I have a high mileage F150 2 wheel drive with the 4.9 Liter straight-6 cylinder engine that seems to be getting lousy gas mileage. It has a slight shake to it which may be a fouled plug or injector, but I haven't had a chance to check anything yet. A few months ago I replaced the spark plug wires, plugs, cap & rotor, but the truck hasn't ran quite right since I bought it. The catalytic converter had been replaced with a straight pipe (courtesy of the previous owner) and the air pump has been by-passed with a shorter serpentine belt, so it isn't being ran anymore either.

There aren't any codes showing up with a code tester, so I don't know where to look. Does anyone reading this have any ideas of things to look at, check out, adjust or replace that might smooth out the engine and improve mileage?
Thanks,
Tom

 

seems to be getting lousy gas mileage?
You need to check your mileage over a few tanks of gas. Can't just seem to get good or bad mileage. The 300 is know for lots of torgue, and a long life if well maintained. It is not know to be super effecient and get great mileage. Especially in traffic and with an auto tranny.
Frank

 

My 1990 4.9, 171,000 mi was running a little rough so I did the Seafoam treatment everyone raves about. I also cleaned the throttle body and all components with carb cleaner. I was a bit skeptical but did it anyway. Truck idles so smooth you can barely tell it is running. Try the carb cleaner and the Seafoam treatment. Costs less than $10 and the results were great!

 

Sea Foam Engine Treatment is something I can try throwing in the tank tomorrow. Perhaps I will get lucky and the truck will run a bit smoother.
Thanks,
Tom

 

Check the instructions, disconnect your brake booster line and pour 1/2 can into it with the engine running. The engine will stall and you let it sit for 20 to 30 minutes. When you start it, it will smoke like hell for a while so make sure you do this outdoors. Then dump the remainder into your tank.

 

Thanks for the tip! I will let you know how it goes. By the way, I went and checked under the hood for loose vacuum lines and noticed that the repair shop while fixing an emissions exhaust leak, replaced the serpentine belt with one that runs the air pump now. What good does that do if the catalytic converter isn't installed anymore?
Tom

 

The cats don't have a thing to do with the air pump.

 

Guys,
I have a new slightly different problem with the truck backfiring and then stalling out. I get to within a 1/2 mile area of where my truck dies while coming home from work each day. It usually will restart while still rolling off the road by putting it into neutral and starting the engine again. Once it took several minutes to get it running again. I checked for codes and it steered me to look at the fuel pressure. My neighbor checked it not running but with the key in the "Run" position.

The pressure started at 41 PSI (not running) and then 50 PSI once started. The pressure did increase by 5 PSI when the vacuum line was removed from the fuel pressure regulator. These pressures were all lower than limits per the Haynes repair manual. Unfortunately, the pressure slowly decreased even with the vacuum line replaced.

Could the fuel pressure regulator be causing it to drop or would you look closer at the fuel pump for this condition? My thought on this is that the fuel pmp was just replaced a couple of months ago, while the fuel pressure regulator ha 300,000 miles on it.

The fuel pump is still under warranty, but I will probably cut an access hole thru the bed of the truck and replace the pump with out dropping the tank. I will put an aluminum cover with self-tapping screws over the hole later. Does it sound to you guys that I am on the right path?
Thanks,
Tom

 

i would just drop the tank or take off the bed to get to the fuel pump.

 

fuel pums is you best bet its easier to take off the bed than drop the tank not having any cats could be causeing some of your trouble it is an obdII vehicle so it has o2 sensors after the cats to if these arnt getting correct readings the there goes gas milage its about 400 to have these cats replaced.

 

I won't be able to do anyrthing till next weekend...waiting on payday. Thanks for the info.
Tom

 

I had a 96 2x4 auto that I just sold. It was really bad on gas when I first got it 84,000mi used, noticeably worse than my 95 4x4 manual tranny truck 246,000. A few things helped me out. Running 93 octane fuel, although $$$ showed better mileage, thereby saving me $$$ in the run. Startron additive, normally for boats is a non-corrosive fuel additive and runs well in these older high mileage trucks. New ignition coil and good cleaning of all components and connectors. Make sure you are running the exact Motorcraft spark plugs called for on the hood tag. When I replaced the crap plugs that were in there, I bought substitutes by another brand, they ran great for two months then they burned very uneven and basically self destructed. My mechanic told me to use only the exact Motorcraft called for and nothing else or I was asking for trouble, he was right. Then check all the sensors for function as listed in the repair books like Haynes, my TPS was dirty and acting bad, I cleaned it up good and was much better.
Good Luck, enjoy your truck!

 

I was convinced by a local mechanic to replace the fuel pump in the front tank (rear tank/pump assy. was pitched a long time ago), especially since it is still under warranty. I am going to spot the center of the pump (directly above the pump), first drilling a 2" hole with a hole saw, then I will cut with a saws-all an 8" x 8" cut-out in the floor of the pickup box. I will fabricate some sort of cover for the access hole to the pump from directly over it as mentioned earlier. I can take another set of pressure readings to see if this has corrected the low-pressure I presently am seeing.
Tom

 

Couple of things I'd like to address,

Post #7

The cats have everything to do with the air pump. Unless I take the reason for your comment out of context.
But even if I do, that is not a correct statement.

Post #10

The O2 sensor after the "cat", obd2 system, does nothing to adjust the fuel/air mixture, only monitors the exhaust gases after the "cat" and triggers the light if its not working.

Edit, seams to be conflicting information on that. I looked it up on the web and the writeup I found states sensor 2 (either bank) does effect injector pulse width. I wanted to see if it was true for all models.

Reading the information in my code reader back when I first got it stated it does not. That and watching bank 1 sensor 2's output (wife's explorer) compared to bank 1 sensor I and bank 2 sensor 1 while it's running leads one to think it was right. It does not continually oscillate up and down, voltage remains constant. A flat line.

So it may vary by model but have found nothing to confirm that yet.