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spankyjr1, Journeyman
Category: Medium and Heavy Trucks
Satisfied Customers: 2621
Experience:  I worked on all types of equipment semis,forklifts,farm,ect.
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I have a 400 big cam 3 cummins with fuel in the oil have replaced

Customer Question

I have a 400 big cam 3 cummins with fuel in the oil have replaced the fuel pump and the o rings in the injectors
Submitted: 2 years ago.
Category: Medium and Heavy Trucks
Expert:  spankyjr1 replied 2 years ago.
Hi, my name is ***** ***** you for your question.
The only other thing that could cause this is injectors which are not common on this and a cracked head.
Let me know if you have stc injectors.
What I would do is get some fuel system dye and add to filters,,run engine and use black light to find leak with valve covers off.
If you can't see a leak on top end pull fuel pump off and see if there is any sign of dye which would indicate a leak on pump front seal.
Its possible you just got a bad pump or when yours was rebuilt they just changed seal and not shaft.
You could also remove fittings in rear of head and pressure check fuel system to eliminate anything under valve cover.
If it does not hold shop air you know where the issue is.
Let me know if you have questions or problems I'm happy to assist.
Thanks in advance for leaving a positive rating. If you happen to need more help, this question will stay open for weeks.