sc1 engine mods

[arcosine]

Hi,

I want to do a couple of things to the engine,

Advance auto parts advertised a 195F thermostat for $13., stock is 185F, 82C. But when I got it home I noticed it said 188F on the box, so I returned it. Bummer, the advertisement and listing is wrong. Saturns have a weird thermostat, like no other, so a regular type won't work.

I also bought a bosch wide range o2 sensor. If the threads fit, I plan to try to get the engine to run lean burn in closed loop by biasing the pump leads with a potentiometer. I don't know If I will have to advance the ignition timing by playing with the map sensor, does any one know how much more the advance should be when in lean burn mode?

... I got the car to run lean with the adjustable potentiometer, but I have a pending code P1133. Need more testing.


... Looking at the flame speed vs equivalence charts, The flame speed is approximately the same for equivalence of 1 and 1.2. So It looks like I can run about 18:1 to 19:1 fuel air ratios with the stock ignition timing. Maximum efficiency for lean burn gasoline engines is near 1.4.

[mwebb]

an AFR sensor can not be substituted for an 02 sensor
the waveform output is different
the ECM that is looking at a AFR waveform will not be happy with the waveform of an 02 sensor and vice versa .

your ECM will become angry if it does not see the 02 sensor cycling
150mv to 850mv and back in 100ms or less OR
what ever the time that is listed in
GM MODE 6 under front 02 sensor testing
-look up
"GM MODE6" select your system from the application list - study , learn.


what do this imply ? 1.4 what ?

...."Maximum efficiency for lean burn gasoline engines is near 1.4"...

[arcosine]

Yes, I saw on the oscilloscope the other day that it wasn't cycling, but it was leaning the mixture as I biased the pump positive. I am going to reset the pending fault, I think I had too much bias on when ECU ran the check. If the pending fault sets again I may abandon the effort, but not without an economy test run and biasing up the map sensor.

Oxygen Sensor P1133 No MAP, IAT, ECT, TP, Fuel trim, Misfire, Cam, 100 seconds after closed loop DTC Type B
System - Too Few EGR, CCP, Voltage and crank DTC's enable, Once per ignition
O2S R/L and L/R Closed loop
Switches 02 Voltage low threshold .300 V
High threshold .600 V
Flow > 7 g/sec
1500 < RPM < 3000
100 seconds after closed loop DTC Type B
enable, Once per ignition
0 V to 1.0 V This DTC
02 sensor switches < 10 counts
determines if the 02 sensor
is functioning properly by
checking its switches
Rationality Check


1.4 is the equivalence its the ratio compared to Lamda ~ 22:1 FAR.

Burning lean is more efficient because air has a lower heat capacity than burnt fuel products, therefore Gamma in the efficiency equation for an Otto cycle is lower. More work is done on the piston per unit of fuel because it heats the leaner mixture hotter, thus producing higher pressure. There is a limit, though because the flame speed slows down as the mixture is leaned, ignition becomes more difficult and combustion is less stable. Max efficiency is at 1.4 times more air than a stoichiometric mixture. Hydrogen, though has a much faster flame speed than gasoline and with an equivalence of over 2, has a thermal efficiency near 50%. There is a lot of research being done to develop a throttleless lean burn engine that meets air pollution standards without a catalyst by mixing hydrogen and gasoline or cracking hydrogen from reformulated gasoline. Peak temperatures in a lean burn engine are lower, thus less NOx is formed. Diesels are not lean burn engines because combustion occurs in rich areas around fuel droplets.



Where:

n = thermal efficiency
r = compression ratio
, gama, specific heat ratio


read, learn:

http://en.wikipedia.org/wiki/Otto_cycle

http://en.wikipedia.org/wiki/Lean_burn

Originally Posted by mwebb

an AFR sensor can not be substituted for an 02 sensor
the waveform output is different
the ECM that is looking at a AFR waveform will not be happy with the waveform of an 02 sensor and vice versa .

your ECM will become angry if it does not see the 02 sensor cycling
150mv to 850mv and back in 100ms or less OR
what ever the time that is listed in
GM MODE 6 under front 02 sensor testing
-look up
"GM MODE6" select your system from the application list - study , learn.


what do this imply ? 1.4 what ?

...."Maximum efficiency for lean burn gasoline engines is near 1.4"...

[mwebb]

the system will go to open loop
when faults are set for Mr 02 sensor

open loop will not ever result in lean condition
================
you may try adding resistance to the 02 sensor ground enough to bring the ground up 100 to 200mv which
MIGHT have the effect of having the ECM compensate for the
"rich bias condition" demonstrated by the 02 sensor

the 02 sensor "average" when cycling as designed will be 450mv
drive the average high and .....
as long as the 02 sensor is still cycling , you MIGHT be able to trick the ECM
to lean bias the system .
but
in theory
it will not work , the system will stay at stoich until the ECM becomes angry with the 02 sensor . when it sets a fault and reverts to
open loop

to see if it will work ...
use your scope to monitor injector pulse width average as you tamper with
02 sensor signal ground - to see if IPW average decreases as you bring the ground voltage higher .

in reality
the AFR sensor will not do what you seek in your system
================================

EQ ratio is not a measurement of an actual condition
it is a
command

EQ ratio will be equal to and opposite of CURRENT lambda
when / if the system is attempting to maintain
stoich
14.64 to 1
at the time

EQ ratio is not usually a valid / active PID on systems with bang bang 02 sensors
such as your system has ?

[arcosine]

No it was running closed loop, for about 120 miles, O2 sensor 2 was reading .04 volts indicating about 18:1 air-fuel ratio. Beyond that the engine bogged. Yes the ECU wasn't competently happy, it reset P1133.

[arcosine]

I modded the thermostat today. Engine temps were 145 to 155 with a 185F thermostat, standard Saturn s-series. I ground the pin down, now the engine temps are 185-190. Thats 40 degrees warmer, so it probably opens at 225F or so. The temperature gauge was at the first line, 1/4 now it's between 1/4 and 1/2. More heat too. Averaging 51 mpg so far this tank, not bad for December weather. I don't know how engine temperature equates to mpg, on the absolute scale its 604 Rankine or 7% hotter, so maybe I''ll see a 3% increase due to volumetric deficiency.

Air inlet temperature is 150F after 15 miles freeway warm up, about 115F above ambient.

[spacemanspif]

Good job with the t-stat, Tony. Where is your temp gauge needle now? I'm pretty sure that your '98 should ride just shy of the 1/2 mark, like mine. Chances are that you could have bumped your temp up with the a new stat and bump it even higher by grinding the pin more. FWIW when I replaced my stat many years ago I didn't notice any difference in mileage...I was keeping track of my mileage but I wasn't trying to hypermile either...

I'm running high 30s so far this winter...

[arcosine]

Its half way between 1/4 and 1/2. ultragauge reads it's about 185F. Saturns have reverse flow, the thermal sensor is in the head, near the coolant inlet, the block is hotter at the outlet.