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1998 Dodge Neon Erratic fuel millage.

Tiny
GGABRIELG
  • MEMBER
  • 1998 DODGE NEON
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 10,500 MILES
NOT KIDDING - NO CRAZY

Changed timing belt recently. Cleaned computer plugs, cam shaft sensor plugs, New spark plugs, New air filter.

Car runs great after a somewhat sluggish start.
Millage varies from 39.1 mpg (best) to 30 mpg last week, 21 mpg today. May be back up to 35 gpm next week. I am not making jack rabbit starts during these test.

''CHECK ENGINE LIGHT on at times and back off.
I have change 02 sensor (spliced wires - oily) Even unhooked the sensor, the CEL may not even come on. It seems as if the o2 sensor is not even recognized at times.

Remember the fuel millage DOES VARRY under same conditions. NOT THE FUEL GAGE. If it would get poor and stay, then make sense. But the 39.1 mpg came after weeks or months of 20-25 mpg.

How can I find problem? Would ScanII help me diagnose a sensor as I drive?


MAYBE I AM CRAZY. LOL
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Thursday, September 24th, 2009 AT 8:56 PM

8 Replies

Tiny
PEAR69
  • MECHANIC
  • 1,482 POSTS
The varied fuel mileage may be caused by many things. Any scan tool that can observe a sensor as you drive, can help you detect a sensor for failure or faulty function.
Your computer may need to be reflashed. Just like updates to your computer at home, a cars computer needs some "cleaning" sometimes.
All of the things you mentioned will improve your fuel mileage - here are some more -- be steady on and off the throttle, obey the speed limit, use the proper octane rated gas for your engine, change your oil and transmission fluid at the proper service mileage, keep the proper air pressure in the tires, Keep the car properly aligned, do not put ground effects on the car---etc etc. My point is, engine care is not the only factor in fuel mileage.
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Friday, September 25th, 2009 AT 5:56 AM
Tiny
GGABRIELG
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Thanks for the good info, but not all my problems are addressed. What typically would cause the 02 light to come on then go off? It may stay off for a 123 miles, then come on for another 55 to 210. I have not been able to PROVE, the mpg is worse or better with 02 light on/off, since it happens at random. When I say the mpg varies, I mean over a week or so. (Over 35 then less than 22, back to 30 mpg. SAME TIRES, SAME DRIVING HABITS, NOTHING CHANGES EXCEPT MILLAGE.

1- What typically would cause the 02 light to come on then go off?

2- with 105,000 miles could the catalytic converter be bad/stopping up, then clearing?

3- the AC was run 20% of one test of 120 miles. Could this cut millage frm 39 mpg to 21 mpg?

I donated money to start with, now I am ask again.
Wait till problem is fixed, then I donate much better.

Gerald
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Friday, September 25th, 2009 AT 7:01 PM
Tiny
GGABRIELG
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  • 5 POSTS
Been reading bad things about 'reflashing' Oh well, it could not hurt my 98 Neon for sure. Couldn't get much worse. Used to spin FW on take off. No more for several years. Quit trying.

Question on 'flashing' (no porn) >
1- Does this have to be done by a Dodge dealer?
2- Is there a third party fix?
3- What is typical cost?

Still working on 98 Neon DOC Auto - varying mpg calculations.

Gerald
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Friday, September 25th, 2009 AT 7:20 PM
Tiny
PEAR69
  • MECHANIC
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What do you mean by "used to spin FW on take off"?
A trouble code related to the O2 sensor can mean many things. What is the actual code?
Reflashing should be done at a dealer, for the simple reason of, they have the latest updates that can potentialy improve your gas mileage.
O2 sensors detect the amount of oxygen in the exhaust gases. The computer uses this detection to calculate the appropriate amount of fuel to send through the injector. It does this by holding the injector open for a certain amount of time. So, if the O2 sensor is giving incorrect information, or if it is failing, too much (or too little) fuel will be delivered. This could cause an increase in fuel consumption. Further more, if too much fuel is delivered, the cat. Converters will eventually fail because raw fuel kills converters.
As I mentioned before, a scan tool with the capability of observing any sensor in real time will allow you to better understand what is going on with any particular sensor - like the O2 sensors.
The 8:01PM posts:
Q1 - There is no typical or common reason that cause O2 trouble codes. Bad wires, too much(or too little) oxygen in the exhaust, failed cat. Converter, plugged up exhaust, low battery etc etc.
Q2 - With 105000 miles on the engine the cat. Converter could be not performing properly - however, stopping up and then clearing is not common.
Q3 - With 4 cylinders, yes fuel mileage will be hurt with the A/C on - BUT not by 18 mpg.
8:20 post
Q1 - Yes
Q2 - Yes, but they must have the scan tool for it, and the Dodge Dealers do not normally give out the updates to third parties (their way of making you come back).
Q-3 -- Cost will vary depending on where you live and what is wrong.

