Hmmm. Boost VE and 2nd fuel pump on a Hobbs

[turboberserker]

Ok, I have a second Walbro 255lph pump that is controled by a Hobbs switch at 5psi. What happens is it kicks on and my fuel pressure jumps from 56ish to 61psi in a nanosecond -- the wideband goes to rich and clouds of black smoke ensue and thre truck begins to feel like an earthquake simulator :banana:

So I know that at my altitude, 5psi is 135kpa and I know I need to reduce the VE boost to account for the second pump.

The question is: How much? I guess I can autotune them but since the wbo2 is just reading rich (aka 9.0 AFR) It's not going to be a one shot deal. I'd rather calculate /estimate how much to pull from the table and at least get it to 10ish AFR and autotune that. The big deal of course is to do this without blowing the motor by setting the boost ve too low :notacrook:

Anyone have any ideas?:help2:

[turboberserker]

How about this:

I could figure out the new IFR based on the extra fuel, take the percentage of the new IFR from the old IFR and reduce the VE accordingly?

[Delco]

If your second pump is still working through the regulator you should not get any fuel pressure spikes unless you are bringing it in too late and the std fuel pressure is dropping off due to inadaquate flow.

On some of our big hp street cars we have three stages of fuel pump , all regualted through a single regualtor and the fuel pressure right through the range stays stable and no fuel spiking.

I would say your system design needs a little fine tuning before you start attacking your VE table.

If you are bringing in the second pump unregulated then you are wasting your time

[turboberserker]

Its regulated by the factory vac ref'd pump. All the guys in trucks line mine seem to have the same thing -- about 10psi jump when the second pump jumps online. before the second pump comes on, it's rock solid.

It doesn't actually spike, it jumps up and stays up. Don't know if that makes a difference or not.

[Delco]

If the regualtor is working properly then it should regulale to the same pressure , unless you are flowing way too much fuel through the regulator and it cant bypass enough fuel. In which case I would recomend changing the regulator to one that can handle the flow rate you have or bring the second pump in at a higher load level where the fuel is needed and being consumed.

[turboberserker]

Gotcha. Thanks for the help -- I'll look into this further.

[MN C5]

Happend to me.. return line was to small with the factory regulator. I just brought the other pump on line later and it fixed it. It was on another setup I had

[turboberserker]

I have it partially solved atm (woooosh) -- I dropped the VE a little and made damn sure there was no PE (grr) -- Since I can't possibly hit 285kPa hehe It was still set at 105kpa from the COS#1 :P

I still see some fuel coming up, so I need to look into a higher psi hobbs or just bite the bullet and do a vic jr, new rails, new regulator, and a90mm tb. Then I need a better couch though, because I will be spending a lot of time on it :)