I have an 1989 RS 305 with a tbi. If I put a vacume adjustable fuel pressure regulator on the tbi, will I need a bigger fuel pump?

 

What do you mean by vacuum adjustable? Why would you want to reference fuel pressure to engine vacuum with a TBI setup? That kinda stuff is only for port fuel injected engines (TPI) where the injectors themselves are exposed to engine vacuum on the business end.

 

i tried that about 3 years ago. failure. i did have a tpi pump. i will go that route again in spring. BUT you will need EBL. check the "tuning with ebl" thread in diy-prom for the info.

 

The horsepower is limited on the GM TBI engines by injector size and fuel pressure. This type regulator assembly allows the use of higher than stock fuel pressures on the standard injector. Standard fuel pressure is 9-13 psi. The fuel delivery is modulated by intake manifold vacuum to help the engine run cleaner at low speed and at idle. Every 2.5 in of vacuum applied to the regulator lowers the fuel pressure by 1 psi. With a base pressure of 17 psi and 14 in of manifold vacuum at idle, the resulting fuel pressure will be 11.4 psi. Under WOT the fuel pressure will go to 17 psi. Custom chip programming may be required to function properly. This regulator is a “must” for installing a 502 or 498 big block in your 87-93 GM truck. Comes complete with required diaphragm, high pressure spring, spring shims and vacuum fittings.
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I got that info from turbocity.com
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Hey Ronny, why did if fail? What is EBL?

 

it failed in that it i attempted to use as a substitute for a proper tune(stock ECU) on a modified engine. i believe it will work without a retune on a 1/4 mile WOT run or a marine application which may be more linear.

maybe someone will explain better that i am able to.

think of an autocross race where you are constantly accellerating- deaccellerating. rpms up-down. map constantly changing. not sure if the sensors can keep up? i believe the ECU(w/o EBL) needs a consistent fuel pressure in TBI applications. the calcs (BPW) need a fundamental constant FP? i believe the EBL modifies the BPW as a function of fuel pressure.

 

The programming in the ECM is built around a certain constant amount of injector flow. i.e. the ECM knows how much fuel will flow through the injector for a given amount of open time- based, of course, on the injector's flow and a given (constant) amount of fuel pressure. If you start varying the fuel pressure based on manifold vacuum the ECM won't be able to take that into account. It seems a mod like that is one where you are basically trying to "trick" the ECM. It'll act like a smaller injector at idle and part throttle but a bigger injector under high load/full throttle. While that may be helpful in certain situations I can't imagine it would work very well without very careful tuning to match.

The ECM's understanding of injector flow is pretty basic- "if I open the injector for this length of time I know this much fuel will flow out of it." That mod would change that simple relationship.

 

darn. i just had my ebl.bin in TP and forgot to look at that table. i am currently not using it. i do have it in another vafpr-ebl.bin provided to me my another member. it too has to be tuned based upon engine config. more HP/TQ= needing more fuel. think it is strictly MAP related. with MAP data feedback to ECU. educated guess there! my FP is currently set to 22lbs with 80 lb inj's. WOT A/F is about 12.70 last i checked. that causes issues with IDLE which i am currently struggling with. with the VAFPR-EBL functional i should be able to have 22 lbs at WOT and whatever it gives me at idle maybe 11-13 lbs? will know in spring,.