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Curtis B.
Curtis B., Technician
Category: Construction and Road Equipment
Satisfied Customers: 966
Experience:  Technican turned service manager with multiple lines of equipment and rental units.
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I have a cat 8h dozer 46a with low fuel pressure. have

Customer Question

I have a cat 8h dozer 46a with low fuel pressure. have checked the supply line from tank for free flow and blown air back thru line. changed the primary fuel screen, replaced the fuel transfer pump and fuel filters.fuel pressure is around 22 psi, drops to about 18 or 19 at full throttle, pressure comes up a bit when decal to half throttle, but drops off at low idle
Submitted: 3 months ago.
Category: Construction and Road Equipment
Expert:  catmastertech replied 3 months ago.


I see no one has been able to help you. I don't have experience on these Old Iron machines but, I have 20+ years on new CATs.

The old book I found says fuel pressure bypass valve is set at 20 psi and this is how the pressure is regulated. So, I would think 22 psi is good.

What is the full serial number for this tractor? Does it have the fuel feed to the torque convertor too?

What trouble are you having? Was anything done to this tractor recently?

Customer: replied 3 months ago.
hello, sn is46a21258 eng is 1969, fuel pressure is supposed to be 32 plus or minus 7 psi, any lower than 25 psi and it reads in the low, red side of the cat gauge. no work has been done, just has low fuel pressure, co the transfer pump, cleaned and checked fuel supply line from tank,new screen and filters, fuel flows freely from tank thru primary screen,and there is no air in the system. I'm stumped,thanks
Customer: replied 3 months ago.
also it does not have fuel feed to the tc.
Expert:  catmastertech replied 3 months ago.

Ok, thanks for the update.

That serial number is ***** than this book covers, it stops at 46A10250. I will try to locate a book to see if I can find anything in the fuel system that could be related to this issue and will post back as soon as I can.

Expert:  catmastertech replied 3 months ago.

I found a newer book but, it still does not show much on fuel pressure and where to test.

I did find the transfer pump and some filter housings had the same bypass valve (pressure regulator) installed in them. The later machines (like yours) has a cover plate over this location on the side of the filter housing. I would assume this could be a source for a bypass leak and could cause a loss of pressure.

Also the hand priming pump has a check valve in its base. This could also cause a loss of pressure. (It depends on the options that came on the engine.)

Other than those spots, shiming the transfer pump bypass spring may increase pressure or check the return fitting of the injection pump could the wrong size.

Some engines have a special return fitting to provide a fixed restriction and this creates the correct pump housing pressure.

Let me know what you think. Have your checked any of these items?

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