Jamesvinar
New member
Well here i am back at 12 mpg. Not sure why, air filter is good, O2 sensors replaced recently, oil changed and i only use what the station says is 93
12 mpg again
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Jamesvinar
New member
Sounds like what im getting, its been in the 40s lately so i havent needed much of a warm up
BlackIceLSC
New member
warm ups waste fuel as it is just sitting at idle so that's a wash.
Clean your MAF
Add seafoam to the fuel tank
replace your fuel filter
and I'm sure you are using defrost or auto which uses the AC compressor.
That plus winter blend = loss of fuel economy. But 12 is an indication something might be wrong. Often times simple maintenance is the best repair. i.e. the fuel filter.
Clean your MAF
Add seafoam to the fuel tank
replace your fuel filter
and I'm sure you are using defrost or auto which uses the AC compressor.
That plus winter blend = loss of fuel economy. But 12 is an indication something might be wrong. Often times simple maintenance is the best repair. i.e. the fuel filter.
MarkVIIIMarc
New member
If you hit reset on your economy while doing a few highway miles do you average something in the 20's?
Last time my mileage took a dip it was a sticking rear caliper. Should be findable by hand (don't burn yourself) if your economy is that bad.
Last time my mileage took a dip it was a sticking rear caliper. Should be findable by hand (don't burn yourself) if your economy is that bad.
Jamesvinar
New member
I get about 28-30 on the highway
Fuel filters the only thing that hasnt been done
Fuel filters the only thing that hasnt been done
MarkVIIIMarc
New member
James, if your car shows 28 mpg on some highway trips I'd be thrilled.
Generally I drive mostly hwy miles and my 230,000 car still shows a 22-23 mpg average.
12 seems lower than I'd expect in all but the most extreme city type driving, but I admit, I start my car and am on the interstate in a mile.
Does your Mark idle nicely? Or have a real sloshy transmission? Do you love launching hard from stop signs? Any performance upgrades?
Hit reset again tomorrow and track the average over the next tank of gas I guess.
Oh, and if you've never changed the fuel filter go ahead and do so. I doubt its the problem but its a good maintenance item to take care of.
Generally I drive mostly hwy miles and my 230,000 car still shows a 22-23 mpg average.
12 seems lower than I'd expect in all but the most extreme city type driving, but I admit, I start my car and am on the interstate in a mile.
Does your Mark idle nicely? Or have a real sloshy transmission? Do you love launching hard from stop signs? Any performance upgrades?
Hit reset again tomorrow and track the average over the next tank of gas I guess.
Oh, and if you've never changed the fuel filter go ahead and do so. I doubt its the problem but its a good maintenance item to take care of.
BlackIceLSC
New member
I've seen restricted fuel filters be the most common cause of poor fuel economy. The car will lack throttle response and power/torque but will hardly be noticed. However, the driver would have to literally "use more gas" to accomplish what used to be accomplished with "less gas". In other words, with low fuel volume, one has to step on the accelerator pedal MORE to accomplish routine driving. Just a thought.
Regardless, it is something always recommended for routine maintenance and to prolong the life of your fuel pump.
Regardless, it is something always recommended for routine maintenance and to prolong the life of your fuel pump.
Jamesvinar
New member
Without the tune it does idle a little rough to be honest, it's about 200 short of the set RPM even with the tune, Trans was rebuilt about 10k miles ago and i made sure to do some upgrades while we were in there to make it shift faster and last longer. I wouldn't say i have any true upgrades the car, mainly small stuff to make it more efficient. I noticed that the average MPG doesn't match the range of it. GPS miles also don't equal what the odometer says.James, if your car shows 28 mpg on some highway trips I'd be thrilled.
Generally I drive mostly hwy miles and my 230,000 car still shows a 22-23 mpg average.
12 seems lower than I'd expect in all but the most extreme city type driving, but I admit, I start my car and am on the interstate in a mile.
Does your Mark idle nicely? Or have a real sloshy transmission? Do you love launching hard from stop signs? Any performance upgrades?
