Current situation on my F150 4.9 is I believe I’m having a gas fuel vapor lock. I drive the vehicle to its regular operating temperature. Engine light will eventually throw. I’ll stop the vehicle quick test to restart and restarts fine. After about 10 minutes of sitting, I’ll try to start again and it will stumble and misfire, non start. The two codes come are the lean fuel mixture situation. The truck was originally equipped with two tanks, and everybody knows the frustration with these 96 4.9 2 tanks system. Mine was pretty much the same as everybody seems to have problem of the fuel bleeding into the rear tank. I deleted the rear tank and plugged off the fuel line going to it. I bought a new fuel pump. It seemed to work for about six months. But again, I’m thinking the return line is not proper because of the original set up. So I’m wondering if there’s a front fuel pump that does not support the rear tank situation. I know there’s a check valve that is funkie within the fuel pump itself, when you flip the switch from one tank to the other. So I’m guessing I’m looking for a fuel pump the original size so I won’t have any jury customization. Looking for simple open return fuel pump. . Is there such a thing for The 4.9 engine? thank you for your help.

 

Well there is no such thing as a single mid-ship tank from the factory. If you have a single tank from Ford, it's the rear one. However, it doesn't make any difference. The rear pump on a '96 is the same no matter if you have 2 tanks or 1, so the same would hold for your situation.

 

Thank you. The truck had originally the 2 tanks. Because of the bleeding into the rear tank I deleted it. If you have experience with this type tuck, what brand of fuel pump would you use. Thanks for your information. Rich

 

I find I very hard to believe that a high pressure fuel system with a return is experiencing vapor lock. Assuming that everything on the engine is working correctly then the lean code is more likely from a failing fuel pump. Have you put a pressure gauge on it to see what is happening? Do you see pumps listed for single tank or does it not specify? I would say it doesn’t list any for a single tank because all the pumps are the same whether you got one or two tanks. Not only that but not having the check valve on the return wouldn’t help with a pump not putting out enough pressure.

 

Earlier in thread have noted fuel pressure. 42psi. But that’s at cold startup. My problem occurs after running temp, then shut down. After 10/15 minutes I try to restart is when the stumbling, no start occurs. Do not think it’s fuel pump, even driving at running temp there’s no hesitation or missing or stumbling even when check light comes on. And to boot, if I try immediately after turning off (2/5 minutes) starts fine. It only occurs when truck sits for 15/20 minutes I get the stumbling, misfiring? Waiting another 20 minutes it starts fine? Summery, only occurring after shutdown with a 15/20 minutes before I try to restart. Rich

 

Since your assessments so far are, or seem to be, mainly fuel problem based, it may be a good idea to get a full-time fuel pressure gauge hooked up so you'll be able to tell what your actual fuel pressure is during good and bad running times. I put one on my 89 4.9L several years back and it was one of the best things I've ever spent money on for that truck. It uses an electrical signal from it's sending unit which mounts on the fuel rail's schrader valve.
Something like this

Also you may wanna ensure all your fuel strainers and/or filters are not clogged up.

-- Maybe get a laser temperature gun and check temps on suspect areas on/near your under-hood systems while they're cold, warm, and at hot (problem) times to get a baseline of heat related problems that you suspect you're dealing with...

Lastly, I hear Delphi fuel pumps are among the better one's out there. I've had good one's and a few bad one's from Spectra Premium models too. Here's a snipped Rock Auto listing example.


Good luck finding the source of the problem! Even better - finding a fix for the problem

 

Have you checked the condition of your coolant and intake air sensors? They are a common cause of a rough running engine and are easy to check.

 

How do you know what is happening to the fuel pressure without watching a mechanical gauge attached while driving? You don’t and are guessing.

 

These are the exact symptoms I had when the high pressure fuel pump was going out on my '88. Although mine is a different fuel system, I would suspect fuel pressure problems.
I tried cycling the key twice on every start up for a week. That resolved the problem. Then I replaced the fuel pump.
Having a fuel pressure gauge connected while the problem is occurring, would be the most direct way to troubleshoot it.