Poor Gas Mileage

GMAN

GMAN

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Lately, I've noticed that by the time I've reach half a tank, I've only driven 100 miles. If I drive it all the way down to about 5miles until empty, I will have reach 260 miles. What can I do to get the mileage up? Has anyone ever experienced anything similar?
 
my first response to gas mileage problems like this is to say Oxygen sensors.
have they been replaced anytime recently?

there are other things to cause this,but i point to thm first when its such a big drop on mpg.

what did you used to get?
 
average about 260-280mpg, and I run it down to under a gallon. Is that low? What does everyone else average?
 
You shouldnt run the car that low on fuel.

Reason being, our fuel pumps are cooled by the gasoline in the tank, and when the gas is low, the pump isnt being cooled properly. Just to give you an idea, you have to drop the exhaust and the gas tank to replace the pump, so you want to avoid undue wear on the pump because its not a fun repair.

Back to GMAN -- Check all the basics. Plugs, wires, air filter, fuel filter, etc.

O2 sensors are a good idea. If they are around 100k, just replace them since you'll have to before long anyway. Thats a good start...
 
Joeychgo said:
You shouldnt run the car that low on fuel.

Reason being, our fuel pumps are cooled by the gasoline in the tank, and when the gas is low, the pump isnt being cooled properly.

Just to give you an idea, you have to drop the exhaust and the gas tank to replace the pump, so you want to avoid undue wear on the pump because its not a fun repair....
Click to expand...

Joey is correct!
I used to run my car low on fuel in hopes that the weight savings would drop my ET.
The only thing it dropped was the life of my fuel pump and the subsequent dropping of the exhaust and Fuel tank.. {not a fun job, but really not that difficult}
My first pump died at 150,000 miles... 150,000 miles later I swapped the pump out again with a 255 Walboro.
Since the first one died at 150,000.. I decided to change it out pre-emptively rather than wait for it to die.. and leave me stranded.

FWIW: My ET's have steadlily dropped since I've began to run the car with a "FULL TANK", rather than running on fumes.
The car is alot happier with a full fuel load as well!

Sorry for the off topic NOVEL!

Back to the topic.
I'd suggest 02 sensors as well... and whatever you do.. USE THE MOTORCRAFT 02's rather than saving a couple of bucks on the bosch 02's.

I got scolded by my mechanic friend for getting the bosch 02's and after replacing them both.. I STILL have an 02 sensor CEL {kicks stuff around}
I'm preparing to "RECHANGE" the 02's with the motorcraft 02's.

I hope some of this helps
tommy
 
There is no way your car will run better ET's with a full tank compared to less than 3 gallons in the tank. The weight difference is substantial, you can even feel the car being heavier with a full tank compared to an almost empty tank. However, this is bad for the fuel pump since the fuel cools down the pump.
 
Joeychgo said:
You shouldnt run the car that low on fuel.

Reason being, our fuel pumps are cooled by the gasoline in the tank, and when the gas is low, the pump isnt being cooled properly. Just to give you an idea, you have to drop the exhaust and the gas tank to replace the pump, so you want to avoid undue wear on the pump because its not a fun repair.
Click to expand...

If there is gasoline enough to run the motor, there is gasoline enough to cool the lines. Though i would think .5 gal would be kinda pushin it.

XLRVIII said:
My first pump died at 150,000 miles... 150,000 miles later I swapped the pump out again with a 255 Walboro.
Click to expand...

Lol, 150K is quite normal for a fuel pump.

GMAN said:
Thanks, I think I will start with replacing the O2 sensors first.
Click to expand...

Id start there definatly. Also, to save yourself some agrivation and or money, pull the codes first, if its starting to go it could have thrown a code by now. if it has, you know it is definatly that.
XLRVIII said:
Back to the topic.
I'd suggest 02 sensors as well... and whatever you do.. USE THE MOTORCRAFT 02's rather than saving a couple of bucks on the bosch 02's.

I got scolded by my mechanic friend for getting the bosch 02's and after replacing them both.. I STILL have an 02 sensor CEL {kicks stuff around}
I'm preparing to "RECHANGE" the 02's with the motorcraft 02's.
Click to expand...

