Quote from a diesel guru. OK... I'm hearing and seeing more and more people having CP3/lift pump problems. I'm going to share my solution to this situation. First some background...
Understanding the CP3.
The CP3 is a 3 piston metered inlet pump. By metered inlet I mean that the Fuel Control Actuator valve controlled by the ECM meters fuel going into the pumping chambers to control how much fuel the CP3 pumps and thus the engine rail pressure. This is in sharp contrast to other pressure control systems that divert large amounts of PRESSURIZED flow OUT of the pump back to the tank. The FCA meters how much fuel actually gets pressurized in the first place. Very neat and efficient.
In order to meter the fuel into the chambers, the CP3 has an internal metering/lift pump built right into it. This pump takes the fuel at supply pressure and boosts it to pressures between 80 and 180 PSI depending on what is required. This fuel is fed to the FCA via the cascade overflow valve located on the side of the pump.
The cascade overflow valve's (COFV) purpose is to prioritize the fuel flow between the pump itself (ie feed the FCA), then flow excess fuel to the lubrication flows to cool and lubricate the pump and finally divert any flow above that to the return line.
The COFV prioritizes the flow in that order. If the flow rate is low, only the FCA will get fed. No cooling or return flow will be provided. If the flow rate increases, the pump will get cooled. Any more flow than that and some fuel will get sent out the return line. Note that this prioritization happens AFTER the internal supply pump and there is NO passage from the CP3 inlet to the CP3 return line. The inlet feeds the internal supply pump PERIOD. Unlike other pumps where the fuel supply pump inlet may feed the interal cooling passages and make its way back to the return line.
BTW: The Dodge shop manuals say the COFV isn't "field serviceable" I've removed mine, disassembled it and re installed it with no problems.
So... the internal supply pump is a constant displacement gear pump. This pump is actually capable of developing enough suction to draw fuel through a filter right from the tank. It actually does this on Duramax installations.
Being a constant displacement pump means that it you can't hook just any supply pump up to it. Whereas an injection pump like a P7100 can tolerate a large difference in flow rates to/through it with relatively little pressure change, the CP3 cannot. If you try to push too much fuel to the CP3, the pressure will skyrocket. There are no internal relief valves in the CP3, only a direct feed to the supply pump. Conversely, if there isn't enough flow to it, the pressure will drop and the supply pump may actually start developing a vacuum in an attempt to get enough fuel.
Supplying the CP3
Users needn't worry about pushing fuel to a CP3 at a high pressure. Because it has a built in supply pump, the CP3 only needs to be supplied at a low pressure OR VACUUM and it will handle supplying the pumping chambers from there. Whereas previous pumps had to be somewhat pressurized, the CP3 handles its own pressurization.
Conversely, users do have to worry about getting enough fuel to the CP3. Remember the COFV ? It prioritizes the flow and when there isn't enough fuel to the CP3, it shuts off internal lubrication and cooling flow. This is very bad news for the longevity of the CP3. Diesel fuel viscosity and lubricity falls dramatically with an increase in temperature. Hot fuel within the CP3 is bad.
Basically, one needs to get enough fuel from the tank to the CP3 inlet to keep the CP3 well fed, yet not over pressure it doing so.
I get very nervous when I read of users having their inlet fuel pressure at the CP3 falling to zero PSI. While the CP3 is capable of sucking fuel from the tank in the Duramax installation, in the Dodge installation there is a restrictive fuel pump between the CP3 and the tank. Thus when one sees 0 PSI at the inlet of a CP3 in the Dodge, it is or is on the verge of starving.
To date a number of solutions have been tried, with varying results.
I understand the first gen3 Cummins used an engine mounted supply pump. I assume that these pumps had an internal pressure relief valve. The problem with such a setup is that the armatures in those sorts of pump are generally cooled by the fuel itself and if the pump is continually operating in relief mode, the fuel tends to heat up within the pump and overheat it. I've seen the guts of such pumps actually melt when operated continuously at low flow rates and high pressure.
I understand that Dodge then moved the lift pump to the fuel tank. While this is generally a better setup, if the pump is internally pressure relieved it will suffer the same problems.
Some ambitious owners have taken to using a frame mounted pump with an external pressure relief. This is generally a better approach, but suffers from a few problems:
a) although the pumps may have a decent flow rate at low pressures, they often starve the CP3 when asked to pump at higher pressures because their flow rates fall off. Most of these pumps are designed to feed carburetor gasoline engines, where a typical supply pressure might be 2 to 5 PSI. When these types of pumps are turned up to 10 or 15 PSI, their volumes fall off dramatically.
b) the relief valves are often not designed to totally shut off the return flow when the pressure drops. These systems were designed for carburetors, which have floats that will fail when run at higher pressures. In order to avoid over pressure surges the relief valves never fully close. Thus when the CP3 is gulping fuel like crazy and the supply pressure drops, some of the fuel flow is still going back to the tank ! Not great.
