05-04-2023, 05:57 AM
I’ll start with the bottom line for anyone in the future searching on this topic.
The check valve for the fuel return line for a Series 60 is NOT on the back of the engine as every Detroit manual and YouTube video shows. It is located in the return line just before the return line enters the tank. Remove the vanity panel, and look for the green return line.
A bit of general explanation may be in order to understand how the system is supposed to work. Fuel enters the fuel filter and exits to the fuel pump. The fuel pump pulls a slight vacuum on the filter and supplies fuel up to 75 psi up to the back of the engine head. It may or may not go through a ProChek air removal device before it reaches the back of the head. The fuel circulates under pressure through passages in the engine head to provide fuel to the injectors. An excess of fuel is supplied, and the excess exits the head, restricted by a 1/16 passage and check valve to a fuel return line that ends in the fuel tank. Since this a loop, the purpose of the check valve in the return line is prevent the return line from siphoning all the fuel out of the passages in the head. If that fuel is siphoned, then the fuel pump has to refill the passages before the injectors have any fuel. This is a chore on a Series 60 because the fuel pump is mechanical. It only pumps if the engine is turning over.
Ok, for the rest of the story, otherwise known as this one got me good. On our first stop out of Florida, the coach would not crank the next morning. Engine computer was ok, no codes, but no signs of firing. No smell of diesel at the exhaust. Fuel level was about 1/2 up the Davco bowl. Hmmmmmm. After grinding on it multiple times it tried to fire, and several grinds later, it cranked and ran smoothly. No problems for the 200 mile drive afterwards. At this point, I am pretty sure the engine just lost prime.
A little giggle research shows bad hoses, loose connections, failed check valve in return line, and the scariest….failed o ring on an injector.
Now, headed to Alaska, you just don’t want to wonder if your coach is going to start each morning, so I went into overdrive mentally. That is not a good thing.
My next clue, was I marked the level of fuel in the Davco before shutting down, and then noticed it was several inches HIGHER the next morning. Ok, that is consistent with losing prime, the fuel is draining back from the head into the fuel filter. That points to a failed check valve. The only problem is that the check valve is purportedly on the back on the engine head. NO WAY to reach the back of the engine head to replace the valve without pulling the bathroom floor. Sigh.
After sleeping on this it hits me that the fuel in the return line does not care where the check valve is located. So concoct a plan to cut the return line in an accessible place and splice in a check valve. More sleep, and it hits me to just install it where the return line enters the tank. No cutting of the fuel line involved.
I was removing the vanity panel to access the top of the tank when I got a pleasant surprise. When removing the fuel fill cap, it was obvious the tank was under a lot of vacuum. Huh? Yep, so much that the tank “bonged” when the cap was removed. Well that would explain why the fuel was draining out of the engine, a vacuum like that would pull the fuel back out of the lines. But why is the tank under vacuum. It has to be the vent line is stopped up. Fortunately, the vent line is readily accessible, so I disconnect it, and try to pull it free to inspect. I cannot pull it free. I have pinched it when I reinstalled the fuel tank this winter. I love it, happy dance, I have a smoking gun. I install a new vent line, and crank the beast.
As I am looking at the top of the tank, I see that Newell installed a check valve in the fuel return line just before it enters the tank. Clever on their part. Far easier access than the rear of the engine.
Enjoy your entertainment at my expense. FWIW, when you hear hoofbeats think horses not zebras. I just wish I could remind myself of that from time to time.
The check valve for the fuel return line for a Series 60 is NOT on the back of the engine as every Detroit manual and YouTube video shows. It is located in the return line just before the return line enters the tank. Remove the vanity panel, and look for the green return line.
A bit of general explanation may be in order to understand how the system is supposed to work. Fuel enters the fuel filter and exits to the fuel pump. The fuel pump pulls a slight vacuum on the filter and supplies fuel up to 75 psi up to the back of the engine head. It may or may not go through a ProChek air removal device before it reaches the back of the head. The fuel circulates under pressure through passages in the engine head to provide fuel to the injectors. An excess of fuel is supplied, and the excess exits the head, restricted by a 1/16 passage and check valve to a fuel return line that ends in the fuel tank. Since this a loop, the purpose of the check valve in the return line is prevent the return line from siphoning all the fuel out of the passages in the head. If that fuel is siphoned, then the fuel pump has to refill the passages before the injectors have any fuel. This is a chore on a Series 60 because the fuel pump is mechanical. It only pumps if the engine is turning over.
Ok, for the rest of the story, otherwise known as this one got me good. On our first stop out of Florida, the coach would not crank the next morning. Engine computer was ok, no codes, but no signs of firing. No smell of diesel at the exhaust. Fuel level was about 1/2 up the Davco bowl. Hmmmmmm. After grinding on it multiple times it tried to fire, and several grinds later, it cranked and ran smoothly. No problems for the 200 mile drive afterwards. At this point, I am pretty sure the engine just lost prime.
A little giggle research shows bad hoses, loose connections, failed check valve in return line, and the scariest….failed o ring on an injector.
Now, headed to Alaska, you just don’t want to wonder if your coach is going to start each morning, so I went into overdrive mentally. That is not a good thing.
My next clue, was I marked the level of fuel in the Davco before shutting down, and then noticed it was several inches HIGHER the next morning. Ok, that is consistent with losing prime, the fuel is draining back from the head into the fuel filter. That points to a failed check valve. The only problem is that the check valve is purportedly on the back on the engine head. NO WAY to reach the back of the engine head to replace the valve without pulling the bathroom floor. Sigh.
After sleeping on this it hits me that the fuel in the return line does not care where the check valve is located. So concoct a plan to cut the return line in an accessible place and splice in a check valve. More sleep, and it hits me to just install it where the return line enters the tank. No cutting of the fuel line involved.
I was removing the vanity panel to access the top of the tank when I got a pleasant surprise. When removing the fuel fill cap, it was obvious the tank was under a lot of vacuum. Huh? Yep, so much that the tank “bonged” when the cap was removed. Well that would explain why the fuel was draining out of the engine, a vacuum like that would pull the fuel back out of the lines. But why is the tank under vacuum. It has to be the vent line is stopped up. Fortunately, the vent line is readily accessible, so I disconnect it, and try to pull it free to inspect. I cannot pull it free. I have pinched it when I reinstalled the fuel tank this winter. I love it, happy dance, I have a smoking gun. I install a new vent line, and crank the beast.
As I am looking at the top of the tank, I see that Newell installed a check valve in the fuel return line just before it enters the tank. Clever on their part. Far easier access than the rear of the engine.
Enjoy your entertainment at my expense. FWIW, when you hear hoofbeats think horses not zebras. I just wish I could remind myself of that from time to time.
Richard and Rhonda Entrekin
99 Newell, 512
Maverick Hybrid Toad
Inverness, FL (when we're home
)