fuel economy Fixs

Soul Shinobi · Post by **Soul Shinobi** » Thu Aug 13, 2009 5:02 pm

Good questions. I get 21 city 28 highway with an average of just 23-24. Funny thing is, I think the cat on my '92 is stock, and I've never measured compression.

I've replaced plugs, wires, filters, PCV, seafoamed the car, rebuilt 3 brake calipers, put synthetic in the rear diff, Extra-S in the tranny, and full synthetic in the engine.

Mods: grounding mod, mudflaps removed, antenna retracted, dead panel where fog light would be removed on the right side, as well as the top weatherstripping on the right corner light to allow higher pressure air to enter the fender where the air pickup is, junk removed from the trunk.

I suspect I have an exhaust leak, and could probably use an O2 badly.

suba · Post by **suba** » Sat Aug 15, 2009 1:42 am

Spent some time today talking with the local parts guy at the dealer and found out that his son's 1992 wagon (NA 5spd) gets about 27 highway and his 95 gets 28. His thought was that I should start with the muffler, his thinking is that it could be messing with the scavenging of the exhaust in turn causing excess back pressure.

I'm not so sure that a bad muffler would have much of an impact on scavenging, however if it had internally collapsed a bit I could see that being a problem. Since the muffler is shot anyway I figure that will be my next plan of action. I did some seafoam on it to check for exhaust leaks and found that I have a completely sealed exhaust system...and a very very bad muffler.

Also, I started rechecking the records and it seems like the last fuel filter change that I have a record of is about 40k miles ago, so I think that will also get changed just for peace of mind. Additionally I can't find a record of when the last wire's were installed so that will probobly also be done, using oem wires.

I see two more potential areas for problems: One being a clogged cat, which right now I don't really have the time or money to look in to, and the second being the O2 sensor. I just replaced it about 1k miles ago (the old one being very bad) with a walker oem (plug already on) replacement. Fuel mileage at that time didn't change, but the car runs exponentially better.

Plan of action:

Replace muffler (tommorow's plan)
Replace fuel filter
Replace Wires

Potential other problems (engine related):

Walker O2 sensor
Clogged cat

Boostedballs · Post by **Boostedballs** » Sun Aug 16, 2009 8:32 pm

I get around 28mpg hwy and about 22mpg in the city. I'm on the boost very often and I like pealing away from traffic when the light turns green.

I have replaced plugs and plug wires with ngk and msd.
k&n filter (lightly oiled)
replaced knock sensor
installed 3" exhaust w/ racing cat
water/meth injection (usually just -20deg windshield washer fluid) @ 150psi
water to air intercooler
nitrous- this does NOT help fuel economy...

I have 170k miles on my 91SS

Soul Shinobi · Post by **Soul Shinobi** » Sun Aug 16, 2009 9:46 pm

I did the nice NGK wires too. I've heard good things about those MSD coils, aren't they the model for a Dodge Neon since they don't make one for our cars? Know what model number(s)?

Boostedballs · Post by **Boostedballs** » Sun Aug 30, 2009 7:38 pm

Soul Shinobi wrote:I did the nice NGK wires too. I've heard good things about those MSD coils, aren't they the model for a Dodge Neon since they don't make one for our cars? Know what model number(s)?

I'm running stock coils, I just have NGK plugs and MSD wires. My plug gaps are set to .030, very narrow I know. I did that as part of troubleshooting a misfire I was having a while back. It runs very strong at .030 with a 70hp shot of nitrous at 11psi.

170,000 or so miles on the ticker

suba · Post by **suba** » Wed Sep 09, 2009 8:55 pm

Update: after finding one of my calipers to be a bit sticky I replaced both fronts with rebuilt calipers. Result: No noticable change. Fuel mileage did not increase more than a few tenths, however I have noticed that stopping at some stoplights in town that formerly I thought were on level ground the car will roll slowly, so I definitely had a little bit of drag going on.

At this point I suspect one of two possibilities: Either my O2 sensor is not cooperating (Since it is a walker brand) or I possibly have a slight exhaust leak before the sensor. Any other theories?

Soul Shinobi · Post by **Soul Shinobi** » Thu Sep 10, 2009 2:12 am

Anything you missed, looking back at the long lists we made?

EDIT: wheel bearings are the only thing I can think of to add.

suba · Post by **suba** » Thu Sep 10, 2009 7:16 am

Which reminds me, whats the best method for checking wheel bearings. I've heard to raise the wheel and check for any movement in the bearing by pushing and pulling on the wheel, any better methods?

Soul Shinobi · Post by **Soul Shinobi** » Thu Sep 10, 2009 8:08 am

They could just be worn but not 'bad'. Also they can be bad, but not have play. Not sure if there's a better method to test, other than just jacking up that end of the car and seeing how easily you can spin the wheel by hand (the wheel on the other side will spin too of course).

Buffman · Post by **Buffman** » Thu Sep 10, 2009 4:28 pm

I'm avergaing around 24mpg right now even with the dumb thing running rich on heavy throttle. Cable is supposed to be here this weekend so I can make some logs. It let black smoke off even when I had the KS unplugged and carefully checked for knock/ping before laying into it. I keep getting a code for the camshaft sensor when it doesn't want to start, but I wouldn't think the CamS would effect fuel economy..

I did a timing belt and new tensioner (main issue) and gained around 1.25mpg.

suba · Post by **suba** » Thu Sep 10, 2009 4:52 pm

hmm, so lets say I have the front end of the car in the air, rear wheels on the ground. If I can turn the wheels,but they don't "spin" as in if i give them a good twist and after I let go they just stop after a few degrees of rotation, is this normal or abnormal?

