just curious if i need to replace my fuel pump or start checking other things.

according to my fuel pressure guage the car pressurizes to 43 psi when you turn the key forward then drops ten points when you start it....and only reaches above 40-43 psi when you go full throttle. doesn't seem right so can some one give me some ideas!

 

That is EXACTLY what is suppose to happen. Generally, just checking with the "Key On/Engine OFF" gives the highest reading of all, so it may not emulate any engine operation.

The best way to measure the Fuel Pressure is with the engine running and the vacuum line off. This will simulate WOT fuel pressure, which should be fairly close to "key on/engine off".

With the vacuum line connected at idle, this results in the lowest readings (actually deceleration gives the lowest) and may be around 10 psi lower than WOT. This is how the fuel pressure works and designed. The reason is you need less fuel at idle and deceleration than you do @ WOT.

Now for the fun stuff, cranking up fuel pressure does not have a linear effect on fuel pressure between idle and WOT. Cranking up the pressure has its greatest effect @ WOT and least effect at idle. A change in fuel pressure really needs to have the eprom adjusted to properly compensate.

The biggest mistake people do on basically stock engines is install an AFPR and then crank up the fuel pressure. While it does produce better atomization, it also causes the engine to be too rich @ WOT. Most basically stock engines are already overly rich by GM's own design (to avoid warranty claims).

I did a lot of experimentation with fuel pressure and the eprom. I found 46-48 psi gave a good atomization while not overworking the fuel pump (too much fuel pressure will prematurely kill it). Then I reprogrammed the eprom to provide the proper mixture throughout the RPM/Load range. FYI, I didn't really have to do too much adjusting in the lower load range (idle, part throttle cruise and deceleration) and the greatest change (lowering injector pulse widths) at max load (WOT).

I hope this helps clarify things about how fuel pressure works.

 

you did.......thank you, but does this sound somewhat right?

my range is 43 or so psi at WOT and about 10 less that at idle.......and it doesn't always hit 43 at WOT only when it kicks in to 4th gear, before then it dances just short of 40 varying at different rpm's as well as gears.

what would be the average range i should expect on a somewhat stock block and is it normal to for the psi to vary this much through acceleration and up shifting?