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gas milage troubles


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16 replies to this topic

#1 myfinalcoffinx

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Posted 16 November 2005 - 04:09 PM

I'll start with a little background:
I used to get around 320 miles per tank (about 26 MPG) and I was quite happy with that. I put a lot of miles on my baby (about 60/day) commuting back and forth from school, work, and home and at the new rate, it's going to cost a LOT more in gas than I can afford. My question is as follows:

Last weekend, I replaced my PCV valve, air filter, both of my fuel filters, and changed my spark plugs (and my ignition coil, but I don't think that has anything to do with this), and changed my oil (every 2000 miles.) I didn't touch anything else, and I'm planning on replacing my O2 sensor in the next week or so. I also checked my tire pressure and its at 38 on all four tires. After doing all of that, I'm down to about 240 miles per tank (about 19 MPG OUCH!) It's going to start cutting into my wallet, and I'm curious about what could have happened to drop my milage so drastically and what I can do about it.

#2 hatchsub

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Posted 16 November 2005 - 04:14 PM

I know its something simple but did you make sure that the ignition coil wire going to the distributor was fully snapped into the coil? I didn't realize that i hadn't done mine all the way cause i heard and felt the snap but it wasn't all the way snapped in. Other than that i got nothing. Im going to let the other guys ponder that one

#3 grossgary

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Posted 16 November 2005 - 04:23 PM

definitely replace the distributor cap and rotor. start with that.

this is a really good thing to check: pull your brake pads and make sure they are wearing evenly. what you want to do is make sure the caliper slide arms are all greased really well. swing the caliper arms up and notice the rubber boots on both ends that the caliper bracket slides on. these boots have the metal rod going through them (don't know the proper names). pull them out and stuff all sort of grease in the boots and all over the slide, then insert it and work it back and forth a bunch of times. wipe away excess grease and don't get it on any rotors or pads. install everything. this makes sure the calipers move in an out very easily and will prevent them from riding against the rotor when you're not braking. most of the 10+ year old subaru brakes i pull are completely bone dry with no grease and dont' operate very smoothly. making it possible for them to constantly drag more than they need to. you probably have rear drum brakes so you'll only have to do this to the fronts.

these previous two items are very important, particularly if you're having a serious drop in mileage.

after that i'd consider having the fuel injectors professionally cleaned, but that is expensive but most old injectors will be dripping.

still having issue - do a compression test and make sure you're not chasing somethign you'll never find. if you have bad compression somewhere then all the tune up and spending in the world won't help unless it's focused in the right place. if you did the plugs yourself you can test compression too. borrow a tester from a friend...autozone has the tool loaner program, they may have those as well.

some will say fuel filter and that's not a terrible idea but i've yet to see one
affect gas mileage even a little. i'd save the money for an extra tank of gas unless you don't know how old it is.

O2 sensor isn't a bad idea, just buy the generic kind and splice it in yourself and save 40 bucks on the OEM plug in kind. never had one of these make a significant difference in mileage either. i've run without them before, disconnected and/or removed with not a ton of effect, though those weren't great running vehicles to begin with in all fairness.

look for a 3.7 final drive transmission, they make for better highway gas mileage.

#4 myfinalcoffinx

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Posted 16 November 2005 - 04:25 PM

I know its something simple but did you make sure that the ignition coil wire going to the distributor was fully snapped into the coil? I didn't realize that i hadn't done mine all the way cause i heard and felt the snap but it wasn't all the way snapped in. Other than that i got nothing. Im going to let the other guys ponder that one


I actually changed the coil out about five tanks ago, and there was no decrease whatsoever, but I did the same thing at first, as well as having two of the plug wires going to the wrong cylinders. Vroomvroom pfut. Thats the noise it made when it fell on it's face for a day or so...

#5 zyewdall

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Posted 16 November 2005 - 04:46 PM

Could you have knocked something wrong on the carbureator when you were in there?

Does it get up to proper operating temperature? Thermostat stuck open, and colder weather is affecting it?

Dunnno. You replaced all the stuff I'd normally say to replace.

#6 robm

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Posted 16 November 2005 - 05:00 PM

Is the choke working properly?

Is the timing set correctly?

Did you change tires (snowies) at the same time?

I just went over to snowies, and lost about 50-100 km/tank. Cold weather, wet roads, and maybe winter gas don't help either.

#7 myfinalcoffinx

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Posted 16 November 2005 - 05:03 PM

grossgary,
Thanks a MILLION for this!

I just changed cap and rotor at the same time as the coil, a couple weeks ago.

Now that I think about it, I'm getting this short squeak (like a little "bark") coming from my brakes in time with my wheel rotating. I hadn't thought anything of it until now, so I"ll get in there and take care of that tonight.

