BAP Question...

[Bob Cosby]

Good Morning,

I am preparing to install my KB and BAP. I have a discussion going with someone that suggests I wire the BAP in such a way that it is always "on", and wired before the FPDM, essentially feeding the FPDM with a certain voltage (18) all the time. The computer is then told (with the tune) that there is 18 volts to work with, and it will control the output of the pumps.

My question is, does anybody know of any problems doing it this way? I'm concerned that the increased voltage might be bad for the long-term health of the FPDM (or perhaps the pumps - I don't know). FYI...the idea behind wiring it this way is to prevent (or lessen) any fuel pressure spikes when the BAP comes on.

Thanks for any input.

 

[JB]

Bob,

my best suggestion would be to contact MJ...he's one of our resident SVT Gods and will be able to answer any questions you have regarding the fuel system on this car :rockon:

http://67.15.62.79/forums/member.php?u=3114

 

[Shadowgray03]

The BAP is in essence a step up transformer so if you have it so it is always on, it will be upping the voltage to the pumps, this in turn will push more fuel which will be sensed by rail sensor and in turn inform the EEC which will then command the FPDM to reduce the duty cycle to the pump until the fuel pressure gets to where it is supposed to be. The end result is that the pumps will only get the voltage they need to supply the fuel that is needed, so if the BAP is on all the time the only time the pumps will be overdriven is when they need to be to supply fuel, which really isnt any different than having the BAP come on via the hobs switch.

 

[Bob Cosby]

That is the kind of info I'm looking for. Many thanks for posting.

Bob

 

[Dana]

I agree with everything Shadowgray said.
The only issue is when the PCM commands the FPDM to reduce pressure to a minimum, will that be low enough? As at idle.
If the PCM requests below a certain level, the pumps actually shut off.
The upper ranges will work fine as Shadowgray mentioned.

I don't see any problems with connecting it the way the KB instructions recommend, using the BAP only as required.

If you replace the Hobbs switch with an adjustable one and set that one to 8 or 9 lbs, the system still has more than enough time to increase pressure as the demand increases. It also eliminates the surge that originally occurred with the 3 1/2 lb switch.

Dana

 

[mjchip]

The only other piece of significant information regarding where to wire in the BAP is as follows:

1. Wired before the FPDM: you will be able to support less HP with the same fuel components because the FPDM will still drop voltage in its internal switching components and the BAP will not be able to compensate for that since the drop occurs AFTER the BAP. This will have better transient response but less full-scale range.

2. Wired after the FPDM: any voltage drop that occurs before the BAP will essentially be regulated out (within reason). This provides the most fuel system range with a given set of components but will have worse transient response.

Personally I use the BAP after the FPDM with an adjustable hobbs switch set to around 8psi.

MJ