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I got a crash course on Cummins 4BT fuel systems that use the Bosch VE Rotary injection pump. That's the most common on 4BT. This system uses a separate 'Lift Pump' to deliver fuel to the VE injection pump. Most common lift pump is the diaphragm type. You can find the diphragm pump at cheap prices by ordering one for an '89 Dodge 5.9L CTD [the Carter M73060] from your local auto parts at 1/2 to 1/3 of Cummins price.
Fuel is pulled from tank by lift pump, and from there it enters fuel filter housing and courses through and then on to the VE injection pump. VE pressurizes and distributes fuel to injector lines and also has a return line to send leftover fuel back to tank. Diaphragm lift pump has a manual pumping lever on the bottom/side. This only works when the pump cam is not already depressed by camshaft eccentric so you often have to bump the starter a couple of times to hit the spot where it manually pumps fuel. If you can't bump starter the engine can be easily turned over with the alternator pulley nut or with the Cummins barring tool.
Fuel comes from tank sender assembly where there are 3 lines connected: 1 pressurized, 1 return line and 1 tank vent. The barbed [has formed lip] line is pressure and return fitting probably doesn't have barb and may be copper. You will probably connect flexible fuel line at the pressure and return outlet/inlet at tank to your fuel hard lines. It MUST BE DIESEL RATED FUEL LINE! NAPA carries Diesel Rated fuel line but not everything they carry is such, so have them double check. The line must be the EXACT SIZE for the inlet or outlet tube from tank as air leaks are death to a diesel. Normal screw type clamps aren't good here so use Fuel Injection line clamps which allow higher clamping force without destroying hose.
Fuel line goes from tank to diaphragm lift pump and on to the fuel filter head. Fuel filter is a spin-on cartridge and for a 4BT the Fleetguard FS1221 works well as it has large capacity and a water separator and drain, and I think Amsoil filters have the water drain also. There is a flat rubber gasket at top of filter which must be lubed at install, and filter is turned only 1/2 more turns after it first tightens, by hand, no wrench. The hard line from lift pump enters fuel filter housing through a 'banjo' fitting. This inlet fitting has a bleeder screw with 10mm head. Fuel goes through filter and out another banjo fitting hard line to front top of VE Rotary injection pump.
The VE pump has a fuel shutoff solenoid at rear top of pump. It is the same solenoid as used on 85-89 VW Golf Diesel so you can find them for less than $30 online, instead of paying Cummins price of up to 3X that. This solenoid is connected to 12VDC ignition Run position, with a connector and 2nd wire going to the KSB Cold Start Timing Advance sender in engine block behind VE pump. The early 4BT uses the 'Wax Motor' KSB.
Excess fuel after injection process is returned to tank through return line. It is just as important to have this line tightly sealed, no leaks, no obstructions as supply lines.
The system is bled by moving manual pumping lever on diaphragm lift pump while cracking fittings. The first fitting to crack is the 10mm hexhead bleed at banjo fitting at fuel inlet to filter housing. Pump until clear diesel with no air bubbles comes out. The next fitting to bleed is the fuel inlet fitting at front of VE pump, but this is only rarely necessary. Hold bottom 17mm while cracking upper 14mm fitting. Now the primary fuel system is bled and engine may start normally. If not, for initial startup you connect a remote start switch to the starter solenoid and with truck in neutral, ignition off, crank the engine while cracking fuel injector 17mm nuts at cylinder head. Again you pump until clear fuel, no bubbles.
The engine may start normally now once everything is tight and remote switch is disconnected. If not then it may be necessary to crack injector fittings while cranking engine with ignition 'ON'. You'll need a helper or else reconnect remote start and turn key on to open fuel solenoid. DANGER: The injectors pump at extremely high pressures, enough that it can inject diesel fuel through your skin! Put a rag over top of injectors when cracking open and expect a good mess. First crack 1 & 3, then 2 & 4 while cranking. It may start during bleeding of 1 & 3, and run rough, so tighten them and crack 2 & 4. This should finish bleeding and engine should smooth out. With engine running you can also very slightly crack the injectors again one by one and check for clear fuel, no bubbles, but be careful of that extreme high pressure.
If engine still will not start or air cannot be bled from system check all your fuel line fittings and clamps. Over-tightening the fuel filter cartridge can cause air leaks also. To troubleshoot for leaks before lift pump remove your flexible line and replace with a temporay install of clear vinyl tubing to lift pump inlet. If this clear line shows bubbles before lift pump then air leaks are between tank and lift pump. If there's fuel to injector pump but not to injectors that indicates a bad fuel shutoff soenoid valve at back top of pump. Try jumpering from battery 12VDC for test purposes and R & R as needed. There is a manual spring-loaded shutdown lever to stop engine, located on driver's side toward bottom of VE pump.
