Which is better for TBI: Adjustable or Vacuum Fuel Pressure Regulator

[dave w]

The answer depends on the Histogram. The picture below shows rich fuel mixture at low Kpa, but lean fuel mixture at high Kpa. In the case of the picture below, a Vacuum Fuel Pressure Regulator is better because at high Kpa the fuel pressure will be higher to increases injector flow and make the fuel mixture rich. At low Kpa the fuel pressure will be low to decreases injector flow and make the fuel mixture lean.

If all the Histogram cells were all green or all red, then an Adjustable Fuel Pressure regulator would a good choice. When the histogram is all RED, the adjustable pressure regulator would be set to lower the fuel pressure to lower injector flow. When the histogram is all GREEN the adjustable fuel pressure regulator would be set to a higher pressure to increase injector flow.

The screen shot is from the first data log of a rebuilt TBI 5.7 liter with an aftermarket 4x4 type performance camshaft.


dave w

 

[sweetk30]

http://coloradok5.com/forums/showthread.php?t=291856

 

[Blue85]

This seems like a strange question. All the pressure regulators I've ever seen are adjusted by a vacuum reference. The fuel pressure does not always follow an exact ratio to the engine vacuum, but it gives a certain size of injectors a lot more dynamic range.

The adjustable versions just have a screw that lets you adjust the preload on the spring - moving the whole curve up or down. I modified my TPI regulator to make it adjustable.

So in the world of TBI is the stock regulator not referenced to engine vacuum? I'm honestly not familiar with them, but would believe such a strange design decision since they also do not measure intake air temperature.

 

[dave w]

So in the world of TBI is the stock regulator not referenced to engine vacuum? I'm honestly not familiar with them, but would believe such a strange design decision since they also do not measure intake air temperature.

Most all stock TBI pressure regulators are not referenced to engine vacuum. A very few factory applications used a engine vacuum referenced pressure regulator. (personally I've never seen a factory vacuum pressure regulator, but I hear they exist) The aftermarket offers a vacuum pressure regulator. http://www.ebay.com/itm/220698940400?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

dave w

 

[ryoken]

vettes had em at one point....

 

[1BEATK5]

jeeps had them too. But yes, not very often

 

[Blue85]

Man, TBI is weird. I guess looking back at a lot of the 1st generation FI systems, they seem a little carb-like.