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No it can't be running when the key is off, just take it off and throw it away and install the Factory LP back on it.
 

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If you mean by "engine running or not", that it runs with the key off, then the installation was done incorrectly or a relay failed catastrophically. If you mean it starts running with the key on, but the engine not running... that's expected. As for the return line... what did they do with the OFV connection on the back of the p-pump? An electric pump that can modulate it's own pressure to keep the IP at 30-ish PSI doesn't really need a return line, I guess? Did they just cap everything off? What'd they do with the return line from the injectors?

Sell it and go back to oem.
Honestly, OP... ^^^ this. Almost nobody needs an airdog/FASS on a 12V, and they tend to get thrown on as a very expensive bandaid instead of properly diagnosing/fixing a fueling problem, or somebody 'heard it was good' without actually understanding why -- they are a significantly better upgrade on some of the newer trucks, but not ours. The stock LP and fueling setup is far more reliable/long-lasting than any electric pump and moves more than enough fuel to support 550-600 HP.
 

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Discussion Starter · #5 ·
I guess I need to clarify. It does NOT run when the key is OFF.
If you mean by "engine running or not", that it runs with the key off, then the installation was done incorrectly or a relay failed catastrophically. If you mean it starts running with the key on, but the engine not running... that's expected. As for the return line... what did they do with the OFV connection on the back of the p-pump? An electric pump that can modulate it's own pressure to keep the IP at 30-ish PSI doesn't really need a return line, I guess? Did they just cap everything off? What'd they do with the return line from the injectors?


Honestly, OP... ^^^ this. Almost nobody needs an airdog/FASS on a 12V, and they tend to get thrown on as a very expensive bandaid instead of properly diagnosing/fixing a fueling problem, or somebody 'heard it was good' without actually understanding why -- they are a significantly better upgrade on some of the newer trucks, but not ours. The stock LP and fueling setup is far more reliable/long-lasting than any electric pump and moves more than enough fuel to support 550-600 HP.
The returns from the injectors are untouched. There's just a 1/2 inch line running into the ppump. I don't wanna take it off because I like the added filtration and I will eventually be turning it up to more than 600hp.
 

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Then the only thing wrong is you have have an expensive and failure prone electric lift pump.
It should run after the key is turned on before the engine is started. Even trucks equipped with electric lift pumps from the factory do that.

FYI, modified stock style mechanical pumps will support more than 600hp. About 750-800hp is when the stock concept mechanical pumps just won’t cut it anymore. But realistically by the time you modify a 12 valve to that power level, it’s no longer a reliable street truck anyway, so it’s no big deal having the failure prone electric lift pumps at those power levels.
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