Hit reset again tomorrow and track the average over the next tank of gas I guess.
Oh, and if you've never changed the fuel filter go ahead and do so. I doubt its the problem but its a good maintenance item to take care of.
BlackIceLSC
New member
do you have the right speedo gear installed in the tranny?
when I bought my 4R70W it was from a 98 Mustang. I had a JMOD done, upgraded the reverse servo and the EPC solenoid. I also installed a Mach 1 TC at the same time. The speedo was off by 5 mph due to the Mustang's tooth count on the shaft. I was showing 450 miles to empty and averaging near 28 mpg all the time. I also put more miles on the odometer because of the gear tooth count. my stock 94 was a 3.07 rear gear...I think the Mustang tranny was for a 3.55 but not sure.
when I bought my 4R70W it was from a 98 Mustang. I had a JMOD done, upgraded the reverse servo and the EPC solenoid. I also installed a Mach 1 TC at the same time. The speedo was off by 5 mph due to the Mustang's tooth count on the shaft. I was showing 450 miles to empty and averaging near 28 mpg all the time. I also put more miles on the odometer because of the gear tooth count. my stock 94 was a 3.07 rear gear...I think the Mustang tranny was for a 3.55 but not sure.
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Jamesvinar
New member
My trannys a mix of the original and my old 2003 PI along with the rebuild kit and they were both set for 3.27 rear ends so i think thats good. The guy i bought the car from said it had a 3.73 LSD in it but to be honest never believed him and still dont, sits at about 2k at 70mph
https://youtu.be/h9RhnPjez5o
This was our test for the diff
https://youtu.be/h9RhnPjez5o
This was our test for the diff
MarkVIIIMarc
New member
The fellas may be onto something with the questions. This down to 12 mpg is a new development though, right?Without the tune it does idle a little rough to be honest, it's about 200 short of the set RPM even with the tune, Trans was rebuilt about 10k miles ago and i made sure to do some upgrades while we were in there to make it shift faster and last longer. I wouldn't say i have any true upgrades the car, mainly small stuff to make it more efficient. I noticed that the average MPG doesn't match the range of it. GPS miles also don't equal what the odometer says.
No chance you have a higher stall converter?
Using "manual" numbers like tracking fuel in and miles driven do you know how your economy is?
Also, have you veriied your speedo is correct? Mayne vs gps, but I'd say against a stock car of some sort is as if not more accurate.
What tune are we talking about? I have changed plugs, and IAC motor and two coil overs on my 98 over the last 94,000 miles but nothing like a tune up on my 68.
Jamesvinar
New member
Converter is slightly higher than stock, 2800 i think.
Havent tested yet
Its within 3mph of the gps so im guessing thats standard error.
I got a custom tune from marty at mos speed shop, mpgs were the same as before though but my idle speed is closer to the norm now
Havent tested yet
Its within 3mph of the gps so im guessing thats standard error.
I got a custom tune from marty at mos speed shop, mpgs were the same as before though but my idle speed is closer to the norm now
MarkVIIIMarc
New member
So your MPG's right after the tune were the same 20ish as before but have since gone to 12 with no further modifications....
I'm suspicious if your stall speed makes your economy REAL sensitive to how you are driving and what kind of driving you are doing in our 4,000 lb cars. On the highway your converter acts like the rest of ours. Around town it flares to the motor's power band like you are trying to drag race or don't have a proper cam grind for idle.
A disclaimer is necessary. I despise loose converters on a street car. My old 383 Chevy, and my current 68's 351 W, always get the lowest stall performance converter I could find. I am prejudiced here and my apologies.
I'm suspicious if your stall speed makes your economy REAL sensitive to how you are driving and what kind of driving you are doing in our 4,000 lb cars. On the highway your converter acts like the rest of ours. Around town it flares to the motor's power band like you are trying to drag race or don't have a proper cam grind for idle.
A disclaimer is necessary. I despise loose converters on a street car. My old 383 Chevy, and my current 68's 351 W, always get the lowest stall performance converter I could find. I am prejudiced here and my apologies.