RedFirebird

This is just a thought i had so don't flame me for it. We all know how the O2 sensor works sending a voltage to the ECM that relates to the oxygen in the exhaust and such. I was thinking that maybe you could splice that wire going to the O2 sensor and run wires from that to an adjustable resistor (i.e. potentiometer) in the dash or someother place inside the car. This would allow you to manipulate (right in the drivers seat) the voltage going from the 02 sensor to the ECM, creating a false lean, or rich (supposing you can find a way "add" voltage to the actual voltage signal), condition to the computer. This would allow you to provide for further enrichment (by creating a false lean condition with low voltage) for performance when you have a lot of compression and a lot of advance to avoid knocking and potential engine damage in high-load situations. If you could somehow increase this voltage (creating a false rich condition), you could lean the mixture when you are cruising on the highway for some extra MPGs. This is just an idea i had and was wondering what the rest of you thought.

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Red '87Formula Firebird
-mostly stock 5.0L LG4 w/cowl induction setup borrowed from '83 TA and T5 tranny.

My newest Ride:

'85 Silver L98 Corvette w/4+3 manual tranny. not bad for $3500.

86TpiTransAm

Sounds great in the perfect world. Problem is actually getting it to work. But I guess if someone's willing to take the time to work on it then anything's possible.


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1986 Trans AM
355 TPI
4 Wheel Disc Brakes
9 bolt Borg Warner Rear (2.77's....oh joy) :P
6" rods, approx. 9.7:1 Compression, Stock TPI (soon to be ported), 24#/hr LTI injectors (cleaned and flowmatched by Cruizin Performance), Hedman Shorty Headers, 3" exhaust with 80 series flowmaster, SBC 993 heads completely redone and modified for 1.6 RR, 1.52 RR (for now), Comp Cams XE262-14 TPI Cam, Holley AFPR, TPIS airfoil, MSD wires, MSD 6-AL Ignition, Hypertech 53,000 volt coil.

Track times to come.

89/90 rs/iroc-z

i guess you could do it but have fun figguring it out and i dont even want to consider how to hook that up. the reason i say that is because the 02 sensor creates it own voltage. and its on a millivote scale. the normal operation of one would lean rich between 200mv and 800mv i think.and normally you have to use a scope to watch the patternns on a millisecond pattern to get a good reading.


just my thoughts

8Mike9

The idea has merit, but by the time you figured it out and dialed it in, you'd be well on your way to burning your own eproms and "never having to touch that dial"

crucial

Actually the idea wouldnt work at all because the ECM doesnt care what the 02 sensor voltage is at WOT. It simply ignores it and goes by predefined tables in the chip.

At part throtle you could do that but you'd have to constantly adjust it. And how would YOU know what the engine needs ? More or less fuel ? I'd say take the time to learn how to burn chips, get a cheap laptop and put a scantool on it then make the necessary changes in the chip to make the engine run at an almost perfect, constant, 14.6 AFR !

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1992 Z28 5.7 TPI

ZZ4 longblock
Harland Sharp roller rockers
Accel base and SLP siamesed runners,
52MM SLP Throttle Body
Hooker Headers & Flowmaster catback
MSD6A ignition
aluminum driveshaft
World Class 5-speed

8Mike9

No, it could work...what you'd need to do is apply a bias voltage to the ECM input of the O2 sensor, this voltage wold have to be constant and add to the voltage of the O2 sensor. This would make the ECM think the car was running richer by the applied voltage amount, hence try to trim the fuel back to keep achieving crosscounts.

In effect, running it leaner through all ranges, except WOT.

Problem is using a voltage source of a very large impedance so as not to cause issues with the O2 sensor output and very small current as well.

But I'd still think that it'd be time better spent on EPROM programming, Glenn has his L98 running 30MPGs in his "highway" mode.

