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Really really bad MPG's

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Old Sep 18, 2010 | 04:20 PM
  #1  
92exploder4x4's Avatar
92exploder4x4
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Unhappy Really really bad MPG's

I have been getting really bad mpg's in my '92 Explorer. I have only had it for about a month, so I don't know if it has ever gotten better mileage (I'm sure it did). As of now, I am only averaging between 7 and 10 miles per gallon. I know these things are tanks and don't get great mileage anyway, but I was hoping to get at least 16 out of it.

So far I have replaced the o2 sensor, plugs,wires,air filter, fuel filter (Which BTW was completely clogged, when I would blow into the old filter I would get a blowback ), IAC, I have cleaned the MAF, Seafoamed the vacuum system, and added the rest in the fuel tank to help clean the fuel lines. I also fixed an exhaust leak on my passenger side manifold.

I pulled one of my plugs and it seemed rather oily, maybe it's not getting enough spark??

I am running out of ideas now and could really use some help on what to check for next.
 
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Old Sep 18, 2010 | 06:11 PM
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aquanaut20
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From: BC Canada
Which of the 3 O2 sensors did you change?
What is the STFT and LTFT
Have you done a compression check yet??
 
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Old Sep 18, 2010 | 09:47 PM
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92exploder4x4
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It was the one right before the cat, on the passenger's side. I was unaware there were three.....

And excuse my ignorance, but what is STFT and LTFT?
 
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Old Sep 19, 2010 | 11:35 AM
  #4  
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aquanaut20
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From: BC Canada
Originally Posted by 92exploder4x4
It was the one right before the cat, on the passenger's side. I was unaware there were three.....

There is an O2 for each bank upstream of the CAT, and one O2 post CAT.

And excuse my ignorance, but what is
STFT = Short term fuel trim, this informs of the present fuel management, should follow O2 switching.

and LTFT? = Long term fuel trim, displays the fuel management over a long period, should be less than 10% +/-
Fuel consumption is regulated by the PCM utilizing information from several sensors,. O2 sensor sniff the amount of oxygen in the exhaust gasses prior to the CAT converter, if it reads too much oxygen it will send sig to PCM, which dumps more fuel into the engine to burn off the extra oxygen. It is important to ensure there is no illegal air entering the system, Check the exhaust system prior to the CAT, and the intake system after the MAF for leaks...
 
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Old Sep 21, 2010 | 09:30 PM
  #5  
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llamaking122
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Spark Plug Analysis
here is a guide i use for my sparkplugs
 
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Old Sep 24, 2010 | 06:45 PM
  #6  
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got some more info on my situation. It has now drove 275 miles so far on one tank. Good, so far.

Well, when I was driving home from work the other night, my X was running like crap, and I barely made it, I had no power whatsoever, and every once in a while, it would seem like it would backfire through the air intake. I got home and looked underneath, and my catylitic converter was glowing......

I checked all vac. lines, they seem to be good, and connected to the right places. I pulled the vac. line off the fuel pressure regulator to see if it would dump gas and it didn't. Is it possible that I have a clogged cat and that this has been causing my poor performance probelm the whole time?
 
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Old Sep 29, 2010 | 07:17 PM
  #7  
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chasd
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For what it's worth, when the MPG dropped on my '93, it was due to a dirty mass air flow sensor. cleaned it and the mpg went up to "normal"
 
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Old Sep 30, 2010 | 10:21 AM
  #8  
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KhanTyranitar
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It sounds like you are way overdue to a tuneup, new plugs and wires, replace faulty vacuum lines, etc. Its possible that whatever is causing your crappy gas mileage has clogged our cat, cats don't clog themselves.

If your cat is glowing, you have a misfire/ incomplete combustion. Replace all the plugs with Motorcraft or Autolite double platinum plugs of the proper gap and heat range. Replace the wires with Motorcraft, OE spec Autolite, or Magnacore wires. The coil pack may have issues, if you still have problems, consider replacing the coil pack with either a Motorcraft or MSD one. The Motorcraft is the better of the two.

The MAF may still be toast, they don't always clean up well. Have you run a compression test to determine the health of the engine? You can trow a lot of money at a motor that is just going to run like crap no matter what due to wear.
 
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