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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8557
Experience:  I am ASE Master Truck Certified.
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I have a Freightliner that when I go up the ll it will drop

Customer Question

I have a Freightliner that when I go up the hill it will drop from 65-70 to 50 miles, I have a code on the system 64-2. Need help
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 1 year ago.
Hi. Thanks for asking your question and requesting me. I will try and help you out.Normally an engine speed timing fault does not cause low power. The engine has two engine speed timing sensors. The engine can run on one if one fails. Does the yellow check engine light come on when this low power happens?
Expert:  Cat Man replied 1 year ago.
The secondary engine speed signal fault indicates the lower of the two engine speed timing sensors has failed. They are located on the drivers side of the engine behind the front cover.
A failed sensor will not cause low power. However I would have the sensor replaced since it apparently has failed. They are sold as a set of two.
As far as the low power. There are two things I have seen cause low power like this.
The first is low fuel pressure. If there is a low fuel pressure problem, the check engine light will not come on and the engine will have low power. Your engine should maintain a fuel pressure between 65 and 85 psi. There is a plug beside of the secondary fuel filter that is used to check the pressure. If it is low, I would first try the fuel filters if you haven’t already. If it is still low, you may have a failed fuel pressure regulator, which is located on the back of the cylinder head. I have replaced a ton of these for low fuel pressure. It is kinda a known problem. You could also have a weak fuel transfer pump or restricted hand primer pump, if your engine has one.
Second I would suspect you have a low boost condition. This can be caused by a leak in the air piping or air to air aftercooler on the truck. I would first inspect all of the piping to see if there is a hole in any of the rubber boots that hold the pipes. From there you may want to cap off one side of the air to air cooler, and pressurize it. They have been known to crack and leak and cause low boost.
Please let me know if you need more help or have more questions.
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.