Batman we have lean burn! 49.6 mpg!

[popimp]

I was getting real high mpg 50mpg at 50mph with the 330 ohm resistor (260F). I didn't get any codes with the 100 ohm resistor (335F). With a short it was reading 375F with check engine light on. Did you notice any difference with your mod?

[diamondlarry]

Originally Posted by popimp

I was getting real high mpg 50mpg at 50mph with the 330 ohm resistor (260F). I didn't get any codes with the 100 ohm resistor (335F). With a short it was reading 375F with check engine light on. Did you notice any difference with your mod?

At 110 ohms I was ok but when I tried 105 ohms I got a light.

[popimp]

Diamondlarry did the mod work for you?

[diamondlarry]

I don't think so. On my '99 SL2 I put the mod on on the way home from Pennsylvania(Sept. '06) and, when I returned it to stock last winter, I didn't see an immediate drop in calculated mpg.

[fabrio]

I don't understand!

The ECU (iaw, bosch motronic, opel etc...) of catalyzed cars, it use the IAT for calculating air density, and delivery the time spark advance only under open-loop .
In the closed-loop the oxigen sensor inform the ECU about actual AFR, and the IAT it is used only for modify the time spark.
I don't have tested, but I suppose with lowering the resistor IAT, a major consumption increase because the advance spark is retarded.
when the iat is forced (modified) to low temperature, and ECU work in closed-loop, the only parameter that allow change it is an advance of spark time, because all the motors work with a sure spark advance time (inferior to that maximum), remain a sure margin.

the new increased spark advance time, this allows a greater fuel saving

[cheapybob]

You need to understand that initially I was trying to maximize the fuel economy without regard to performance. There are 2 variables in my intake setup that differ from normal.

I have the hot air intake, and its setup to provide air no hotter than 200 degrees even on the hottest day. I got it to where it is by adjusting aluminum vent closer or farther from the header. If it gets too hot, the motor loses too much power, and uses MORE fuel instead of less. I noticed that the ignition doesn't advance if it gets to hot, so assume that it might be retarding spark because maybe its getting some preignition. I'm no automotive engineer, but found that if I keep the actual intake air temp under 200 it was running ok. I do also recall when I had that problem that when water temp went up over 210 or so, I was having problems also. It may have been at the same time at intake temp went way high, sorry, but it was 2 yrs ago and my memory has faded because I no longer have problems. I had to stop 2 or 3 times on the turnpike coming back from PA to keep moving the intake farther and farther from the header till the temps stayed reasonable and the ignition got back to normal (37-39 on highway), at which point it also ran fine again.

The second variable is my sensor bypass switch that allows me to tell the ECM that the air is 242 degrees or the actual sensor reading, or 36 degrees. I found that the optimum was to get actual air temp up around 175-180 and at the same time tell the ECM it was 242. Any higher it sets a code, and lower I lose mpgs. My scangage is calibrated for tire size and a 12.9% additional fuel factor, and has been set there for 2 years now. It usually comes up within 1 or 2 tenths of a gallon vs what it actually takes to fill it, therfore the scangage mpgs are logically correct or close also.

By the way, the car passed the more stringent than normal Chicago epa tests with all mods on and operational. Not sure if it would pass CA test, but I think it would have good odds if is an ECM check or sniffer test. All I'm doing is simulating a VERY hot day in the desert, and letting GM'ss ECM do what they told it to do on VERY hot days, thats all. No rocket science.

Its been running like that since 2005 with no troubles except for longer starting time when warm, which I've gotten used to. In "cheapy mode" its definitely down on power, but gets great mileage. With 3 adults in the car from Detroit to Chicago at 70-75 mph it got 45 mpg, and that was running a/c off and on. If I was willing to drive at TPS of 7, I can get between 65 and 70 mpg, but who wants to drive 40-45 mph all the time? BTW, if I flip the switch from "111 ohm cheapy mode" to sensor, gas mileage on the scangage drops within 5 seconds.

