Recently I had a Full Blown double pumper running on the stock fuel line and stock pump wiring and have had no problems on my 03 evo8, car running great. I decided to upgrade the supply fuel line to a larger 3/8 ID and the stock wiring to a 10ga wire with a relay. I have drawn up a diagram attached to this post.

I double checked everything and started the vehicle. When the car started, it went extremely lean right away (--- on my AEM wideband) and rough idle. I took a look at my FPR pressure guage and instead of reading ~43 psi at idle, its reading ~65 psi. Voltage out of the relay was reading perfectly normal. I am not sure why the car ran great with the stock line and wiring then now is reading really lean and higher than normal fuel pressure. The stock power line doesnt run any pulse width modulation to control pump speed or anything does it?

Any ideas?

 

anyone?

 

Maybe it's not relevant, but I was wondering what your complete mod list is. Are your pumps both on full time, or are they staged, or a progressive secondary pump? Is it the stock FPR? If not, what brand? What is voltage at the pump(s) at idle? Why did you change to thicker gauge wiring and the larger feed line if it was running perfectly? Why didn't you go to a larger diameter return line as well?

 

ok... Answers:

Some of the essential mods are (many for full list):

2.3L stroker, shep tranny, FPBlack, FuelLab FPR, FullBlown Double Pumper, FIC 1450cc. Built and Tuned by MAPerformance on E85.

1. Both pumps are on full time and have been from the install with no problems until now
2. Fuel Lab FPR
3. voltage looks to be 14.5v @ idle
4. I changed out the wiring and supply line to bigger to support my upcoming tune and increase in boost which will need an upgrade in the supply and return. The stock wiring is pretty small to support the double pumper and read that most people do this upgrade to alliviate any potential problems which only makes sence.

I am going to call MAP tomorrow as well to see what they may have as ideas.

 

Stock pump wiring doesn't provide full voltage at idle and low load (cruising).

 

You may want to try it on only a single pump at idle. If this cures it then you'd probably want to consider staging the second pump with a Hobbes switch to kick in at about 10-12 PSI of boost. Incidentally, are you running the stock fuel rail?

 

The Hobbs switch is what i see slot of people doing but seems to create a boost spike when it kicks in. Is there a progressive switch that would bring in the 2nd pump gradually at a predetermined boost level? If not, I might have to design one...

Ok... so what I have upgraded so far may cause the boost in fuel pressure but why would the wideband read super lean? Is the computer trying to compensate too much for the increase in fuel?

 

The Hobbes switched secondary pump should not create a boost spike when activated, AFAIK. In my experience, there is a slight blip of the FP gauge's needle when the secondary pump is activated. However, it is just a miniscule blip of 1#. But, the FP regulator instantly corrects this and it is not an issue whatsoever.