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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8412
Experience:  I am ASE Master Truck Certified.
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I'm working on a late 3406b model cat with electric governor

Customer Question

I'm working on a late 3406b model cat with electric governor that has very low boost pressure and low power. I got 40 psi fuel pressure,good supply to injection pump,return is open to tank. Checked air to air was cracked replaced,checked all hoses are good. Turbo seems to be good. Checked hoses that going from governor housing to intake no oil inside. Once in a great while it will get decent boost. Not sure where to go next? Speed sensor??
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 engine have low power?

Does the yellow check engine light come on while driving?

Customer: replied 1 year ago.
very low power, once in a you get 15 lbs of boost but then you grab another gear is low power,hardly any boost. Doesn't appear to have check engine light on.
Expert:  Cat Man replied 1 year ago.

Thanks for the information.

There are several things that can cause low power on these engine and no check engine light. You have already checked or replaced two of them. Cooler and turbo.

The first is low fuel pressure. The engine should maintain 35 psi at all times. If it's low, you most likely have a weak fuel pump or restricted fuel inlet line.

Second is a restricted fuel return line. When it's resticted the fuel will stay in the pump too long and get hot.

Third is a faulty rack position sensor. They have been known to read off and cause low power.

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.