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Hi, new to this page and can’t find out anything on this issue. I have a 95 k3500 with a hx40 installed. It keeps throwing code 78 of the highway. My understanding is that this if from too much boost for too long basically. I DO NOT have a vaccume pump for it was removed. There was no longer a need for it with the hx40. The big question I am after is this, is there a way to bypass the solenoid so it will stop throwing the code and sending the truck into limp mode??? I am not really worried about the amount of boost that it produces on the highway I just need it to stop sending it into limp mode. Thanks.
 

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Welcome to DieselPlace
With an upgraded Turbo like the HX40 you need a mechanical wastegate controller and a good set of gauges to monitor boost.
With the mechanical wastegate controller you can set the boost for a max. of 10-11psi.
Anything above that will trigger the code you see and put the engine into limp mode to protect things.
To eliminate that you would need a tune.
 

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Discussion Starter #3
Welcome to DieselPlace
With an upgraded Turbo like the HX40 you need a mechanical wastegate controller and a good set of gauges to monitor boost.
With the mechanical wastegate controller you can set the boost for a max. of 10-11psi.
Anything above that will trigger the code you see and put the engine into limp mode to protect things.
To eliminate that you would need a tune.
Ok this helped a lot. Thank you for the quick reply I will defiantly be looking at a tuner now.
 
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