90c350

Hey I just put in an adjustable fuel pressure regulator from Jet. As well as a tpi fuel pump. Now I can not get my fuel pressure below 17psi!!! Even when it is all the way down I still get 17psi. Any suggestions on how I can get back down to about 14 to 15psi??? Right now it over fueling a little bit and i have to compensate with the timing. Any help would be greatly appreciated. I have the 350 running quite well right now and only need to resolve this issue until I get the EBL set up.

dimented24x7

iTrader: (2)

Its due to the restrictiveness of the TBI passages and fuel lines.

I have this issue as well. Even after porting the passages in my holley pod, the best I can get with no spring installed is 11 PSI with a walbro 255. Your only solution may be to turn the pressure up to 20-25 PSI (need a different spring) and adjust the BPC as needed. This will allow you to still regulate the fuel pressure. If you left it as it is now, the pressure would drop off as soon as the injectors place a demand on the fuel system.

90c350

I'm not quite sure what you are saying?? I have no problem getting a higher than 15 psi at the pod. But my problem is that I cannot reduce the pressure below 17psi!! Im assuming that you are saying that because of the small passage ports that the regulator will not respond to any lower changes?? If that is so, How do you adjust your pressure below 17psi??? Where would I get a different spring?? I can get about 20psi with the regulator maxed out, and it doesnt seem as though I losing any pressure under load. I could be wrong though?? I guess running 20psi and adjusting the bpc would help?? Where is the table and calculations for bpc adjustments?? With EBL that is. Im only A newb at this so far!! THanks for the help. Greatly appreciated.

dimented24x7

iTrader: (2)

The problem is that it takes alot of pressure to squeeze 50-70 GPH of gas through the small passages. The stock pump hardly moves anything at all, so there isnt alot of residual pressure. With aftermarket pumps, though, they circulate lots of fuel, so you start seeing alot of pressure on the supply side from the pump trying to push fuel through the pod and return lines.

One way to tell for sure if you really have a problem is to snap the throttle all teh way open and watch the fuel pressure. If it drops more then 1 PSI or so, then you need to figure out how to fix it by either using a smaller fuel pump or some other solution.

As for the regulator, to go over 20 PSI, youll need a stiffer spring of the same type used in GM regulators. I suspect that the springs also have to be of a special type that have a low spring coeff. and allow for lots of travel so the force supplied by the spring on the regulator remains nearly constant as the diaphram moves. There are still some NOS high pressure GM regulators floating around that allow for 28-32 PSI of fuel pressure. If you take teh spring out of the regulator on your TBI and you still cant get less then 17 PSI, then running the high pressure regulator assembly with smaller injectors is a way around it. Currently, your fuel pressure is totally unregulated.

Im having this same issue as well. I ordered one of the GM high pressure regulators. Hopefully the factory spring and cleaned up pod will fix it.

Fast355

iTrader: (2)

I have a pretty good feeling it will fix it. It should also help you get more fuel, quicker on acceleration.

I'll post a picture of one of the high pressure springs I have in the garage and post it up.

90c350

So your saying that I may be able to drop my pressure down if I remove the spring right?? I currently dont have an option of tuning yet!!! Its in the mail!! I'm not currently having any major problems but what happens when you cant regulate the fuel going to the injectors??? I know that I need a tune but it also feels like I may not be getting enough fuel or maybe to much!! Not sure?? Thanks for the advice and I will try the no spring thing, but let me know about the tuning side and if you ideas work out as well!! THanks again

dimented24x7

iTrader: (2)

Removing the spring is the sure fire way to tell if there is a problem, and how bad it is. Ideally, with no spring, you should have no fuel pressure at all as the return port in the injector pod is fully open. As long as your fuel pressure remains high like that, you cant really drive the vehicle as there is NO REGULATION. Your fuel pressure will vary with load, which is bad.

