Hello,I am new and this is my first post on the forum. I have a 92 f150 4.9 liter that is having some problems. The truck will start sometimes and sometimes it won't. It will start and run fine sometimes and sometimes the check engine light will come on and the truck will lose tons of power ( it feels like I am trying to drive it with the parking brake on ). I have scanned for computer codes and everything checks out fine. I think I have narrowed it down to fuel related. I notice my fuel pump will not stop running when I turn key in on position, this is when my truck will not start/ it cranks just does not start. Sometimes when I turn key in on position the fuel pump will prime for 2-3 seconds and turn off, the truck will start when this happens. I have replaced fuel pump relay/ fuel pressure regulator with no luck. I no I need to due a fuel pressure test but where is the schrader valve on a 92 f150 4.9, I do not see any spot on the fuel rail to due a test. I think this problem could be caused by bad fuel pump or faulty computer. Any help or tips would greatly be appreciated.

thanks, mike

 

Welcome to the forum! Pressure chek valve is located on fuel ramp near a firewall next to intake mainfold. I agree that checking fuel pressure is a good starting point, because it really looks like fuel delivery problem to me.

 

I finally got a fuel pressure testing tool and finally did a fuel pressure test. My truck won't run because the fuel pumps (both front&rear ) will not stop running when key is in on position "koeo". My fuel pump readings with key on engine off where 55lbs, I checked several times with both tanks, fuel pressure regulator vacume hose on and off and got same reading every time. That seems kind of high to me but what is normal for 92 f150 4.9 liter. The pressure in both tanks held very well, it must of been a half hour or more before pressure went back to 0. I have changed fuel filter, fuel relay, fuel pressure regulator with one off of a junkyard truck(probably not a good idea) with no luck. I am strongly pointing to a bad computer causing this. Has anyone ever experienced this and is there anything else that would cause the fuel pumps to keep running when fuel pressure seems good. Any help would be appreciated.
thanks,mike

 

35-40PSI is normal fuel pressure. 55 is pretty high but i don't think it might affect that way. Try to read error codes, and post the result here. Also check ECU (computer) connector to see if it's attached right way (it's located on firewall on driver side under master brake cylinder and it has a 1/2" bolt in it's center).

 

I am having the exact same problem on my 93 F-150. I am still trying to narrow down the problem. I am going to change the fuel pressure regulator today to see if that fixes it. If not, I will then replace the fuel pump. Normal fuel pressure is 50-60psi, so your fuel pressure isn't high (mine is 58). After you do the pressure test, your fuel pressure shouldn't leak down to 0 in 30 minutes. My fuel pressure is leaking down like that too. If you are able to fix your problem before I fix mine, please post what the solution was and I will do the same for you. thanks.

 

I only have one tank and one fuel pump. Both of your fuel pumps doing it makes me think maybe it's not the fuel pump, but you described the exact problem I am having and I am hoping we can help each other out.

 

I'm following this post as my 1995, 4.9L 6cyl exhibits similar symptoms.

Here's a video post on using a fuel pressure gauge that was informative:

http://www.2carpros.com/how_to/how_t...l_pressure.htm


Also, a couple pages that might be helpful:

http://www.aa1car.com/library/2003/us60324.htm

http://www.mobiloil.com/USA-English/...sure_Test.aspx

https://www.f150forum.com/f10/fuel-pump-diagnostics-96-f-150-4-9l-12148/

 

thanks for all the help everyone, The truck gets no engine codes. It used to do this from time to time starting a few months ago. I would try to start it and it wouldn't,I would try switching tanks and turning ignition key on and off and it would start, but this was when the fuel pump primed for 3-4 seconds and went off but eventually it would not start and fuel pumps would just keep running and not shutting off. My next question is How long should it take for fuel pressure to drop to 0, I said it took 30 minutes for mine to drop but I just estimated because it seemed like a long time before it went to 0. I will check the ecm connection and make sure everything is tight down near the firewall. Hopefully today I will be a little closer to having this truck running again.

 

Mike,
Were you able to fix your truck? I have possibly fixed mine. You know how sometimes it runs fine and other times it acts up? For that reason I hesitate to say I have it fixed, but it has ran fine for the past 2 weeks.

 

Keep me posted on the results fellow southern son. Too often a thread ends when someone 'fixes' the problem, BUT they don't post that 'XYZ' was the cause of the symptoms and 'xyzII' fixed said problem.