I've been messing around doing a bit of fine tuning on my Turbo system, and wanted to check the fuel pressure relative to the factory specs. Not having the Factory fuel pressure testing kit ( although I DO have the factory adapter that came in my factory Geo Tracker service kit ) I purchased a liquid filled fuel pressure gauge from my local tuner shop. It's made by Russell, the line and fitting people, very good quality. All I had to do was remove the end plug on the fuel rail, and drill and tap it to 1/8th NPT, and screw the gauge right in. Pretty simple. I was pretty surprised at the initial reading: 31lbs at idle. The factory fsm calls for 37 to 43lbs! The fuel pump seemed to be working fine, and I changed the fuel filter a few thousand miles ago, so back to the tuner shop I went in search of answers. I was initially thinking of a rising rate fuel pressure regulator to enhance my current set up of larger injectors , but the guys at the tuner shop came up with a much easier and cheaper solution to both issues: an adjustable fuel pressure regulator that utilises the stock pressure regulator, modified, and fitted with a new externally adjustable spring. It's a device made by B+M that's really for turbo'ed Honda's ( what else) but with just a few mods to my regulator it fit well. I was instantly able to bump up the pressure to 45 lbs, and after testing found the throttle response much crisper, and high load boost situations required no timing retard at all now. In fact it actually pulls a bit harder throughout the rev range. All you guys running MPFI 16V engines should at least check you fuel pressure, to take advantage of all the power these little engines can generate.

Just wanted to add a couple more photo's. The junk yard practice regulator has some obvious water damage , Probably from sitting for so long. For good measure I purchased a new regulator that I used to modify, and it too had some of the same white crusty stuff inside after I cut it open.  I cleaned it thouroughly before assembling everything and it seems to work fine. I saved the stock one for " just in case." Basiclly, you have to cut the "hat " off the regulator, without destroying the diaphram or seat. I used a dremal with a cut off wheel to make a nice cut, then sanded the edges smooth. The outer diameter of the Zuk regulator is slightly bigger than the Honda part, and had to be ground down a bit to fit. I finished it with a belt sander, then fine sand paper. The B+M parts fit over the now cut off hat area, and seal with an o-ring, and simple clamping system. The vacume tube is threaded which allows for preloading the internal spring that controls the diaphram release. Very simple and effective.

One more.

Factory specs for 16V fuel pressure psi (taken from the suzuki FSM)......

fuel pump operating and engine stopped......35.6-42.7 psi.
at specified idle speed.......29.8-37.0 psi.
1 minute after engine (fuel pump) stop (pressure reduces as time passes).....over 25.6 psi.

  Ya got me Ranger, I rounded up the numbers. The point wasn't to give a tutorial on the stock pressure though, it was about  INCREASING the pressure to take advantage of the higher flow rate of the bigger injectors. This is an easy and cheap ( $50 ) way to do that. I guess I should have been more specific. With this simple modification I was able to go back to stock timing specs, without any ping or detonation under boost. I apoligize for any confusion.

Ya got me Ranger, I rounded up the numbers. The point wasn't to give a tutorial on the stock pressure though, it was about  INCREASING the pressure to take advantage of the higher flow rate of the bigger injectors. This is an easy and cheap ( $50 ) way to do that. I guess I should have been more specific. With this simple modification I was able to go back to stock timing specs, without any ping or detonation under boost. I apoligize for any confusion.

Yeah, I knew what you were doing.  I was just posting the info for reference.

  No Prob Bud. Btw, had any time to mess around with your turbo setup?

No Prob Bud. Btw, had any time to mess around with your turbo setup?

Unfortunately not.  I have kinda put it on the back burner for now.  I would still like to do it, but I got too many other things going on right now.  I am trying to sell the sidekick that I was going to put it on (it is a 5 speed).  I am thinking an auto will work better for the turbo setup anyway.

IMO, the auto works better for everything.

Now I'm one step closer to spending too much $$$ on my engine  Might be a dumb question, but I'd need to run 92 octane all the time right 

Would this mod have much effect on a non turbo motor? Would the larger injectors be overkill on a non turbo motor? I want to rebuild my 16v and would like to squeeze as much out of it as possible but don't want to go turbo. Do you have part numbers for the adjustable regulator and the larger injectors?

IMO, the auto works better for everything.

'cept mileage.  But I don't complain about that much.

Now I'm one step closer to spending too much $$$ on my engine  Might be a dumb question, but I'd need to run 92 octane all the time right 

I do run premium mostly for saftey. I've run regular in the past with no ill effects, but the quality of the fuel here, especially in the winter with the added ethenol or MTB, leaves a lot to be desired.

Would this mod have much effect on a non turbo motor? Would the larger injectors be overkill on a non turbo motor? I want to rebuild my 16v and would like to squeeze as much out of it as possible but don't want to go turbo. Do you have part numbers for the adjustable regulator and the larger injectors?

The adjustable regulator  is a B+M part made for the Honda tuners. I imagine if you did a major job on your intake system, flowed, ported and cc'd head, high compression pistons ( I hear Honda's work) modded crank and rev limiter, really good exhaust system, The larger injectors and regulator may be an advantage. The injectors I'm useing are from a v6 late 90's early 2k Nissan pathfinder and are rated at 210cc, the stock injectors are a 175cc injector. when my turbo was out for the new manifold build, I did notice the motor ran better with a K+N filter, the bigger injectors, and a Calmini header with 2" exhaust and no cat. 

Quote from: bentparts on March 22, 2009, 07:04:45 AM

IMO, the auto works better for everything.

'cept mileage.  But I don't complain about that much.

Yeah, you got me there, but it's so much better for just about everything else, especially crawling.