What caused my random spike in MPG today? from ~45mpg to 52-55mpg at 45mph??
 

Ok... so here is the long version, skip below to the * marked short version if you wish.

I was thinking about unhooking 2 injectors (cyl 2 and 3) to see what the MPG impact would be. I started it up, ran as I expected, engine vibrated quite a lot, but ran kind of like a 2 cyl engine under a load. When I reved it a bit to see if it would smooth out, the check engine light started flashing, and when it idled back down it went solid. Engine codes E0300 and 2 other 3xx codes were set. I cleared them, hooked up the fuel injectors and drove home like I normally do.

Driving while cold got me my normal ~30mpg at 40mph, once 130F hit, it shifted and I sped up to 45 and got lockup.

Couple turns later (about 10 miles) I was shocked my instant MPG gauge was saying 55mpg and I was traveling 45mph. I normally get around 42-45mpg at this speed. I put it off as a down hill slop since this is only my 3rd drive home with the scan gauge. Well 3-4 miles down the road it was still 52-55mpg... I was able to keep it over 50mpg until my next stop including a couple small up hills. After the stop I got to speed and it resumed the 50+mpg.

In the last ~4 miles of the trip, I was looking at the different sensors to see what one(s) were out of the normal. Only one I could find is the IGN, normaly it rides around 37-39, but it was running solid at 24. When I sped up slightly it would jump to 37 or 39 instantly with very light gas and lifting off it a little it went back to 24.

*** Short version ***

-I unhooked 2 injectors and was going to drive home like that to test the MPG difference, it set engine codes so I hooked them back up and cleared the codes
-Cold MPG was normal
- around 10 miles into the trip I was getting 55mpg at 45mph, normal is around 42-45 mpg
-IGN reading was 24 instead of the normal 37-39

*** Trip Stats ***

44.7MPG average
36 Miles
204F max WT (192 thermostat installed a few weeks ago, old one stuck open)
49MPH max
38MPH Avg


****

So to me it sounds like my timing is too fast or the gas I have isn't running very well at the more advanced timing (low octane?). I 95% of the time fill up at the same station and same pump because their pumps always gave me the best gas mileage when driving my Camry (before a scan gauge).

Comment what you think is causing this, because what ever it is, I am loving the better MPG. My last best was the same trip, same speed, tiny bit colder day, and it was 41.7mpg, I didn't have 50+ mpg figures at 45mph except going down hills.

Just to note, I have been getting right around 38-39mpg before I dropped my speed to 45mph instead of 50mph. I have yet to have a tank 40mpg+. Comparing to other users, most get 32-38mpg on this site, one I saw at 42mpg. Only mods on my car is a upper grill block, cardboard in radiator (still there when thermostat was stuck open), and the scangauge. The last 3 tanks have had no changes, and the outside temps are around the same +- 5 degrees.

If I can figure this out, I might be able to hit 50mpg average + with such little mods with a car rated for 26mpg average (where the hell they get that low IDK..)

My guess is your Scangauge initialized itself to the factory default settings (3 liter engine, etc.). Check your vehicle setup and calibration settings.

Scangauge appears to be as it was, 1.8L engine, etc. Driving to work today, I got my normal MPG for at night. I was able to get my car to do the same actions I saw yesterday, but couldn't keep the speed. For at night my TPS reads 18 and sometimes dips to 17. If I let off just a tad bit, say where 17.5 should be, the IGN reading goes from 37/39 down to 24 and mpg instantly jumps to 52-55! So what I'm thinking is that the ECU thinks I'm coasting and it leans the AF mixure and retards the timing. Theory of mine is that there was a slight wind pushing me (north) and since I was running the gas peddel low enough, it was kind of doing a lean burn setup even though this car does not have that function (same engine in other cars can). When I perform more aero mods on the car, I should see this "lean burn" more often if my theory is correct.

