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Fuel line size E-7 400


Ak47
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Wondering what the fuel line going to my filters and pump should be. 96’ E-7 400 talked to Mack and they said #8 or #10 Line found out I have #8 line from tank to fuel pump bleeder. Then it goes to a #6 line. Bought truck from old mechanic in area wondering if this is suppose to be this way or am I getting less fuel than I should?

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Thank you or the reply but I am still a little confused on the answer, the pressure side wouldn’t be till after fuel pump right? Everything up to fuel pump including filter lines should be bigger than #6an lines right. If I’m on the right track here what would be the size I want to go with #8an or #10an?

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6 minutes ago, JoeH said:

Are you having problems with boost?

If the truck is making power all the way to the governed rpm and can hold full power there then you're probably just fine as is.

I’ve always felt since I got the truck about a year ago that it was under powered. Definitely not enough to pull a trailer. I’ve done the injectors and head gasket about 9 months ago. Turbo is in great shape. 

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I went from ENDT676 motors with 2 stick transmissions to an e7-350 with an 8LL about 6 years ago.  Took me a couple years to realize everything was just fine on the e7, it's just a different motor with different pulling characteristics.  It moves, but it certainly doesn't have the same feel as our old 1979 R model.  Don't know what you were used to before this truck.  How much pressure is your turbo generating?

The E7s are also a lower rpm motor.  My ENDT676 motors you wind up to 2100+ before shifting, but the E7 usually gets shifted between 1700-1800 rpms. 

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The endt676 also hit its power band around 1000-1200 rpms depending on which fuel pump you had.  It makes 90%+ power from 1000-1200 all the way to the governor at 2100.  Going from that to an engine that never really felt like it kicked into any sort of a power and was an adjustment.

Edited by JoeH
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56 minutes ago, Ak47 said:

Thank you or the reply but I am still a little confused on the answer, the pressure side wouldn’t be till after fuel pump right? Everything up to fuel pump including filter lines should be bigger than #6an lines right. If I’m on the right track here what would be the size I want to go with #8an or #10an?

Yup, 8 till pump would be best. What is the “fuel pump bleeder”, can’t picture what your talking about? 

Your low pressure system is........tank, to primary filter, to fuel pump. 

Then.....

high pressure pump outlet, to secondary filter, to injection pump inlet & helix gallery, through restricted orifice overflow valve, to ~atmosphere~(tank) combined along with injector nozzle leakage fuel. 

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33 minutes ago, JoeH said:

I went from ENDT676 motors with 2 stick transmissions to an e7-350 with an 8LL about 6 years ago.  Took me a couple years to realize everything was just fine on the e7, it's just a different motor with different pulling characteristics.  It moves, but it certainly doesn't have the same feel as our old 1979 R model.  Don't know what you were used to before this truck.  How much pressure is your turbo generating?

The E7s are also a lower rpm motor.  My ENDT676 motors you wind up to 2100+ before shifting, but the E7 usually gets shifted between 1700-1800 rpms. 

I totally get that, honestly this truck has been a project. Was running a big cam400 before this one so they are very different power wise. Big cam finally seized up because of crumby head work done by previous owner. Still in my shop awaiting rebuild. My truck I run as a solo dump 56k and pulling hills plus shift hang up isn’t there. 

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19 minutes ago, Mack Technician said:

Yup, 8 till pump would be best. What is the “fuel pump bleeder”, can’t picture what your talking about? 

Your low pressure system is........tank, to primary filter, to fuel pump. 

Then.....

high pressure pump outlet, to secondary filter, to injection pump inlet & helix gallery, through restricted orifice overflow valve, to ~atmosphere~(tank) combined along with injector nozzle leakage fuel. 

Sorry the primer hand pump. Perfect and thank you, as soon as I can I’m swapping it all back to #8 line I don’t know who dumbed it down to #6 but I’m sure I’ll find other problems after this like higher egts. And from joeH I don’t know my boost pressures, there isn’t a gauge equipped on the truck but in time once this thing is all performing properly I plan to install one. Running my own operation and doing the mechanics plus family is a lot. Waiting for the day I’m not so worried about my old girl and can grease, fluids and wash instead of whole weekend jobs. 

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Realize the Kevlar braid line Mack uses is outrageously priced....but change the suction lines if they look old. They love to capillary tear inside when they’re old and make flaps. 

If you substitute use a line branded as “suction” hose. Seems ridiculous to think, but some 5,000psi hydraulic hoses can’t withstand the vacuum created in a suction application. They are engineered for high positive pressure only and don’t hold up well in negative pressure.

Mack E7 PLN is a great motor, worth restoration. Saw a handful of line hauls continue past the million mile mark with original base engine. 

Edited by Mack Technician
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Also, your primer is most likely your transfer pump. It’s unitized. You are set up right if the downsizing of lines occur at that juncture. Your transfer/lift pump is mounted to your high pressure injection pump. So you have three pumps in one location....manual hand pump....mounted to......driven transfer lift pump....mounted to.....injection delivery (jerk) pump...married by fasteners, seals and gaskets.

Edited by Mack Technician
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My lines are as follows #8 to first filter, #6 out of primary/first filter and on to injection pump. Then hard lines to injectors and return line to tank is a #6 as well. Does it sound right still?

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