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Little big mack

Lack of power

9 posts in this topic

I don't know where to start new to this stuff. 

Majority of the time truck won't build over 22 to 25 pounds of boost. Sounds like the waste gate is sticking open. I used to have 35 psi. Ive had fault code 4-5 pop up on the lighting bolt. Mack told me it was my turbo speed senor replaced it. Ran good for about 2 days and back to tail between its legs. Turbo is fairly new. Motor was rebuilt about 80000mi ago. I've replaced fuel pump, number 1 unit pump, and had them do a ride along loaded with logs and can't figure anything out. Fuel pressure was between 80 to 90 I believe if I'm not mistaken. Need help with problem. Also could it be the VGT air solenoid located on driver side of motor?

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does it have a waste gate ???????

if a  turbo diesel motor doesnt make boost there is really on three reasons 

turbo is stuffed 

lack of fuel (you need the fuel to make the boost)

or lack of air (air cleaner blocked or a leak in the air system and the compressed air is leaking out) 

it really is that simple would be surprised if it has a waste gate at all I have never noticed a waste gate on large diesel turbo motors 

If you can hear air escaping as the boost builds that would be a pretty good indication of a leak somewhere I would think

 

Paul

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Welcome to big Mack trucks. There are lots of guys here who will hopefully help you out. 

We have had new turbos on cummins and cat which needed the wastegate adjusted. They will tell you it's within spec but the range can be quite wide. 

Anyway, best of luck with it. 

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You should have around 33 psi boost , check air filter, check muffler for broken baffle.  pressure test entire intake system , not just the after cooler. Also a big over looked part is the boost pressure relief valve on top of the intake manifold.  Ill attach pictures of what it looks like soon . 

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Remove it and see if i the end of the valve  unscrewing its self  and causing it to dump boost 

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as mentioned before test the charge air cooler and all related components  

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