Be sure to reply to my question on what you mean by "spin FW on take off"
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Saturday, September 26th, 2009 AT 12:24 AM
Tiny
GGABRIELG
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Thaks 'pear69',

Well, not important I guess. PLEASE PARDON MY LONG RESPONSE, but I want to make sure I give a true picture of what I have done.

a) This vehicle would spin the front wheels several feet at the red light. Now, it is very, very sluggish on take off (serveral years now). Once the rpm gets up, it performs very well. I have a cold air intake right into the air filter, through the hood scoop.

b) I can not find my print out now (check engine code) I will get it checked again at Auto Zone. It seams heater bank 1/2 failure, but this should not hurt, once the engine is hot. I forget the other. I have checked the o2 sensor, and even faked a signal 0-1 volt directly into the rear o2 plug going to ECM. No adjustment seem to affect the idle (the sensor produces voltage when heated with torch.

One thing I forgot to mention. Several years ago, when this thing began > low millage, (I had forgot and was not sure for a long time). A friend of mine put a new exhaust gasket on the engine. That is when I first begin to feel the millage dropped the first time. When I finally checked it, 25 mpg or so. It is mostly always 20-28 mpg. and mostly stays low. When I changed the timing belt, I had the battery loose off weeks, I guess. I did clean the computer plugs, and found large amounts of oil on one of them. After I got everything going again, the first millage produced 39.1 mpg. Next time 30 mpg,, Since then it has been going back to 'normal' 25 mpg, mostly.

General info > The reason for changing timing belt was PM. The vehicle had cut off one day when I went to back up. After belt replacement, I checked coil, wires, cleaned ECM plugs, checked position sensors etc, When I got ready to go again, it still had NO FIRE as before. I worked backwards and finally found a fuse to Fuel Pump blown (why I do not know) Never before or after. SIMPLE solution, huh? I did spend hours getting a new belt...

Questions

1) Anything special about changing the exhaust manifold gasket to cause this poor gas millage, ie, new leak, cut wire, gasket on wrong, etc. ?

2) Does the ECM computer have oil inside for any reason? if so, it is leaking out...

By the way. The 'check engine lite' came on yesterday, was on a few miles this morning, and is now off again.

Thanks a bunch for your info, time and patience, so far. If you read all this, you are a GREAT guy. You have stimulated me to keep checking things. There should be some fix for this thing. LIKE ALL PROBLEMs, ONCE FIXED, THE PROBLEM AND SOLUTION WILL SEEM SIMPLE.

Photo result of BROKE neon and having to drive my Dodge Ram truck 12-15 mpg

Gerald


http://www.2carpros.com/forum/automotive_pictures/413523_SCOOTER_1.jpg

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Saturday, September 26th, 2009 AT 9:42 AM
Tiny
GGABRIELG
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The heat shield for the exhaust manifold was never put back on.

C) Is this important?
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Saturday, September 26th, 2009 AT 9:46 AM
Tiny
GGABRIELG
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I just checked millage (gas gauge correct for miles driven). I got it memorized by now. 70.3 miles on 2.075 gallons (All I could get in it on level, same statiion)

33.8 MPG > Light off all the time.

Gerald
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Saturday, September 26th, 2009 AT 5:23 PM
Tiny
PEAR69
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Oh Gerald. In your first post you mentioned that you were not making "jack rabbit starts". If that is so, then how do you know that the front wheels do not spin anymore. LOL. Oh well--anyway--your gas mileage issue should not be so far off, meaning the variation in mileage.
To get a true reading on fuel mileage, fill the tank up at the same pump. Do not "top off the tank". When the pump kicks off -- thats it. Then reset the trip meter to zero. Then drive the car around until the tank is down to -a little less than 1/4 tank. Then fill it up again - at the same pump - the same way and then record the mpg. Also, gasoline expands at different temperatures--why is this important? When you fill your tank, try to do it at the same temperature as it was during the previous fill up. You will get more gas in the tank in the morning (when it is cool) than during the day when it is warmer. Just a little known fact for you.
A leaking exhaust gasket will most definitly hurt fuel mileage, but you would notice a loud sound along with serious mifiring of cylinders.
As far as I know, there is no oil inside of the computer. You may have an oil leak that sprays oil on the computer and then it gets inside of it and messes with the fuel injection signal.
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Sunday, September 27th, 2009 AT 1:21 AM

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