How can I adjust the fuel pressure on my TBI system?

  1. Bolt on an aftermarket adjustable TBI regulator from Turbo City, Hypertech, JET, etc. All of these will adjust up to about almost 15psig, depending upon your setup and pump voltage. This would be a logical replacement for a factory 9-13psig unit, for an engine that has been warmed over with a few mods.
  2. A step beyond......GM TBI regulator P/N 17113186 is a direct bolt-on jobbie, and will give you about 18-20psig fuel pressure. Additionally, this regulator has vacuum compensation capability. If you hook the included vac port to manifold vacuum, then you'll get a part throttle fuel pressure decay of roughly 1psig per every 2"Hg manifold vacuum. This comes from certain marine and HT502 applications.
  3. A little bigger step beyond.......GM TBI regulator P/N 17113079 is a direct bolt-on jobbie, and will give you about 26-32psig. It does not have vac compensation. This comes from some of the late 90's BBC applications.
  4. You can add vac compensation to any TBI regulator, if you have the time and patience to get creative. Basically, you just need to make the can assembly that surrounds the backside of the diaphragm "sealed", and then plumb it to manifold vacuum. You can either do this thru sealing/welding shut the existing can, or machining a new can. The shop manual tells you not to disassemble these regulators, but in truth they are quite easy to dis/re assemble if you are careful.
  5. You can change the setpoint of your stock regulator by roughly +/- 2psig, quite easily. Sometimes without even having to disassemble it. Remove the whole fuel meter cover and regulator assembly from your TBI and flip it upside down in your left hand. You should note a rectangular window cut in the side of the regulator can, with the end of a tang visibly located somewhere between the extreme ends of that window. The tang is attached to the spring perch within, and it's relative up/down position is roughly proportional to the setpoint of the regulator. Move tang up, more pressure, move tang down, less pressure. Now, look at the bottom of the can and you will probably see a beefy collar with what appears to be a screw tack welded in the middle. You can either dremel away the tack weld and manipulate the screw, or, you can try this next approach. Firmly grasp the collar with a good set of vice grips or channel-lock pliers, and gently attempt to force the collar counter clockwise. Chances are pretty good that the tack welds between the can and the collar will snap, and you can then proceed to turn the whole collar assembly counter clockwise to raise the pressure slightly. If this does not work for you, or if your regulator does not have a collar (as some don't), then you'll have to disassemble the regulator to modify it. Again, spin the perch counter clockwise on the screw shaft to compress the spring and raise the pressure.
  6. The external regulator approach.........You can also leave your stock TBI regulator in place (no need to gut it unless planning to get really wild with pressures, and fear a burst diaphragm), and then graft in any flavour of external regulator, into the TBI return fuel line, remote from the TBI assembly. The external regulator can either be a "fixed" pressure jobbie without vac compensation (intended to continually override the setpoint of the stock TBI regulator), or, it can be a "variable" vac compensated jobbie (intended to provide more fuel when needed and then cut back and allow the stock TBI regulator to take control during cruise).
  7. Whether to run a fixed pressure, or a variable pressure, at the TBI injectors all comes down to your personal level of comfort with the TBI software at hand. The most elegant approach is to select a fixed pressure operating point, then modify the software injector BPC's to suit, and then cal the VE's to suit your engine mods (this carries with it the assumption that you will either measure or calculate your new injector flow rates at your new pressure setpoint). But, if software modifications are troublesome, then variable pressures can be used to at least get things pretty durn close, and then rely upon the INT/BLM features to reign things into control.
  8. As a general rule of thumb, I've found that most GM Rochester TBI injectors will comfortably tolerate up to 30'ish psig without issue, assuming that they are connected to individual 4/1 amp drivers. There are some TBI injectors that can be driven has high as 70psig, but they are an exception rather than the norm. Posted by Walt Sherwin.

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