fastnblu

iTrader: (2)

I did just notice in lookin thru fuel system area, BAP & FPCM is somethin others are tryin to figure out on their builds. And that was just 1 thread, so I can see the confusion is out there.

I remember lookin at BAP & Magnavolt to see if I needed, or a pc. of mind thing. Been so long, I forgot, but figure it may only be needed if I go beyond a certain boost. I have no plans on a stock piston 5.3 of exceedin 10#.

carbongmc

iTrader: (10)

Just FYI, the camaro FPCM is pinned differently then our trucks. This was something I looked into when I was in the trial process of this as well. Ive heard the same thing on many camaro forums. Some people have them working great, and some dont. But the bad thing Ive found, is the people the say they are working great somehow cant seem to describe how its wired in, either because they paid a shop to install it, or they have no idea about the workings of it. It just seems to me that its a quick fix for something that surely doesnt need to be cut corners on. If you have good luck with this, please post how the install was done, because I would like to be wrong on this and see a BAP work correctly on our trucks.

Boober

Was going to chime in to say this. So, lets set the record straight. BAP's will NOT work (alone) on the GM truck returnless systems. Period. Camaro's, though also returnless, are different. The FPCM does not care what voltage it sees, it will still output the same voltage to the fuel pump.

Maybe we can get a dialog going on what actually works for NNBS flex fuel and non-flex fuel returnless fuel system trucks. Some things I have heard:

The flex fuel pump flows as much or more than a 255. Some people have disconnected the FPCM, wired the stock flex fuel pump to a relay (NO idea on specifics) and used a BAP to raise voltage to the pump. There are apparently codes thrown but if the FPCM is completely disconnected, the codes can be disabled in the tune.

Another method is to put in an aftermarket pump (or more than 1), again get rid of FPCM and run it as "stand alone".

I have also heard of people attempting to put an in-line external pump but this has been met with very mixed results. More ifo is definitly needed on this one.

Lastly, many shops are just converting customers trucks to return style and doing away with all of the hassle. From what I can remember, a new in-tank pump is installed with some kind of relay setup, a new -10AN feed line is run to the fuel rail and a pressure regulator is installed on the rail. The original feed line is used for return. There is not alot of info on this (because it seems that the truck owner is oblivious to what the shop it doing), but this is probably the best solution, unfortunately, also the most expensive and complicated.

Anyone else with some ideas??

Boober

Unfortunately, BAP's have worked with other GM returnless systems (WITH FPCM's in place) so thats why people try them on the trucks. I haven't got a clue why GM engineers chose to do it that way but they obviously had their reasons.

I certainly havent got much of a clue how the system works other than rudimentary knowlege, but the problem is that it seems there aren't that many folks who ACTUALLY know all about the NNBS truck fuel systems. All I have heard is that the FPCM in the trucks outputs a lower voltage (like 5V or something) to the pump and that the flex fuel pump is not pulse-modulated like other returnless systems. This may not be true, but it would be nice to know. Obviously, the FPCM is referencing the rail pressure somehow because, when I log my pressure, it is at 58psi until boost kicks in.

One thing I do know from manipulating my own tune, you can command 58psi in all of the tables, but increasing pressure beyond that with do NOTHING. There is NO way to control the FPCM in your tune. It would solve alot of problems if we could just command a higher rail pressure but it's just not possible.

smokeshow

iTrader: (16)

You can increase pressure, but as I said, you need to remove the in-tank bleeder valve. It is basically a blow off valve for fuel pressure, and you have no control over it. Also, there is a fuel pressure sensor in the fuel line under the vehicle that serves as a closed loop feedback sensor to let the FPCM intelligently control the fuel pressure delta. Its a smart way of handling the fueling, but obviously GM engineers included that bleeder valve to prevent runaway pressure and didn't expect people to be strapping turbos and blowers to these trucks. lol

Boober

Very interesting. So, removing this bleeder valve would allow higher rail pressures and one "should" be able to adjust the desired (high flow) pressure in tune? Would this effect the FPCM/ throw codes?

smokeshow

iTrader: (16)

Yep. I figured this out because I watched fuel pressure peg my autometer gauge at 100psi when the pump was priming. The valve is tiny so its easy to miss if you build your own fuel system I had to get another look at the fuel bucket to see what I was missing, and found that little guy...

tiffo60

iTrader: (2)

This is some very useful info in this thread

Boober

OK, so here is a question after some research... As mentioned before, the BAP will blow it's inline fuse if wired between the FPCM and the pump. It's just not capable of handling the lower voltage of the FPCM when it is driving the fuel pump at low flow. I read somewhere that if you wire up a RPM activated window switch (I assume that this is a different setup than the hobbs switch used to raise BAP voltage) to set the BAP to only come on when (essentially) the FPCM is sending 12V to the pump, it won't blow the fuse and will do as is is designed and raise rail pressure to 50psi+. Thoughts? I'm a little confused myself. If the BAP is not on until its activated, how is the FPCM able to send voltage to the pump? Is the BAP set up so that even if it's not turned on, it will send voltage? Also, I guess my earlier assumption that the pump is not pulse modulated is false (completely unconfirmed though) as I've read that there is a 25hz PVM sent from the FPCM to the pump, how would this effect the BAP?

Lastly, I read this and will be looking into it further. Mr, Smokeshow mentioned the in-tank bleeder valve and it's effect on rail pressure. I read elsewhere that rail pressure is greatly effected by fuel level in the tank. The person stated that he saw a difference of 10psi at WOT between a full tank and a 1/4 tank. Maybe as a general rule, we boosted returnless guys need to keep our tanks full!

Edit: Sorry, more rambling thoughts. I guess I'm obsessed with this! Supposedly, the stock bleeder (relief) valve for our trucks should be around 58psi. The Caddy supposedly has a 65psi mechanical relief valve and the ZR1 supposedly has an 87psi relief valve. So, my question is (and who is going to try it?) if one were to swap out the stock relief valve for a ZR1 relief valve, couldn't the commanded pressures be adjusted in tune to regulate the rail pressure so that the pump is not burned up? Seems logical.

silverstreak07

Well guys added the msd BAP tonite seems to work great!!!!the truck use to drop off to 42 43 psi say from 4500 6000 rpm now the truck stays right at 52 53 psi..Its set up to not give it more than 17volts.it was wired in under the hood if u pull the fuse tray out its wired in between the one wire thats for the fuel pump fuse!!cut the wire thats for that fuse than splice the wires in from the BAP.and the other ones are ground and live to the battery..One quick question ARE trucks start at 43 psi and go to what MY truck says 53.5..We changed the truck to always have 53 psi.When i started truck its now at 53psi is that ok did anyone else set the pressure at 53 psi...