If you could see inside the fuel pressure regulator, the diaphram would likely be pushed all the way back from the excess pressure head, leaving the fuel pressure unregulated.

dimented24x7

iTrader: (2)

Heres a pic of the regulator disassembled. This may help you understand how it works and what may be wrong.

dimented24x7

iTrader: (2)

The regulator works by a spring holding the diaphram and seat against the return port. The return port is what the green arrow is pointing to. The diaphram seat is at teh origin of the arrow. When there is no fuel pressure, the seat is forced up against the return port. As teh fuel pressure builds, the spring loaded seat is pushed back from the return port, allowing fuel to return. The spring allows the seat to move far enough away that the fuel pressure reaches some equilibruim thats set by how much spring tension there is. When the force from teh fuel pressure is equal to the force from the spring, teh fuel pressure stabilizes at the pressure that you set it to. This forms whats called a proportional control system.

Teh problem is that theres LOTS of fuel going through the regulator with the new pump. So much that it takes lots of pressure to squeeze it through the passages. This pressure is greater then what the regulator is set to. Even with the seat pushed all the way back by the fuel pressure, its still not enough to releave it. Now with the seat at its farthest position, the regulator no longer controls the fuel pressure.

90c350

Ok so I do totaly understand what you guys are talking about and the fact that I need to do some sort of mod to be able to adjust the fuel pressure. Maybe an aftermarket regulator plumbed inline some where would be a quick fix???? Any thoughts???? What are the bad things about not being able to regulate the fuel pressure???? I know that I can go from 20psi to 17psi with the afpr right now but thats not enough right??? will I hurt the motor?? Or blow the injectors?? It runs pretty decent right now and I wont see any Tuning equipment for about a month from now!!! What will happen?? I think that if its a bad Idea I will pick up an aftermarket regulator and do some fuel line mods. Easy right?? Would this be a quick fix?? Sorry for all the quesitons again but I dont want to Hurt a new motor before I get her tuned!! Thanks for all the help again.

RBob

iTrader: (1)

Try putting the stock regulator back on and see if that corrects the high fuel pressure problem. It just may be that the Jet FPR is set up for a higher then stock pressure.

You mentioned a TPI FP, can you elaborate a little. Which pump was installed?

RBob.

90c350

The Pump is part# EP241 should be for a 90+ camero/firebird. That is the acdelco #. I think that its good to about 45/60 psi!! I will try the factory regulator and see what happens. If there is no difference would it be better to run My 305 injector at the higher pressure instead?? Could you elaborate on what this could do to my engine??? Or fuel system?? Thanks again and let me know what damage could cause and Ill let you know on Monday what happens with the stock regulator.

dimented24x7

iTrader: (2)

Man, I read right past that

Thats probably the cause...

dimented24x7

iTrader: (2)

Jet lists the range of adjustability from 10-20 PSI. Pull the spring out and reinstall the diaphram and regulator housing alone. Activate teh fuel pump, but dont start the engine and read the pressure. This will tell you for sure what pressure is needed to get through the fuel system. If its only a couple of PSI, then I wouldnt loose any sleep over it.

90c350

Thanks once again Dimented. You guys have all the great info. So I may just be running a little rich then?? Is that correct to assume?? I will swap out the spring and also try the stock reg on Monday. Its at work right now so no access to it on the weekends. Thanks again

RBob

iTrader: (1)

With the stock style port TPI replacement pump there shoudn't be an issue with too much fuel.

Double check the lines back at the tank. The return and purge lines may have gotten reversed upon re-connecting them. This is a common problem. The purge line has a small restrictor in it that will back pressure the return line.

RBob.

xjcamaro89

I have a holley TBI unit and the max i can get out of it is like 17 PSI, i have my car tuned to 17 PSI, but is it possible to get a stiffer spring that will fit the holley unit and get more pressure? Just curious after all this PSI talk!

dimented24x7

iTrader: (2)

There are high pressure springs. The regulator is the same as a GM unit, so a high pressure spring for a standard unit will also work. Another thing you should do with the unit is port out the return passages. The angles that the passages in the pod where drilled at are incorrect in at least some of them, resulting in the return passages from the injectors being severly restricted. I can post a pic later on of what needs to be done. These passages need to be open, or itll skew the fuel pressure at teh injectors.

dimented24x7

iTrader: (2)

Good stuff... I vaugely remmeber checking that, but it probably wouldnt hurt to check it again. Still cant get lower then 11 PSI with no regulation on my setup.