my 98 f150 reg cab short box 4.6l 4x4 is having some issues. truck has 185k miles. the truck doesn't have much power. it is getting terrible mpgs 5-7 city driving. the only this has done to it is that it has dual pipes with separate mufflers. the only code i am getting is for lean fuel mixture. it is progessivly getting worse. i changed the fuel filter once and and the truck ran great. next day it ran the way it was before the filter change. i proceeded to check the dpfe, vacuum lines, and spark plugs; all were good. i then replaced the fuel tank, fuel pump, and filter(again). no improvement showed.

i don't know where to go from here, i am more than capable of fixing the problem myself but cannot identify it.

note: the egr tube was busted at the manifold and was welded back on, may leak slightly, don't know if this contributes to the issue.

also truck was like this when i bought it at 176k, but ran decent( not quite as much power as it should) and got decent mpg(12 city). has been terrible the last 4-5k miles.

please help, i don't want to get rid of it due to this issue.

 

Do you have CEL/MIL illumination ? If so, scan it again, but this time write down all DTC's as that will help us help you most.

Your going to have to go thru it, -ignition system complete, O2 sensors and if your running True duals, that will kill your usable power and torque. - Specially without converters, IF that's the case. The exhaust set up matters a lot, - has to be set right for the tune or vice verso and shouldn't leak anywhere within the Y/engine compartment.
Your PCV system most likely has issues from the sounds of it. You may have to change the air filter and clean the MAF (BY HAND, not a hose down.) At 185,000 miles it needs a good going thru, - a real tune up.

 

Thank you for your reply,
I will have to buy a cheap scanner. A mechanic scanned it for me at cost($10). He said it was showing a lean condition, i would assume both banks, but i wouldn't know for sure. I'm not ready to throw a bunch of money at it, so i would like to narrow it down as much as possible. As for the exhaust, the cats are still there. The mufflers are right in front of the tire with down pipes right off them. The piping is 2.5". The only thing i have done to the truck was replace the mufflers with thrush mufflers.
The PCV system seems to be all good from what I checked, which was what i could see, could still have a problem though.
Also what steps would ensure a thorough tune up? And how exactly should i go about cleaning the MAF and what to use?

 

I'm betting that your cats are plugged.

Parts stores do scans free, unless you are in California or Canada.

 

What makes you say the cats are plugged?
Also, i am 1 hour away form a parts store and the vehicle is not registered or insured.

I'm willing to follow any reasonable track, so your ideas on the cats would be appreciated, thank you

 

edit: The fuel pump was replaced by a used one from the local junk yard and was then replaced with a cheap pump motor from ebay(less than $20) which failed after about a month(300 miles). The used pump is back in the vehicle now.
The fuel filter that was originally replaced was full of rust.

 

Get someone to rev it up, and feel the exhaust outlets to see just how much they are blowing. With good cats and Thrush mufflers, it should also be LOUD.

Cheap scanner:

 

Exhaust feels like it has a good steady pulse and is loud but not too much louder than stock