VAFC question

[schwett]

i think this has been covered before... but i can't find it.

if i install a VAFC (still on the fence) how would it possibly ever make the engine run richer? doesn't it do this by manipulating the map signal? given an atmospheric reading, what can it do to trick the ECU into sending *more* fuel?

also, what effect do the MAP converter and BTC have? would the VAFC get spliced in *after* or *before* the JR electronics :

engine signals -> JR STUFF -> VAFC -> ECU?

thanks in advance.

[dbman96]

BINGO! VAFC is perfectly happy to deliver a 4.5V map signal to your ECU and throw CELs all day. The way to use a VAFC for fuel management is to design a fuel system that would run too rich ie bigger injectors higher pressure stronger pump whatever you need, and then use the VAFC to reduce the map signal when you're off boost.

Here's the fun part!!! When the VAFC trims the MAP signal down to lean out your fuel - say at 2-4 psi you're still trimming out -15% on the VAFC - if you're not at WOT the ECU won't switch into open loop! It will stay closed-loop until the VAFC allows the MAP signal getting to the ECU gets up to near atmospheric. That's right - you too can have massive part throttle tip-in detonation!

The VAFC IS a workable solution but it takes a LOT of workarounds to get it all right. In my opinion it should be the last piece in your signal chain if you've got a lot of electronics since it gives you the most ability to monitor the incoming and outgoing voltages; if you put it before the JR map mod you will only succeed in confusing the JR electronics.



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