Poor gas mileage after tune up

a cool trick i learned when my MSD wires went bad is to touch the wires at the coil pack to se if the voltage is leaking out, it'll give you a nice little jolt, warning it hurts like a b****, so just do it like a quick tap motion otherwise well it'll hurt worse lol

BTW to just make sure, when you figure the mileage are you using 15.7 gallons every time? it was kinda odd how you threw that out there when it's not any important information

I threw out the 15.7 just to ensure that the tank is actually 15.7 gal - figured if I was wrong someone would correct me. Or perhaps tell me that late model 2k v6 mustangs had smaller gas tanks or something. The math I am doin is based on a 15.7 gallon tank on a snazzy iPhone app "gas buddy".

I'll check the plugs this afternoon... Thanks all for the tips

OBTW, gas mileage isn't computed based upon the size of the tank. It's figured based upon how many gallons of gas put into the tank. The gas tanks could be 100 gallons but if only 10 gallons are pumped in, then 100 is the figure to use. Divide the miles driven by the number of gallons PUMPED.

Instead of touching the plug wires and turning yourself into a human spark plug tester, try this old racer's trick. Run the car in a totally dark location. Look for the blue hue of escaping spark. Inspect the spark plug wires for white spots which is evidence of arcing.

If the app is computing gas mileage based upon the size of the tank, then you may have your answer right there.

i believe the way the app works, is that it figures the miles driven and then how much gas i put in the car. Last fill up i drove until the low fuel light popped on and then i put in about 13 gallons, not sure how big the "reserve" tank or section of the tank is on the mustang. Its about one gallon on my 5 gallon motorcycle tank, so two-ish gallons on a 15.7 gallon sounds about right to trigger the low fuel light.

other than that, if the wire has a short couldn't i just ring it out with my dvm? if the shielding is bad and its leaking voltage it should show with little to no resistance... what is a satisfactory OHM reading for a spark plug cable if this way will even work?

Stop wasting money on fuel injection cleaners, they do nothing. THey will never clean anything but money out of your wallet.

Write down your mileages and fill-up amounts. Do the math on paper. They may be "smart" phones but they are far from perfect. Even still, 15mpg is not THAT bad for combined. If you spend more time in the city than highway then it is going to be low. I find that if I get on my car even a little my mileage suffers dramatically per tank but driving good all the time has the benefit of stretching gas. These cars will burn alot of gas in a hurry if you let your right foot off the leash.

pulled the plugs (which were all black and cruddy) and they were not the ones that my Chilton's manual said to use. When i compared them to the replacements i bought they were also much shorter (leaving a bigger space to fill and be ignited than the replacements i bought).

so i am going to put 250 miles on the car today and see what kind of mileage i get, the car does feel subtly different with these new plugs in.

I pulled out all the spark plug wires and checked their resistance, the shorter ones read around 600-800 ohms, the longer ones read around 2000 ohms, so because i was unable to find a definitive answer on the webs, i bought a set of replacement wires (which were too short to use) and checked their resistances and they were within 100-150 ohms of my existing wires.

While messing around with the wires it made me question the rigging, are the wires supposed to go over the engine, or up and around the engine via the cable at the back of the compartment. Because the set that i picked up at the auto store and was told definitively that would work by the schmuck behind the counter, required me to stretch the cable very tightly on the top of the engine, and even then they barely fit. These were aftermarket cables, not ford cables. What is everyones experience?

b1lk1 said:

Stop wasting money on fuel injection cleaners, they do nothing. THey will never clean anything but money out of your wallet...

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Thanks for the info, I think I picked up a box of those engine gumout things for something like 2 bucks at a store that was going out of business, so i've been using them and giving them to all my friends and family to use, thought they were octane boosters that i could use in my bike, plus the fuel where i live uses plenty of ethanol which supposedly dirties up a engine quicker than usual. Either way its good info.

Most of my driving is city, and I do have a frisky right foot, but I figured that my isolated (maybe once a week) frisky right foot craziness wouldn't be enough to knock down my MPG's for a whole tank.

Like i said, I am taking a couple hour drive today and will see what my mileage is with the cruise control on the way there, and w/o on the way back.

TJV said:

Most of my driving is city, and I do have a frisky right foot, but I figured that my isolated (maybe once a week) frisky right foot craziness wouldn't be enough to knock down my MPG's for a whole tank.

Like i said, I am taking a couple hour drive today and will see what my mileage is with the cruise control on the way there, and w/o on the way back.

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i drive decently "spirited" with a built top end in my sixer and i got 18mpg last time, ~70% city driving, if your getting 15 something is up big time especially since you "don't get on it that much" :hihi:

wonder how bad it will be on the road trip :headscratch:

so i topped the car off and went on a 150 mile drive or so, i have a obd2 gizmo that allows me to pump live data to my iphone so i used that to monitor my fuel consumption and even on the highway i only seemed to manage an average of around 20mpg's.

my old man said that since that car had been sitting for a while i just may need to run it for a while to burn off any carbon build up or something... i've put maybe 5 tanks of gas through it so far and haven't really taken it on a long road trip (this little 150-200 mile drive was the longest so far). as stated throughout this post, i've replaced fuel filter, air filter, oil, oil filter, spark plugs, checked the spark plug cables.

Is there anything else that a shop would do if i took it in for a legit tune up? is there anything else i am missing?