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I have a Mack MP8 445 with lose of power issue. Changed fuel…

I have a Mack...

I have a Mack MP8 445 with lose of power issue. Changed fuel filters still having the issue

Mechanic's Assistant: What's the make/model/year of your truck? Engine type?

Mack CHU(###) ###-####

Mechanic's Assistant: Are you fixing your truck yourself? What have you tried so far?

Yes

Mechanic's Assistant: Anything else you want the Truck Mechanic to know before I connect you?

Changed fuel filters

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Answered in 3 minutes by:
2/11/2020
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 2 years ago
Mike Mcmillan
Mike Mcmillan, Shop Foreman/Triage Tech
Category: Medium and Heavy Trucks
Satisfied Customers: 6,440
Experience: Volvo/Mack Master Tech, Certified with Cummins, Eaton, GM, Hino, Detroit Diesel
Verified
Hello and thank you for using Just Answer. My name is ***** ***** I’d like to help. Are you getting any fault codes thru the dash?
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Customer reply replied 2 years ago
no codes
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 2 years ago

Okay, thank you for that. If there is no faults present then I would check for any charge air system leaks, Check the egr tubes for any leaks as well. If those are fine, Then check for any biased sensors, Monitor fuel pressure and make sure it is in the 45-75 psi range thru the rpm range of the engine. Check the egr differential pressure sensor and make sure it is not stuck open this is common on these engines. If all of that is fine, then I would run a regen and monitor for any ex restrictions. I hope this helps you on the right path. Thank you.

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Customer reply replied 2 years ago
This truck has a dpf and egr delete. Tubro will not build more than 10 psi of boost. Not sure what the fuel presures are I havent check them.
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 2 years ago

You need to have fuel pressure to have boost pressure. I would also make sure the boost pressure sensor is reading properly as well.

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Customer reply replied 2 years ago
we put a new boost pressure sensor on it. I think we got some dirty fuel. Other than the 2 main fuel filters is there anyplace contaminants can get caught or plug
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 2 years ago

Do you have a davco filter on the frame rail? Or do you have the 2 filters on the engine?

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Customer reply replied 2 years ago
2 spin on filters on the engine
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 2 years ago

Okay, Remove the fuel lines at the ecm cooler plate and at the fuel filter housing and check for debris at those locations. We have had issues with plugging at these locations. Mostly the debris will get stuck in the banjo fittings.

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Customer reply replied 2 years ago
Ok Ill check this out Thanks
Customer reply replied 2 years ago
Checked the banjo fitting on the ecm cooler it was built up with junk. I cleaned both sides of the cooler and blew air through the lines. Put everything back together and test drove. Truck ran great for about 10 minutes or 3 miles then it acted the same as it has been. No power, no more than 12 psi boost? Whats next?
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 2 years ago

I would check those fittings again. and possibly blow them back to the tank in case something else dislodged.

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Customer reply replied 2 years ago
Cooler and lines were clean this time. Injectors??
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 2 years ago

Are you getting air out of the return on the fuel.

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Customer reply replied 2 years ago
There's small bubbles then every 2 sec there is a big bubble.
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 2 years ago
That’s usually a sign of an injector cup leaking
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Customer reply replied 2 years ago
What might it be if there were no air bubbles
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 2 years ago
I would have to say the fuel pressure would have to be monitored. I’d make sure the pressure is not dropping out. The fuel pumps on these have a non serviceable valve in them that can dump off pressure and there is an overflow valve in the front of the head that can go bad as well just when that valve goes bad it usually causes a hard start
Mike Mcmillan
Mike Mcmillan, Shop Foreman/Triage Tech
Category: Medium and Heavy Trucks
Satisfied Customers: 6,440
Experience: Volvo/Mack Master Tech, Certified with Cummins, Eaton, GM, Hino, Detroit Diesel
Verified
Mike Mcmillan and 87 other Medium and Heavy Trucks Specialists are ready to help you
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Customer reply replied 2 years ago
Thanks for all your help
Technician: Mike Mcmillan, Shop Foreman/Triage Tech replied 2 years ago
My pleasure
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