Boost Controller Versus PCM

[FRM3]

Can someone explain to me how one can use their own boost controller without the PCM adjusting the boost and thus negating the actions of the boost controller?

I am assuming that the boost controller acts after the PCM boost level decision. If that is the case then doesn't the boost controller increase detonation, etc. risks?

I clearly don't understand this and will appreciate your help.

Thanks

[TripleJackInGA]

Most Boost Controllers slip the PCM a beer or two to keep it busy while it ratchets up the whooshey-noises.

[RODRUN]

Triple your killing me. That is the best. Why was I thinking there would be more tech. junk to learn. I love it.

[3BarBoost]

quote:Originally posted by FRM3

Can someone explain to me how one can use their own boost controller without the PCM adjusting the boost and thus negating the actions of the boost controller?

I am assuming that the boost controller acts after the PCM boost level decision. If that is the case then doesn't the boost controller increase detonation, etc. risks?

I clearly don't understand this and will appreciate your help.

Thanks

Most (nearly all) boost controllers take control of the wastegate solenoid (which regulates the flow of pressure that opens the wastegate) away from the PCM. Some fool the PCM into thinking it is making less boost that it actually is - but those would be more appropriately called piggy-back controllers. Anyhow, once the PCM no longer controls boost the only things it controls are spark and fuel (which strangely enough is essentially all PCMs do anyway).

If you increase boost with a controller to levels beyond which the PCM can control to (say, exceeding the range of the manifold absolute pressure [MAP] sensor) - then you get a fuel cut until pressure drops back into a useful range, and the check engine light [CEL] comes on. If you try to hold boost at high engine speeds (to make more power), eventually the injectors run out of flow and the mixture leans out and knocks, which the knock sensor can compensate for somewhat - but then exhaust gas temperatures [EGT] skyrocket and eventually will warp your exhaust manifold and cause leaks.

Basically, I'm saying absent any other changes (specifically getting more/higher octane fuel) the engine is making about as much as it can and still idle and pass emissions/durability tests.