Gas milage help!!

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cinz4064

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When i first got my 96 mark viii when driveing on the highway doing around 70 mph if i reset the mpg display it would show about 28 mpg and around 16 on the streets since then it has droped to 20 at the most on the highway and 13 on the street. I recently replaced plugs wires coil packs fuel injectors fuel pump fuel filter 3 of the 4 oxygen sensors also has a new lms mas air kit. what confuses me though is that when i step on the gas i get better pickup with the pedal 1/2 to 3/4 down then to the floor. Does anyone have any ideas on how to get it running right again is there something im missing any ideas would be very helpfull!!!
 
Start by scanning for any codes. Even if the CEL is off, there might be something in there that is helpful.

"I recently replaced plugs wires coil packs fuel injectors fuel pump fuel filter 3 of the 4 oxygen sensors"

What brands were all the parts used? Did you use anything that is a different spec than factory?

May be worth doing a fuel pressure test as well.....
 
pressure tested okay according to my mechanic i used 2 boch o2 sens and 1 standard do you think the last o2 sens would make that much of a dif
 
put the stock air meter back on and see if the problem goes away.

in all honesty there is no reason to put a larger air meter on a car that has a meter that will support 400HP.

Anytime your run into issues such as this, it's always better to undo any easy mods and rule them out as a contribuiting factor.
 
Did you unplug the battery when you put the MAF sensor in had the same problem just unplug the batt let it set for ten minutes and let it reset.
 
when i put the mas air it used the same meter the housing just changed i also left the bat unpluged over night ill try putting the old setup back in
 
cinz4064 said:
pressure tested okay according to my mechanic i used 2 boch o2 sens and 1 standard do you think the last o2 sens would make that much of a dif
Click to expand...

The downstream sensors don't affect a/f ratio, they are there only to check the functionality of the catalytic converters.

How about your plugs, wires, coil packs, etc. What brand are they?
 
cinz4064 said:
when i put the mas air it used the same meter the housing just changed i also left the bat unpluged over night ill try putting the old setup back in
Click to expand...

I'm very familiar with the C&L air meter, what I am telling you is from my own experience, I'm not guessing.

Put the stock meter back in and drive it for a week and see if the problem still exists.

I'm saying this because I understand how the PCM works in conjunction with the MAF.

I'm not saying the C&L meter is the problem, I'm leaning towards an underlying issue with your car.. and the meter is making the problem more likely to occur.

It's a easy test, and I PROMISE you wont die from withdrawals because you dont have that SLICKAZZED open filter and nice exposed Housing under your hood.
 
My fuel mileage isn't that great either. Have replaced plugs, wires, coils, fuel filter, pcv valve, cleaned air filter, O2 sensors and had Monroe do a valve/throttle body/injector flush. Unfortunetly, don't remember precisely when mileage dropped. It's dropped about 4 mpg. Two questions. I had transmission rebuilt by Aamco. Any chance they put in different gears or is that part of a rebuild ? If so, can I tell by looking underneath ?
 
Tell by looking underneath? Have you even seen a transmission?

Anyway. I put money on the MAF too. Everything looks up to snuff. But I would consider a stuck IMRC. I know you dont have a CE, but ya never know.
 
RedCellSix said:
It's dropped about 4 mpg. ?
Click to expand...

If the gas in your area changes from a summer to a winter blend then that could easily be your 4MPG loss.

The 10% ethanol is literally like losing 10% of your gas.
it takes twice as much enthanol to make the same power as gas, so when you replace 10% of your gas with ethanol now you have to put 10% more gas into the cylinder to get the same energy.

ALSO... the enthanol evaporates out of your gas tank
If you do the math... 10% of 18 gallons is 1.8 gallons...

400 miles 18 gallons = 22.2MPG
400 miles 19.8 gallons = 20.20 there is 2 of your 4 missing MPG
 
FYI ethanol is more stable than gasoline. If anything evaporates faster than ethanol is gas.
 
Thx. XLRVIII for the response. We don't have ethanol in town. But that seasonal blend could be the key.
 
Get rid of that LMS maf....

What brand O2's did you put in btw, if it was Bosch you might as well have old worn out Motocrafts...
 
I don't drive the Mark much in the winter but my 5.0 Mustang takes a drop in mileage every October and it comes back to normal in the spring, around April. The first time it happened, I had just had the radiator replaced and some other work done and thought they might have done something to cause the drop in MPG but it happened again the following year, exact same time of year. I attribute it to the change over to the seasonal blend of fuel.

YMMV.
 
thanks for the help my check engine light is on now gotta find a scanner i hope it will resolve my issue i'll post again when i find out what the code is
 
cinz4064 said:
thanks for the help my check engine light is on now gotta find a scanner i hope it will resolve my issue i'll post again when i find out what the code is
Click to expand...

pre game bet.

Lean bank 1
Lean bank 2

or another code that might be MAF related.

place you bets!
(SPINS THE BIG WHEEL OF POSSIBLE PROBLEMS)
 
id check wheel bearings too- my car had toasted bearings and i grabbed a few mpgs by replacing them- i guess these cars are known for that and its a pretty simple fix.
 
luxuryrules said:
How about your plugs, wires, coil packs, etc. What brand are they?
Click to expand...

This question has yet to be answered as well. A lot of times I hear the line about all the stuff they have replaced, come to find out the person is using coil packs made in India, Bosch platinum four-tip spark plugs, and a lot of other non-OE spec stuff that is absolutely destroying their fuel economy.

If you aren't using good quality plugs, wires/boots, and coil packs, I'd throw down that you stand to gain by putting MC or equivalent back on there.
 
I tend to run my mark kind of hard love playing with the power, I ave 18.5 running hard. Only thing I did was new plugs and wires and keep it waxed lol Leaves slip off my car I have so much wax on it lol
 
luxuryrules said:
This question has yet to be answered as well. A lot of times I hear the line about all the stuff they have replaced, come to find out the person is using coil packs made in India, Bosch platinum four-tip spark plugs, and a lot of other non-OE spec stuff that is absolutely destroying their fuel economy.

If you aren't using good quality plugs, wires/boots, and coil packs, I'd throw down that you stand to gain by putting MC or equivalent back on there.
Click to expand...

AMEN!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
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