Hi All : I have a 91 F150 5.0 EFI . Truck was used very little , as in driven once or twice per month for several years by my dad. I recieved it as a "gift". The engine runs really rough. I replaced ignition wires, plugs, and fuel filter. I also used 2 cans of sea foam in each fuel tank. ( front and rear tank) in about a 2 week period. Both tanks were filed with fresh gasoline after running the tanks dry. The check engine light is not on and no codes are displayed after doing a check with a "code reader". Without replacing parts until I hit the correct part, can anyone advise what trouble-shooting methods, and in what sequence of trouble shooting to use to try to isolate the problem ? "Pumping" the acelerator pedal seems to help add power slightly which I suspect could be pointing to a fuel delivery problem. A friend checked the fuel pressure and found it to be normal but said it could possibly be a flow problem even tho the pressure is ok. Im uncertain what the correct pressure is. Thanks !

 

do a fuel pressure test and see if its operating within specification that way.

 

Can you explain the symptoms a little more. How are the cold starts? Any change once it warms up? Idle surge?

 

sounds like a vacuum leak

 

Hi there and thank you for the replies !
I cant tell a difference in cold versus warm engine performance.
When in park, and accelerator is pressed to raise the RPM to near 2500, it seems to run much smoother. however , on a road test, it feels like it is only firing on instead of all 8.
That is only a guess on my part. Any tips on how to best check for vacum leak ?

 

carb cleaner, or starting fluid

 

A compression check would eliminate engine mechanical problems.

I recommend Gumout with regane on the label for fuel system cleaning. It has a different active ingredient.

Check all vacuum lines.

 

HI all ..
Update on F150 trouble. 2 fuel injectors were found to be bad , and the fuel filter was indicating that the fuel tank is in need of cleaning. Apparently , the small amount of use by my dad took it's toll on the fuel system. Two of the "new" ignition wires were also found to be failing. Once again, the old saying "you get what you pay for" is proving to be correct. The ignition wire set was of the Cheap variety.
A new set of injectors are being installed at this writing followed by a fuel tank overhaul.
Ill keep you posted on the results and once again , I thank you all for your response !
VANMAN

 

Thanks for the feedback. Often times we are never told what the problems turned out to be. We all learn something this way.

 

Hi all ,,
roadie, for the purpose of helping others that may be in the same boat i was in , here's the deal on my 91 f150 ...
I ordered from ebay , a matched set of remanufactured injectors, price 80 bucks and some change, that old truck has never ran so good ,,
i still plan to drop both tanks and give a good cleaning due to the age and the fact of how little the truck was driven over the years.
Thank you to all that sent a reply to my post !

thanks again for the site !