I don't have fuel injectors, but I do have a question about the O2 sensor. I have a hitachi type 1 carb and I'm curious about the diagram. It shows the sensor on the diagram, but does not specifiy where it goes. When replacing the sensor, is it a part on the manifold or carb that I swap out, or is it a part somewhere in the exhaust that sends a signal to the carb? In other words, where exactly is the part that I want to change?

Again, thanks a TON for all of that info!

-Kevin

#8 myfinalcoffinx

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Posted 16 November 2005 - 06:07 PM

I'm not sure where to adjust the choke, so I'll check into that tonight, and the timing is fine...

I haven't gone to snowies yet, but I can't wait until I have to... snowboarding season woo hooooo!

Is the choke working properly?

Is the timing set correctly?

Did you change tires (snowies) at the same time?

I just went over to snowies, and lost about 50-100 km/tank. Cold weather, wet roads, and maybe winter gas don't help either.



#9 myfinalcoffinx

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Posted 16 November 2005 - 06:09 PM

Could you have knocked something wrong on the carbureator when you were in there?


I thought about that, but I wasn't sure what I could have touched. Any ideas would be helpful!

And yes, it is getting up to operating temp.

#10 robm

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Posted 17 November 2005 - 11:10 AM

How about the vacuum advance? Is it connected at both ends, and is it still working? Check that if you suck on the hose, and plug it with your tongue (yes, this does taste bad, but a new, clean vacuum hose helps) the distributor moves, and stays there. Check for leaks and cracks in the hose.

The vacuum line could be connected to either tha manifold or the carb, so that could be what got knocked loose.

#11 Subarian

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Posted 17 November 2005 - 11:39 AM

The O2 sensor is in the Y pipe on the exhaust. But I doubt that's the cause of your problem. If your mileage dropped immediately after the maintenance you described, it's most likely linked to something there. I would look at the following:

1. Are all of the plug wires firmly seated on the plugs and the cap?

2. What plugs did you use? I've seen some cars that would absolutely refuse to run on certain brands of plugs. I like NGK, Denso, or Bosch in my Subaru.

3. It's not really likely you could have done anything in replacing your air filter that would affect mileage, but I would check the hoses on the PCV and make sure they're tight. A vacuum leak can really affect mileage.
BTW, at 2000 miles, you're probably changing oil far more often than you need to, unless you're subjecting your car to really extreme conditions.

#12 myfinalcoffinx

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Posted 17 November 2005 - 12:12 PM

1. Are all of the plug wires firmly seated on the plugs and the cap?

2. What plugs did you use? I've seen some cars that would absolutely refuse to run on certain brands of plugs. I like NGK, Denso, or Bosch in my Subaru.

3. It's not really likely you could have done anything in replacing your air filter that would affect mileage, but I would check the hoses on the PCV and make sure they're tight. A vacuum leak can really affect mileage.
BTW, at 2000 miles, you're probably changing oil far more often than you need to, unless you're subjecting your car to really extreme conditions.


1) Yes

2) I used NGK, the same ones I always get.

3) I'll check that PCV Valve connection tonight

Thanks!
-Kevin

#13 Subarian

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Posted 17 November 2005 - 01:03 PM

One other possibility I thought of. Does the engine miss at all? A friend of mine put new plugs in her Subaru and it wouldn't run right. After troubleshooting it for a while, I determined that one of the new plugs was bad, but it only missed sporadically.

#14 myfinalcoffinx

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Posted 17 November 2005 - 02:06 PM

I actually thought about that, and went ahead and checked, but they all four get sparks.

One other possibility I thought of. Does the engine miss at all? A friend of mine put new plugs in her Subaru and it wouldn't run right. After troubleshooting it for a while, I determined that one of the new plugs was bad, but it only missed sporadically.



#15 oldude

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Posted 17 November 2005 - 05:39 PM

Along the line of the brakes dragging possibly, could the same be said for bearings. Make sure the are greased well. I just bought my 83 Subie and that is one of the things I did for preventitive maint.

Good Luck

#16 Zorrro

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Posted 18 November 2005 - 12:47 AM

grossgary,
Thanks a MILLION for this!


I don't have fuel injectors, but I do have a question about the O2 sensor. I have a hitachi type 1 carb and I'm curious about the diagram. It shows the sensor on the diagram, but does not specifiy where it goes. When replacing the sensor, is it a part on the manifold or carb that I swap out, or is it a part somewhere in the exhaust that sends a signal to the carb? In other words, where exactly is the part that I want to change?



-Kevin


I have the same question. Where is the O2 sensor on these carbed cars? I have wanted to check mine, looked all over the exhaust (like FI) and found nothing. I just assumed I had some bad info......Z

#17 myfinalcoffinx

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Posted 18 November 2005 - 06:09 AM

After further inspection of the manual, only one of the two hitachi carbs had an o2 sensor. I'll check which one, and let you know.

I have the same question. Where is the O2 sensor on these carbed cars? I have wanted to check mine, looked all over the exhaust (like FI) and found nothing. I just assumed I had some bad info......Z






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