SN95 Mustang 1994-2004 Mustangs Member Tech & Restoration Discussion

Terrible, Terrible Mileage

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Old 1/19/13, 12:43 PM
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Terrible, Terrible Mileage

In the past couple of tanks I have been getting about 15-16 mpg down from 19-20... Last tank I got 180 miles...

At idle it almost sounds like there is a backfire every once in a while. I pulled a couple plugs and noticed there was a white residue on them after only about a year of having them in since my head gasket was changed. I read that it could be a clogged air filter, and the guy at the parts store said that I should check vacuum lines.

Where are all the vacuum lines? Is there a way to test the plastic ones, or do I just have to listen to them and see if I can hear anything? Do you guys have any other things I should look for?

Thanks in advance.
Old 1/19/13, 01:16 PM
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Clean air filter, change oil, check tires.
Old 1/19/13, 01:30 PM
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Originally Posted by Getportfolio
Clean air filter, change oil, check tires.
1. Will do.

2. Did 2 days ago.

3. All four are at 33psi.
Old 1/19/13, 02:35 PM
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Originally Posted by cntchds
In the past couple of tanks I have been getting about 15-16 mpg down from 19-20... Last tank I got 180 miles...

At idle it almost sounds like there is a backfire every once in a while. I pulled a couple plugs and noticed there was a white residue on them after only about a year of having them in since my head gasket was changed. I read that it could be a clogged air filter, and the guy at the parts store said that I should check vacuum lines.

Where are all the vacuum lines? Is there a way to test the plastic ones, or do I just have to listen to them and see if I can hear anything? Do you guys have any other things I should look for?

Thanks in advance.
You can take a can of starting fluid and spray a little at a time around the vacuum lines to see if you have a leak. If the engine speeds up when you spray it around a certain one, its leaking and pulling in the starting fluid.
Old 1/19/13, 02:48 PM
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This might be a very dumb question, but wouldn't a vacuum leak like that make it run more lean since it would be pulling in more air than expected?
Old 1/19/13, 03:20 PM
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Originally Posted by Rather B.Blown
You can take a can of starting fluid and spray a little at a time around the vacuum lines to see if you have a leak. If the engine speeds up when you spray it around a certain one, its leaking and pulling in the starting fluid.
Good trick.
Old 1/19/13, 06:35 PM
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Jack up the rear end then put your car in n and see how easy the rear wheels turn. Engine off of course. I had a rear caliper hanging up and after I fixed that my MPG's increased. just a thought
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