air/fuel gauge goes back and forth like a pendulum

[hunyango]

I put in an air/fuel gauge in my '94 Civic 4door with a t25 turbo (no intercooler) and it reads like a pendulum while cruising, reads zero fuel when I let go of the gas. Is it my engine? Is it normal? Is it the gauge? Thanks.

[ghettoturbo]

thats normal...its the reading at wot that matters

[TurboEF9]

The reason it does this is because your ECU has 3 modes it runs in when dealing witht he fuel interpolation routine.

1) Open loop. This mode is initated by ~80+% throttle position, and on newer ECUs, engine load. It reads from the fuel and ignition tables, and interpolates the pulse width duration, and degree advance strictly from this. This is the most basic mode, wide open throttle.

2) Closed loop. Closed loop is the "fuel economy" mode. Basically, below 80% throttle, your ECU uses the fuel and ignition tables as a base for calcuating pulse width, and degree of advance. Other things are factored in depending on ECU generation like O2 (all ECUs), engine load and so forth. During this mode, your ECU attempts to calculate a "perfect" 14.7:1 stoichometric air/fuel mix. This is the cause of your "bouncing" A/F gauge. The constant recalculation by the ECU of your air/fuel ratio. This mode is not particularly easy to tune in, and is not recommended because of the ECU's constant compensation.

3) Limp Mode. Not much is known about this except it is initiated when your ECU cannot read from the EEPROMs (when chipped). I have not heard of it dropping into limp mode on a an unmodifed ECU, but anyway, the characteristics are normally a 3333rpm rev limit, and solid CEL(0). It is believed your car is getting the fuel and ignition readings from a look up table other than the stock maps, because your car can run, but it runs like crap. However, the locations of the fuel and timing settings for this is not confirmed.

[hunyango]

So.... in english, it's about normal. Right? It does this 'coz of the turbo? Thanks, professor.

[oscarmayer]

here's the deal, those aftermarket a/f readers are a joke. they do not at all offer any realtime nor accurate readings. if you want it to work proeprly you have to ge yourself a real wideband o2 setup. aem, and many others have them for starting about $320 and up.

if anyone here is relying on those cheap a/f readers to tune your car, i feel really sad for here becasue you will melt down your pistons and ruin the motor.

that gauge is more like for looks than functionality.[/img]

[AudioMan]

Yes, alot of that guage is for looks, but it is helpful. It should nver be use for tuning, but it is helpful.

Say you get on the car and the af is reading a little rich (green), you know that you are ok. Now, while your on it, the guage drops to lean (red). This is a sign to get your foot off the gas asap. now that $60 guage just saved you from blowing your motor.

Every car that i build gets and a/f guage and a fire extinguisher always.

[Bizzar]

if anyone here is relying on those cheap a/f readers to tune your car, i feel really sad for here becasue you will melt down your pistons and ruin the motor.

[/img]

hmm supercharged D15B7 8lb pulley peaking at 10psi, 245k miles and counting, boosted for 35,000... tuned off a cheapo air/fuel guage. Nope they must not work. Sure a wide band would be nice for fine tuning but what are we really tuning for anyways? WOT correct!!! And thats where a cheap guage will do just fine. Tuning at WIDE OPEN THROTTLE. I started real rich (guage pegged out under wot) then slowly decreased the fuel pressure untill it backed down. Making a test run each time of course. Then I bumped the pressure just a tad high and advanced my timing a few degrees. Now it sits about 3 bars into rich under full throttle. Sure seems to work for a poor mans way to tune. 36mpg and runs like a bat outta hell. I hope you feel sorry for me :lol:

[oscarmayer]

well yea wot, but you have to remember when you let off the accelerator the ecu stiops all fuel from flowing to the engine, thus if your not tuned for the rest of the casr, your goign to run very lean at the wrong times and can end up with detonation badly. deceleration detenation is the msot dangerous type ever. why? well the motor is being told to let everything relax and prepare for lower rpms and less performance elvels and yada yada, now if it is detonating dueing thsi time. there is NO fuel to save anything. no way to enrichen anything to prefent the issue, thus bare motor runnign on it's own. all this happens in about 1/20 of a second.

looka t it this way. every 4000 rpm the motor has turned over about 460 times a second. so do you think you'll hear the issue before it does damage? wot tuning only is dangerous. it shoudl only be peforumed after normal tuning is done, but hey to eaches own. i woudl never tune a car that way but if your comfortable with it, i respect that.