Tonight, I'm modifying my 5.7L 6 speed Trans Am Convt. I like to use it to tow the sailboat for long trips because its more comfy to drive than the Saturn and has a hitch on it. Towing without a hitch doesn't work well, and they want about $150 for a hitch installed with electrics on the Saturn, which translates to needing to save over 50 gal of fuel to make it economical to do. I imagine it would pay for itself in a 5 or 10 year stretch, but its pretty rare I tow the boat to Canada or anywhere far. This will be the 2nd time in 10 or 15 yrs. I'm not going to put a hot air intake on the T/A because I don't want to hack it up, and in the T/A I want performance on demand. I'm just going to come up with a resistor/switch setup that the T/A is happy with that will improve mpgs without pushing it to the limits like I did with the Saturn. On a short test run I was getting 23 mpg on the scangage pulling the boat at 62 mph. The scangage hasn't been calibrated for the T/A's injectors, so I really don't know how accurate that is. I know the T/A can get 27 mpg without the boat out on the highway. Anyway, those are the starting points. I'm hoping to eek another 3 mpg (15%) out of it on the highway towing the boat. Anything more is gravy. Those numbers are on 87 octane fuel, no additives. I've always been impressed by GM's efficiency and ability to build somewhat high compression motors that can adjust to regular gas, and still get gobs of performance out of it. We'll see if I can improve on it a bit.

PS: Maybe this only works for specific Saturn models, maybe only GM, or maybe it only worked on my car, but it certainly did and does work on my car

[cheapybob]

I contrived a potentiometer (old radio volume slider) + 2200 ohm resistor setup across it and hooked that up to the Trans Am completely bypassing the actual sensor. A guy called "Charcoal" on Saturnfans suggested the idea, but with a 1000 ohm resistor. I came to the conclusion that cold starts could be a problem at 1000 ohm, so put in a 2200 ohm instead. I set it for 220 degrees IAT on the scangage. Car starts and runs fine. Ignition advancing 41 degrees (best ever seen on Saturn was 39), fuel economy on scangage increased as expected. If the tank actually takes as many gallons as the scangage says it used, then the numbers are right. IAT sensor readings on the Pontiac appear to be the same as the Saturn, and mpg went up when higher temp faked in, so therefore it seems it should work on other GM OBD II setups with IAT sensor, I'd guess. I'll try to remember to come back and post the mpg (on the highway towing the trailer) when I get back. I didn't notice much difference in performance, maybe a bit less power in 6th gear.

[cheapybob]

Mod worked for the Trans Am. Got 24.9 mpg towing my boat across from Detroit to Chicago at 70 mph on cruise most of the way. Scangage was accurate to under 1/10 gal on a 10 gal fill. The T/A is rated at 26 highway without a boat behind it. It should get about 32 or 33 mpg at 60-65 mph sans boat would be my guess.

[fabrio]

Alt! we do not make confusion.

efficiency of combustion and, better mileage, it is not the same thing.
engine glabal efficency is rappresented by the thermodynamic cycle, it is equals at Po/Pi (Power output, Pouwr input)
The power inpunt is the energy at unit of time developed from the combustion of the fuel (calculated about an optimal combustion)
The Power output, is the energy utilizable under kinetic shape.

The power lose, is under shape of thermal energy.

the greater glabal efficiency of lean burn engine, derives from power decreases of pumping lose between the throttle body.

A good efficiency of combustion with reduced fuel in A/F ratio, it is true only when all fuel is burned.

[cheapybob]

Sorry, but real world results trump theory.

The 98 Trans Am, with its 5.7L V8 just ran the same 22 mi 60 mph test loop that I was using for my Saturn before. At 60 mph on cruise, it got 32.3 mpg. EPA ratings for the car when new were 17/26, and the best it has ever done before since the day it was new was 28 mpg on the highway.

BTW, if you noticed, my spark is not retarding. If it were, my fuel economy would drop. If the water temp or actual air temp gets too high, it will retard, and lose both power and economy. As I see it, the engine sensors did not detect preignition, therefore they did not retard spark. The engine is obviously in closed loop. My guess is that the programming is self tuning as it runs, and that it isn't sensing any problem, so it just tunes as best it can on the basis of what it reads from the sensors. It thinks the air is hot and less dense, and injects less fuel by reducing the pulse width on the injectors, just like it would if it were actually hot outside. The result must not be seen as a problem at the O2 sensors, or it would be trying to compensate.

Why are you so sure the IAT temp is not looked at by the computer? If it wasn't, it would have no effect. On my Saturn, if I change the switch from 100 degrees to 241 degrees or the other way around while driving down the highway at steady throttle on level ground, fuel economy changes by 10 or 15% up or down within 5 seconds, and it stays changed.