Amen to that, I dont know what the specific diffrences are between the two, but when i did mine a while back i put the bosch in, one week later, they failed, and i went with motorcrap ones.
 
Hey Mr. Wilson...........

Not to hijack the thread, but Mr. Wilson, I had a 77 TA with a 400 under the hood. Definately a very fun car to drive. For some reason that I just can not fathom, the car seemed to be sideways most of the time.

I do agree with Joey that there needs to be a couple of gallons of fuel in the tank to keep the pump cool. It is not the lines thatyou are trying to cool, but the pump itself. And I believe if memory serves me correctly, that the pump starts to become uncovered with about 2 - 2 1/2 gallons. My BMW's were always the same. I learned that lesson the hard way.

As for the ET's coming down with more fuel in the car, it is possible to get lower ET's with more weight if that extra weight gives better traction, which in this case, fuel weight over the back wheels will definately do.
 
bufordtpisser said:
Not to hijack the thread, but Mr. Wilson, I had a 77 TA with a 400 under the hood. Definately a very fun car to drive. For some reason that I just can not fathom, the car seemed to be sideways most of the time.

I do agree with Joey that there needs to be a couple of gallons of fuel in the tank to keep the pump cool. It is not the lines thatyou are trying to cool, but the pump itself. And I believe if memory serves me correctly, that the pump starts to become uncovered with about 2 - 2 1/2 gallons. My BMW's were always the same. I learned that lesson the hard way.

As for the ET's coming down with more fuel in the car, it is possible to get lower ET's with more weight if that extra weight gives better traction, which in this case, fuel weight over the back wheels will definately do.
Click to expand...

You are right on the money buford.

I wish i could find a good deal on a 77 or 78, they are my FAVORITES of the second gen. I may end up cloning it.
 
95LSC32V said:
There is no way your car will run better ET's with a full tank compared to less than 3 gallons in the tank. The weight difference is substantial, you can even feel the car being heavier with a full tank compared to an almost empty tank. However, this is bad for the fuel pump since the fuel cools down the pump.
Click to expand...

I wasn't speculating, the 5000+ timeslips that I have do not lie.

My best pass ever to date was ran in "bracket racing trim"
IE, Full tank of gas, leaving from 1000 rpms. vrs 3-5 gallons and leaving "off idle".

My best 60' foot was also on a full tank of gas.

When I was shooting for low ET and running 3-5 gallons of gas, my best 60' was 2.15

After I gave up the quest for low et and focused on consistancy I got my best 60' a 2.10 and my lowest ET as well.. 9.31 in the 1/8th mile.

I understand how some might think "it doesnt make sense", but more often than not.. reality, doesnt make sense.
 
I get about 14.5 mpg. All "city" driving. I got this car in November, and it has only been on the highway 3 times since then.
 
I think the O2s are like 60 to 80 a piece. Don't quote me on that though. I get about 13-14 in the city and 23-24 highway doing 80.
 
GMAN said:
Lately, I've noticed that by the time I've reach half a tank, I've only driven 100 miles. If I drive it all the way down to about 5miles until empty, I will have reach 260 miles. What can I do to get the mileage up? Has anyone ever experienced anything similar?
Click to expand...

OK everyone, I am reviving this thread. I just took my Mark to my mechanic to have the codes checked. I've been seeing my check enging light come on while I was sitting still idiling. The diagnostic came back lean fuel bank 1 and bank 2. My mechanic said sounds like the fuel pump is going out. I believe this could be why my mileage has gone down so much. The other problem it came up with was the Variable Relay Control Module. Has anyone experienced these problems? I figure the fuel pump is the most difficult. I understand the tank has to be dropped?

Thanks..
 
If the VCRM is bad your electric fan will not be working... sorry I can't help anymore over the internet. Changing the fuel pump isn't that hard but make sure you don't have a lot of fuel in the tank...
 
Not seen the VCRM fail. You would really see an issue in the summer- no cooling fan.