Fuel is pulled from tank by lift pump, and from there it enters fuel filter housing and courses through and then on to the VE injection pump. VE pressurizes and distributes fuel to injector lines and also has a return line to send leftover fuel back to tank. Diaphragm lift pump has a manual pumping lever on the bottom/side. This only works when the pump cam is not already depressed by camshaft eccentric so you often have to bump the starter a couple of times to hit the spot where it manually pumps fuel. If you can't bump starter the engine can be easily turned over with the alternator pulley nut or with the Cummins barring tool.
Fuel comes from tank sender assembly where there are 3 lines connected: 1 pressurized, 1 return line and 1 tank vent. The barbed [has formed lip] line is pressure and return fitting probably doesn't have barb and may be copper. You will probably connect flexible fuel line at the pressure and return outlet/inlet at tank to your fuel hard lines. It MUST BE DIESEL RATED FUEL LINE! NAPA carries Diesel Rated fuel line but not everything they carry is such, so have them double check. The line must be the EXACT SIZE for the inlet or outlet tube from tank as air leaks are death to a diesel. Normal screw type clamps aren't good here so use Fuel Injection line clamps which allow higher clamping force without destroying hose.
Fuel line goes from tank to diaphragm lift pump and on to the fuel filter head. Fuel filter is a spin-on cartridge and for a 4BT the Fleetguard FS1221 works well as it has large capacity and a water separator and drain, and I think Amsoil filters have the water drain also. There is a flat rubber gasket at top of filter which must be lubed at install, and filter is turned only 1/2 more turns after it first tightens, by hand, no wrench. The hard line from lift pump enters fuel filter housing through a 'banjo' fitting. This inlet fitting has a bleeder screw with 10mm head. Fuel goes through filter and out another banjo fitting hard line to front top of VE Rotary injection pump.
The VE pump has a fuel shutoff solenoid at rear top of pump. It is the same solenoid as used on 85-89 VW Golf Diesel so you can find them for less than $30 online, instead of paying Cummins price of up to 3X that. This solenoid is connected to 12VDC ignition Run position, with a connector and 2nd wire going to the KSB Cold Start Timing Advance sender in engine block behind VE pump. The early 4BT uses the 'Wax Motor' KSB.
Excess fuel after injection process is returned to tank through return line. It is just as important to have this line tightly sealed, no leaks, no obstructions as supply lines.
The system is bled by moving manual pumping lever on diaphragm lift pump while cracking fittings. The first fitting to crack is the 10mm hexhead bleed at banjo fitting at fuel inlet to filter housing. Pump until clear diesel with no air bubbles comes out. The next fitting to bleed is the fuel inlet fitting at front of VE pump, but this is only rarely necessary. Hold bottom 17mm while cracking upper 14mm fitting. Now the primary fuel system is bled and engine may start normally. If not, for initial startup you connect a remote start switch to the starter solenoid and with truck in neutral, ignition off, crank the engine while cracking fuel injector 17mm nuts at cylinder head. Again you pump until clear fuel, no bubbles.
The engine may start normally now once everything is tight and remote switch is disconnected. If not then it may be necessary to crack injector fittings while cranking engine with ignition 'ON'. You'll need a helper or else reconnect remote start and turn key on to open fuel solenoid. DANGER: The injectors pump at extremely high pressures, enough that it can inject diesel fuel through your skin! Put a rag over top of injectors when cracking open and expect a good mess. First crack 1 & 3, then 2 & 4 while cranking. It may start during bleeding of 1 & 3, and run rough, so tighten them and crack 2 & 4. This should finish bleeding and engine should smooth out. With engine running you can also very slightly crack the injectors again one by one and check for clear fuel, no bubbles, but be careful of that extreme high pressure.
If engine still will not start or air cannot be bled from system check all your fuel line fittings and clamps. Over-tightening the fuel filter cartridge can cause air leaks also. To troubleshoot for leaks before lift pump remove your flexible line and replace with a temporay install of clear vinyl tubing to lift pump inlet. If this clear line shows bubbles before lift pump then air leaks are between tank and lift pump. If there's fuel to injector pump but not to injectors that indicates a bad fuel shutoff soenoid valve at back top of pump. Try jumpering from battery 12VDC for test purposes and R & R as needed. There is a manual spring-loaded shutdown lever to stop engine, located on driver's side toward bottom of VE pump.
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