I can't figure out this problem. I do not drive the Mark VIII aggressively, but I'm getting real bad fuel effeciency. 16/21.

I only use 93 octane gas.
The fuel pump is new. 255 lph unit.
The fuel filter has less than 25k miles on.
the tires are new.
tire pressure is monitored.
the air suspension is new.
everything is aligned.
I'm going to replace the control arms shortly, the passenger one needs replacement.
The engine has about 180k on it now.
And the torque converter on the transmission isn't in the best shape.

I want to get 26 mpg cruising on the highway at 70-75mph.
What do I need to do?

I can't figure out this problem. I do not drive the Mark VIII aggressively, but I'm getting real bad fuel effeciency. 16/21.

I only use 93 octane gas.
The fuel pump is new. 255 lph unit.
The fuel filter has less than 25k miles on.
the tires are new.
tire pressure is monitored.
the air suspension is new.
everything is aligned.
I'm going to replace the control arms shortly, the passenger one needs replacement.
The engine has about 180k on it now.
And the torque converter on the transmission isn't in the best shape.

I want to get 26 mpg cruising on the highway at 70-75mph.
What do I need to do?


the first place to usually look when fuel econ is poor is your O2 sensors,after that,regular tuneup items,air filter,plugs,pcv vavle,clean egr ports.etc..

You might want to try seafoam to clean everything out. Just remember to do this before you change your plugs and 02 sensors.

I forgot to add:

all new plugs and wires within 6k miles.
both 02 sensors have been replaced
air filter new
pcv valve new
and seafoam was used as well.
new synthetic oil.
brand new cooling system (radiator, hoses, fanmotor, pump, coolant, ect.)



The EGR valve could result in that dramatic a drop in efficiency? Isn't that a nightmare to access on a Gen1?

The EGR valve could result in that dramatic a drop in efficiency? Isn't that a nightmare to access on a Gen1?

well,i dout it would make that much difference,


check that adjustable thing at the end of your ankle.....maybe the foot thingy is moving too far causing more fuel to be used than is neccesary.

lol

just kidding.i dont know what else to tell ya,none of your wheels are hot after a 10 min drive are they?like brakes dragging....

Hey, your lucky you're getting 16...

I'll get 12 if I'm lucky. I had 13 this week, but I replaced my airfilter at the begining of the week, so It did help a little bit.

I checked my mileage on Saturday on a 40 mile trip the went up some good hills. I averaged 32 mpgs to my driveway.

I did a long haul down 95/295 to go to AC and I was averaging 26.x mpg. I was thrilled cause I got over 400 miles out of a tank :D

I reset the mpg gage and around town driving after I ran a can of BG44K through the tank I was able to get 19mpg around town driving. However it seems since they changed the gas at the Sunoco my mileage has gone down? Now I am getting 18.7 average and with the gas prices so stinkin hi I want every bit I can get!

My car idles bad in that it surges sometimes and when the cell light comes on it reads Bank1 Bank2 lean. So I am between a vacuum leak or bad O2 sensors??

I've done as controlled an experiment with the mileage as possible. Filled up the tank, set it up on cruise control at 70mph and ran it 65miles, then pulled off, refilled the tank, and did the math. (the onboard computer in the message center gives me completely inaccurate numbers, so I did it the paper and pencil method)

Sadly, the message center tells me numbers that are too high. So, according to it, I might be getting 26mpg. Then, when I refill the tank I learn that it's thinks I've used almost a full gallon less than I have.

Think the trouble in transmission, I know the torque converter needs to be replaced, could cause that severe a loss of mileage?

If the torque convertor isn't locking up on the highway it can definately cause a noticable loss of mileage.

I had an issue with a particular brand of gas. I was using a el - cheapo ( still 93 octane) gas. My mileage went from 17.5 down to 15 over a full tank and the CEL came on ( gas cap was tight)- even had some slight bucking at idle. I thought at first my O2 was going, but I used Sunoco premium and within two tank fulls I am back at 17.5 and no check engine light and idles smooth. It could have been a lot of water in the off brand as well. I used a can of isopropyl gas dryer in the first tank-full afterward.

I was relieved it was so simple of a fix. :wrench

I almost religiously use Sunoco as my one car was tuned for it specifically. There seems to be almost to many spots for a vacuum leak for me to find where it is?