Fuel pumps are not too bad but require extra caution due to vapors and such. I cut an access panel in the trunk pan of my Grand Marque to gain access - was easier than dropping a full tank of gas and I didnt have to jack the car up on a gravel lot where the car died.

I had been under the car before and knew where to cut without hitting lines and such. I saved $300 by doing it myself, but looking back If I could afford to I would have it done by a pro.
 
VCRM {variable control relay module} contains the relays for the electric fan, the high and low speed fuel pump and alot of other "Crap" that shouldn't be bundled into ONE MODULE.

But a bad VCRM will create/cause a whole host of problems.
I'd suggest replacing the VCRM before you dive into the fuel pump.

I've seen 3-4 of them fail
once we lost all "injector signal"...we changed the vcrm.. and WALA, the car started
once we lost the cooling fan.. we changed the vcrm POOF.. the fan works.

when my fuel pump died at 150,000 miles... we changed the vcrm.. and (Buzzer sounds) it didn't fix the problem, BUT.. it was far easier than pulling the tank.. so we tried the VCRM first, then we dropped the tank {grins}

I cant remember all the things that go on inside that box, but I do know it plays a role in "injector firing", cooling fan control, and the dual speed fuel pump.
way TOO much stuff.. depending on a single module.

But.. I guess the entire CAR depends on a single battery so my opinion might be clouded.

your mechanic is probably right about a weak fuel pump though.. depending on the mileage on your car.
My first pump died at 150,000 miles.

I hope some of this helps

Tommy
 
If it turns out to be the fuel pump, I wouldn't suggest buying one from a local parts store.. they are prohibitively EXPENSIVE.

when mine died I had little choice because my car was stranded at the dragstrip.. so I bought the entire pump assembly from pep boys, to the tune of 329.00!!!!!!
I didn't know what to expect, so I bought ALL OF IT.

After the fact, After performing the job I realized that I could have replaced "JUST THE PUMP" and not the entire assembly.. BUT..
No-one had "just the pump".

150,000 miles after I changed the pump I "changed the pump" again, in a pre-emptive attempt to "not get stranded again".
BUT.. rather than paying WAY TO MUCH for a BS stock pump.
I got the 255lph walboro pump from www.50resto.com for right AT 109.00.

Changing "just the pump" is the hot ticket!!!!

Just FYI... I hope my spending WAY TO MUCH money will prevent you from making the same mistake that "I" did.
 
correction.. in my ford service CD they refer to that module as VLCM {variable LOAD control module}

pin 1 ground (wire color BK)
pin 2 cooling fan motor (Wire Color LB)
pin 3 cooling fan motor (LB)
pin 4 BATT - fan and AC (Y)
pin 5 BATT - fan and AC (Y)
pin 6 BATT - for fuel pump (Y)
pin 7 Power to fuel pump {low speed} (PK/BK)
pin 10 High Speed fuel pump relay output (BR/W)
no pin 11
pin 12 Fuel pump input (LB/O)
no pin 13
pin 15 Vehicle power (R)
pin 16 Ground (BK/W)
no pin 17 (P)
pin 18 power to AC clutch
no pin 19 or 20
pin 21 SCP(+) (T/O) dunno what color "T" is?
pin 22 Ground(BK/W)
pin 29 SCP(-) (PK/LB)
 
I bought my Fuel Pump from http://www.jdsperformance.com/index.asp
$95 shipped to my door. He is interested in becoming a vendor on the site.

Very pleased with the pump.

The pump is not hard to replace. Just a little time consuming.

You have to drop you pipes and your tank.

Make sure you have run most of your gas out of the tank before you drop the tank as it will be much easier to handle the tank.

All you need are good jack stands and a good jack to help lower the tank.
 
mespock said:
Make sure you have run most of your gas out of the tank before you drop the tank as it will be much easier to handle the tank.

All you need are good jack stands and a good jack to help lower the tank.
Click to expand...

No wiser words were ever spoken...
 
I am going to go with the VRCM first. Any idea how much these cost new? I am a little weary going to the junk yard, since I don't know what I'm going to get.
 
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