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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8816
Experience:  I am ASE Master Truck Certified.
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I have a 2004 f650 with a cat c7. Was running fine until

Customer Question

I have a 2004 f650 with a cat c7. Was running fine until parked after work 2 days ago. Following morning it spins fine but won't start. Replaced both fuel filters and elbow and fuel regulator at rear of head to return line. Still won't start. Tried disconnecting IAP sensor, still won't start. Disconnected fuel line from tank to inlet side of fuel filter below cab, cranked engine and not a drop of fuel flow.disconnected output fuel line from transfer pump bolted to side of HEUI where it feeds into secondary fuel filter and no flow visible. Does this mean that the transfer pump is bad? Or is it a false results because the loop is not closed? Truck will start briefly with ether but otherwise dead. Not sure how it goes from running fine to no start overnight. Any ideas would be greatly appreciated
JA: We'll do all we can to help. Is there anything else important you think the Heavy Equipment Mechanic should know?
Customer: No, that is a thorough synopsis of my last 2 days
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Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 1 year ago.
Thanks for asking your question. I will try and help you out.
Does the yellow check engine light come on when the key is turned to the on position?
Customer: replied 1 year ago.
it has cruise, so I checked the flash codes. Came back with 39, 21, 35, and 49. The 49 is from the air intake heater being shot. The positive post was melted and wobbling in the housing. The 39 led me to try disconnecting IAP sensor and still wouldn't start. Do I need to clear the code before trying to start with IAP unplugged?
Expert:  Cat Man replied 1 year ago.
Thanks for the information.
No. The codes do not need to be cleared to try and start the engine.
Code 21 is 5 volt supply sensor fault. This should not cause a no start
Code 35 is an engine overspeed code. This code occurs if the RPMs go over 3300
Code 39 is an injection actuation pressure system fault. This is most likely the problem. This code is caused by three things.
First and most common is a faulty heui pump.
Second is a faulty IAP sensor.
And lastly is an injector leaking oil and lowering the pressure below 870. The engine needs at least 870 psi actuation pressure to start.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 1 year ago.
If I disconnected the fuel line from the transfer pump to the fuel filter by the heui pump and I know there's fuel in the system and crank the engine, why is there no fuel flow? This is still upstream from the heui and I have no fuel
Expert:  Cat Man replied 1 year ago.

Thanks for the information.

These engine have a low fuel flow. However, it should have some fuel coming out. If it does not, You most likely have a failed fuel pump on the back of the HEUI pump, or a failed HEUI pump. I have seen the gears on the front of the HEUI pump come loose and spin free. When this happens, the engine will not start and there will be no fuel coming from the pump.

Please reply back if you need more help.

Customer: replied 1 year ago.
Just wondering if the 39 code for low pressure at the IAP has been thrown, what does this cause the ecm to shut down or interrupt? Does it just stop the heui from pressurizing the rail? Does it have any impact on the transfer pump? Transfer pump appears to be entirely mechanical
Expert:  Cat Man replied 1 year ago.
Transfer pump is completely mechanical.
When a code 39 is active. The engine cut back fuel to the engine. The reason is when the system can not produce the correct actuation pressure, it can't burn the fuel. So the ECM cuts back the fuel and causes low power. If the actuation pressure drops below 870 psi. The engine will shut off. It takes at least 870 psi to activate the injectors.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 1 year ago.
Would it be correct to describe the heui pump's function as timing and metering the fuel to the injectors? Does the heui actually pump and add pressure to the fuel flow? Or is all fuel pressure generated by the transfer pump?
Expert:  Cat Man replied 1 year ago.
All the heui pump does is make oil pressure to the injectors. It can range from 870 psi to 3300. The higher the pressure the more the fuel is atomized. The pressure is higher at high rpm or at high loads.
The timing and fuel delivery Is controlled by the ECM with AC pulses.
The transfer pumps job is only to refill the injectors after it fires.Please reply back if you need more help or have more questions. I am happy to assist.
Expert:  Cat Man replied 1 year ago.
Hey. I just wanted to see how things were going. Please let me know if you need more help. I am happy to assist. If my information was helpful, please leave a good or higher rating so that I receive credit. Thanks.

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