PALM BEACH IROC-ER

Actually VOLVO used this method on its 700 series BOSCH electric injected cars up through 1988. The AMM which is a smaller version of what is on most of our TPI motors same amount of wires too! It has a dash pot adjuster under the emissions cover A/F ratio meter helps here. Maybe the volvo units guts can be applied to the TPI housing, it appears they "the guts" are the size.

Just my $.02 on this!

Grim Reaper

No, crucial is correct. In PE (WOT), the ECM could careless what the O2 sensor is saying. 500, 600 or 900 mVs, the ECM does NOTHING to adjust the fuel trim.

In part throttle, it's useless as the ECM purposely adjustes between rich and lean (much faster than displayed on Diacom) to produce 14.7:1. Altering it would just result in "faking" the O2 sensor to give a different Air Fuel Ratio - you can do that inside the eprom.

The last problem is the O2 sensor itself is inaccurate at PE/WOT. Only a WB O2 sensor can provide an accurate O2 reading in PE/WOT. There is currently a DIY version that you can look at building yourself.

But, there is no way currently to get the output from a WB O2 sensor to be read by the stock ECM. And IF it ever get's figured out, there is still no way for the ECM to adust the AF Ratio.

8Mike9

I understand he's correct, but the idea would work, if the O2 sensor voltage was purposely held say, 100mv higher all the time, i/e run the O2 sensor output +100mv, then the ECM would would use the higher reading (without knowing it) to compensate, wouldn't it?

It's the same thing you're doing in the PROM, but just from the "other end".

Grim Reaper

What it is most likely to do is give an SES code (ie. the oscillations are not within the proper range when in part throttle). There is a range where the O2 sensor must oscillate and it cannot remain too high or too low outside of the range or it will trigger a rich/lean O2 sensor.

Doing it inside the eprom is different as it still needs the proper O2 readings for the oscillations. The only time the O2 readings don't oscillate is when in WOT or if you invoke Highway Mode which causes a "commanded AFR ratio".

Typically, when I have Highway Mode invoked, the O2 readings are in the 40-80 mV range (with 17:1 AF ratio). This is because the ECM runs off the tables for Highway Mode and the O2 sensor is "just for the ride" like WOT. This is why you need to have your BLM/INTs fairly close to 128/128 perfect for Highway Mode to work properly.

Initially, when I first invoked Highway Mode, my BLM/INTs were quite a bit off (I was actually running in the 115-118 BLMs, the minimum BLM for Highway Mode to work on SD). Because my BIN was still on the "rich side", when it invoked Highway Mode it no longer did "corrections" based on the O2 sensor. Thus it tried to lean my AF ratio based on my overly rich BLMS. The net result was I ended up running richer with Highway Mode invoked than just leaving it at 14.7:1, and burnt MORE GAS.

Only when I got my BLM/INTs close to the proper 128/128, did Highway Mode produce the results that I was expecting.

Bottom line, I see no advantage to "faking" the O2 sensor. With computers, "Garbage In = Garbage Out". And this will just cause "Garbage In". What is needed is "better information in" (ie. increased accuracy of the O2 sensor) so the ECM can rely on it to do other things.

This is why getting the ECM to properly handle a WB O2 sensor is a "hot" project with some people. This will offer new "tuning" possibilites within the ECM. Of course, there still isn't anything within the ECM to make "corrections" to Air/Fuel in WOT based on the O2 readings. But, if a WB O2 sensor can be successfully married to the ECM, then some "clever lad" may just write such a correction routine.

Mike, when are you going to start looking at Eprom Burning? Send me an e-mail if you are interested.

Vader

Glenn,

I'm guessing that there are no intense emissions inspections in Kamloops (still my favorite name for a Canadian city), but do you have any idea what the NOX emission are like at 17:1, or how hot the cat(s) might be getting?

Just curious. I know that it likely wouldn't be a factor on the sniffer dyno, since you probably wouldn't enter Highway Mode, but I'll bet your exhaust pipe gets pretty white while cruising down the road. Do you throw extra EGR at the intake during Highway Mode? Any heating problems?

