MUst be a brain fart I guess But can someone explain to me this...

A stock 1985 fuel pressure reading on a stock set up would be 39psi to 34psi idle and movement toward the max of 39 at zero or loss of vacuum as being good. and the gauge holding 34 or more forever with engine/pump off is good.

K the question I'm guessing the stock fuel pump puts out over the 39psi, but is limited by the spring in the pressure regulator to max at 39psi that is called for in my stock setup.. and that installing an AFSR and raising it to max would let the fuel pressure go upto what ever the fuel pump is able to do?

Am I lost on this or? how does it work will the stock pump put out more then 39psi (assuming its a good pump) if an AFPR is put on and adjusted higher?

Also when installing the AFPR is it just bolt on, jump ALDL and adjust pressure a starting point say 41 43 or so ect?

 

pull the vacumme hose and then measure your fuel pressure. That'll be your starting point, or base. and write that # down somewhere.

I also suggest reading your BLM's before doing anything..

 

fuel pressure should be between 30 and 35 psi on an '85. Later years used higher pressure. Most AFPR's range from 35-60psi. Yes you can raise it higher but you'll run rich and possibly stall out.

 

First, your stock pump will handle the additional fuel pressure to handle the AFPR range. Second, with your stock set up an AFPR will not be a large benefit to you. You can increase the pressure and run a little richer, but remember that the O2 sensor and computer will make some minor adjustments than may reverse the changes you made with the AFPR.

The advantage to the AFPR is when you start mods to the engine. Then you can increase or decrease the pressure to match new injectors, heads, cam or other changes. The AFPR allows you (or your tuner) to fine tune your set up to get the very most from your engine.

Unless you are planning future modifications, the stock unit will be fine.

-John

 

The "stock" pump will make more pressure than the 40 (or so) psi that a stock regulator holds. How much more depends on the pump, but at least "some". You can get much higher flow/pressure pumps..

That said - the only real use for an adjustable regulator is to raise/lower the whole fuel delivery "curve" Without going into the PROM and editing the injector pulse width tables.

In other words - if you wanted to increase the amount of fuel delivered across the entire load range you could do it by changing the fuel pressure, by changing the actual injectors to larger/smaller, or by editing the PROM. If you wanted to change only Some parts of the load range then PROM editing is the only way.

The ECM will compensate for fuel delivery changes using the O2 sensor feedback loop to hold the target A/F ratio. The measure/indications of how much the ECM is having to compensate for an "incorrect" fuel load are the Integrator (INT) and Block Learn (BLM) numbers.

Mechanically changing the fuel delivery with the pressure or with different injectors will just be corrected for by the ECM.

Best way to determine if your fuel pump is "enough" is to put a pressure gage on the car, then go for a blast down the strip/dyno. It should be able to hold the same (or very near) fuel Pressure under full throttle/load as it does sitting still. If the pressure doesn't stay up, you have a problem with the pump, filter, something.

 

ThX for the replies guys

The reason I was asking about the AFPR was that engine has been slightly modded
The original cam didn't have 2 lobes on it anywhere that had the same lift it was worn pretty bad.
So I kinda used a crane 2040 that was taking space on the bench for another engine and put it in. I ported everything I could find info on with the intake system from plenum to base and then the heads and knocked off the sharp edges and rounded out the stock exhaust manifolds (till the headers and exhaust Santa come AKA wife) I'm still talking my way thru a new lower intake base and 1.6 rollers but time will tell.

A few lifter issues here and there later I ended up with a car that sets a code 42 and 43 whenever It gets WOT, I have checked/replaced egr knock sensor and the other normal parts to change on a tune up. The injectors are still stock and all ohm check fine. and pump did the volume test fine.

I can Clear codes and they are gone till I mash it hard and they reappear. I have checked fuel pump pressure and it holdes at 39psi at WOT with hose removed but the car will still fall flat on its face at 4200 to 4500rpm after hearing alot of pinging then codes set, car shifts timing is gone car recovers and gets back to 4k ish falls flat ect ect but still has 39 psi on gauge. Even then with the timing curve from the ecm its scarey quick VS the way it was with the bad cam.

The part with a AFPR I wasn't clear on and may not even be thinking in the right direction was the pump limited to the 39psi or was it the FPR doing it. And is putting a AFPR on the stock fuel pump is pointless?

What pump do I then need to go with to get more pressure? with a AFPR, if this even sounds like a fuel problem.

Thanks in advance for any help guys

jim

 

If the pump were limited to 39 psi fuel pressure, GM wouldn't have wasted their money on a fuel pressure regulator.



RACE ON!!!

 

Your stock fuel pump is good up to 400 HP.

Have you checked the computer to see what chip you have in it? If you have the aftermarket HYPETECH that may be your problem. Also, if you changed the cam without reworking the chip that could also be the source.