Soul Shinobi · Post by **Soul Shinobi** » Thu Sep 10, 2009 5:07 pm

I just went into the garage and played with my '92 to get an idea. I've never done this with a new Subaru so I don't know what its supposed to ideally feel like. Mechanical drag of the differential seems to prevent free-spinning. You can rotate the wheel back and fourth a couple of degrees relatively easily, that's free-play in the axles and differential. Within that free-play it should feel as though it could free-spin for several rotations with the flick of a wrist. If not, like on my '92, you can feel pretty clearly if the brakes are dragging (I could hear the pads on the disk). Evaluating the wheel bearings or axle joints is a bit difficult, especially if the brakes are dragging.

I admit I'm speculating a bit, using common sense. I don't know if there's a similar 'professional' technique for checking these things.

mexicanzero · Post by **mexicanzero** » Fri Sep 11, 2009 12:40 am

the "professional" way of checking a wheel bearing is to take it up to highway speed and check for noise (humming noise usually) and in the air there should be no play what so ever of the wheel side to side up or down back and forth or any way, if there is then check closely to see where it is coming from (bj, tie rod, wheel bearing etc.)

for axles or cv shafts as i call them make sure neither of the rubber boots are torn, if they're cracked replace the boot before its torn if its torn replace the whole shaft because even if its not making noise now it WILL 95% of the time a few weeks down the road as dirt has already gotten in and will act like sand paper wearing down the balls/sockets etc.. to check them for noise turn the wheel all the way to one side and slowlyish drive in a circle if theres clicking or grinding ish type noise or if it feels like its binding when the wheel is turned all the way theres a very good chance its the cv joint
this can also be checked in the air again with the wheel turned all the way to one side (and then the other) if its not as smooth or quiet as with the wheel centered then thers an issue.

at least this is the way i check them and its never done me wrong, i'm an apprentice in an auto shop.

in both cases i HIGHLY doubt a wheel bearing or an axle would cause big enough of an issue to affect gas mileage. if theyre bad you'll know it and they should be replaced, if not then leave them be.

hope i helped someone
-Alex

smh0101 · Post by **smh0101** » Fri Sep 11, 2009 5:26 am

I shall refrain from making mileage comments as my car is a freak of nature and getting occasional insane mileage on a built motor when hwy driving.

LOL

roundeye · Post by **roundeye** » Fri Sep 11, 2009 5:52 am

unless a wheel bearing or cv is incredibly worn and grinding, it wont cost you any mileage. new ones would have more drag. if they're quiet and tight, i wouldnt worry about them. if it will rev beyond 4k, a restricted exhaust isn't likely. maybe a bad injector? have you done a power balance test? injector leakdown? both are pretty easy, and can tell you a lot.

suba · Post by **suba** » Fri Sep 11, 2009 6:26 am

Well, the wheel bearing was a shot in the dark, I've had bad wheel bearings before and road noise is not an issue with this car (depending how you rate idaho pavement...). The front end on this car is tight and issue free, haven't checked the back but a quick feel test of the rotors the other day says that I don't have any rear brake drag.

Engine revs smooth, so at this point I would agree that restricted exhaust is unlikely.

Not entirely sure what a power balance test is...

Leaky injector is slightly suspect, I've been having the occasional misfire/stumble at idle lately that would indicate a sticky or leaky injector, but could also mean a leaky intake area gasket or vacuum connection (though nothing has been found yet). I should do an injector leakdown test soon here to verify for sure.

Soul Shinobi · Post by **Soul Shinobi** » Fri Sep 11, 2009 6:39 am

Exhaust restriction would likely cause hard starting above all else (I think). Have you cleaned your IAC (Idle Air Control valve) lately? More-or-less, pour some seafoam into it; even Subaru recommends that procedure.

roundeye · Post by **roundeye** » Fri Sep 11, 2009 3:43 pm

power balance tests what each cyl. is contributing- you disable one at a time, by unplugging injector, and see what rpm drops to. if it drops less with one particular cyl. disabled, that one's weak. could be compression/ valves/ ignition/ fuel or whatever, but points you in the (hopefully) right direction. you need an accurate tach, like on the scantool, or one you can hook to a plug wire.

suba · Post by **suba** » Fri Sep 11, 2009 11:38 pm

I do have a digital tach/timing light that should work as well as a scan tool that I can run. I'll try to get to that tomorrow if I can and see what that tells me.

jefferson · Post by **jefferson** » Sat Sep 12, 2009 4:40 am

I will just say that putting a downpipe with a new cat gave me my biggest mileage increase of anything I have done. I have always heard of high mileage cats being a problem when it comes to mpg. It sure helped mine.
My brother picked up mileage in his Dakota when he replaced his and my sons Ranger did the same when we had to replace it to pass inspection. My other son had his cut out of his Accord. Eventually he decided he didn't like the way it sounded and he put a new cat back in. the car ran better and got better mileage than without the cat. Food for thought.

Soul Shinobi · Post by **Soul Shinobi** » Sat Sep 12, 2009 4:45 am

A degraded cat can certainly be very restrictive, just keep in mind that aftermarket cats never last as long as the OEM ones, cheaper ones needing replacement after 50,000 miles.

suba · Post by **suba** » Sun Sep 27, 2009 1:11 am

Well I did the power balance test. No noticeable difference in rpm drop between cylinders, which I would take to mean that there is no sticking or excessively leaky injectors.

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fuel economy Fixs