Homemade TBI adjustable fuel pressure regulator

[Daveo91Burb]

Thought I'd share my take on the adjustable FPR for the TBI crowd. You can buy one online that replaces the factory regulator, but they're like $70. There's also lots of variants of the homemade style online, and I'm sure someone has already done what I've done, but the writeup many refer to is on 3rd gen and with that one you have to take the injector pod off to adjust. All I did was drill out the cap on the bottom cup of the regulator, which exposes the screw assembly that will raise or lower the spring perch. (it's factory set at the lowest setting or close, which provides the least amount of pressure) I ended up drilling and tapping that assembly for a 10-32 screw and installing a matching SS thumbscrew. It screws in tight and will turn the spring perch easily without unscrewing itself, but I think I will epoxy in the thumb screw for added security.

I'm going to start out with the factory spring to see what kind of pressure range I can get. @4WDKC gave me a link to a stiffer spring (thanks!), which I bought, but I think I'll be able to get what I need (~13 psi) out of the stock spring, since I'm using 454 injectors.

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[4WDKC]

That is exactly what I did, problem is when you have the fuel lines connected you cant turn that without removing them and taking the tb apart. Find an allen screw the same size and you might be able to adjust it without taking it apart.

 

[Snoots]

Great idea!

Why not use a SS washer and locking nut instead of epoxy?

 

[73c20jim]

Glad I use a carburetor.

 

[Daveo91Burb]

That is exactly what I did, problem is when you have the fuel lines connected you cant turn that without removing them and taking the tb apart. Find an allen screw the same size and you might be able to adjust it without taking it apart.

Bummer, I was a little worried there'd be some sort of conflict like that, but some of the aftermarket options use a similar design so I thought I'd be OK. But I just googled it and there are definitely others that use an allen head screw instead. Well, I'll give it a shot with the way I have it (haven't epoxied anything yet) and realize that I may have to switch out the thumb screw. I'm using the TBI spacer that came stock on the early 454 TBI units which is pretty thick, so maybe there will still be enough room.

Great idea!

Why not use a SS washer and locking nut instead of epoxy?

I'm not sure I see how that would work. I think the lock nut would have to be small enough to fit inside that recessed hole, to keep my thumb screw tight against the shaft that raises/lowers the spring perch. As it is currently it's definitely going to fine for compressing the spring since the thumb screw is bottomed out in the tapped hole, but if I need to back it off, there's a possibility it would back out itself, rather than turning the spring perch. A few drops of epoxy will prevent that.

 

[4WDKC]

Bummer, I was a little worried there'd be some sort of conflict like that, but some of the aftermarket options use a similar design so I thought I'd be OK. But I just googled it and there are definitely others that use an allen head screw instead. Well, I'll give it a shot with the way I have it (haven't epoxied anything yet) and realize that I may have to switch out the thumb screw. I'm using the TBI spacer that came stock on the early 454 TBI units which is pretty thick, so maybe there will still be enough room.



I'm not sure I see how that would work. I think the lock nut would have to be small enough to fit inside that recessed hole, to keep my thumb screw tight against the shaft that raises/lowers the spring perch. As it is currently it's definitely going to fine for compressing the spring since the thumb screw is bottomed out in the tapped hole, but if I need to back it off, there's a possibility it would back out itself, rather than turning the spring perch. A few drops of epoxy will prevent that.

I used the existing cage nut for mine and put a jam nut on it just in case. It is probably overkill but I want sure and definitely requires the lines to be removed to loosen.

 

[Snoots]

I'm not sure I see how that would work. I think the lock nut would have to be small enough to fit inside that recessed hole, to keep my thumb screw tight against the shaft that raises/lowers the spring perch. As it is currently it's definitely going to fine for compressing the spring since the thumb screw is bottomed out in the tapped hole, but if I need to back it off, there's a possibility it would back out itself, rather than turning the spring perch. A few drops of epoxy will prevent that.

What I'm trying to show is that if the adjusting screw you have passes thru a washer that has a larger diameter than the access hole and you have a nut over a star lock washer and jam-nut above it, then it should not move out of adjustment.
Just my 2 cents. Not against epoxy.

 

[Daveo91Burb]

I used the existing cage nut for mine and put a jam nut on it just in case. It is probably overkill but I want sure and definitely requires the lines to be removed to loosen.

Yeah, I had to abandon the idea of in-place adjustability. I had already taken out the thumb screw and replaced with an allen head screw, but the problem was it was too long and I didn't know it was running in to the rigid vacuum port right underneath there. It completely closed off the diaphragm and when I turned the key to prime the system, pressure shot way up and actually pegged my gauge on the wrong side of the zero peg so now its reads 8 psi as its zero point. Damn. I have a shorter screw in there now and tomorrow I'll put it all back together and see where I am.

Yeah, I think I'm OK with taking out the 8 screws of the injector pod to adjust the pressure. It takes less than five minutes and it's not something I'll have to do everyday.