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383 fuel pressure

crazy427

crazy427

1/2 ton status
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Edison , NJ
im running a 383 smallblock... 350 hp and 450 torque. I am still running the tbi fuel injection and i was wondering if anyone had some ideas on a good base fuel pressure setting.I know stock is around 8 to 12.i never checked it before i did my modifications /forums/images/graemlins/doah.gif. I am now running a 670 throttle body with venom injectors and a adjustable regulator. I also have a fuel pressure guage permenataly mounted to monitior fuel pressure. any suggestions?
 
My TBI 454 has an vacuum adjustable FPR on it and it sits at 12psi at idle and hits 18psi at high-load WOT. Unfortunately, my pump is dying (it is only 8 months old) from me cranking up the FP, so I am going to be putting an external Aeroquipe pump on when my tank is empty at the end of next week.

I have had excellent luck with the vacuum adjustable FPR. The Jet FPR was great, but it was too damn lean at WOT. It turns out that the 13.5 to 14 psi I had it set at and the flow problems I am having with the stock pump did not equate to good WOT performance.

If you are going to keep pressure regulator you have now, I suggest about 13.5psi or so depending on your mods. The absolute BEST way to check it is via the O2 sensor reading (either with a scanner or a voltmeter) to see what is happening with the fuel mixture...

It was pretty clear to me that the Jet regulator wasn't enough for my 454 b/c I pulled the plugs after just 1000miles and they had the tell-tale signs of lean operation condition; white deposits....When I check the O2, it was sure enough too lean..I haven't check the O2 yet with the new FPR but the plugs are looking MUCH MUCH better...I am waiting on the O2 reading until I get me 4-wire o2 installed, whihc just so happens to be on my list to do next week /forums/images/graemlins/woot.gif

Chris
 
GM vacuum reference Fuel Pressure Regulator

3685VRPR02.jpg



Jet FPR (its for sale if anybody wants it) /forums/images/graemlins/whistling.gif /forums/images/graemlins/whistling.gif
3685Jet01.jpg
 
does anyone know the part # for that regulator or where i can get 1 /forums/images/graemlins/peace.gifi like those, i didnt know they made them for the tbi's /forums/images/graemlins/peace.gif
 
Won't your chip be all wrong if you switch to vacuum controlled fuel pressure? If the thing works on pulse width to control fuel flow, it needs to make the right assumptions about fuel pressure, which would be all wrong if the fuel pressure moved around.

But I don't really know what I'm talking about.
 
im not sure ... /forums/images/graemlins/dunno.gifthats a new one to me. my engine did come with a custom chip programed for 383ci, my throttle body , the venom injectors,edelbrock aluminum intake and dual exhuast with headers, also made adjustments for the gears and tires 2 but he didnt ask me anything about the fuel pressure or regulator. i did a search and found a forum here on ck5 with the part # from gm for that regulator so i called and ordered it. shipped next day from michigan becuase no one had it localy. I Guess will try it and see. now does that have any adjustment or do you just bolt it on and hook up manifold vacuum to it?

Thanks
 
I THINK the vacuum-referenced FPR basically ensures that the fuel pressure stays constant at the set pressure, no matter what demand the motor is seeing. I could be wrong, but I think that's the case.
Bumping up fuel pressure will cause more fuel flow through the injector for a given pulse width (and will also give better atomization of the fuel), but the computer determines pulse width after seeing what all the sensors say, including MAP (in a TBI sys.) and exhaust O2. So it'll compensate, to a degree. Of course if you boost the fuel pressure through the roof, the computer won't be able to keep up, but TBI's a relatively low-pressure system so that's not really a factor.
 
[ QUOTE ]
Won't your chip be all wrong if you switch to vacuum controlled fuel pressure? If the thing works on pulse width to control fuel flow, it needs to make the right assumptions about fuel pressure, which would be all wrong if the fuel pressure moved around.

But I don't really know what I'm talking about.

[/ QUOTE ]

You are correct in that statement.

The best way to adjust your fuel pressure is to get a scan tool and adjust the fuel pressure in small increment over a periode of a week or so, until the scan tool shows the BLM and INTEGRATER are hovering around 128. At 128 the computer think the fuel mixture is perfect.
A BLM below 128 indicate a long term rich condition at that RPM. And above indicates a long term lean condition at that RPM.
And the same aplies to the INTEGRATER but it is the instant correction at that RPM.

This is the methode I used on my 383 and the computer is a happy camper now.

Good luck
 
[ QUOTE ]
I Guess will try it and see. now does that have any adjustment or do you just bolt it on and hook up manifold vacuum to it?

[/ QUOTE ]

I think it was originally designed to reference the vacuum under the injector. But I , like most of the guys at 454ss that run them, cut the reference tube off at the elbow and hook the regulator straight to manifold vacuum from the "J" port.

Chris
 
cool thanks... kept the tips coming. Im gonna do some tuning tommorow. i alreadyset the timing to 2deg with the spout disconnected and my regulator should be in to so ill see what i can get done.. /forums/images/graemlins/peace.gif /forums/images/graemlins/k5.gif /forums/images/graemlins/usaflag.gif
 
[ QUOTE ]
I THINK the vacuum-referenced FPR basically ensures that the fuel pressure stays constant at the set pressure, no matter what demand the motor is seeing.

