fuel delivery problem?

[garagedog369]

i have a 91 4x4 4.0 engine. when first start it, it runs great for a few miles, then i start loosing peddle. have to find the sweat spot to keep it traveling at same speed. then, just like fuel is shut off it starts to die. i turn the engine off , on the fly, and restart it. i still have to find the sweat spot but i can run it pretty good down the road. i have replaced the spark plugs,air filter, wires, gas filter,pressure regulator, and most of the vacuum lines. i replaced the fuel pump a year ago.

 

[motopsycho650]

Try the idle air control motor, and clean the mass airflow sensor with carb cleaning. Also, if you can get it to act up in the garage, pull spark plug wires one at a time to see if you have a dead cylinder. (i.e. pulling the wire on a dead cylinder will not change the way it runs.) If you have a dead cylinder, you may need to clean or replace that fuel injector.

 

[marragtop]

Also pull the codes. There may be a code present even if the CEL is off.

 

[garagedog369]

checked mass flow seams ok. all electrical checks out . did try to get it to act up in garage but didn't.going to pick up new fuel pump . cant think of any thing else. didn't check idle control. don't know why that would cause a problem at running speed.

 

[motopsycho650]

didn't check idle control. don't know why that would cause a problem at running speed.

Trust me, these can cause all sorts of weird running problems. Everything from hard starting/idling, to loss of power while driving. And they can even cause the rpm's to stick/rise while driving too. All depends of if it's sticking open or closed... This is a lot cheaper than a fuel pump. About 80 bucks at Napa.

Also, if you didn't clean the mass airflow, just do it. Mine looked pretty clean, but I hosed out the small hole with carb cleaner and suddenly got quite a power increase. Now I'm doing it every 6 months just because...

I would check the fuel pressure at the rail before you go buy an expensive fuel pump. Mine recently tested 35 psi idling, 45psi at mid throttle, and held at 25psi after sitting an hour, all that is normal.

Lastly, if you do replace a fuel pump, I would bite the bullet and buy it from Ford. I work at a 4x4 shop that has replaced countless ford fuel pumps, and aftermarket pumps are all junk and cause the customers to come back.

Speaking of that, the fuel pump you put in a year ago, was it a motorcraft or an aftermarket?

 

[garagedog369]

thanks i'll spray my mass flow.and check the idle switch.there's a couple reasons i'm replacing the fuel pump. my fuel gauge went out over the summer,i've developed a small leek in the brake line.where else behind the gas tank.and third thing,was in doing to pressure test it bled off in under a minute.so i figure that i've either got a leek in the rubber hose connecting the fuel pump or it's going bad. i picked up the bosch fuel pump thanks for your help. i'll keep you informed.

 

[MEANEXPLODER]

yeah.. that little rubber hose that connects the actual pump to the pickup tube has gotten me before..sucks air and causes all kinds of running issues... might as well drop the tank..if u got tall enough jackstands its not a bad job

 

[garagedog369]

ok now

problem resolved the fuel hose between the fuel pump and the fuel line was blown replaced whole unite because i went the cheap way the first time and just replaced the fuel pump and not the whole unit.because i was broke. the fuel gauge went out. and the replacement part cost as much as the whole unit it's self. i went with the bosch . because i plan on owning this one for a while.