Hello all. Heres the problem. I just installed both in tank pump and frame mounted fuel pumps and replaced the fuel filter in my 1986 F150 5.0 Liter. It still has the bad miss in it as it had it before I replaced all that. It idles smooth and for the most part runs great until you put a load on the throttle. I hooked a fuel pressure gauge to the fuel rail and every time it missed the fuel pressure dropped down to around 15-20 psi and then shot back up to around normal pressure of around 40 psi and the engines straightened out. It does this at the same engine speed everytime. Other than that it has great fuel pressure 35-45 psi. One more thing when I unhook the vacuum line from the fuel pressure regulator the fuel pressures jumps up on the gauge 10 psi. I'm not real sure how to test the fuel pressure regulator but I suspect that may the problem. I just wondered if anyone else may know what gives or if someone else meybe had the same thing happen before. Any suggestions are welcome. Thank you.

 

Your on the right track it sounds like. You are probably right about the regulator. Check your fuel lines real good for any pin holes also.
The regulator from Checkers is 30.00. It might be worth just changing it out anyway beens you already did both fuel pumps.
Let me know what happens. Hope this helped.





Larry

 

Yeah that's what I was thinking too but wasn't sure. Lines are in great shape, lol had to inspect them because I had both the lines on the sending literaly rust off and after that happened I figured it would be wise to inspect the lines as well. But I'll run out get a regulator and let you know how it turns out. Thanks for the advice.

 

Hey solved the problem. Had some dying injectors. Replaced all the injectors and it's running like a new truck again. Thanks for all the help.