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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 having an issue with a C7 CAT. It started with the truck

Customer Question

I'm having an issue with a C7 CAT. It started with the truck completely quiting on the road... Driver stated when he was down shifting going up a hill, it just quit. He finally limped back into our shop.. Truck would barely idle, no power what so ever. So I check the fuel filters and air filter. The primary was only half full of fuel. So I blew air through all the lines, changed the filter, primed the system and the truck started with a very rough idle and still would not run very well. When we shut the truck off, I decided to check the tank. It was either under pressure or vacuum when I took the cap off. So I cleaned out the vent and changed the cap. Truck would run, but still starved for full. I changed the fuel regulator in the back of the head as well as the the fuel injection accuation sensor. Truck started great and took off like normal. After about 5 minutes of driving, it started missing again like it was starved for fuel. I'm stuck. Any suggestions? I have yet to check the fuel pressure. I'll try to do that in the morning.
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 the engine is running with low power? Or is there low power with no light?

Customer: replied 11 months ago.
The check did not, but the "engine heat"light did. It's down next to the steering column on the right.
Customer: replied 11 months ago.
check engine
Expert:  Cat Man replied 11 months ago.

Thanks for the information.

Since the check engine light does not come on, 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 65 and 85 psi at all times even driving under a load. 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.

Customer: replied 11 months ago.
I'll check the fuel pressure in the morning and get back to you.
Expert:  Cat Man replied 11 months ago.

Ok sounds good. Let me know how you make out. Talk to you tomorrow.

Expert:  Cat Man replied 11 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.