fuel economy Fixs

yazmo · Post by **yazmo** » Fri Jul 24, 2009 12:21 am

wow josh your really a good source of information geez impresive

mexicanzero · Post by **mexicanzero** » Wed Jul 29, 2009 3:53 pm

for freeing up your exhaust if you dont have emissions tests then yeah get rid of the cats and go 3" turbo back and if you need to have a cat get e high flowing one

for the intake you can start by doing the snorkus removal (all the piping in the passenger side fender) drop in a k&n filter and do the coffee cup mod (replacing the muffle like thing between the airbox and the turbo with a straight pipe. in the future you can fab up a cold air intake if you feel like it.

msd is a pretty well known ignition component company. they dont make stuff for subarus but they make a coil for neons that works perfectly and is cheap! you do need to get the connector that plugs into the coil off a neon and splice it into the stock wiring and you will need plug wires off an imprezza or something with female ends on the wire to fit on the male ends of the msd coil. or you can just crimp the ends of the stock wire with pliers and squeeze them on it worked for me before i found the right wires. let me knoe if you want more details i'll have to dig up my past to find numbers for you.

-Alex

suba · Post by **suba** » Wed Aug 05, 2009 4:47 am

In search of both fuel mileage as well as engine smoothness I've done the following:

new O2 (old one was DEAD), new air filter, new plugs (old, but mostly just WAY out of tolerance), clean MAF, oil change, trans change to subaru synthetic (5mt), diff change, pcv valve.

The result was so so, the engine runs much smoother, more like when we bought it but gas mileage didn't change, still getting 22 to 24 (but never higher) on the highway. The car is N/A with 200K and yakima racks on the top. I didn't expect much of a change, but at least something would have been nice.

One thing we have done recently was start using 89 octane, the car has a little excess oil usage which seems to have been inducing some knock from oil vapor which the higher octane seems to have cured. Power and smoothness increased noticeably but again, no fuel mileage change.

The one thing I'm curious about is the temp sensor, anyone change just this sensor, and what result did you have? Also, anybody test it before they changed it?

Soul Shinobi · Post by **Soul Shinobi** » Wed Aug 05, 2009 4:56 am

If you're having knocking you may have a clogged fuel filter (they're easy to replace and can help economy if fuel flow is poor), a dying fuel pump (test pressure/flow), and/or excessive carbon build in the cylinders (SeaFoam it). The car may also be knocking from running too hot, not just too lean, maybe a coolant temp sensor's not a bad idea, I have heard about worn ones causing issues in these forums before; there are two, you only need to replace the digital one (has the electrical connector).

How do you like the transmission fluid? A lot of us have poor shifting and sometimes a good fluid can help.

Also, after drastic changes you should reset the ECU.

kimokalihi · Post by **kimokalihi** » Wed Aug 05, 2009 11:57 am

suba wrote: The result was so so, the engine runs much smoother, more like when we bought it but gas mileage didn't change, still getting 22 to 24 (but never higher) on the highway. The car is N/A with 200K and yakima racks on the top. I didn't expect much of a change, but at least something would have been nice.

One thing we have done recently was start using 89 octane, the car has a little excess oil usage which seems to have been inducing some knock from oil vapor which the higher octane seems to have cured. Power and smoothness increased noticeably but again, no fuel mileage change.

Only 22-24? Are you putting your foot in it frequently? Last time I filled up my 90 L wagon AWD 4EAT and calculated the fuel economy it was 27.5! That's with the automatic(from a 94L).

I thought if you ran higher octane fuel than it takes it will cause your engine to knock and change your timing causing you to get worse MPG.

evolutionmovement · Post by **evolutionmovement** » Wed Aug 05, 2009 2:20 pm

No. Higher octane resists knocking. Putting a higher grade than necessary just wastes money. A lower grade might cause knock and trigger timing retard.

kimokalihi · Post by **kimokalihi** » Wed Aug 05, 2009 2:34 pm

Man, I swear I read an article on octane grades and timing and how you shouldn't run higher octane than your car is supposed to use. I know it said that it would give you less performance and cost you more.

Buffman · Post by **Buffman** » Wed Aug 05, 2009 2:51 pm

it will just cost you more and offer no real gains unless you have pinging knock using the lower grade..

I'm still averaging around 23-24mpg on my 92. it's up almost a solid 2mpg from changing the T-belt and T-belt tensioner pulley. I'm hoping once I can figure out whether the igniter or the camshaft sensor is causing the no-start and rich on heavy load issue, it will improve.

I did take a two hour trip with it, 95% highway and I got 27.7mpg. I've yet to re-check the compression but when I first bought it all cylinders were at 185, save for the rear driver's at 165 ish. No headgasket leak, so the rings must be worn.

suba · Post by **suba** » Wed Aug 05, 2009 4:16 pm

The Transmission fluid is amazing, I definitely wouldn't run anything else. It only comes in bulk, but if you ask nicely and bring in your own container usually the parts counter guys will sell you just what you need.

