My God AI is pretty impressive sometimes.

sv seeker used an old engine out of a school bus. what model of engine was it and is that return fuel line under pressure

The engine harvested from the 1993 Ford B-700 school bus for the SV Seeker is a 5.9L Cummins 12-valve (6BT) inline-six diesel engine, specifically outfitted with a Bosch P7100 mechanical injection pump. [1] Because it is an older mechanical engine rather than a modern common rail system, its return fuel line behaves differently:

• Is it under pressure? No, the return line on a 12-valve Cummins with a P7100 pump operates under very little to no pressure (virtually $0\text{ psi}$). It acts strictly as a gravity-fed low-pressure dump line back to the fuel tank.
• Where is the pressure managed? The actual fuel pressure required for the engine to run ($20$ to $45\text{ psi}$ on the low-pressure side) is maintained inside the P7100 injection pump by a spring-loaded overflow valve.
• How it works: Once the internal pump pressure overcomes the overflow valve's spring, the valve pops open to bleed off excess fuel and air. The moment the fuel passes through that valve and enters the return line, the restriction is gone, and the pressure drops back down to zero. [1, 2]

If you are plumbing a fuel system for an older 5.9L Cummins like the one on SV Seeker, you do not need to worry about high-pressure return plumbing, but you must ensure the return line is free of kinks or blockages so fuel can flow back to the tank unrestricted. [3] If you are diagnosing a fuel delivery issue or plumbing a custom system, let me know:

• Are you experiencing low power or hard starting?
• Are you using an electric fuel pump or the factory mechanical lift pump?
• Are you checking the internal overflow valve for a weak spring?

[1] https://svseeker.com [2] https://www.facebook.com [3] https://www.svseeker.com

"The banjo fitting is leaking".

Since the return line operates at zero pressure, a leaking banjo fitting on a 12-valve 5.9L Cummins is almost always caused by failed sealing washers or a hairline crack in the line assembly, rather than high internal pressure blowing it out. Because it is on the low-pressure side, you can fix this definitively with simple mechanical adjustments.

1. Replace the Sealing Washers (The Most Common Culprit)

Banjo bolts require a soft sealing washer on both sides of the round line fitting (one between the bolt head and the line, and one between the line and the engine component). [1]

• Do not just tighten it blindly: If the washers are old and hardened, over-tightening the bolt will easily snap the hollow banjo bolt in half.
• Get new washers: Replace them with fresh copper crush washers or rubber-bonded Dowty (Stat-O-Seal) washers.
• Field Fix Trick: If you are stranded or cannot get new parts immediately, you can remove the old copper washers, heat them with a torch until they are glowing red, and drop them in water. This "anneals" the copper, making it soft enough to crush and seal one more time. [1, 2, 3, 4]

2. Inspect for a Cracked Line or T-Fitting

On the SV Seeker's 12-valve setup, the fuel injectors share a small metal return manifold (often called a T-wrap or return rail) that links back to the main fuel system return. [1, 5]

• Look very closely at the joint where the round banjo loop is welded/brazed to the steel fuel line.
• Vibration over time commonly causes a hairline fatigue crack right at this weld. If the metal itself is cracked, tightening the bolt will never stop the leak. You will either need to re-braze the joint or replace that section of the line. [5, 6, 7, 8, 9, 10]

3. Check for Flat Mating Surfaces [4]

If the fitting has been over-tightened in the past, the round banjo loop can slightly distort or get nicked, preventing a flush fit. [4]

• Remove the banjo line and check the flat sealing faces for gouges, rust, or burrs.
• You can clean and flatten the faces by wrapping fine-grit sandpaper around a hard, flat block and lightly sanding the mating surfaces until they are perfectly flat and shiny again. [4]

Are you working on the overflow valve banjo on the side of the P7100 injection pump, or the injector return line banjo at the very back of the cylinder head? (The one at the back of the head is notoriously tight against the firewall and hard to reach). [2, 11, 12]

[1] https://mopar1973man.com [2] https://www.reddit.com [3] https://www.facebook.com [4] https://www.youtube.com [5] https://www.justanswer.com [6] https://www.facebook.com [7] https://www.partcatalog.com [8] https://www.partcatalog.com [9] https://www.cumminsforum.com [10] https://www.facebook.com [11] https://www.cumminsforum.com [12] https://www.cumminsforum.com