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Ask Alex Olsen Your Own Question
Alex Olsen
Alex Olsen,
Category: Medium and Heavy Trucks
Satisfied Customers: 93
Experience:  Lead technican at Astleford international trucks
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Fuel is being derated due to boost pressure check air

Customer Question

fuel is being derated due to boost pressure check air intake
JA: What's the make/model/year of your truck? Engine type?
Customer: 1999 international 9900 n14 cummins inframe been done for 2 months
JA: Are you fixing your truck yourself? What have you tried so far?
Customer: yes new fuel lines new eps sensor new boost sensor checked turbo and filters nes fuel filter new fuel pump and running out of money lol
JA: Anything else you want the truck mechanic to know before I connect you?
Customer: no
Submitted: 1 month ago.
Category: Medium and Heavy Trucks
Expert:  Alex Olsen replied 1 month ago.

hi im alex, could i get your engine SN please

Customer: replied 1 month ago.
11929846
Expert:  Alex Olsen replied 1 month ago.

ok thank you, ***** ***** are you getting?

Customer: replied 1 month ago.
the truck runs fine at idle and pulls good has 30 -40 psi turbo pressure when its pulling i get to 7 or 8th gear bobtailing and it starts to act like is running out of fuel if i push into neutral and push gas it clears up but as soon as you put pressure back on it it does it again cummins insite says
"the engine fueling is being limited due to lack of oxygen (boost pressure)
Customer: replied 1 month ago.
no codes at all
Expert:  Alex Olsen replied 1 month ago.

have you checked the fuel pressure?

Customer: replied 1 month ago.
no i dont have a guage but i have replace fuel pump off another working truck doing the exact same thing
Expert:  Alex Olsen replied 1 month ago.

so the boost is dropping off? or it just thinks it is?

Customer: replied 1 month ago.
when its starts missing the boost drops to like 10 psi when its happening
Expert:  Alex Olsen replied 1 month ago.

ok so it is actually dropping, have you pressure tested the CAC?

Customer: replied 1 month ago.
are you talking about the air to air what is cac
Expert:  Alex Olsen replied 1 month ago.

yes charge air cooler

Customer: replied 1 month ago.
ok i just replaced that but i havent pressure tested it i dont have the tools for that but at a idle and hitting the gas it works
Expert:  Alex Olsen replied 1 month ago.

ok does it smoke when it starts acting up?

Customer: replied 1 month ago.
NO
Expert:  Alex Olsen replied 1 month ago.

have you tried with a trailer?

Customer: replied 1 month ago.
it starts earlier
Expert:  Alex Olsen replied 1 month ago.

ok perfect sounds to me like you have a fuel restriction under heavy load i would get a fuel pressure gauge on and drive it

Expert:  Alex Olsen replied 1 month ago.

ecm cooling plates like to plug on these

Customer: replied 1 month ago.
how would it be a fuel restriction i have tried 2 diffrent fuel pumps and i have even ran a line straight from pump to a bucket of fuel and had the same problem
Customer: replied 1 month ago.
i have bypassed all of them coming straight from fuel pump into a bucket of fuel with same results
Expert:  Alex Olsen replied 1 month ago.

i only have what you tell my to go off of please remember that, if it starts missing under load and you take it out of gear and has no load and then clears up sounds like a fuel issue to me, i would get a gauge on it to be sure, low boost wont make it miss it would just have low power, but if you have low fuel pressure you wont make boost

Expert:  Alex Olsen replied 1 month ago.

have you checked intake and exhaust restriction?

Customer: replied 1 month ago.
i pulled all the hoses loose from air intake and exhaust no blockage
Expert:  Alex Olsen replied 1 month ago.

this all started right after the inframe

Customer: replied 1 month ago.
The inframe was done beginning of august this just happened last week
Customer: replied 1 month ago.
How would I tell if my ecm is bad and I do have Cummins insite if that help
Expert:  Alex Olsen replied 1 month ago.

well with no codes it will be hard to tell other than swapping it with another ecm

Customer: replied 1 month ago.
Dag
Expert:  Alex Olsen replied 1 month ago.

yeah i would really get a fuel pressure gauge could be a damaged fuel injector o ring just to be sure you are not chasing your tail rule all the easy stuff out sounds like you have checked it over pretty good

Customer: replied 1 month ago.
If it was a injector orings was bad wouldn't it miss
Expert:  Alex Olsen replied 1 month ago.

no could be just under heavy load when engine is pulling fuel hard

Customer: replied 1 month ago.
I've cranked the engine and unplugged all the injectors except one and it ran the engine and I moved all the way down and each one ran the engine I figured if oring was bad it would cut off on that injector because of loss of compression
Customer: replied 1 month ago.
Is that correct or not
Expert:  Alex Olsen replied 1 month ago.

i have never heard of that or done that, i always just use insite, i still feel you should get a fuel pressure gauge on it just to be sure, here is the low boost troubleshooting go down that and see what you have or havent done

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