While in the "lean burn" thing yesterday, I did notice the engine was a lot smoother than normal and sounded like it was under less load. When my car is fully warmed up, it idles around 675-700rpm and is very smooth running, just before peak temp, it runs 850-900 rpm and vibrates quite a lot. When it is idled to 700 and I give it gas to get the rpm to around 900, it vibrates as well. I think this is just the nature of this engine, but maybe it could be timing or fuel quality (E10+)? My engine spects say 9.5:1 compression, so maybe I should run 89 or 91 gas instead of 87?

Sounds like a phenomenon called Super Atkinson Highway Mode. I've searched in vain for SAHM in my cars, but can't hold it very long. I think it's found/held easiest by holding the TPS at a specific value over idle position (i.e., 8 over 12 TPS idle, or 20 TPS), or keeping IGN advance high (>40). Google SAHM Atkinson.

Very interesting read on the SAHM Atkinson mode.

Quick stats for when I'm in the high mpg mode:

RPM around 1550-1650 depending for uphill vs down hill etc
LOD 42-46, at about 47 it kicks out of the mode
IGN 24, today I saw it dip to 23 with a lower load (around 35) down a hill
Speed 40-50mph (target of mine is 43-45)
MPG 50-55, mainly around 52-53 on normal flat ground

Now when I'm not in the mode my specs are

RPM around 1550-1650 (same as above, it is in lockup lol)
LOD 50-54
IGN 36-39, spikes to 40 here and there
Speed 40-50mph (target of mine is 43-45)
MPG 40-44


It is very hard to keep it in this mode, 2 days ago I drove home a large % of my trip home in the mode, somewhere around 60-70%. I didn't even know how I stayed in the mode, just knew to keep the foot lightly on the gas. I think there was a small wind pushing me since this is out of the norm. I hope further aero mods will keep me in this mode. On the way home at around 50-55mph I could get it in the mode and at 46 LOD (still slowing down though) it read around 48-51mpg, much better than 37-40...

The only really weird thing is... SAHM mode appears to be based on high ign advanced which my car does very easy when warm. It is when the ign is not advanced as much when I get the better MPG. I really wonder if I ran better gas if it would get better MPG due to the very high ign advanced? I think my next fillup will either be mid grade or prem to test. $3.69 for reg, $389 for prem, 20% better mpg would be a ~$0.54 savings per gal!

New find....

File:Timingmap.jpg - Wikipedia, the free encyclopedia

According to my readings and that map, my 45mph at ~46-50 load should be around 22 for spark advance.

When I deaccerate, IGN reads 12... according to that map, it should be higher not lower? When I give it a tiny bit more gas (around 60% load) IGN reads around 33 while going 45mph (1600rpm)

I have yet to understand this... been half thinking about unhooking my battery for a while to reset the ECU settings and let it rebuild, or keep them and run a higher grade gas.

It sounds to me like it is your torque converter locking that is giving the increased MPG.
To test this you might try tracing your TCC circuit and then wiring in an over-ride switch.

Most newer vehicles use a PWM type of TCC activation strategy to make this function seem smoother to the driver. Even my S10 had this.
An over-ride will force a signal for 100% lock-up of the TCC at will, and will instantly show you the gain on your S.G.2.

Some (perhaps most) TCC circuits supply 12 volts to the pressure solenoid, and pulse the ground signal based on calculated duty cycle. In this case you would over-ride the ground signal using a SPDT relay.
Single Pole Double Throw (SPDT), Single Pole Single Throw (SPST) Automotive Relays

Advancing the timing too much in the idle/low-load range can lead to an erratic, rough idle. That's why the timing is retarded so much.

I think the car is going into lockup fine since it shifts 4 times (4 speed) and has another spot that feels like another gear (lockup). It is doing about the same RPM in both good mpg vs not so good and going faster, say 50mph or 55 does not show better mpg but worse.


I need to check the idle IGN readings, I think it is around 8-12.

I talked to an engeneer today about this since he had pc issues (i'm a computer tech), and he thinks it is the knock sensor.

