I just replaced the high pressure fuel pump on a 650J. I was wondering what the normal operating fuel rail pressure is supposed to be? I’m getting a reading of 7540 psi at full throttle. Thanks Joe
Machine serial number? This will help to determine the exact fuel system on the engine. Why was the HPCR pump replaced? Are you having rail pressure mismatch codes? Any other codes? What symptoms are you experiencing? What is the fuel pressure reading in the monitor first thing in the morning with the key on, engine off? There is no published spec for High Pressure Common Rail fuel pressures. On a "J", which has an older HPCR system (if your serial is over 159987), I would think a no load fast idle reading would be in the 12,000-15,000 range and higher when loaded, going maybe as high as 18,000-25,000 at full load.
Hello there, The SN is T0650JX160150. HPCR pump was replaced because of rough running at idle and only developing 2250 at full throttle no load. The pump replacement fixed the above problems. No rough idle and max rpm is 2350 no load with new pump. As per my original message only showing 7450 psi on fuel rail full throttle no load. Was wondering if that was normal as it seems low to me. Machine is running fine with new pump. No codes. Original code was low fuel rail pressure. I will look at the cold fuel rail pressure engine off and let you know. Thanks Joe
Was your rail pressure in spec? The specs MG2361 sent you are what i remember also.
Fuel rail pressure fluctuating between 7k and 10k?
Pressure cold was 7.5k
If the actual pressure is really that low and the commanded pressure (which you cannot see without Service Advisor) was more than 700 psi higher, then it would throw pressure mismatch codes. If the machine is running fine, and there are no pressure mismatch codes, then ignore it and run it. Maybe there is a glitch in the software and it is not reading or reporting correctly. I looked up your serial number, your machine has new ECU software available. Might be worth having it updated.
A software update would be good. One thing i have seen on these high-pressure common rail systems is your old high-pressure pump may have had a faulty suction control valve. When you replaced the pump, your engine run good. Many times, i have seen the SCV valve spike the rail relief valve, and this causes damage to the valve. The valve will leak fuel to return causing fluctuating rail pressure. Can be a small dribble or a large leak. An easy check is to disconnect the return line at fuel rail relief I use a plug or a hose to run return line to catch container as fuel will come out of line. Start engine absolutely no fuel should come out of rail relief valve.
Thank you everyone for the input and advise. Machine is running fine so I'm going to schedule a software update as mg2361 suggested.
Here is the video of the fuel rail pressure releif valve test. Lookss like the valve is bad because its allowing by pass of fuel at idle.
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Here is the video of the fuel rail pressure releif valve test. Lookss like the valve is bad because its allowing by pass of fuel at id Just uploaded the vodeo mg2361
Yep, that is why you can't develop more than 7-8000 psi.