Have a 1996 f150 4.9l 4wd. Truck has 60k. Have been having issues with starting once hot and have posted before. I believe I have got it down to being a fuel issue. Hooked up fuel pressure gauge on truck and let set overnight. Truck has 0 pressure on first key on cycle. Turn key to off then Back on and builds up pressure usually about 10 psi at a time. Starts fine. Also once truck is started and turned off and then cranked back up psi drops 10 to 15 psi at start up. Also noticed fuel pressure gauge needle is pretty sporadic while running instead of steady during idle. Is this a sign of bad fuel pump?

 

Could be pump, clogged filter, FPR diaphragm stuck open or damaged, injector stuck open.

You can rule out the FPR by pulling the vac line to it, if it smells like gas you found your problem. You can also test to make sure the diaphragm is closing by apply suction, preferably with a vacuum pump but sucking on it works as well.

Filter is just a replacement deal, if it looks original, which it probably is, it could stand to be replaced regardless.

Rule those things out then move on to the pump/injectors. Usually if you can hear the pump kicking on it's good. Not unheard of for them to get weak but they usually just quit.

 

" If you can hear the pump kicking on its good " Great diagnostics ! LMAO

 

Like I said they can get weak, but these pumps will usually die as opposed to not being able to provide enough pressure because they will continue to run while they try to build up enough pressure and burn themselves out. Unless you have any suggestions for him?

 

Yea i do ,,replace the damn FUEL PUMP ! Oh wait, He hasn`t replaced everything under the hood yet ,,, never mind ,,carry on throwing parts at it ,,,,

 

I didn't say anything about replacing any parts under the hood, I did say to test and rule them out before moving on to the fuel pump. For someone talking about throwing parts at it that is the only thing you are suggesting-replace the pump. What if the pump isn't the problem??? ???

That sounds like kid logic: Fuel issue, must be the pump-replace it. Electrical issue, must be the alternator-replace it. Why not take 20 minutes and preform a few simple tests to, if nothing else, rule out possibilities and maybe find the actual cause of the problem? Anytime you have issues most peoples gut instinct is to replace the most obvious choice when they should be asking why?why?why?. If you don't work down the line you may not find the real reason behind the problem. A new pump may temporarily fix the issue but what if something else was causing the pump to run excessively? Fast forward 6 months down the road and the issue returns as the pump is wearing itself out. How many times would you suggest he just replace the pump until he takes the time to pinpoint the actual cause of the problem?

 

You're right fltdriver. Does kinda sound like a pump though.

 

He`s having a fuel pressure problem,,He has replaced the injectors and fuel filter,, FPR either work or do not,,Never heard of one working cold then not hot.. On top of that he replaced the TPS,, ECT ,plugs,,wires ,,distributor,,crank sensor ,, So yea i`m the ******* !

 

Yes but everybody's just trying to get bmusick's truck fixed. Let's all play nice and get along.

 

I didn't see anywhere in his post where he said he replaced any of that.

I don't disagree that it could be the pump, just saying it's better to rule other possibilities out before purchasing something.

Edit: and the only reason I brought up the FPR was because he was having pressure bleed-down, a weak pump wouldn't allow bleed-down like that unless shuttle valve was stuck open. I assumed he had dual tanks and he didn't mention anything about cross-filling so I figured the valves were still operational, which leaves the FPR.