Yes, I realized that it would feel like that, - that the converter had already locked. The purpose of the PWM strategy (which is based on engine loading by the way) is to make the TCC function less perceptible to the driver.
Also, due to the function of the PWM, you will not see such a clear change in engine RPM at certain loads. This is exactly why the PWM strategy makes the function smoother in terms of driver perception. That's why I suggested a test to rule this out, or confirm.
Most scan/datalogging software will show you the TCC function flag (on or off) and some will show the duty cycle as well.

Speaking of knock sensors, that same scan/datalogging software will show you knock sensor output in a term called "knock counts", or "knock retard", - the retard being the result of the adaptive spark logic in the PCM.

One more thing to check is your EGR function if your car has a PCM controlled EGR valve. Again there are two strategies for EGR function: either on/off, or a PWM or stepper-motor controlled solenoid that delivers based on a calculated duty cycle. When EGR function is active, the spark advance is increased. When you fall below the thresholds for EGR operation (different for different PCM/calibrations), then the spark advance will drop, - usually in the neighborhood of 10*.
The EGR delivery decreases combustion efficiency, hence the need to start the spark sooner, so depending on engine loading & conditions it will definitely affect your fuel mileage.
The SG2 will often report EGR duty cycle on many models once you add it via x-gauge.

All of these (TCC, KR, and EGR) are based on variations in engine loading, so their effects will be noticeable as you change loading by backing off of the throttle while driving.

Given your curiosity about this sort of thing, it sounds like you would be a lot happier if you invested in one of those scan/datalogging smart-phone apps so that you could monitor what exactly is going on in your car. All you would need extra is a Y-cable (one male end plug, and two female plugs) for the ALDL port.

There are other more sophisticated datalogging software that will display the reported data in optional units, and ranges of resolution. For example instead of seeing your throttle position as 15%, you could have it display as 15.34%. This sort of thing comes in handy when working towards higher MPG.

Using the same method (some software will show instant MPG or fuel consumption), you could have your instant fuel economy reported to several extra decimal places in order to monitor very small changes in a narrow range of test conditions.

OP, you have an interesting situation. I don't think higher octane fuel will help, since its only benefit is knock reduction. Still, it's worth the price of a tank to test if it helps.

Your timing should advance under lighter loads. I don't know why your Corolla behaves differently. The normal timing advance occurs under decreased load because of ECU mapping to avoid knocking. So, tossing higher octane into the picture may allow more operating time with less advanced timing. It's worth a try.

Here's some visuals of a spark table, a PE spark adder table, and an EGR spark adder table. They are not for your vehicle, but may help with understanding the functionality of what I mentioned earlier.
Newer vehicles have a fairly complex adaptive spark logic with several other extra spark tables that include things like "low-octane spark", and "high octane spark".

Here, the bottom 2-Dimension table is the spark adder for EGR, or "Spark added vs %EGR". The top table is the VE compensation table.
http://i702.photobucket.com/albums/w...EGRscreen1.jpg
http://i702.photobucket.com/albums/w...EGRscreen1.jpg

Next is another 3-dimensional main spark table (from a different vehicle) and a smaller 2-dimensional PE (Power Enrichment) spark adder table. It shows spark added when increased load is triggering Power-Enrichment mode of operation for added fuel delivery.

http://carphotos.cardomain.com/ride_...0082_large.jpg
http://carphotos.cardomain.com/ride_...0082_large.jpg

There is some further explanation of EGR operation here in this thread on Ecomodder: http://ecomodder.com/forum/showthrea...e-7358-17.html

Very interesting details, I'm pretty sure my car is more on the simple side of things since the mid 90s Toyota seem to have that factor, and the corolla is more of a base model type of a car. So I'm pretty sure when I feel/see the lockup, it is on fully or off fully.

The EGR related effects could be what is going on, the car does have 230k miles and similar models have EGR clogging issues at lower miles (97-2001 camry) which I have seen first hand in 2 of 3 cars, 3rd being only 126k miles (no issues), other two are around 180k (rise and lower of idle rpm, one throws the EGR code).

