c. Fuel flow should be at least 5.6 ounces for 10 seconds operation.
d. If the fuel pump performs as indicated, the pump is operating properly. Check for other engine or electrical problem.
e. If fuel pressure are satisfactory, but fuel flow is not, check for blocked fuel filters and lines. After correcting, recheck fuel pump operation. If fuel flow is still not satisfactory, replace pump and sender assembly.
f. If pressure and fuel flow are satisfactory, but system does not maintain pressure after engine shut down, check for leaking pressure regulator or injector. If injectors and pressure regulator are satisfactory, replace pump and sender assembly, as check valve in pump outlet is damaged.
g. If no pump pressure or fuel flow is evidenced, check pump electrical circuit. If no problems are found in the electrical circuit, replace fuel pump and sender unit.
15. Remove modified fuel pump relay and reinstall fuel pump control relay.