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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8725
Experience:  I am ASE Master Truck Certified.
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I have a c15 cat go to 6 loose power truck won't accelerate.

Customer Question

I have a c15 cat go to 6 loose power truck won't accelerate. RPM hand goes up and down
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.
Does the yellow check engine light come on when this happens? Or no light at all?
Customer: replied 1 year ago.
flasl on and off do not stay on
Expert:  Cat Man replied 1 year ago.
Thanks for the information.
Since the engine light comes on when this happens. I would like to try and pull the flash codes. If you have never done this. Here is how.
Use the following procedure to retrieve the flash codes from the check engine light:
Turn the ignition key switch to the On position/ Engine OFF.
Turn the cruise control ON/OFF switch to the OFF position.
Move the SET/RESUME switch to either position. Hold that position until the yellow lamp begins to flash.
The yellow lamp will flash in order to indicate a two digit flash code and the SET/RESUME switch may be released. The sequence of flashes represents the system diagnostic message. Count the first sequence of flashes in order to determine the first digit of the flash code. After a two second pause, the second sequence of flashes will identify the second digit of the flash code.
Any additional flash codes will follow after a pause. These codes will be displayed in the same manner. Flash Code 55 indicates that No Detected Faults have occurred since the ignition key switch has been turned to the ON position.
Let me know what two digit code you get and I can tell you what the problem is.
Customer: replied 1 year ago.
55
Expert:  Cat Man replied 1 year ago.
Thanks for the information.
Since there are no codes, I would suspect 1 of 2 things are causing your problem.
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 75 and 90 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 underneath the bottom of the filter housing. 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.
Customer: replied 1 year ago.
have cruse set at 68 mph speed hand move up and down and speed up
Expert:  Cat Man replied 1 year ago.
Does the engine have low power? Or just surge at 68?
Customer: replied 1 year ago.
has power just speed up and sometime goes back to 8 have a 8 speed 9 auto
Expert:  Cat Man replied 1 year ago.
I see. Thanks for the information.
That sounds like a vehicle speed sensor problem. The signal may be fluctuating and causing this.
Customer: replied 1 year ago.
put one on tran
Expert:  Cat Man replied 1 year ago.
Then I would next suspect a problem in the trans where the sensor reads. It reads a chopper wheel. You could also have a problem in the wiring that connects to the sensor.
Customer: replied 1 year ago.
what make tire spin making left turn
Expert:  Cat Man replied 1 year ago.
Not sure. Sorry. I'm more of an engine expert. Sorry.
Customer: replied 1 year ago.
all this is what worng
Expert:  Cat Man replied 1 year ago.
I suspect a vehicle speed signal problem. To confirm you would need to have a service tool connected to monitor the speed signal.
Please reply back if you need more help or have more questions. I am happy to assist.

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