I know this horse has been kicked to death but after a few weeks of research ive come up empty. I've got a 96 f150 4.9 5speed 4x4 that just turned over 200k. When i get on the interstate for an hour or so it starts acting like it wasn't getting fuel and would lose all power and start missing past 1/4 pedal. But when i stop and fill it up she runs like a champ for about 40 miles then back to acting up.So When I come home from the last job (500miles away) Last week I pulled the bed and replaced the fuel pump and filter. Took her on a 150 mile trip today and she ran great! But as i was about a mile from home it started bucking and trying to stall but would stop if i let off the pedal so I idled on home. I could hold it to the floor in neutral and it would go to 1500 rpms and pop and crack and sputter but it would idle ok. Put it on the scanner and the only code is the bank 2 o2 sensor. So I'm at a loss and ready to shoot her between the headlights. Any ideas? The list of new parts include new tank, 3 fuel pumps (spectra), tps, maf, plugs, wires, coil, distributor and cap, egr rail, exhaust, oil pan, all new felpro gaskets, injector o-rings, fuel pressure regulator, both temp sensors, water pump and fan clutch. What am i missing? Is the ecm going bad? I let it cool down and drove it to town and it acted up all the way home. Sorry for the long post but please if someone has had this problem and know how to fix it enlighten me.

 

I've had a similar problem but it's only been when it's hot out 85+ and after going up steep hills and then coming to a stop or slow speed then my 95 4.9 would sputter and die. I would let it sit and cool down for 20 min or so and it would start up and run fine. My fuel pressure is lower then specs so I'm changing the pump out this weekend. It's never showed the symptoms driving on level ground or when it's cool out.

 

It was only giving trouble when i got on the interstate and it didnt seem to act up as much when it was cold outside. But now if i drive it more than 8 miles and it starts acting up if you floor it it either tries to die or its like your cutting the switch on and off every second. The more i think about it im thinking its the computer. Its just throwing an o2 code. No miss fire or lean or rich condition or anything else. I've got to pack my tools and head to Indiana in a week so im hoping i can figure it out pretty quick. Im too cheap to go buy a new truck

 

You need to check the fuel pressure and spark when the problem happens. Both can give very similar symptoms. Throwing money before knowing the root cause is dangerous to your wallet thickness. If the O2 code indicates a lean condition you should start there....(fuel pressure). If it's rich...start with spark.

 

Thats the problem its not throwing any codes but a bad bank 2 o2 sensor. The 3rd new fuel pump is not quite a week old. I thought when it would start acting up that surely it would throw another code but its not.

 

When the first pump went bad it was throwing a lean condition code and that was because it was only holding 38 psi on the fuel rail. Put the new pump in and reset the codes and she was all good for a couple of years. I never checked the pressure of the 2nd pump i just assumed it was dropping pressure when it was hot because when i filled up it would run great for a while then as the gage moved it was back to the same thing.

 

What is that code by number?

 

Never assume new means good.

 

Well i think i found the problem. Another bad fuel pump. Is there something that could cause a pump to burn out besides the normal or do i need to look at a different brand pump. Ive had 3 spectra's and all of them have went bad during the warranty

 

Low battery voltage will burn up a fuel pump. In light of the multiple pumps I suggest taking a look at the fuel pressure regulator. Pull the vacuum line off of it when the truck is idling. The pressure should jump to 50+ PSI. Also take a look for signs of a raw gas at the vacuum line fitting. A ruptured internal diaphragm leaks fuel into the intake via that vacuum line.

 

Fuel pressure regulator is new. It was replaced not quite a month ago in the motel parking lot where i was staying. Battery is a year old 1000 ca walmart battery. And the alternator is doing its job the gage stays right dead center of normal. Pump relay and fuse for the pump are new and have spares in the glove box. Fuel pressure will not move any higher than 38psi with the vac line on or off. It has a new fuel filter and I replace them every 10k. Only thing i can think of is the + post on the battery got some corrosion on it and lost connection and i had to clean them.

 

Well, there is smoking gun evidence of yet another bad pump.

 

I've done a little research on this and talk to autozone and in their system its calling for the same pump no matter the engine. Best I understand the 4.9 running fuel pressure is 45-60psi and the 5.0 and 5.8 is 30-45psi which is where all 3 of the pumps I've got have been. I can't find any information on the pump but the part # is B5311001 and its made by spectra. Could it be the pumps are fine and they've been giving me the wrong one?

 

The pump(s) is the same for all gas engines (4.9/5.0/5.8/7.5). The difference is the fuel pressure regulator and the injector size.

 

That's what I'm being told but im also being told that the max pressure the pump will hold is 45psi which is within spec for the 5.0 and 5.8 but the 4.9 spec is 45-60 on the rail. I may be over thinking it but it just dont add up