Hello everyone, I own a Fend 724 with a deutz engine, having ~700h working hours. Bought new and used for light duties(seeding mostly).
It used to start right away - 1 second of cranking and it fires up.
It started to have trouble starting. Would crank for 2-3 seconds then start. Now it cranks and doesn't start.
Knowing myself how these diesel fuel systems work, I undertook the challenge to fix it myself.
I'll drop a schematic of the fuel system:
My tractor doesn't have 2 fuel tanks, so lets use the one on the lower left half as the only fuel tank.
1-fuel tank
2-water/fuel separator
3-manual priming pump
4-lift/transfer/low pressure fuel pump
5-main fuel filter
6- 2 high presure fuel pumps
7-common rail accumulator
8-overpressure limiting valve
Component description: the transfer pump ensures a 5-10 bar pressure at the input of the fuel dispensing unit Y091. The fuel dispensing unit regulates the flow/pressure that goes towards the high pressure fuel pumps, thus regulating the pressure in the common rail. This solenoid is normally open, i.e. fuel flows through it when it is NOT energised. This allows the pressure from the lift pump to enter the 2 high pressure fuel pumps and build pressure in the common rail to feed the injectors. When the target pressure in the common rail is met, the solenoid closes, the diesel flow towards the high pressure pumps ceases, and as the injectors use the fuel in the common rail, the pressure drops until the solenoid is de-energised and so the high pressure fuel pumps receive fuel again.
A detailed hydraulic schematic:
I have ensured the lift/low pressure pump receives fuel - by gravity feeding it from a 20L jug. I have inspected the 5-10 bar valve that controls the pressure at the entrance of the Y091 and have even elongated the spring inside to cancel out leaks. While cranking, that Y091 does NOT flow any fuel out of the return line. Yet, the pressure at the intake of the Y091 does not raise at all and no fuel is pumped.
My issue is that the lift pump does not seem to produce any pressure at its output - as measured by sensor B087. I can prime the system untill fuel exits out of the fuel pipe that enters Y091 - so the system is primed with fuel so air leaks are out of the question. However, if I manage to build up 1-2 bar in the low pressure system by using the manual priming pump, the engine starts and the low pressure pump manages to keep a healthy pressure in the system, past 7 bar that the sensor B087 can measure. Once started, the engine runs perfectly and will not quit for any reason.
I have tried the following:
-changing the water/fuel separator and main fuel filter
-bleeding and priming the system
-gravity feeding the low pressure pump
-bypassing the main filter( i.e. low pressure pump straight to Y091 dispensing unit)
-restricting return flow out of Y091
-checking the seal effect of the pressure control valve inside the Y091(mechanical one, spring and plunger type)
-ensured the solenoid Y091 works and that fuel can pass through it, it can be blown through very easily; so fuel is getting through the high pressure fuel pumps if 1.5-2 bar of pressure is fed to them
-checked the return flow of the injectors, there is none(while cranking the engine)
-checked the return flow out of the Y091 fuel dispenser; while cranking there is no fuel coming out of the return, and once the engine started there is a heavy flow of return fuel, fills a regular hose with ease;
-checked the low pressure system pressure via the B087 sensor - as expected, once the engine runs at 800 rpm I get over 7 bar pressure, but while cranking I get no pressure at all
I am all out of ideeas as to what is my cause. I feel the low pressure pump has plenty of diesel on its intake and can flow enough, but all this flow is lost somewhere! A lot of flow and a lot of leak back to tank = no pressure.
Where am I leaking? What else could I test ?
It used to start right away - 1 second of cranking and it fires up.
It started to have trouble starting. Would crank for 2-3 seconds then start. Now it cranks and doesn't start.
Knowing myself how these diesel fuel systems work, I undertook the challenge to fix it myself.
I'll drop a schematic of the fuel system:
My tractor doesn't have 2 fuel tanks, so lets use the one on the lower left half as the only fuel tank.
1-fuel tank
2-water/fuel separator
3-manual priming pump
4-lift/transfer/low pressure fuel pump
5-main fuel filter
6- 2 high presure fuel pumps
7-common rail accumulator
8-overpressure limiting valve
Component description: the transfer pump ensures a 5-10 bar pressure at the input of the fuel dispensing unit Y091. The fuel dispensing unit regulates the flow/pressure that goes towards the high pressure fuel pumps, thus regulating the pressure in the common rail. This solenoid is normally open, i.e. fuel flows through it when it is NOT energised. This allows the pressure from the lift pump to enter the 2 high pressure fuel pumps and build pressure in the common rail to feed the injectors. When the target pressure in the common rail is met, the solenoid closes, the diesel flow towards the high pressure pumps ceases, and as the injectors use the fuel in the common rail, the pressure drops until the solenoid is de-energised and so the high pressure fuel pumps receive fuel again.
A detailed hydraulic schematic:
I have ensured the lift/low pressure pump receives fuel - by gravity feeding it from a 20L jug. I have inspected the 5-10 bar valve that controls the pressure at the entrance of the Y091 and have even elongated the spring inside to cancel out leaks. While cranking, that Y091 does NOT flow any fuel out of the return line. Yet, the pressure at the intake of the Y091 does not raise at all and no fuel is pumped.
My issue is that the lift pump does not seem to produce any pressure at its output - as measured by sensor B087. I can prime the system untill fuel exits out of the fuel pipe that enters Y091 - so the system is primed with fuel so air leaks are out of the question. However, if I manage to build up 1-2 bar in the low pressure system by using the manual priming pump, the engine starts and the low pressure pump manages to keep a healthy pressure in the system, past 7 bar that the sensor B087 can measure. Once started, the engine runs perfectly and will not quit for any reason.
I have tried the following:
-changing the water/fuel separator and main fuel filter
-bleeding and priming the system
-gravity feeding the low pressure pump
-bypassing the main filter( i.e. low pressure pump straight to Y091 dispensing unit)
-restricting return flow out of Y091
-checking the seal effect of the pressure control valve inside the Y091(mechanical one, spring and plunger type)
-ensured the solenoid Y091 works and that fuel can pass through it, it can be blown through very easily; so fuel is getting through the high pressure fuel pumps if 1.5-2 bar of pressure is fed to them
-checked the return flow of the injectors, there is none(while cranking the engine)
-checked the return flow out of the Y091 fuel dispenser; while cranking there is no fuel coming out of the return, and once the engine started there is a heavy flow of return fuel, fills a regular hose with ease;
-checked the low pressure system pressure via the B087 sensor - as expected, once the engine runs at 800 rpm I get over 7 bar pressure, but while cranking I get no pressure at all
I am all out of ideeas as to what is my cause. I feel the low pressure pump has plenty of diesel on its intake and can flow enough, but all this flow is lost somewhere! A lot of flow and a lot of leak back to tank = no pressure.
Where am I leaking? What else could I test ?
