Engine/Transmission (1998.5 - 2002) overflow valve

[RClark]

How do you know if the Bosch VP44 overflow valve is bad?

I have had several instances when starting the engine it fires and quits. Cranking does not start the engine until I doo the pump boot and run the fuel pump for several minutes. (FASS System). Once started it runs fine.

 

[JLandry]

The service manual has a test procedure...

DIAGNOSIS AND TESTING - OVERFLOW VALVE

Fuel volume from the fuel transfer (lift) pump will always provide more fuel than the fuel injection pump requires. The overflow valve (a check valve) is used to route excess fuel through the fuel return line and back to the fuel tank. Approximately 70% of supplied fuel is returned to the fuel tank. The valve is located on the side of the injection pump. It is also used to connect the fuel return line (banjo fitting) to the fuel injection pump. The valve opens at approximately 97 kPa (14 psi). If the check valve within the assembly is sticking, low engine power or hard starting may result.

If a Diagnostic Trouble Code (DTC) has been stored for “decreased engine performance due to high injec- tion pump fuel temperature”, the overflow valve may be stuck in closed position.

A rubber tipped blow gun with regulated air line pressure is needed for this test.

(1) Clean area around overflow valve and fuel return line at injection pump before removal.
(2) Remove valve from pump and banjo fitting.
(3) Discard old sealing gaskets.
(4) Set regulated air pressure to approximately 97 kPa (14-16 psi).
(5) Using blow gun, apply pressure to overflow valve inlet end (end that goes into injection pump).
(6) Internal check valve should release, and air should pass through valve at 97 kPa (14-16 psi). If not, replace valve.
(7) Reduce regulated air pressure to 10 psi and observe valve. Valve should stay shut. If not, replace valve.
(8) Install new sealing gaskets to valve.
(9) Install valve through banjo fitting and into pump.
(10) Tighten to 30 N·m (24 ft. lbs. ) torque.

 

[SnoKing]

That is very interesting! If a person has a lift pump that never makes over 14 lbs of fuel pressure, does that mean they never return fuel and cool the pump? Or does the injection pump increase the pressure above that point and excess fuel is returned to the tank? SNOKNG

 

[JLandry]

SnoKing,

In short... no.

The VP44 has an internal low-pressure mechanical fuel pump. The overflow valve is there to relieve the INTERNAL pressure generated from this mechanical fuel pump by sending the excess fuel not needed (for high-pressure injection) back to the tank.

When you measure fuel pressure at the VP44 inlet, you're only measuring the external electric lift-pump pressure and not the pressure being generated by the VP44's internal low-pressure mechanical fuel pump. Assuming the overflow valve is doing its job, the internal pressure is limited to 14psi no matter what the external pressure is.

In simple terms, no matter whether you have 5 psi or 25 psi at the VP44 inlet, as long as the fuel supply volume is sufficient, the INTERNAL pressure in the VP44's mechanical fuel pump will always be 14 psi (or whatever exact pressure the overflow valve is calibrated at).

I hope that helps,

John L.

 

[RClark]

Interesting but when you are on the road without test facilities what do you do?

Today it did the same, fired and quit. 34 cycles of running the pump and about 15-20 seconds of cranking and it finally ran.

Stoped it after an hours running and it restarted. Hope it starts when I leave the campgroung.

 

[RClark]

Change the 34 cycles to 4 cycles.

 

[JLandry]

Today it did the same, fired and quit.

Are you monitoring the fuel pressure at the VP44 inlet?



If yes, what pressure are you observing immediately after you start the engine normally before it quits?



John L.

 

[cerberusiam]

When it messes up starting, try disconnecting the coolant temp sensor connection and see if that helps.

 

[RClark]

Don't remember exactly but tried to start while FASS pump runningat 14 PSI and nothing right away.
Will try and note tomorrow.

Where is the coolant temp sensor and why should it make a difference?

 

[cerberusiam]

Don't remember exactly but tried to start while FASS pump runningat 14 PSI and nothing right away.

Will try and note tomorrow.



Where is the coolant temp sensor and why should it make a difference?

Does you LP run for more than 2 seconds when you turn the key on?



I am assuming this is happening periodically when the engine is warm and you try to restart it? Try disconnecting the LP before starting and see if that helps. The engine should fire immeditely and keep idling. There is an internal fuel solenoid that as it gets older does not like high inlet fuel pressure and will cause a random hard\no start condition.



There is a flash to change the LP cycle from 10 seconds to 2 seconds to address this. Have an 01 that would do roughly the same thing you describe. Had the ECM flashed and problem solved.



Disconnecting the coolant temp sensor sets the ECU into some kind of recovery or limp mode and will occasionally cure a no start condition but not always. Just one of the thigns to try.

 

[RClark]

Tried it this morning. Pump seems to only run for 2-4 seconds if engine doesn't start.
I found a tempsensor, right by the thermostat. After one try with no start after the initial
start,several seconds of running and then just cranking, I disconnected the sensor and after about 4-5- seconds of cranking it started. Of course the temp gage went to max so will have to remember to get out and plug it in asap.
Have an appointment with Sorce Automotive in Clackamas, OR for Monday.
Checked my mileage and this pump has over 60k on it, and it was a Dodge replacement.

 

[cerberusiam]

The next time you try to start warm, unplug the LP and see if that makes a difference. The engine should fire on the second cylinder up or so and idle indefinitely. Don't let it go for much more than a minute or it is hard on the IP.



The LP should only run for 2 seconds when you turn the key on, just enough to prime the pump. If it runs more than that its probably over pressuring the fuel control solenoid.



If it doesn't fire and idle with the LP disconnected its probably something in the pump. On our 01 we found it will always fire if the LP is disconnected warm and generally fire when cold with the LP connected but it was getting longer and longer crank times intermittently.

 

[RClark]

The lift pump was factory programed to only run 2 seconds-from the manual

 

[RClark]

Final report-hopefully.

Source Automotive found a leaking fuel like from the filter to the IP, leaking out fule and letting air in.

While replavine the fuel line a I had them chance the overflow valve just to be ahead of the game. Sofar it is starting.

 

[Dieseldemon]

I had a cust with a no start problem when hot changed to the 12v ck valve cured the problem he had a Fass LP

 

[RClark]

What where is the 12v check valve

 

[Dieseldemon]

The 12v check valve for the Injection pump is on the right side of the inj pump between the pump and the head at the front of the engine that is the fuel supply. The return check valve is on the filter.

 

[RClark]

Since my truck is a 24v I guess this doesn't apply.

 

[cerberusiam]

Since my truck is a 24v I guess this doesn't apply.

I think he means 12 volt, not 12 valve.



The fuel supply to the VP is control by a 12 volt solenoid on the pump that can stick and\or get weak causing issues.