So... having these things in mind, I have implemented a fuel system that has worked flawlessly for 3000 miles now.
Keep in mind that this system is implemented on a '99 FORD SUPERDUTY and not a Dodge truck. The implementation details and operation on a Doge should be similar.
Aside: it is funny that Dodge has so many problems with lift pumps given that the supply requirements are relatively benign. For example, most Cummins fuel pumps only need a few PSI of pressure to be adequately supplied. By contrast a PowerStroke diesel engine needs fuel supplied at a pressure of at LEAST 60 PSI or there are issues with inadequate injector filling.
I believe the reason Dodge has had so many lift pump problems is because they are relying on low pressure pumps with internal pressure relief, whereas Ford uses a high pressure BOSCH pump and uses a pressure relief built right into the fuel filter bowl. Anyway... I digress.
The fuel pump in my system is a Walbro GSL392. THIS IS A HIGH PRESSURE FUEL PUMP DESIGNED FOR GASOLINE INJECTION SYSTEMS, but is also tested for diesel. It is interally relieved at about 100 PSI, but will be on the verge of stalling there. This is a gerotor pump. This pump must be used with an external pressure relief. Failure to use a pressure relief on a stock Gen3 engine will result in a cracked fuel filter housing lid. I speak from experience.
The GSL392 pumps 255L/hour at lower pressures and falls off only a bit until it sees 60+ PSI. What this means is that no matter how plugged the fuel filter gets, the GSL will get the fuel to the CP3.
Aside: I'm told the stock Dodge fuel flow spec is 420 ml/ 10 secs, which equates to 150L/hour. So the GSL is more than adequate. It will flow more than this at 70 PSI.
Here is one source of GSL392 pumps:
http://www.fuel-pumps.net/inline.html It is a common pump available from lots of sources. Google will find others.
I've been running the pump in my truck for 5 years operating at 60 PSI feeding the Powerstroke that USED TO be in it. No problems whatsoever.
The GSL 392 is a frame mounted pump. I used to have the flow/pressure/supply current curves for it, but I don't have them handy.
The GSL392 connects directly to the stock fuel filter assembly via the stock lines.
The key to my system is the CP3 fuel bypass line. Remember that I said the GSL needs to have an external pressure relief ? And remember that the CP3 has a positive displacement internal pump capable of sucking fuel from a low restriction source ? Well, instead of trying to force feed the CP3 supply pump, I chose to run a high volume of fuel right to the CP3 inlet and let the CP3 supply pump decide how much or how little fuel it needs. This avoids all sorts of problems with over pressuring the CP3 at low flow rates, running a fuel pump at high pressures, under flowing fuel to the CP3 at high fuel rates, etc.
Here is a picture of the bypass line:
http://www.dieseltruckresource.com/pics ... ypass1.jpg So my system works like this:
a) the GSL 392 sucks fuel from the tank via the stock fuel pickup.
b) this fuel is pushed through the stock fuel filter assembly to the CP3 inlet
c) at the CP3 fuel inlet, the CP3 sucks all the fuel it needs into the pump for its use. Thus the interal supply pump is fed at a low positive pressure all the time. It gets as much clean, cool fuel as it needs. The internal supply pump is sized such that if it is properly supplied the CP3 will always have enough flow for good cooling and lubrication
d) at the CP3 fuel inlet, any excess fuel that the CP3 doesn't use is routed to the return line, where it goes harmlessly back to the fuel tank. Furthermore, any excess fuel flow from the CP3 supply pump also goes back to the tank via the return line.
It has the following benefits:
a) simple and relatively inexpensive to implement
b) no worries about running low pressure fuel pumps on their internal pressure reliefs
c) it uses a high pressure/high flow pump that will literally last forever
d) all the fuel pumped goes to the CP3 and there is never a worry about starving the CP3
e) the system operates at low pressure, not over pressuring the CP3, nor requiring it to operate at a significant vacuum.
f) the full pressure capabilities of the high pressure fuel pump are available to push fuel through the fuel filter. And all the fuel flow goes through the filter to the CP3. What this means is that flow to the CP3 does't fall off significantly as the filter gets dirty.
I used a colored plastic bypass line on my CP3. Such line material is not recommend for use in a hot engine compartment although this particular line is rated for fluids to 200F. I used it so that I could see if any air was in the fuel. Incidently, an air bubble sometimes appears when the truck is shut off, but otherwise there is no evidence of air in the fuel. As soon as the pump is started there is no air.
I've had my truck parked and running beside other gen3 Dodge trucks. My engine seems to be smoother and quieter than the others. It might be a coincidence.
I hopes this helps people with CP3/lift pump problems. quote.
My installation above with bypass fitted to top of filter head. Note if you look at your stock filter head casting there is provision to drill and tap a return pipe back to the tank.
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of export 2010 Jeep crd fuel sender.
2nd photo fuel sender from 2010 crd export. My computer skills are limited?
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