The Free Mod Series - Part IV Cheaply Monitoring the ECU & A/F

[Toysrme]

There are soo many ways you can have fun with cheap electronics! First there was the ECT mod for adding .5-1* advance of ignition timing, and increase base fuel trim up to 4%.




Reading and deciphering what your car is doing

Background:
So you're running stock, have some upgrades, or maybe even have a low power Turbo, or S/C system and you're still running the stock ECU. How can you possibly tune the engine without hundreds of dollars of expensive 1 time dyno tuning???

Theory
A tuned engine is a happy, powerful, and economic engine! The OEM doesn't understand this.

The Vf signal. Our lifeline into what the ECU is doing to the base fuel map!!!

The Vf signal is the ECU's way of letting the world know what it is deciding to do with the fuel mixture. When all the sensors have sensed, the ECU has picked a map to run in, and everything else is said and done, the Vf signal shows you what the ECU has decided to do. (This is your long and short term fuel trims in an OBD-I car)

By connecting any type of volt meter to the ECU/diagnostic port, you can read the votlage of the Vf signal.
0V = Rich mixture 11-20% from normal (ECU is leaning the mixture)
1.25V = Slightly rich mixture 4-10% from normal (ECU is leaning the mixture)
2.5V = Within 3% of the basic map
3.75V = Slightly lean mixture 4-10% from normal (ECU is richening the mixture)
5V = Lean mixture 11-20% from the mixture (ECU is richening the mixture)



I have two wired up. One reading each Vf signal (Vf1, Vf2) One is for the front bank, while the other is for the rear bank. (Obviously I4's will have one Vf signal) If you feel like figuring out what the new voltages will be, you can bridge Vf1 and Vf2 and read the entire thing at the same time, but I wouldn't do it.



The o2 sensor. The only way to see the end result of the ECU's tuning!

The Vf signal shows you what the engine is doing in an attempt at perfect tuning. The o2 sensor shows you the end result o f what *actually* happened. By comparing the o2 voltage to the Vf voltage gives you a fairly accurate representation of what your engine is doing in the current conditions, and where you need to go.

This works with older lambda (narrow band) o2 sensors... You just can't accurately tell the A/F ratio.

If you can find a 1v, 1.5v, or 2v volt meter, you can wire those up to the oxygen sensor's themselves, or the oxygen sensor simulators from the ECU, or the diagnostics port under the hood.
450mV should correspond with 14.7 air/fuel ratio. The ECU will try to achieve this basically any time you are not more than 80% throttle. The smaller the voltage, the leaner, the larger the voltage, the richer.

*note* there is the *real* o2 sensor voltage, and there is the *simulated* o2 voltage delivered to the diagnostic port. The simulated o2 sensor is a stead, averaged signal that will like a tiny bit behind current conditions (.1-.5 second). The o2 sensor, while live, fluctuates quickly (a good sensor will fluctuate at least 8-10 times a second @ 2500rpm, and between 400-550mv at idle/cruise)
(bank 1 sensor 1 is the front bank o2 sensor, bank 2 sensor 1 is the rear bank o2 sensor)

The combination of the three allows you to see what the ECU originally wants to do with the A/F ratio, what the ECU is trying to do with the A/F ratio, and if it is successful in doing so. From that, if you have any idea about tuning you can interpolate fairly well how to do something.

Now! Someone will ask if it matters that you do both sets of signals. Not really, considering only the ECU itself can tune every individual signal. *However* I have all ready found that the signals do not always match each other... Often times during, and immediately after transition periods, the sensors will not match by a setting or two.



CEL's are fucking annoying

You can wire up a switch in your cabin to check, and clear CEL's!!! This is very easy to do since above the driver's left foot is a diagnostic port which contains the second set of E1 and TE1 terminals. Simply splice the two wires together with a switch/hold button, and whenever you want to check/clear a code, simply hit the switch which will connect (ground) TE1 to E1!!! Instant basic diagnostic mode!!!




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Other Articles in the Series:
Part I Quicker Transmission Shifting
Part II Adding Airflow
Part III Taking Advantage of Intake/Exhaust Upgrades
Part IV Cheaply Monitoring the ECU & A/F
Part V How to pick up MPG, and sleep with her too!
Part VI Acing Aerodynamics
Part VII Cheap Water Injection
Part VIII Electronic Transmission Controller
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[noofa]

its all good info in the 'Free Mod Series'

Worth having a sticky that has links to all these threads which you can update to add new ideas. Kepp them coming, anything that improves your car for free is worth it

[dna59]

Finally another part of the wonderful series.

[CrawlingEye]

Interesting tid bit on voltage tuning with the o2 sensor. I've never found something actually laid out on voltage tuning (like x volts = a/f ratio of: **:*).

I'm wondering though, since you obvioulsy tune using these methods, have you found most narrowbands to be fairly accurate with o2 sensor tuning or no?

[Toysrme]

Yes and no. Whatever the average voltage the o2 signal dances around, is most likely going to be 14.7. That's going to be around 450mV. After that it doesn't really matter, because even if I could tell you what the top and bottom of the scale are, we don't know what the middle of the scale is so it's a moot discussion. It's just richer and leaner.

That being said... If you know what direction to go with fuel and what you want to do with peformance; it's not hard at all to figure out what to do.




Is what a narrow band votlage output looks like. It's accurate at 14.7, and nothing else. However... The higher the voltage, the richer, and the lower the voltage the lower. Just because it can't tlel you (you're running 12.5-1 A/F ratio) doesn't mean it's as useless as many people make it out to be. You simply have to know how to interprit the data.

It's basically a "relative" answer. By watching the Vf signal, you get to see what the ECU is *trying* to do. By compairing the o2 sensor voltage to whatever it previously was, you get to see if it is successful or not.

[Toysrme]

I've been asked constantly for what do the voltages mean. You can see on the scale above, that they are not entierly accurate. However, once the sensor is up to temperature and the car is running, they're a good deal more accurate than the graph as you to believe.

Now. One thing to keep in mind is that a narrow band o2 sensor will varry it's output as much with TEMPERATURE as it will oxygen! ONLY use this once the o2 sensor has come up to temperature.

A good tip to remember is this. If the engine is at a constant load (idle, cruise) under 80% throttle the o2 sensor is GOING to varry around 450mv... The ECU is GOING to find a way to tune the A/F ratio around 450mv. If you are at a constant load and it reads sometime else, don't worry about it. The temperature is fluctuating it. The ECU knows this, but most people do not.

Anyways... At a normal operating temperature of 600F.
Volts A/F ratio:

0.1 - 17:1
0.2 - 16.5
0.3 - 16:1
0.4 - 15.4
0.5 - 14.9
0.6 - 14.4
0.7 - 13.8
0.8 - 13.2
0.9 - 12.7
0.985 - 12.1

[CrawlingEye]

good info, maybe I'll go out in a bit and tune my car to 13.2
gotta find my multimeter though.

[aych]

pictures please! all these terminal things are jumbling my mind. i have a 88 camry le (gen2) I4

[bigbluemonkey502]

would it be safe to assume that for an i4 camry, since it only have one cyl bank, that bank one senser one of the diag port would be the simulated o2 or would it be else were in an effort to complicate life? lol

[rgm1800]

is this applicable to 4efte engine?

[Camry LE 94]

how do i know which one is the TE1/E1 terminal?