I'm not sure how soon I can investigate this further since I'm still on shift at work and I just had a large load of computers/printers come in (recycle them as a hobby/ side income). With an estimated 500 pound load (3 servers, 6 desktops, and a few printers/printer parts) with the trunk open I averaged 38mpg @ ~45mph :).

I think I'm going to need to learn about the x-gauge feature a bit more for my car, the egr details would be interesting to see.

For the smart phone app thing, I don't own a smart phone, I use a $20/3 months prepaid since I never use it. I did look into running similar software on a laptop though.

For a few more IGN readings...

Idel when cold - 22
Idle when fully warmed up - 11-12

While under a larger load than normal it dropped in the 33-36 range on hills, and steady speed it kept around 37 more with 39s here and there.

I found I can stay in the higher mpg "mode" when my MAP sensor is at 7 or lower, to maintain 45mph it needs to run at around 6.6-6.9 which is hard to keep in that range, but once there I can basically freeze my foot there and be good to go till hills/stops. Normal 45mph the MAP sensor is 8-8.3, HPR goes to about 14hp when saving gas, 18 when it seems to waste it.

I think you're treading new ground for AT Corolla owners. Looking forward to seeing more of your results.

Thanks for the support!

I'm not doing any extreme hypermileing either, just coasting in drive, upper grill block, 55psi tires, 45mph instead of 55. Funny thing is, I'm not even sure if the car is in tip top running shape, the last owner did NOTHING on the car and he owned it for a year with burnt out lights (can't seed speed at night b4), nearly no brakes, headlights about falling out, HUGE alignment problem, worn out tires, and struts blown out.


One thing I should point out, this car has the more desirable engine/trans setup since the 1.6L gets worse mileage for an average (automatic based on EPA). Besides what I think is the better engine (max torq at 2800rpm vs 5600rpm), it has the 4 speed with lockup vs the 1.6L normaly having a 3 speed no lockup.



I have noticed while still warming up I can get about the same MPG figures as when the engine is fully warmed up going at a given speed. Since I travel 45mph, I get into lockup at about 140F (130 for overdrive) and MPG reads around 30 for a while. Once it is around 170F It runs close to 40MPG, and around 185-195ish I can get 45mpg. Once I hit around 198-202 (my normal temp) it advances the timing and kills my mpg...

One thing to note.... I have a 192F thermostat in it under the idea a warmer engine should have better MPG (thinner oil, warmer air, etc), and factory it came with a 180F one.

I'm thinking about changing plugs and wires, and have not changed the oil yet (looked fine when I bought the car ~1500 miles ago), since the money the car has saved me in gas costs will pay for it (1 month of driving).




Yesterday was the first time I had any kind of a negitive reaction from other drivers with my 45mph standard besides their normal stomp on it and pass reaction. I had two people at different times pass me on a section of road with a left turn lane in the middle. I had a large 250 pound printer in the trunk, I figured people would have been better "understanding" for the speed I traveled at since I had a load. Anyway, the only other time I have seen a similar reaction was close to the same stretch of road but infront of a school. Car infront of me was going ~40mph and the car behind me wasn't happy about it. They did their pass, and the car behind them followed them around... after they got past the van, the blue and red lights came on ^.^

Sorry for the long post, I guess I'm in story mode today or something.

Just the other day, I had a guy flashing headlights at me as I was coasting to a stop at a red light. Apparently, he wanted to make sure to get into the occupied left-turn lane. As it were, I was able to continue through (the light turned green while I was still rolling), and he had to come to a complete stop and wait because there were still three cars stopped ahead of him in the left-turn lane. I guess he wanted me to hurry up and slam on my brakes too.

Have you played with the xgauge yet?
It would be interesting to see some more information that might help you figure out what's going on. You may be able to watch your Long-Term-Fuel-Trims. Our Focus displays that and it can be very useful.

Ok added 4 xgauges. Two of them don't work which are Air to Fuel Mix (tried bank 1 - sensor 1, and Bank General). The two that do work are O11 and SF1.