As for the fuel mileage, the fuel filter was *supposedly changed right before we bought the car about 20k ago, though after my recent tuneup I'm starting to wonder what was actually done. The timing belt and tensioner along with the front and rear seals and cam seals are all new as of about 10k miles ago. ECU was reset, using the fuse pull, idle to temp method, though I may use the approved method as well just to check.

The knocking we were getting was definitely coming from oil vapor entering the cylinders and essentially lowering the octane of the fuel/air mixture. The cylinders and/or valve seals are allowing quite a bit of oil past (well, compared to normal).

I assume the temp sensor (digital one) is not the one that tells the dashboard indicator its position and is only for the ecu, is there any way to test that little guy, or should I just go ahead and change it and see what happens.

Soul Shinobi · Post by **Soul Shinobi** » Wed Aug 05, 2009 5:31 pm

suba wrote:The Transmission fluid is amazing, I definitely wouldn't run anything else. It only comes in bulk, but if you ask nicely and bring in your own container usually the parts counter guys will sell you just what you need.

You must be referring to Subaru Extra-S, which is in fact non-synthetic but highly acclaimed by by the Subaru community. I have the 20L drum in my garage right now. Most people love it, though it was only so-so for me, likely because a good fluid can't fix 271,000 miles of wear.

suba wrote:I assume the temp sensor (digital one) is not the one that tells the dashboard indicator its position and is only for the ecu, is there any way to test that little guy, or should I just go ahead and change it and see what happens.

Correct. At 20C (68F) the resistance between the two terminals should be 2.5k Ohms.

entirelyturbo · Post by **entirelyturbo** » Wed Aug 05, 2009 8:01 pm

kimokalihi wrote:Man, I swear I read an article on octane grades and timing and how you shouldn't run higher octane than your car is supposed to use. I know it said that it would give you less performance and cost you more.

Higher octane fuel requires more energy to burn. The engine has to work harder to burn it.

Now your ECU may notice the extra octane and bump timing up slightly. But a stock ECU still plays it safe, and won't allow enough timing advance to actually get you any noticeable performance.

If your engine has high CR or is force-fed, then it has to have the high-octane fuel just so it doesn't knock itself to death.

But yes, putting high-octane fuel in a car that doesn't require it is indeed just wasting your money... with the exception of some new cars that REQUIRE low-octane fuel. I've heard of some GM trucks that require low-octane fuel and have had serious problems running high-octane fuel.

suba · Post by **suba** » Wed Aug 05, 2009 10:37 pm

After talking with the guys at the dealership (they all seem to have ej22's) sounds like a potential culprit for my car is the temp sensor, and at $28 I figure it's worth a shot. So the new plan is to change the sensor, and nothing else, and see what happens. I'll be doing a longer highway drive this weekend so when I get back from that I'll report on my findings.

Soul Shinobi · Post by **Soul Shinobi** » Thu Aug 06, 2009 2:14 am

Definitely keep us posted, and keep in mind you'll likely have to drain the coolant enough so that the crossover pipe the sensor is in is empty (or you'll make a big freaking mess!). Might be a good excuse to do a coolant flush and thermostat (which can certainly have an effect on economy if it's old or bad). I know you're looking forward to measuring the effect of just the sensor, but perhaps better safe than sorry.

Post by **Legacy777** » Thu Aug 06, 2009 2:45 am

I found 89 octane worked the best in my non-turbo engine.

entirelyturbo · Post by **entirelyturbo** » Thu Aug 06, 2009 3:32 am

Legacy777 wrote:I found 89 octane worked the best in my non-turbo engine.

As have I.

It would still ping occasionally on 89 (carbon buildup I'm sure), but it actually felt a slight bit slower on 93.

Shinobi makes a good point. You'll make a big mess if you just pull the sensor out with a full cooling system.

suba · Post by **suba** » Fri Aug 07, 2009 5:09 pm

Changed the sensor (using the 'quick hands method', not too much of a mess), reset ecu and away we go. No actual info as of yet, but I noticed that this morning the car started instantly while cold, but of course that could just be my hope for improvement shining through. When I picked up the sensor here is what the parts guy said:

"The sensors don't usually 'fail' but they get corroded over time (it is after all sitting in coolant for decades). They start to read incorrectly and the first indication that it may not be functioning correctly is that, when cold, the engine cranks for a little bit longer before firing, but will often start right away when warm. What is happening is that the ecu is reading a slightly higher temperature and is actually leaning the mixture rather than enriching it for a cold start. As the sensor gets older it can also read incorrect at other temperatures and cause rich running conditions during driving."

My theory on this for rich running with an incorrect reading sensor is that the ecu will always try and prevent damage by avoiding a lean condition that could damage the engine, especially on turbo models. Most car manufactures, especially in the earlier days of efi leaned more towards rich running engines to provide longevity (except honda, but those guys are just crazy).

Of course, this may all just be nonsense if it turns out that the temp sensor had no effect, but as soon as I have actual numbers I shall let everyone know.

suba · Post by **suba** » Mon Aug 10, 2009 3:25 am

Okay, returned from weekend trip and have some preliminary results:

Previously we were getting about an average of 23 mpg with 90% highway. After this weekend we got 25.1 mpg BUT this is not an accurate comparison. During the drive about 1/3 was on twisty back roads in mostly 3rd gear, and the highway portion contained excessive amounts of passing and high speeds (I was keeping up with a pair of bikes).