[hunyango]

What's WOT mean? My last vehicle was a '54 Willy's Jeep, so I'm pretty new at this. Is it normal that my cheapa** air/fuel gauge goes back and forth like a pendulum? Anybody? In hobo english? hehe.

[TurboEF9]

So.... in english, it's about normal. Right? It does this 'coz of the turbo? Thanks, professor.

If you're not willing to read, then why should I post?

NO, it does not do this because of the turbo.

It does it because of the ECU's closed loop routines. Reread my previous post, and if there is something in that you don't understand, use Google to look it up. There is nothing out of the realm of simple understanding in there. I feel you can do it.

WOT means Wide Open Throttle.

[ghettoturbo]

well yea wot, but you have to remember when you let off the accelerator the ecu stiops all fuel from flowing to the engine, thus if your not tuned for the rest of the casr, your goign to run very lean at the wrong times and can end up with detonation badly. deceleration detenation is the msot dangerous type ever. why? well the motor is being told to let everything relax and prepare for lower rpms and less performance elvels and yada yada, now if it is detonating dueing thsi time. there is NO fuel to save anything. no way to enrichen anything to prefent the issue, thus bare motor runnign on it's own. all this happens in about 1/20 of a second.

looka t it this way. every 4000 rpm the motor has turned over about 460 times a second. so do you think you'll hear the issue before it does damage? wot tuning only is dangerous. it shoudl only be peforumed after normal tuning is done, but hey to eaches own. i woudl never tune a car that way but if your comfortable with it, i respect that.

what? when you let off the gas there is still fuel flwoing to the motor, just not as much. and if your motor was turning over 460 times a second, you would be at 27600 rpm, unless im not understanding what youre saying. if youre worried about not having enough fuel upon decelerating, you could richen up your part-throttle settings.

[Rexinre]

A little story!

No one told me about the wide band O2. I tryed to tune my car with it at the Englishtown track. It kept saying I was leaning out so I gave it more and more fuel, now I was up to like 90% fuel and my fuel injectors were maxing out. I got mad and made an appoitment with Bob Ida to get some dyno time.

We put in a Wide band O2 and the computer told me I was getting waaayyyyyyy toooooo much fuel! I turned it down to like 20% and gained a whole lot of HP. I was overloading my car with fuel... Anyways my point being the narrow band O2 didn't do shit for me! Some Food For Thought!

[transzex]

throttle closed decel, the fuel injectors are shutoff TOTALLY.

At 1100 rpms, the ecu brings the injectors back online.

[konigcivic]

you guys can talk shit about the gauge all you want... your damn right about not being able to tune off of it but it will tell you when you are running lean. it saved my ass 2 times and its the best 60 or whatever i paid for it, that i have spent!!id rather pay 60 for that and it says im running lean than to have to pay for a tow and a new motor cause a damn vacuume line fell off the zex nmu.

[transzex]

konig, I hear ya!!!!!!!

[ghettoturbo]

throttle closed decel, the fuel injectors are shutoff TOTALLY.

At 1100 rpms, the ecu brings the injectors back online.

i stand corrected, ive never heard of that

[Rexinre]

Me either, learn something new everyday!

[civicstyle]

at idle my car reads lean bad does this happen to anyone else? it does go back and forth like it is so post to do but it will go down to the last notch of lean and sometimes disapear off the gauge for a sec .is this normal?

[gear]

What's WOT mean? My last vehicle was a '54 Willy's Jeep, so I'm pretty new at this. Is it normal that my cheapa** air/fuel gauge goes back and forth like a pendulum? Anybody? In hobo english? hehe.

WOT = Wide open throttle. Your a/f gauge should swing like a pendilum while in Stoich. Mine does it as well. Also your car should read in the green (rich) under full throttle aka WOT as mentioned before.

[Lule]

Mista Bone is completely correct about the injectors shutting off. It's just AMAZING what you'll find in a Helms manual. While I'm all for the A/F gauge, I'd spend that $60 on a manual first. Knowledge is horsepower.

[Bindegal]

Here´s a link to a very good description of both narrow-band (standard) and wideband sensors and how they work.

http://www.autoshop101.com/forms/h37.pdf


/Bindegal

[csaddict]

Um, I'm new to turbos but couldn't you look at your plugs? Thats the old school way. I dont care if the A/F gauge is a piece of shit or not, I'm getting one. When an injector craps out or something it would be good to have.