I just noticed down further it has Long Trim Fuel Trim >,<, got to add that yet.

Anyway, O2 sensor reads mainly in the 70s-80s most of the time and dips to 30s-40s at times which should mean it is working right, but beyond that I don't know.

The SF1 reading was jumping around from -4 to 3. When I dropped my speed to around 30-35mph SF1 read a little lower averaged out than at higher speeds.

For my 45mph test, I couldn't see any large difference from IGN running at 39 (normal) and when i'm doing the trick to make it run 24. When I get a chance to test out LF1, I'll update this post.

Oops, forgot to update, LF1 does not work for some reason :(.

Good news... today's trip home averaged 44mpg with wind working aginst me for 1/3rd the trip, and the rest it was helping and was able to stick in the 24 IGN 95% of the time not counting take offs. Did a couple small aero mods in hopes of hitting 24 IGN more often and easier.

Watching O2 output is almost useless, and watching STFT is completely useless, so don't even bother with those.

The LTFT is something you definitely want to watch. Keep in mind you change to different load cells with different stored LTFT values as you drive.

Block Learn Multiplier and Integrator

BLM (block learn multiplier) is the older original term for LTFT - long term fuel trim.

Being that you have a drop in SA (spark advance) going on, you want to keep an eye on KR - knock-retard if at all possible.
You should also try to monitor your EGR duty cycle.

If for some reason your EGR wasn't functioning, or was clogged, then you may be getting knock retard under certain driving conditions when the EGR becomes active.

Knock retard can also be caused by any number of mechanical rattles on the car, which can occur under certain driving conditions.

Very good read, I like learning a bit more of the actual programming on the ECU and other engine related computers (programmer by hobby, IT Tech by career).

Anyway, on the offical site for scangauge I either can't get the values to work in X-Gauge, or the sensors are not listed.

BLM/LTFT - Has bank 5-8, but is called LF1 - LF4, I tried bank 5 and it never populates
KR - I see no where to monitor this on their page or default gauges
EGR duty cycle - Same as KR, with 230k miles, the EGR is probably partly blocked off.


If the EGR is messing it, it could actually increase FE? I always thought it was the opposite, big time if I'm getting spark knock.

As for engine rattles, there are some and different RPMs. At low speed just starting off really easy, the engine sounds almost like a bad wheel bearing (last owner said it needed one, all are good).

At some point in time, I plan to hit the car with seafoam to clear out the carbon, and check the EGR ports, idle control valve, etc. I would just hate to loose FE by "fixing" the engine lol.

Back to more info on this "mode", even in warmer weather (60s-70s now) it is almost exactly the same setup except the car can move easier though the wind I guess. Instead of fighting about 6.6-6.8 MAP values to stay in the mode (under 7), I was going 45mph with as low as 5.8-6.2 most of the flat land travel. Instant mpg was reading between 60-65mpg, a few spikes to 70mpg but I was probably slowing down ever so slightly. At first I kepted hitting 50mph with my normal MAP readings, I was going WTF for a few miles lol. Trip average hit a new high as well, 49.9 and about 6 miles shorter (stopped at gas station), so it could have been at least 50.2 by the time I got home.This is from the same tank of gas I hit my last 2 high figures, 45.3 and 47 and my last aero mods. Can't wait for summer gas (if it isn't here yet).

With out this "mode" I rarely hit over 40mpg average on a trip.

I would call the tech guy at Scangauge about getting the parameters right for reading those values on your car. He has been very helpful to me in the past.
I have seen EGR passages clog with only 50,xxx miles, so yeah that's a good possibility.



When dealing with tuning parameters like that there is never any hard rule where you can say x-change has x-effect, because it always depends on the specific tuning conditions you are starting from, and the particulars of how the engine is being loaded at the time you are examining.

It does often happen that MPG goes up when the EGR flow is blocked.

The MPG going up when spark knock triggers knock retard is not as common, but just as possible. It all depends on what the engine needs at that particular time. With certain loading conditions, less spark advance requires significantly less fuel in order to maintain stoich operation.