[/ QUOTE ]

no...That is the point of a standard pressure regulator. The vacuum referenced FPR adjust the FP depending on the vacuum of the engine. In high vacuum siutations like idle and decel, the FP will be LOW and that is fine since the fuel requirement for the enigne are also LOW. As load on an engine decreases, the vacuum decrases and as the vacuum decreases, the fuel pressure rises. And this works well since under low vacuum situations, the engines fuel demands are higher.


Like I stated earlier, I have 12psi at idle and up to 18psi at WOT. but, becasue of my dieing fuel pump, once I hit about 2500rpm at WOT, the FP starts to wheeze and the FP drops to 15 sometimes as low as 13.5psi..I am hoping my bigger, external pump that I am going to install will cure that problem.

Chris
 
[ QUOTE ]
[ QUOTE ]
Won't your chip be all wrong if you switch to vacuum controlled fuel pressure? If the thing works on pulse width to control fuel flow, it needs to make the right assumptions about fuel pressure, which would be all wrong if the fuel pressure moved around.

But I don't really know what I'm talking about.

[/ QUOTE ]

You are correct in that statement.

The best way to adjust your fuel pressure is to get a scan tool and adjust the fuel pressure in small increment over a periode of a week or so, until the scan tool shows the BLM and INTEGRATER are hovering around 128. At 128 the computer think the fuel mixture is perfect.
A BLM below 128 indicate a long term rich condition at that RPM. And above indicates a long term lean condition at that RPM.
And the same aplies to the INTEGRATER but it is the instant correction at that RPM.

This is the methode I used on my 383 and the computer is a happy camper now.

Good luck

[/ QUOTE ]


BINGO..That is the real way to tune these TBI's. Adjust FP until the BLM is as close to 128 as you can get it...I did that for my 350 and it was happy at 129...I have yet to hook the scanner up to the BBC but have just been using the o2 voltage readings at WOT to get the WOT mixture dialed in as much as I can. My hope with the VRFPR was that it will give me a decent mixture at WOT and still sit stoich at idle...

With the Jet regulator on there, I had the FP cranked up to 14psi and it still needed more fuel at WOT but it was WAY too rich at idle...
/forums/images/graemlins/rolleyes.gif /forums/images/graemlins/rolleyes.gif


Chris
 
ok..... so where i am at right now, I got the regulator. i installed it unmodified to see how it operates stock. i set my timing to 2 deg with the spout disconnected . and just broke the engine in.The fuel presure at a idle is about 15 lbs and jumps to about 20 when you gas it. i scanned it and everything looks good (no check engine light) and my block intergrator is at 130. what i am goin to do now is take it on its 1st run nice and easy and see how it performs. the one thing that sucks right now is i have 3/4 of a tank of regular in it and i know im gonna have to run mid grade or even premium. so now the fun of tuning.... ill let everyone know howits doin later on today /forums/images/graemlins/thumb.gif

thanks /forums/images/graemlins/usaflag.gif /forums/images/graemlins/k5.gif
 
Ahhhh... /forums/images/graemlins/doah.gif /forums/images/graemlins/doah.gif /forums/images/graemlins/doah.gif

My bad.
 
well everything is looking good... im havin 1 small problemo...when i start the truck up cold (after sitting over nite) it hesitates and backfires for like the 1st miniate of driving. after that it is all good, and if i shut if off for an hour or 2 or 3 it is fine. only over nite does it act up. Now i recall it doin this on occasion before but would like to rectify it.sofar i have scanned it while it was doin it to make sure all the sensors were operating properly--like the temp sensor or somthing) and all is good. also i made sure i had good fuel pressure which i do also. so im sort of stumped, Has anyone else heard of this goin on?

Thanks
 
Is it that it's running bad open loop and gets better when it goes closed loop? What does the O2 sensor say when it's running crappy?
 
i didnt see what the o2 sensor readswhen it is cold. but it does cycle and operate proberly when warm. the o2 sensor is new and i bought a header collector with the o2 sensor bung welded in so it is located in the driverside collector, if that matters.
 
[ QUOTE ]
i didnt see what the o2 sensor readswhen it is cold. but it does cycle and operate proberly when warm. the o2 sensor is new and i bought a header collector with the o2 sensor bung welded in so it is located in the driverside collector, if that matters.

[/ QUOTE ]

I'm still learning how TBI works at this point. I was thinking that maybe it runs okay when warm because it's in closed loop mode. In closed loop, maybe the O2 sensor is forcing the pulse width far from its basic table. When you are in open loop, maybe it runs off the base table without reference to O2 (and without BLM corrections), so it's all screwed up. If you could see the O2 readings when cold, you could find out if it's running really lean or rich.

WinALDL displays the flag for closed loop. You could watch and see if the O2 gets better and it runs smoother when it changes over. I think it just keys off of temperature to go closed loop.

Like I said though, I'm just learning still, so this is speculation. If this theory is right, you might just want to collect a bunch of WinALDL data and get a new chip burned based on the block learn data. That might clear up the open loop performance.
 
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