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Later,
Vader
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If you want to beat the World, it might reach up and pull you down...
Adobe Acrobat Reader

Grim Reaper

Jeff, nothing "white hot" from the AF ratio. Actually, everything looks nice and "tanned" (plug wise). Never looked better.

The question as to what this does to the cat, especially in the long-term, is an unknown that I am currently testing. I have over 1 year and 20,000 miles with using Highway Mode. So I do have some "on-going" time on this.

The cat does not appear to be any hotter, but then again, it basically functions on the highway where you have more air movement.

I don't invoke it until 32 MPH. So, on IM240 test the highway mode wouldn't even be be invoked. I no longer required to take IM240 testing, but in other regions of the province, they are still subject to IM240 testing. When I was living in the Lower Mainland early last year, I took a test, so I do have some a "comparative".

I have been planning to take my car through "voluntarily" just to see what my current readings are. Personally, I expect it to be the same or better.

I did alter my EGR's operation. Highway Mode won't work unless the EGR is functioning. I modified my eprom to enable/disable the EGR based on MPH instead of MAT temp and basically my EGR is working all the time once I am exceeding 15 mph, except in WOT and Deceleration Enlean.

So far, it appears to have worked well over the last year. I think the more important question is "what happens in 2 or 3 years". I will keep everyone posted.

I should add that GM has "logic" to "cycle" the AF ratio between Highway Mode and "14.&7". You pick the period of time that you want the "cycle" to occur and how long it must remain in "14.7" before going back to Highway Mode. If I have long term problems, then a solution may be to run "14.7" every 10 seconds and then HM for 60 seconds, to prolong the cat's life.

Tell you in a year or two.

Grim Reaper

BTW, I should add that Kamloops doesn't have a rush hour, probably more like a a "rush minute". And I don't drive to work, I live close enough to walk to work. I would say that 99.9% of my 20,000 miles last year were all on the Highway.

[This message has been edited by Glenn91L98GTA (edited November 18, 2001).]

crucial

Glenn is correct. The ECM reads the "counts" which is how many times the 02 goes past the 14:7 mark or below it.

To hold it 100mV higher wouldnt work at all. You would need some sort of comparator circuit that looks the incoming voltage and quickly adds 100mV to it then ouputs it to the ECM. That wouldn't be exactly easy to build and not worth the effort IMO. Just go get an EPROM burner. Much cheaper!

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1992 Z28 5.7 TPI

ZZ4 longblock
Harland Sharp roller rockers
Accel base and SLP siamesed runners,
52MM SLP Throttle Body
Hooker Headers & Flowmaster catback
MSD6A ignition
aluminum driveshaft
World Class 5-speed

8Mike9

I could easily be wrong, but I thought a cross-count was made at 450mvs? At leats when I scan my O2 readings rich/lean occurs at about that point (450mvs).

If I always had an extra amount of voltage (100mv was just an example) then the O2 sensor would be reporting a condition richer (by the added voltage) that what it actually is.

Wouldn't it?

If so, then wouldn't the ECM try to compensate for it by leaning the mixture?

8Mike9

Thinking about it a little bit more, you wouldn't need to add any voltage, but run the output voltage from the O2 sensor through a simple OpAmp with a 1.x gain. Of course the voltage could never be zero volts, but what would it matter?

siuol

I know this is a very old thread. However I was doing a search for the normal voltage range of the o2 sensor and came across this. Adjusting the o2 sensor voltage is doable.

The reason I am looking for the sensor voltage is that I removed all emissions on my car and its running a little rich.

Is called an EFIE. See link below for explanation. It shifts the air/fuel ratio. I built one for a jeep that I converted to run on hydrogen and it works great. You can buy them already made on this link. Disclaimer, I am not associated with this concern.

Louis

https://www.fuelsaver-mpg.com/the-di...83b1eab8ae34a4