Maybe one of the belt-driven accessories is going bad. It's usually a quick and easy test to remove the belt and start up the engine for a few seconds as a test.


Seafoaming doesn't always work out for the best, especially on very high mileage engines. If you do it, be sure to change your engine oil not long after the cleaning is done.

EGR passages can usually be easily cleaned out with some Acetone, Mineral Spirits, or a combination of both, and some compressed air at around 100 PSI.


Yeah our Focus gains around 10 MPG during warm weather, and I've traced most of this gain (ours) to warmer engine oil. I'm going to address this issue more before next winter comes. There are multiple factors involved with fuel usage vs outside temp though.

As for the precise adjustment of the throttle position it seems you could really use an increase in throttle resolution to make it easier to get your high mileage. The range of TPS is extremely narrow between the point of acceleration and deceleration. Take a look at your throttle cable interface with the throttle lever on your throttle-body and you may be able to do a small modification to make it easier to drive in this narrow range of operation. Increasing throttle resolution means that it requires more gas pedal movement to translate into the same movement at the throttle.

On our Focus there is a cam-shaped throttle cable guide on the throttle lever, and it was easy to increase resolution by changing the inner shape of the cam-groove with a piece of aluminum foil as a quick mod. Be careful not to bind the cable or it could break, - unlikely if you don't go WOT, and also be careful that the cable will not come out of the groove during operation.

http://i702.photobucket.com/albums/w...cablephoto.jpg
http://i702.photobucket.com/albums/w...cablephoto.jpg

I just put in seafoam in my gas tank, it is due for an oil change any time, so planning to hit it with seafoam via vacuum system too. Change oil, plugs, wires, and check cap/router.

For the noises, it is really weird, just barely moving like in a parking lot the engine makes some noises similar to a bad wheel bearing, any more gas, or less it don't do it. I suspect it is something with the ignition system not up to par. My dad is an ASE tech, so I could have him look into it some time when he has the time.

For the EGR system, I'm sure it will be carboned up, but if it kills my FE some, I would want to find out why, and be able to adjust the engine to be more efficient at cruise. Either way it needs to be cleaned. My Camry needs it too probably with 303k miles.

Updates...


Yesterday I did the much needed oil change after a seafoam treatment and added a bottle of system 48 to the oil (oil treatment, reduces friction etc). Instantly I noticed my MPG is a bit higher when driving 55 (while performing the system 48 treatment run). Drove it to work and ran it 55 most of the way, averaged 47mpg which I could only touch if I went 45mph the whole distance before. The trip home I hit a new record for my self at 51.5 mpg with temps around 55. On that trip, the first 1/3 I could bearly hit the high MPG mode, so I had an average of around 42 at my turn north. From then on I was in the high MPG mode and was seeing instant MPG of 55-62 and was much easier to keep it in the high MPG mode than normal. I also added the 2nd half of my lower block for the trip home so that had a factor as well (last record was with it in at warmer temps).

The High MPG mode seems to be the same condictions, map sensor reading of under 7.0 and trans in 4th w\ lockup.

The last couple of times turning off the car when parking I noticed the idle is higher than before, probably from such a huge change the ECU needs to relearn the idle (which I am never doing except for coasting). I still don't know why the car gets better mpg when in this mode, either it is running lean, or maybe the EGR is being activated or stuck open.

Again, the only differences from "normal" mode and the higher mpg mode is the timing. To get into the mode I have to go 45mph, let off the gas to about map reading of 5, and re apply to about 6.0-6.6 to maintain speed. Timing reads around 23-25. In "Normal" mode, at map readings of 6.0-6.6 it is about 20% lower MPG at a given speed (which is normaly slowing down) and timing says 38 to 40

Just a side note on the sea foam treatment (my dad did it for me), he said he smoked out the area, and when he took it for a drive, it stopped smoking in about 4-5 miles.

With some aero mods I hope to hit the top 10 list for % over epa and highest mpg cars (60mpg = 130.8% over epa)