I bought an AFPR but am not sure if I actually should install it! I've been reading a lot posts on these and they seem to contradict each other. One says they are a good add on and the next post says they are a waste of time because the computer sets the fuel pressure.
The only place I can see the PCM setting the 'pressure' would be at the injector by only allowing 'x' amount through. By increasing the pressure at the regulator wouldn't more get through???? I really have no idea!
Can someone with some REAL knowledge on this chime in and set this straight?

Thanks.

 

You have an EW tune so just ask him.
An AFPR can be used to adjust the whole fuel curve all at once instead od just adjusting what needs work. This whole adjustment thing will make the computer play with pulse width to get the part throttle mix back where it belongs, if you lowered pressure you will make part throttle lean the pcm will correct(can't see pressure but can see O2 readings) and when it corrects for a lean condition it adds fuel at WOT above what it is programmed for. If upping pressure for more fuel then if the tune was good before you just made it too rich and will be slower, the pcm will have to work harder to keep part throttle operation at the right AFR.

Some guys sucessfully use them to boost pressure in order to get by with injectors that are actually too small, your 30# should be fine for your application at the stock pressure. Fuel curves can be finely manipulated in the pcm so why make changes to the whole curve, plus tuning for OBD1 cars is cheaper than an AFPR and can do more than precisely optomize fueling whereas all an adjustable can do is make halfassed broad changes.

 

In CLOSED LOOP(this is important) the PCM calculates the amount of fuel needed for a 14.7:1 AFR... this is based on injector size and fuel pressure set by the FPR which cannot be changed within the PCM calibrations. When you increase the fuel pressure, the injectors flow more fuel than they were designed to in the stock application. This then causes the fuel calculation to go rich however in closed loop the oxygen sensors detect an overly rich condition and pull back fuel leaving you right where you started. Now this is only in closed loop where there is oxygen sensor feedback. If you were to run the car in open loop then the affects would stay and the motor would basically run rich all the time. In fact LT1s generally tend to run rich anyway or so I have heard. And none of what I said applies to 93 Fbods.

 

Currently I only have stock 24# injectors but am in the process of installing the 30 pounders. I guess then when I have the new injectors in and get it reprogrammed there will be no need for an AFPR, correct?

 

Yes if you install larger injectors w/o letting the computer know then you will basically be doing the same thing as installing an AFPR... the motor will run rich.

 

I had bad fuel pressure and turned out to be a crynny regulator... I've nopticed thAT THE REGULATOR stays where youset it... as long as it's in the stock range

 

In the case if a large cam and idle vacuum is low, wouldnt it be a good idea to get an AFPR since the stock one needs a sufficient amount of vacuum to operate? Not sure, just a question.

Brandon

 

No. The fuel pressure regualtor is trying to maintain a fixed DIFFERENTIAL pressure. The flow through the injector is determined by the pressure in the rail, plus the vacuum (or minus the absolute pressure) in the intake manifold. If you have less intake vacuum, because of a high overlap cam, the FPR will correctly boost the rail pressure to maintain a fixed "differential" between the fuel rail and the intake manifold. That's the purpose of the vacuum compensation line.