I'm working with a 7747 and am finding that my VE values want to be significantly over 100 as I tune. I'm using a ARJT bin, which actually has a few spots where VE1+VE2 exceeds 100 right from the factory. ?

Reading around on here I gather that the BPW in the factory bin is set based on a nominal fuel pressure of 12 PSI. My gauge shows barely 10 PSI, which I think is in spec, but would seem to indicate a BPW of 160+. Is that the right way to think about it?

The factory is already up to 100 and now I have lower fuel pressure plus a possibly more efficient engine due to headers. Should I go ahead and just pump up the BPW as needed to keep my VE values under 100?

 

As long as there is enough injector to feed the engine it will work. Note that there is an individual BPC (BPW) value for when EGR is off. Then a table of BPC values for when EGR is active.

Once the injector duty cycle goes over 85% the injector flow rate needs to be increased.

RBob.

 

Thanks for the help. I think you're saying to go ahead and bump the BPW as needed? I have no EGR so I'm just going after that one value. It is true that the ECM will clip the VE1+VE2 to 100, right?

 

Yes, as long you you don't run out of injector, bump up the BPC.

Yes, ECM will add VE1 & VE2 together and clip at 100%.

RBob.

 

I'm reaching the end of my rope here! I have the BPW at 200 and the BLMs are still huge. In fact, they are pegged at the BLM max for a large part of the table. I don't think this can be a computer/bin/software problem. It must be something more basic. The pump is a brand new in-tank factory style item, as is the filter. I show 11 psi at idle (underhood gauge, can't see when driving).

I'm attaching a screenshot of what I have going on. Anyone have any ideas? It seems to me like the injectors are giving it all they've got and it's not enough. Logically, either the fuel pressure isn't getting there or then engine wants a lot for some reason. Is it possible for a mildly built engine to be fuel starved by the factory setup, even at only 1000 RPM?

 

I would enlist a passanger. Add a line to TB and monitor the FP by passanger. It can be duct taped to windshield. Hard acceleration will tell the tale as under load. If FP falls off at load may be filter or the sock clogged or pump itself. Increasing FP may or may not help. top down solutions sells the next step stronger FP spring if you reach that point. At idle is the spray nice and conical, no drips? What injectors? What HP estimate?

 

I'm not sure on HP exactly. It's an "aftermarket" SBC, but it idles smoothly, nothing radical. Has an Edelbrock intake and headers, no emissions except cat. The spray pattern looks good. I previously had cop car injectors, now have regular 5.7L injectors. FPR just replaced with no change.

I'll see about rounding up the adapters I need to get the gauge out from underhood. I might just buy a electronic sensor gauge from Summit and be done with it too. The thing about the fuel pressure that confuses me is that the symptoms are constant before and after I completely replaced the fuel system (pump, filter, lines, FPR). I can't figure that out.

 

Can anyone explain how BPC could be increased without BLM going down? I would have expected that if I turned up BPC by 15%, BLM would go down by 15%. Is that an oversimplification?

I'm using a bin (ARJT) which already has VE1+VE2 > 100 from the factory. I don't see any alternative way to tune this except to turn up the BPC until the BLM values are near 128 for cells that have no headroom. After that I can adjust the VE for the other cells. Am I missing something?