Bad gas mileage in gen 2

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Lincoln Brothers

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Hello. i have a 1998 Mark VIII with 113,000 miles on it. I only drive around the city and i average out to 11-13mpg every time. i don't just rely on the dash, i do the math. Ive done fuel filter, air filter, and spark plugs. i put the high octane fuel in too, to get better gas mileage. My last resort is the 02 sensors... but im not sure. Someone help me.

Thanks, Jon
 
It's worth $200 for O2 sensors to keep your mark running right, it's not worth it for a small if any noticeable gain in MPG. Drop the exhaust for the passenger side and the drivers side it's a PITA but doable. I would buy a wrench to cut up to fit in there better (that's what I did) or get the special O2 tool.
 
My '98 gets much worse MPG than my '96 did. That and I'm on my second '98 LSC both of em with well under 100k. Both get around 5 MPG worse (19 average) than my '96 Base (24 ave) but not near as bad as what you are seeing :confused:
 
I thought it was a known fact that gen 1's get better gas mileage than gen 2's. My 93 gets 30mpgs on the highway where my 98 gets 25 with 18 inch Speedstars on it. Around town with the 98 I'm getting 20.8 but i drive it easy. I'm in no hurry when I'm driving that car.
 
At 150k, I lost one of my coils and my car started to miss. Well I had Coil replaced and it stopped missing. I then took a trip and got 20.2 mpg on the highway. Had a guy connect his computer and he showed me couple of the coils were missing but I wasn't feeling them. I replaced all the coils and got 24.7 mpg the last trip I took. Again, mine was hand calculated too. Not saying that could be it but it could be a possibility. I personally would replace the o2 first though, it seems like you have done all the other stuff that needs attention.
 
Buy, or rent, an O2 removal tool as mentioned. With a crows foot both are pretty easy to do. The only problem I had was getting to the passenger side connector. THAT was a pain. There are many universal options for O2 sensors. I paid $20 for mine, motorcraft. Avoid BOSCH at all cost.
 
unity said:
Nope. Not one bit. Only to monitor the cats and make sure they work.
Click to expand...

ya they do actually...more then just a tattletail for the cats

infact watching all my o2's on our auto ingenuity labtop based scanner showed just how lazy my rear o2 sensors were vs my pre cat sensors and replaced down stream only and picked up an average of 2-3 more mpg
 
87TTOPGT420 said:
ya they do actually...more then just a tattletail for the cats

infact watching all my o2's on our auto ingenuity labtop based scanner showed just how lazy my rear o2 sensors were vs my pre cat sensors and replaced down stream only and picked up an average of 2-3 more mpg
Click to expand...

Odd. In all the programing I did there was nothing related to the rear O2s for fuel/air mix. In fact, the rears should be "lazy". If they switch as fast as the fronts that is a sign that the cat is dead.
 
Would using a code reader with live data and looking at the fuel trims yield any useful information?
 
If youre mileage is that bad... start cleaning, and air your tires up
 
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