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Poor Gas Milage - Need Help

 
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Old 08 Aug 2013, 07:54 pm
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Default Poor Gas Milage - Need Help

hello,

I am new to this forum. I looks like a lot of good information. I know this topic comes up a lot and I have been reading all the post trying to figure this problem out for the last 3 hours but no luck.

I am a professional diesel mechanic and somewhat know what to check. But I am having big time problems with this. I just bought my wife a 2003 PT Cruiser non turbo Touring edition 140,00 miles. This car runs good, with no active or pending codes. it is getting 17.5 mpg on the highway. Driving speed is 70 mph at the most. Very, very easy take offs. after the 1st tank I started checking out some things. I found the spark plug were horrible. wasnt much left of them. The gap was about well over double of what is should have been. I just knew I found the problem. So i change the plug wires to along with the pcv valve, since I broke it, and added injector cleaner. But no change at all. I checked out the Cat and it seems to be ok. its about 200 degrees diffrence between front and rear of the the cat. Tires are inflated correctly. Air filter is clean. This car is getting about 50 miles per 1/4 tank. You can almost watch the needle fall. I have figured out the mpg the proper way by dividing the miles driven by the gallons used. I fill up at the same pump at the same station.

Is there anything I am missing? I cant find any vacuum leaks anywhere, no sparks jumping from the coil. I see people talking about reseting the computer, is that something that may work? as i am typing this the battery is disconected.

Thanks for any help.
Eric
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Old 08 Aug 2013, 08:05 pm
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Default Re: Poor Gas Milage - Need Help

The more ethanol in your fuel the worse gas mileage will be. I read once that someone replaced the map sensor. Even though it was operating within speck. They reported that this help with there gas mileage.
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Old 08 Aug 2013, 10:22 pm
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Question Re: Poor Gas Milage - Need Help

Have you tried attaching a magnetizer like 'The Fuel Boss' to the fuel line to help re-arrange the positive & negative fuel molecules????......Or a vortex generator like the 'Tornado' to help increase centrifugal air flow to the throttle body???? Looking For A Miracle: We Test Automotive 'Fuel Savers' - Popular Mechanics By the way,in case you haven't figured it out by now....I'm just kidding;Don't kill me Danny....lol
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Old 09 Aug 2013, 06:37 am
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Default Re: Poor Gas Milage - Need Help

ehs; run tire pressure 2 psi above door sticker --- temp gage should stay at halfway after warm-up --- if an auto trans, 65 mph = 2500 rpm , and should stay there to about half throttle [this tells you your in overdrive and the convertor is locked up --- check for unusual tire wear --- check for brake drag --- check engine codes --- check for intake manifold leak at the horizontal flange surface --- smooth idle? --- check timing marks on timing belt --- change #1 o2 sensor [on the exhaust manifold] --- change [or check] map sensor only if o2 sensor didn't help.

You should get 25 mpg on the highway. Over 70 mph sucks gas.

Let us know how things turn out!!!
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Old 09 Aug 2013, 10:43 am
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Default Re: Poor Gas Milage - Need Help

I recently started driving my pt, so what I did. I Run the PSI at 40 on each tire, and I notice that when you drive above 65MPH you get less MPG.

run your tires at 40 PSI and try for one week, see if you notice a difference

ps- what kind of gas are you using? Because it makes a difference.
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Old 09 Aug 2013, 06:10 pm
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Default Re: Poor Gas Milage - Need Help

Exhaust manifold cracks will do this, and they do crack.
I'm sure as a mechanic you're familiar with how a crack upstream O2 sensor will cause it to think engine is lean;

and puke in fuel!!

Here's my latest find, I scrap LOTS of Cruisers, and near everyone has a broke manifold (not usually THIS bad!!!)
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Old 10 Aug 2013, 02:57 am
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Default Re: Poor Gas Milage - Need Help

Quote:
Originally Posted by Busted_PT View Post
The more ethanol in your fuel the worse gas mileage will be. I read once that someone replaced the map sensor. Even though it was operating within speck. They reported that this help with there gas mileage.
I resemble that remark!
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Old 10 Aug 2013, 04:35 am
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Default Re: Poor Gas Milage - Need Help

This test is kind of a PITA on a PT because the heat shields have to be removed but to check for exhaust manifold leaks...with the engine cold, set up a shop vac as a blower and hook it to the tailpipe and thus pressurize the exhaust system...spray soap solution on the manifold and look for bubbles.
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Old 10 Aug 2013, 08:56 am
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Default Re: Poor Gas Milage - Need Help

There is a lot of helpful information you all have shared. as soon as it quits raining here I will check some of this out. Should I replace the O2 sensors or map sensor without having any codes for them? also the sticker on the door says the tire pressure should be 34 psi. my tires on the car says 44 psi and that is the psi that I am using. i am using 87 octane gas. that is correct for this car? the idle is smooth.

thanks again for the help and ill get back with my results soon.
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Old 11 Aug 2013, 03:29 am
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Default Re: Poor Gas Milage - Need Help

An O2 sensor can get "lazy" and not cause a code. A defective upstream O2 sensor will cause poor gas mileage.
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