Hi, I’m new to the forum, and just a backyard mechanic, but when my 93 E-250 I6 300ci w/ 225,000 miles, suddenly dropped from 18mpg hiway to 5-6 mpg I came here looking for help, came across the sticky post about always more power and thought hey, great idea. If that post was actually what it’s creator intended it would have saved me a few hours of searches and looking through posts such as “mpg” “low mpg” “HELP!!!” “More Power” and other posts which are SO detailed in their titles. So, I went though and compiled all the information I found along with my own limited knowledge. Experts – please copy this post and add/remove/correct anything you think needs it, and then repost(please don’t add things like chips / new gearing / turbo etc, I’m hoping to keep this more along the lines of hundred dollar not thousand dollar improvements for the DIY type, not turning a I6 300ci into a 500HP monster, etc. Maybe after a few versions this post will contain all the standard MPG / Power related answers.

Oh, and everybody please don’t turn this into a “I have this, this, and this, would like to do this, would this brand / part help me”.
Start a new thread with a DETAILED title for that, don’t clog up this one.



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Try checking/changing/cleaning/doing the following for better MPG and Power:

Exhaust – Open up the exhaust with bigger pipes / manifolds / cat / muffler. Also wrapping(insulating) the exhaust seems to keep the inside cleaner and to keep down engine compartment temps which helps bring in cooler air.

Cold / Ram Air Intake – Cold air provides more power than hot air and as such drawing air from around the engine is not the best idea. This spring on mine I added a homemade “scoop” just to the side of the radiator behind the grill and piped it up to my air intake, gave me 2 more MPG, but am unsure if it might be causing it to run too lean at 60mph(experts, chime in here) and if I’ll have problems this winter. A plain aftermarket cold air intake might work better.

Catalytic converter – If plugged causes loss of power and mpg.

Oxygen Sensor – Can cause engine to run too rich or too lean.

Air Intake Sensors - Same

Throttle Position Sensor – Same

Fuel Regulator - Same

Coolant Temp Sensor – a bad temp sensor can cause your engine to run with the “choke” open and run rich. This can also be caused by using the wrong thermostat.

Spark Plugs / Wires / Coil / Distributor Rotor / Cap – Basically bad spark = Bad MPG and Power. Use Autolite or MotorCraft plugs, put on high quality wires, use anti-seize(you’ll thank yourself later), silicone dielectric gel on all electrical contacts, new rotor and cap (no dielectric gel inside distributor but always on wire connections) every time you change the plugs. If you have a little money to toss around, you might invest in a high voltage coil.

Air Filter – Maybe switch to a K&N high flow at the very least make sure to change a paper one often.

Fuel Filter – If it has been a while change it and then change it again in about 1000 miles, you would be surprised how much dirt is sitting in your tank waiting to clog up your new one.

Fuel Pressure – May indicate bad fuel pump or dirty filter.

PCV Valve – Experts???.

EGR Valve – Experts???.

Tire Pressure – Low tire pressure increases rolling resistance and so decreases MPG and can also feel like the engine has less power.

Change Oil / Filter / Use Oil Additives / Flush – I have had very good luck with these. Every oil change I use that 5-minuter engine flush that you pour in your crankcase and run the engine for about 5-minutes before draining oil. Then I pour about half a quart through the engine with the drain plug removed to try and “wash” out as much of the old oil as possible and then I let the engine drain for AT LEAST an hour before replacing the drain. On refill I add 2 bottles of Lucas Oil Stabilizer and a bottle of Engine Restorer (the kind that recoats your piston walls). They really do seem to make the engine run smoother, I can actually feel a difference in power after a 3000-4000 mile oil change.

Change Tran Fluid / Filter / Use Trans Additives / Flush - I do about the same when I change the trans filter…use a cleaner, open and drain, don’t forget to open up trans cooler lines to get it all out and to clean the pan magnet well, allow to drain for at least an hour, refill with trans fluid and Lucas Trans Stabilizer. It may seem like overkill but when I first got my vehicle I thought it needed a new trans because of poor shifting / slipping / and failure to downshift at stop lights (killing the engine) but after a little of the aforementioned TLC it now shifts so smooth you can’t even feel it. And if the trans filter is really dirty and/or there is lots of shavings stuck to the pan magnet, don’t be afraid to change it again at your next oil change, a auto trans has lots of little places for dirt and grime to get stuck and then come out later to fill up your new trans filter.

Clean Your Intake Manifold and Throttle Plate - Amazing what a this little bit can do. And add a some Seafoam to every few tanks.

Remove Lead from Foot - Run between 55-65 mph and don’t “punch it”; this will not only save some gas but will save on tickets as well.

 

I have to take opposition to the engine flush advice. If you have done this since day one or have a relitively clean (internally) engine you will probibly be ok, but if you try this with a 100k+ engine that has never seen a good cleaning or has a questionable maintenance history you are asking for trouble. If you have any questionable gaskets they are toast, you have a good chance of clogging the oil pump, and possibly damaging the bearings. Bearing damage can occur quickly in a situation like this. The engine flush can knock enough crud loose to clog the oil filter very quickly, at which point the bypass valve will open and let all the chunks of crud go right to your bearings. I have personally turned a motor from dependable transportation to an anchor using one of these products for whatever thats worth.

If you want to clean your engine use something a little gentler like one quart of Marvel Mystery Oil with your oil change and up your oil change intervals (at minimum change the filter more often). You could also use oil formulated for diesels as it contains more detergents than oil for gas engines. There is much less risk involved using these methods.

the TPS sensor can also cause hard starts and stumbling

 

More Power and MPG Carbed

Rebuild Carburetor
Always replace Fuel Filters with new/rebuilt Carb
Open Element Air Filter
Conver to Electronic Ignition if using points
Headers with Dual Exhaust
Most people along with myself report negative effects of using platinum plugs, most recommend Autolite or Motorcraft.

Once your get into 4bbl and Intake Manifolds it gets expensive and you stop gaining mpg.