I have noticed that cold starts are significantly more consistent regardless of outside air temp. So my conclusion at this point is that temp sensor has made a fair improvement, but I can't say exactly how much yet. After this weeks commuting I will be able to make a direct before and after comparison and I'll let you all know.

ericem · Post by **ericem** » Mon Aug 10, 2009 4:07 am

DerFahrer wrote:
Legacy777 wrote:I found 89 octane worked the best in my non-turbo engine.
As have I.

It would still ping occasionally on 89 (carbon buildup I'm sure), but it actually felt a slight bit slower on 93.

Shinobi makes a good point. You'll make a big mess if you just pull the sensor out with a full cooling system.

You know whats weird with my 94 SS when I remove the CTS no coolant spills out :S unless I open the rad cap on top. With my 93 N/A even with the cap on leaks out. Why? Is it because the rad cap is on top instead of on the rad?

suba · Post by **suba** » Mon Aug 10, 2009 4:11 pm

Hmm, the turbo's have the sensor on the drivers side of the manifold right? I have no idea why that would make a difference though. odd

suba · Post by **suba** » Thu Aug 13, 2009 2:37 am

Well, the numbers are in and the results are....abysmal.

Previous average with 90% highway was 23, with a range of 22 to 24 mpg

With the new (Subaru) temp sensor: 22 mpg.

I'm at a total loss now folks. I can't figure out why I'm getting such horrendous gas mileage, so if anyone has any other ideas I'm open to anything at this point.

Soul Shinobi · Post by **Soul Shinobi** » Thu Aug 13, 2009 2:44 am

Clogged catalytic converter maybe? Or internally collapsed muffler? Intake clog? Check the whole tract. What's your compression? Does your car have EGR? Maybe a pre-O2 exhaust leak? What's your tire pressure; how's your alignment? How are the brakes, are they dragging? dragging brakes can be a big issue.

Anything else guys? God help us if this topic doesn't help us boost economy.

Max Headroom · Post by **Max Headroom** » Thu Aug 13, 2009 9:17 am

Soul Shinobi wrote:Clogged catalytic converter maybe? Or internally collapsed muffler? Intake clog? Check the whole tract. What's your compression? Does your car have EGR? Maybe a pre-O2 exhaust leak? What's your tire pressure; how's your alignment? How are the brakes, are they dragging? dragging brakes can be a big issue.

Anything else guys? God help us if this topic doesn't help us boost economy.

Excellent summary!

I've just fitted new tyres recently (six weeks ago), and monitor the tyre pressures religiously with 36psi fr, 34psi rear. I had a wheel alignment done when the new tyres went on. The brakes have just been overhauled fr & rear with new pads, new front discs and the rear discs skimmed. I've just fitted a fresh K&N element, fitted new sparkplugs, and had all the driveline fluids replaced. Next step for my car is a de-cat, with the hope that it will improve economy. Initial research suggests that it will.

When I first got my car it was covering less than 200 miles out of a tank of gas. I'm now getting 250 miles. My goal is a range of 300 miles.

(Car is a JDM BF5 with EJ20T & 4EAT)

suba · Post by **suba** » Thu Aug 13, 2009 4:02 pm

Previously I had gone through the entire intake up to the throttle body and now she's clean as a whistle (assuming you have a clean whistle that is) so i'm certain that isn't an issue. I don't belive this car has an egr system, though it does have a fairly intensive pcv system with a new valve. I should recheck and verify that the other connections are not letting in any air however. The muffler on this car is shot, but given the number of holes it has at the moment I doubt its causing excessive back pressure, though it was next on the list of repairs. Last time I had the wheels off I inspected the brakes and they appear to be working exactly as their supposed to. Alignment is good, tire pressures at 36 psi (205 55 16). Condition of the cat is unknown however, though at the moment but the rest of the exhaust is in great condition.

So... I think my next step will be to recheck all the extra intake lines running around the engine bay, do a compression test and then possibly replace/remove the cat if time and money allow.

Soul Shinobi · Post by **Soul Shinobi** » Thu Aug 13, 2009 4:11 pm

There are pressure testers that can screw into the O2 sensor hole so you can measure back pressure. Brakes can be deceiving, I just sent a whole day on mine and they're still a bit tight; freaking rust takes up all the clearances. When I suspect a brake is dragging I take out my non-contact infrared temperature sensor and check the hottest reading on each disk.

Don't top off when you fill up on gas, it can screw up the EVAP system operation. Maybe timing can be check too, as well as spark voltage to see how the igniter and coil packs are holding up (I'm not too sharp on ignition systems, maybe someone could give a better/more accurate suggestion). Also good sensor operation requires good electrical connections, consider a grounding kit mod if you haven't already.

suba · Post by **suba** » Thu Aug 13, 2009 4:16 pm

On a related note, here is a couple questions for you guys getting better than 25 mpg in your N/A cars (especially the stock ones):

How old are you catalytic converters?

What major components have you replaced in your vehicle (coil, sensors, etc)?

What compression numbers are you seeing?

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fuel economy Fixs