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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8823
Experience:  I am ASE Master Truck Certified.
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I'm working on a cat C7 Acert in a coach, when its pulling a

Customer Question

I'm working on a cat C7 Acert in a coach, when its pulling a hill the low boost code alarms, ive replaced the map/ boost sensor, its not constant and it will go away if they let out of the throttle on the other hand though it does not loose power at all
JA: We'll do all we can to help. Is there anything else important you think the Heavy Truck Mechanic should know?
Customer: it doesn't have any stored codes when I hook up the scanner it throws that until they back out of it
Submitted: 11 months ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 11 months ago.
Thanks for asking your question. I will try and help you out.
Does the yellow check engine light come on when this low power happens?
Customer: replied 11 months ago.
It's the stop engine light that comes on, I have not been in it when it happens but I hook up immediately after they get back and no stored codes
Expert:  Cat Man replied 11 months ago.
Thanks for the information.
If the light is coming on, there should be a code.
What tool are you using to read the ECM? Is it Cat ET software?
Customer: replied 11 months ago.
Nexiq pro link
Expert:  Cat Man replied 11 months ago.
Thanks for the information.
Unfortunately not all tools are able to read all Cat codes. Sorry. Many times Cat ET is the best way.
If the red engine light is coming on, I would suspect you have an injection actuation pressure system fault or a boost not responding. These will cause low boost and turn on the red light. These codes will turn on the red light
Customer: replied 11 months ago.
What would cause those codes
Expert:  Cat Man replied 11 months ago.
The IAP codes are caused by a faulty heui pump, leaking injector, or faulty IAP sensor.
The boost not responding code is caused by a faulty wastegate on the turbo, a plugged wastegate vent, or faulty boost sensor.
Customer: replied 11 months ago.
With a faulty waste gate would that still cause it to not loose power it seems to hold pressure and pull all the way through the range, also what is normal boost pressure for that engine
Expert:  Cat Man replied 11 months ago.
Normally when the wastegate is faulty. The engine has low power all the time
The highest boost pressure for you engine is around 30 psi at high load.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 11 months ago.
The engine does not seem to lack any power builds 27psi no problem, and still pulls through hills
Expert:  Cat Man replied 11 months ago.
I see.
If you are not losing power. I would more suspect an IAP problem. They can occur and cause the light to come on. I would have the engine ECM read with ET to verify the code. That way you can better troubleshoot the issue. If there was a real boost problem, you would be seeing some low power.
Customer: replied 11 months ago.
the IAP sensor would throw the low boost code, the coach has a display for the engine and that's the code that throws when the light comes on
Expert:  Cat Man replied 11 months ago.
Normally it does not throw a low boost code unless the IAP problem is severe.
Customer: replied 11 months ago.
With the IAP problem severe I would think injection pressure low, fuel in oil, starting problems
Expert:  Cat Man replied 11 months ago.
injection pressure will be low but there will not be any fuel in the oil and not any starting problems. Not with a heui system like this.
Customer: replied 11 months ago.
What should the injection pressure be in a C7
Expert:  Cat Man replied 11 months ago.
It depends on the load and rpm.
The lower the rpm and load, the lower the pressure. It can be 870 to 1450 at low RPMs and load. At high RPMs and load it can be 1800 to 3000 psi.
Customer: replied 11 months ago.
It was idling right under 1400psi
Expert:  Cat Man replied 11 months ago.
That is the correct pressure at idle
Customer: replied 11 months ago.
has correct pressures at rpm so it's doesn't seem it would be that
Expert:  Cat Man replied 11 months ago.
Thanks for the information.
I would have the ECM read with Cat ET software. If the light is coming on, there should be a code in the ECM. Knowing the code will prevent a lot of guessing.
Please reply back if you need more help or have more questions. I am happy to assist.
Expert:  Cat Man replied 10 months 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.

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