Ok guys here is my list of problems. I have a 1996 F150 4.9 inline 6. Bought the truck a little over a year ago. I started out having problems that seemed like not having enough power. I changed both fuel pumps because one of them I knew was bad because it would pump gas into the other tank. Ok so I changed those and continued to drive the truck. So several months later after fixing other parts going out like wheel bearings and shock I finally came back to fuel issues. The truck runs and starts right up just lacks power. Trying to pull a trailer with a car on it, the truck would lope and die. Finally I had talked to a mechanic friend and he told me that sounds to him like fuel pumps. After looking stuff up on line I finally herd stuff about FPR so that was replaced. Still same issues so then I replaced the rear fuel pump because I had gotten a gauge and it was dramatically lower than the front tank. Still same issues. Friend told me a way to check regulator about pinching return hose and if pressure rises then its bad. That was replaced again. So here is the problem.... 2 fuel pumps replaced in rear, 1 pump replaced in front tank, and 2 FPR replace. Several vac lines replaced. 1 more issue that arose after the last FPR change......... When I hook up the fuel pressure gauge to fuel rail and turn the key on with the engine off the pressure will go up to about 51/52 which is in normal specs. With the key still on and engine off the fuel pressure will drop really fast like within 10-15 sec and rest at 10psi. I have called Autozone about maybe they giving me bad fuel pumps and the guy told me very unlikely. He told me to look into leaky injectors. Which I think it is. My mechanic friend still thinks my fuel pumps are bad or fuel selector valve but their is no fuel selector valve that I seen. If anyone has any info please help.

 

If the pressure drops that much that quickly your injectors are stuck/leaking. You can try running a bottle of injector cleaner through it (I would do it with only 1/3 to 1/2 tank so it's more concentrated), but you are probably looking at having to replace them or have them cleaned professionally.

What I would do: go to a junk yard and pull a set of injectors, put them in your truck and send yours off to be cleaned (assuming the JY injectors aren't as bad as yours). Then when you get them back send the JY off to be cleaned, you will end up with 2 sets of injectors that are back to factory specs for the price of 1 set of new/reman injectors. You can keep them for backup or sell them along with the printout you get from the shop detailing the cleaning/testing, you could end up getting more than half your money back.

 

And after putting the last FPR on i had done the pinch return line test again the pressure went to 90psi and was spraying gas where the fpr connects to the fuel rail. So after 3 times of taking it of i put it on with an extra o-ring. Called autozone but they had no info on how to properly put it on. Because it has two nipple big and small. Big nipple has two o-ring then their is a flat rubber piece that connects both nipples. My original fpr i took off the first time had the 2 o-rings on the big nipple and another on the small one. So im still unsure if thats on correct.

 

You may want to find something that will work for that FPR, if it sprays like that when you pinch it then it's not connected properly.

 

What fltdriver said about the injectors is probably the issue.
You'll have to sort that FPR connection of course.
90 psi is way too high under any conditions I think, so I get the feeling there's something wrong there. If you get the FPR sealed, try that again and see if it will maintain pressure.
Contrary to what autozone told you, faulty fuel pumps is not highly unlikely. With cheaper pumps (as in not Motorcraft, Walbro etc) it is actually quite often highly likely. Happens a lot.
You said you changed a pump because it was faulty because it was pumping fuel into the other tank. Actually in that case it would've been the pump in the other tank that was faulty (check valve failing). I know you changed them both, just explaining something.
To understand this system better - both pumps are always connected up to the fuel rail and the return line. The only thing stopping your pressure from bleeding off into whatever tank it wants are check valves in the pumps (check valve on the pressure side and a shuttle valve on the return).
When the selected pump is running, the valves in that pump will be open and the valves in the other pump will be closed - to maintain pressure in the system. If any one of those 4 check valves is even slightly faulty then you have a pressure issue.
Just to summarize it all, you can lose pressure at 3 points - check valves in the pumps, vacuum line on the FPR, or the injectors. There are no other places for it to go.
Try what fltdriver said about injector cleaner in the gas first, you may be able to clean out some crap that's stopping one or more from sealing but maybe you'll have to change them.
Just don't rule out the pumps because they're new - I've been there done that and I know (now) that a new pump doesn't mean it can't be the problem.

 

Thanks everyone for the help. By no means am i stupid i just been looking for more opinions i guess cause im hesitant on changing injectors. Im probably 85% sure it is injectors so i been working extra so i can replace them next weekend. Everyone here has gave me better answers in the past couple days than autozone in the time owning my truck.

 

New injectors sure can't hurt (they're probably 20 years old).
And if that doesn't do the trick, you've got a new FPR so you won't have any trouble telling someone that their pumps are junk (if it's not injectors).
Hope they work though !

 

Next question, how do I know what fuel injector flow per lb. do I get and what's a good brand? Accel fuel injector 17lb/hr flow rate???? Im not really interested in buying them off line, I know it may be cheaper but I would like to just drive somewhere, pick them up, and go change them. Cant afford to wait a week or longer.

 

Stock is 12lb injectors. I am not familiar enough to know if going to a 15 or 17 lb will need to have the FPR modified or changed. I am sure someone with more knowledge with chime in.

 

I don't knew if this helps at all but ive heard many people say the aftermarket fuel pumps are junk and they can break within a couple months. You should only buy motorcraft fuel pumps.