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hand-made Air/Fuel ratio gauge

8761 Views 24 Replies 11 Participants Last post by  Stavros
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I got this from a friend of my uncle. He makes them from scratch. It is pretty precise, since it has 30 LEDs in all. Has helped me solve two problems so far: O2 sensor, and an exhaust manifold leak.


The red light on the far left is the power light. it stays on. sensor hasnt warmed up enough to send a signal yet.


Green for Rich


Orange for middle

And red is for lean.
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Thats interesting. It's good to see stuff like that being homemade rather than just buying name brands.
any chance of him making one for us?
Im guessing its narrow band running of the stock o2?
Possibly work with an wideband? I like how its setup...looks sweet!
Tiersin, i can ask the guy... he lives in Greece though. I will see what kinda price he is asking. mine was a gift cuz im awesome

ill see what he says about narrowband and wideband sensors... mine's just the stock single wire sensor (narrow).
lots of LEDs = cool looking stuff.

also nice that you fixed problems with it. Nifty.
Are the LED's pretty stable, or does it doe the back and forth light show like the Autometer one?
if youre gunning it, the LEDs jump to rich... and stay until you let go

if youre decellerating, they jump to lean... and stay until you apply the gas...

if youre coasting on the freeway... they jump from borderline rich to borderline lean

at idle it cycles from rich to lean.

unless my car is broken (which it has been known to be broken a lot) i think thats how its supposed to work.

ill let you take it for a spin tonight... ill give you a call. youll see :)
stickershop said:
Are the LED's pretty stable, or does it doe the back and forth light show like the Autometer one?
I have the autometer one. Its useless
Richrowa said:
stickershop said:
Are the LED's pretty stable, or does it doe the back and forth light show like the Autometer one?
I have the autometer one. Its useless
Useless unless your car is running abnormally rich or lean...or if your oxygen sensor is toast. That's about all it can tell you.
Everytime someone says that the autometer one is useless, I just think to myself that I don't think they knew what they bought. I have found like 5 problems using mine... it's all relative. It definitely helps if you mess around with NG series roms if you get into chipping (not to tune but to find problems).

The dancing lights are what is supposed to happen. The catalytic converter needs a rich lean rich lean condition to operate properly.
its not worthles because of what it displays. its worthless because of what its hooked up to.

the stock narrowband 02 sensor can only really tell if you are richer or leaner then stoich, anything outside that range of just a few tenths lambda, and its not very useful. I dont know what kind of problem it could alert you to that you wouldnt already know.

the dancing light part is when you are in closed loop. if you disable closed loop, the lights wont jump back and forth.

I use an autometer guage hooked up to the recalibrated output of an innovate lc1 wideband, and it actually is useful as a quick reference to whereabouts my AF is. in my case, the leds on the guage actually mean something, and the gauge has full lambda resolution, from 10:1 to 18:1.

I run open loop all the time (while still breaking 40mpg on my way to N) yay for tuning.

i like that guage though, great for a DIY deal, if it was hooked up to a W02 it would be that much more useful.
When using some NG series roms it would not run in closed loop until you forced it into a full lean condition at least one time, then it would run if closed loop..... ecu didn't know that it was a problem. You could drive forever without it going into closed loop at all if you didn't force a full lean condition. Autometer o2 readings clearly showed this problem.

When I used a pr5 ecu it couldn't tell me that my o2 sensor wire was cut in half (header is low to the ground). Autometer o2 reading clearly showed the problem.

I have used some older roms that showed they would not go lean in closed loop mode, on the autometer gauge it would only sweep from stoich to full rich. Showing that it was a pretty rich rom.

I think there was 2 other times when the autometer o2 gauge showed me something was wrong and the ecu didn't know.
interesting. ok, im willing to accept those as valid haha, i didnt realize those old bins were so screwy. id be scared to run my car on somehting so flaky...

when the o2 wire was cut in half wouldnt you get a code 1?
Neato.... now hook it up to a wideband sensor, and you'll have somethin nice :)

Just a neat example... i had a car come in to tune, and the 'lightshow' showed it being rich. When hooked into the Innovate Wideband i have, it was showing 16:1 (this is with it in a bung that was right on the downpipe, not on the tailpipe).... WAAAAAAY too lean. Got it running right with the wideband, and doing 12.5-ish:1 under boost, and it was running 100x better. So just to show, even if your lightshow is showing rich, you may not exactly be right still.
akirarex said:
I have used some older roms that showed they would not go lean in closed loop mode, on the autometer gauge it would only sweep from stoich to full rich. Showing that it was a pretty rich rom.
were these aftermarket ROMs? my uncles use these guages in their race car set-ups for customers... and from what ive heard, a lean mixture under high performance circumstances means detonation. could it be that these roms were set-up for race applications? or is it that im not reading things right
oh yeah one more thing to note, when you wire up these gauges you really shoul dbe wiring them right to the ecu for signal and ground. if you use your chassis ground, it is likely off from the ecu groudn and the voltage differential will really screw up your readings. on a gauge that reads from 0-1v a .1v ground differential can really screw you up.

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Matt, with a pr5 ecu it would not throw a code1, with a pm6 yes it did.
Matt also makes a very good point about proper connections, I know I had to use a ground strap from the chassis to the o2 sensor body to get a more accurate reading (rust).

The NG series is from Turboedit, which has gone through many revisions and versions.

The lean condition is normal, but how lean and how long it stays there is what you have to worry about. The only reason that the computer makes the engine run rich to lean to rich to lean etc.. is to make the catalyst in the catalytic converter be at a high enough temperature (to operate the rhidium and platinum as catalysts). Obviously too much either way burns the engine or the o2 and converter. So going lean doesn't alway mean detonation, it is a normal part of the operation.

If you were to use this same homemade kit on a wideband it wouldn't be right because right now it's dividing about a 1 volt range into blocks, widebands are 5 volt so you would need some tuning (a different voltage divider layout) to this piece of equipment to make it read accurately for a wideband. Or is it programmable??
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most W02s have programmable linear analog outputs. I ust output 1 recalibrated perfectly for my autometer gauge (which i tested on a workbench to get actual voltage range per LED (its not linear!)) and output 2 recalibrated to run from 0 up to 3.75volts (the max input on my ecu)

[email protected]
ComposiMo said:
Neato.... now hook it up to a wideband sensor, and you'll have somethin nice :)

Just a neat example... i had a car come in to tune, and the 'lightshow' showed it being rich. When hooked into the Innovate Wideband i have, it was showing 16:1 (this is with it in a bung that was right on the downpipe, not on the tailpipe).... WAAAAAAY too lean. Got it running right with the wideband, and doing 12.5-ish:1 under boost, and it was running 100x better. So just to show, even if your lightshow is showing rich, you may not exactly be right still.
I think you are right. If it was wide band if would be more useful. I tried to tune but it was never right using the narrow band. Went to the tuners with wideband and dyno, and with my S200 its like a different car, better car. Amazingly smooth, b16, idles fine cold and hot, 33 mpg, and good power. My buddy with a chipped ecu, cannot believe how much better my car runs then his. His farts and bucks when cold and I think runs much to rich generally. Thats the problem with chipping, it was made for someone elses setup, probably not yours.
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