First you have 25K on the fuel filter, I would change it first. Where I live they change fuel blends in the winter and it breaks alot of crud loose. We need to change fuel filters once a year here. Second, You said you have new tires. Are they the same brand and style? I did alot of work to get my milage up from 18 mpg, I did get it up to 29 mpg. I bought new tires and lost 4 mpg. Tires have what they call resistance to roll, and the differance between brands and styles can be drastic. It can effect your milage big time.

Good luck
Raoul

You think the tires might be making that significant of a difference?
I have Fuzion Zri on there.
http://www.tirerack.com/tires/tires.jsp?tireMake=Fuzion&tireModel=ZRi

I get about 16.8-17.0 mpg in town, and that's driving normal with very minimal lead footing. and around 22-23 on the highway. I also wish for more MPG. the best I have got is 18 in town and 25 on the highway.

Yes it can! I drove about 50 miles a day to work and tracked my milage closely. Like I said I dropped 4 mpg and the only thing differant was the new tires. This was avaraged over months of driving. My old tires were Bridgestone Potenza RE730's and they quit making them of course. ( great tires )The new skins are Goodyear Eagle F1 GS-D3. Like I said that was the ONLY change! Try a new fuel filter, you might just get lucky and it sure can't hurt.

Raoul

I've done as controlled an experiment with the mileage as possible. Filled up the tank, set it up on cruise control at 70mph and ran it 65miles, then pulled off, refilled the tank, and did the math. (the onboard computer in the message center gives me completely inaccurate numbers, so I did it the paper and pencil method)

Sadly, the message center tells me numbers that are too high. So, according to it, I might be getting 26mpg. Then, when I refill the tank I learn that it's thinks I've used almost a full gallon less than I have.

Think the trouble in transmission, I know the torque converter needs to be replaced, could cause that severe a loss of mileage?

driving without cruise uses much less gas than the cruise....the cruise cannot adapt to driving situations, hills, etc, and can't see ahead....it usually gets pretty bad gas mileage.

I get 500 miles a tank when I drive mine on the highway. Maybe 300 highway / city combined. So that's between 29 and 31 highway.

I get about 16.8-17.0 mpg in town, and that's driving normal with very minimal lead footing. and around 22-23 on the highway. I also wish for more MPG. the best I have got is 18 in town and 25 on the highway.


But don't you have higher gears?

And it now appears I have a bad strut rod bushing and the upper balljoint doesn't look very well either. I wonder if replacing them will get me about 5mpg.

But don't you have higher gears?

And it now appears I have a bad strut rod bushing and the upper balljoint doesn't look very well either. I wonder if replacing them will get me about 5mpg.
When I got my car it needed a outer tie rod joint and the opposite upper control arm ball joint. It did not seem to help my gas mileage any :(

Did you scan the car for trouble codes?

Did you scan the car for trouble codes?
The only thing I have been getting from the Cel light that occasionally pops up is Bank1, Bank2 are running lean.

It has a surging idle when it is colder out and sometimes it surges at idle just cause it feels like it? A 1993 Mark VIII came into my friends garage with the same idle problems as I have. So I am waiting to see what the diagnosis is so I can fix mine.

I think I had a slight leak in the lower connector to the fuel filter. The O-rings were dissolved. replaced that.

Replaced the upper control arm (bad ball joint)

Replaced the passenger strut rod bushing.

New wheels and tires. (grand touring tires instead of super high performance)

I think I was was getting 24mpg the other day. The other night I was only getting about 20mpg, but I was in a tropical storm with a headwind.

Next two weeks:
New transmission/torque converter.
New 2.5" exhaust system.

Maybe I'll put new coil packs on it too?

I'd better be at 28-30mpg after all this.

Injectors.

I am thinking that I should replace my injectors. When I sit and idle for a long time my Cell light comes on. When I scan it, it reads lean bank 1, lean bank 2 :confused:

geez cal...all these problems lately, im pritty sure your turning into me!

geez cal...all these problems lately, im pritty sure your turning into me!

Unfortunately, I've got about 110k more miles than you. :D

Unfortunately, I've got about 110k more miles than you. :D


daaaaaamn. well with any luck, ittl be 110k more miles before more strings of problems. :)

on my last long trip, i got 418 miles out of 1 tank of fuel, with 45 miles left to empty on the tripminder.

i am sitting at 114k miles