Interesting thread. While I believe the MSD setups are fine ignition systems, I'm going add another vote for the oxygen sensor being responsible for the mpg gain.
I've seen many a car that the owner complained of terrible mileage and the fault was a bad or damaged oxygen sensor. And the engine light won't always come on for particular types of failures. Thus you could be driving with a bad sensor and only be aware of the rotten mileage. Some vehicles tend to pickup on sensor problems better than others. Some older Volvos were so bad not to set an oxygen sensor code a common Volvo mechanic's test was to raise the car and bonk the catalytic converter with a rubber hammer. If he heard a rattle he could reasonably assume the oxygen sensor had come apart and needed replacing. It was actually the most expedient way of checking an oxygen sensor. Also suprising was how many times the test found the dead sensor rattle, particularly with the turbo cars.
The same test method doesn't really work for other brands and newer vehicles. Sensors most often fail without any visible or physical damage. They can also degrade very slowly over a long period time making it less likely to be noticed until one finally gets bad enough to set a check engine code. And of course many oxygen sensors last the life of the vehicle and then some with no problems. One thing is for sure, if you have a faulty oxygen sensor, you gas mileage WILL suffer noticeably.
I don't think I could credit an MSD setup with more than maybe a MPG, never 10. Ford OEM electronic ignitions may have their weak points but they're not THAT bad!

 

Thanks to all for the education on this thread. I've had my 94 Bronco 302 for three years and not done a thing to it but change the oil every 5K and watch the 32gal needle drop like a second hand. My Bronc's poor gas mileage & relatively small cab made me think of getting a late model F250 for hauling a pop-up and family, but they are mucho $$$. Much cheaper to make some upgrades to improve gas mileage, performance, and extend the life. FTE has made me much smarter.

95% of my driving is pavement so I'm not looking for top of the line products designed for off-roading. I installed a K&N FIPK last night and I've got a laundry list of other chores: plugs/wires/rotor, shocks, and exhaust top the list (now I'm aware of O2 sensor?).

Where do I start and not break the bank just for a namebrand while getting the performance for hauling a trailer in the mountains? Currently get ~10 mpg city. Don't drive much hwy but will do so on upcoming trip. Don't know if the K&N will make a difference at the pump, but certainly gives better response on the pedal.

Thanks again!

 

I'm with you Jeter.
I am good with the removal/replacement of almost anything on my truck. BUT when it comes to problem determination or reading posts about MSD or other branded replacement parts I just get so frustrated.

-I get 10 MPG if Im lucky.
-When wet my truck misses and sputters.
-When I floor it or turn on the A/C my truck rattles/pings/whatever you want to call it.
-I have no CEL.

I am willing to spend $500 on parts if I can figure out what I need.

I have replaced:
O2 sensor
Cap and rotor
Fuel filter
Wires
Plugs
I have FIPK from K&N.

Maybe the parts i replaced are crap....I don't know.

I have had tranny leaks from hell. One from cooler and the other was an o-ring where the connector comes out of the tranny.

THIS TURCK IS DRIVING ME NUTS.....I actually considered canning it and getting a Pontiac Pursuit to save money.
I love the fact that my truck will run anything over....but it has to stay still so I can ping my way over it.


PLEASE TELL US WHERE TO START AND WHAT PART NAMES ARE RESONABLE.

Thank ya...i feel better now that I vented.

 

I would have to agree, Although there is a noticeable performance inprovement to be had with the msd equipment, a 9mpg increase is quite a stretch unless mayby your praying in toungs. I would guess you gained 7-8 mpg with the o2 sensors and mayby 1-2 with the msd.

But I guess it doesnt really matter at this point 22 mpg from 13mpg is quite an improvement

 

Alright i'll try and help you out some as to where to start so here it go's i'm borrowing some of this stuff from another post i saw in the forum.

I'd look for vaccum leaks to start with the 300-6 is prone to egr valve (malfunctions) for lack of a better term. For your truck i would make sure the truck is timed correctly if your pinging that's detonation which can be caused from running too advanced of timing. Also try running higher octane fuel until you can get your problem figured out. Pinging can also be caused by the engine getting too hot. so maybe try flushing your engine and radiaters coolant.
If your truck is mass air flow i'd replace the maf sensor. Also what gear are in your truck? is it a automatic? a 5 speed? if so which automatic or manual do you have and what rear end gears do you have. A lot of the newer model 300-6s ran 2.72 rear gears which is a huge gas milage killer while in town. 4.10s are good gears with the m5ods and should leave your highway rpms at about 2200 rpms at 65 which in my opinion is about perfect.

Here's some parts that can cause vaccum leaks which is a killer for gas mileage and engine performance in general.

Throttle body gasket to upper plenum sucked in (most common)
Upper to lower plenum gasket leaking
EGR system leaking vacuum....includes valve, regulator, vacuum source, sensor, etc....
PCV Valve not closing / leaking
PCV hose leaking around vacuum fitting on intake and/or at valve
Coffee cannister (Vacuum Reservoir) system leaking / not holding vacuum
Brake booster / vacuum hose leaking
Allen head nut (on top of the throttle body leaking)
Idle Air Control Valve leaking
Vacuum lines going to the Charcoal Cannister leaking
Fuel Pressure Regulator vacuum hose leaking
Vacuum hose that goes to the interior HVAC leaking
Vacuum tree loose in upper intake & leaking
Caps on the Vacuum Tree cracked and leaking

 

Thank you...I will go through the list. I just took out the original PCV and replaced it (15 mins ago).

114000 miles or 190000 kms on the truck right now.
Truck info is in my signature.
Not sure of the rear gears.(no tag on diff.)
EGR makes a hmm / vibration noise after you shut off the engine.

 

post a topic of what your door code reads and someone will be able to tell you what rear gears you have.

 

Mine is doing that too, Id be curious if thats a sign that they are bad since i dont have a vacume pump to test it out.

 

try spraying a aerosol can liquid of some sort around like wd40 or such and see if it bubbles up. If so you know theres a vaccum leak. I check to see if my stuff is leaking the same way that i check tires for holes lol.

 

Just a follow up - I used exactly the same parts that Randy did, and saw absolutely no improvement at all. 15 mpg before, 15 mpg after.