Is my AFPR bad

[Steves LX]

O.k. guys last week I took the car out for a drive and got on the hywy and as soon as I got into 3rd gear and got up to 5000 RPMs the car started bucking and missing so I got out of it. I had the control module checked out and it was bad so I replaced it. The plug wires are only about a month old. I looked at those in the dark and nothing is arcing. I put my factory coil back in and it still did it. So I continued to drive the car and it would only do this up at the top end and primarily in 3rd or 4th gear. So today I go to leave work and I take off and as soon as I get into 2nd gear it starts backfiring and wouldn't stop unless I let off the gas and drove with the flow of traffic. As soon as I gave it any amount of gas in 2nd 3rd 4th or 5th it would immediately start backfiring and bucking and no power. So when I got home I disconnected my return line which I beleive is the one without the shrader valve and I plugged it off with a large heater hose and a hose clamp because thats all I had and I stuck a half inch ratchet end in the other side of the hose and I grounded the fuel pump test point and had someone turn the key and my guage on my BBK AFPR shot up to 80PSI and then very slowly drooped off after we turned the key back. I have the pressure adjusted to be at 38 PSI. So should it have done this? I dont know what else to do or what can be causing all this. I know if I start the car and diconnect my vacum to the AFPR and rev up the motor and hold the rpms up, the pressure guage will jump back and forth, up and down and sometimes it will stay up. I also replaced the fuel filter. The fuel pump is only about 4 months old. Its a 255.

[Foxxx5oh]

if the BBK is rebuildable, it may just need a new diaphragm because it seems like it is letting fuel come through at pump pressure...

[Steves LX]

So just to clarify is that a good thing that its letting fuel thru at pump pressure or a bad thing? I dont think you can buy a rebuild kit for thr BBK's. All of my back fire is coming thru the exhaust, for what its worth

[Foxxx5oh]

if it was a good thing, then you wouldn't need a fuel pressure regulator...the backfiring through the exhaust is the unburnt fuel combusting in the exhaust since it didn't in the cylinder...i would baby the car so as not to blow something up...

[Foxxx5oh]

and also, IIRC, the fuel pressure should hold unless released at the schrader valve...

[Steves LX]

O.K. so I assume that its my AFPR thats causing all this from what you are saying.

[Foxxx5oh]

i would put your stock back on and test the pressure that way, stock pressure is about 38-40 PSI...if it holds with the stock, then you found your issue, if not, then its something else...

[Paul408Notch]

Pressure regulators bleed off. My aeromotive bleeds off almost all of it's pressure after a few minutes. It sounds like your flow is the issue. Maybe the sock on the pump is clogged up, or the filter is messed up again or something. How much is the pressure jumping when you rev it?

If you plug the return line, there's no flow, so your regulator can't regulate.

If your motor is fuel starved it'll backfire out of the intake, which sounds like what it's doing.

[Steves LX]

When I rev the motor up the pressure goes back and forth about 4-6 PSI. Its kinda hard to tell exactly what it flucuateing at because the needle jumps back and forth pretty quick. I had just read something a while back that said if you plug your return line and trick your fuel pump into running all the time and turn the key forward and your pressure climbs past 55psi right away then your fuel pump is good and your pressure regulator is bad. If the pressure does not hit 55psi in more than a few seconds, the pump is bad or its electical problems. If the pressure drops more than 15psi within 60 seconds, the check valve in the pump is bad. If the pressure holds and does not drop off, then the fuel pressure regulator is suspect to be the cause of your pressure drop off. And mine shot straight up to 80psi within a second. I just dont know how true those statements are and not sure if that test is just good for a stock regulator or if its good to use on AFPR's also. I just dont want to start parts chasing. I just replaced the fuel filter yestarday.

[dedpedal]

I hate to point you in the wrong direction, but your symtoms sound just like mine when the o2s went bad on my 88. If I floored it, it would quit bucking and run hard since the o2s were out of the loop at WOT. Easy enough to check.

[chad393na]

With the return side blocked, fuel pressure should never drop off. The only place it can go is into the vac. line, or leak externally.

[lxcoupe347]

correct me if im wrong gys if you plugg off the return line its going to act like an fmu and spike the fuel pressure really high,because it wont let the fuel through- i think its the electronics in the dizzy!! its not letting u burn the fuel that u already have,but when it does fire u have a backfire