Dodge SRT Forum banner

1 - 20 of 25 Posts

·
Registered
Joined
·
13 Posts
Discussion Starter #1
Don't waste your money. I'm on my 2nd SC car and had looked into buying an A/F gauge untill I read up on them. A typical A/F or "Rich/Lean" gauge is a complete waste of money. It is NOT accurate at WOT conditions. Why? Because it reads off of your stock O2 sensor. The problem lies with how the o2 sensor produces "stoich" voltage. Stoich in most cars is 14.7 A/F ratio (far too lean in a forced induction car) which gives the most complete burn and best emissions. An 02 sensor voltage will "cross" or alternate "around" this voltage (the exact voltage is dependent upon which brand of sensor you use.) The factory ECU looks not at the voltage, but at the rate of "crossings" it sees from the sensor. It will adjust the A/F ratio to give a continuous high rate of "crossings." This means that any "A/F gauge (actually a simple voltmeter) you use will usually dance around pretty good...not much use. Even worse, at WOT conditions, the voltage of the sensor will be at a non-linear portion of the response curve that is not accurate and is not intended to be. You will not get accurate WOT readings at the portion of the curve you want to look at for a turbo or SC vehicle (11/1 to 13.5/1 A/F.)

I'm new to this board, but I have read a lot of BS here about "get an A/F gauge" and so forth. Don't do it. They are useless. If you want accurate A/F readings in-car, buy a wideband o2 setup ($750 or so) that reads off of a wideband o2 sensor (this produces a current, not a voltage, therefore a simple voltmeter A/F indicator will not work.)

Hope this helps some of you from making a potentially costly mistake.
 

·
Premium Member
Joined
·
5,578 Posts
any pics of your car?

*hi-jack over*
 

·
Registered
Joined
·
180 Posts
Gotta disagree. A/F ratio indicators working off of stock Mopar O2 sensors work great for lots of people, including myself. The PCM uses the stock O2 sensor, not a wideband. Sure, wideband is probably better if you have the electronics to handle it, but certainly not necessary--especially when you quote figures around $750. :shock:

You make some pretty strong blanket statements there. "A complete waste of money," "not accurate at WOT," "dance around pretty good," "not much use," "they are useless," etc. All of this because you "read up" on it? Sounds to me like you've been reading someone's advertisement for a wideband O2 sensor!

I've found my a/f ratio indicator extremely helpful, and it doesn't bounce around at WOT. I also use an EGT.

Using an A/F/R indicator isn't going to hurt anything. You don't think we should monitor our a/f ratio? Here's what's really costly, cranking up the boost without monitoring anything but the boost gauge and the speedometer.
 

·
Registered
Joined
·
13 Posts
Discussion Starter #4
MIKE B. Read an ad for a wideband? WRONG buddy. I researched quite some time ago how stock o2 sensors operate because I had heard or read time and time again that rich/lean gauges or a/f gauges were not effective. So you are incorrect, they are not effective. Ask any reputable tuner. In fact, use an a/f gauge plugged into a stock o2 meter and run your car on a dyno with a wideband sniffer and see how the results compare. I witnessed this on a friends car...a/f gauge indicated "rich" (and was jumping around as usual) during the run. Black smoke was also pouring out of the tailpipe..."its running so rich that it smokes..." is what he said. Well, after the run we looked at the a/f ratio...15+ in the powerband on his blown GT. I talked to the tuner about it and he confirmed that they are not accurate at WOT...but he could not tell me exactly why. After seeing this I decided I was going to see WHY the a/f gauges are not useful and how I could possibly use a microcontroller with a lookup table to make one at least somewhat useful for my car. I gave up because, my money would have been better spent by buying a wideband 02 sensor and the proper current reading display tool.

I think I know a little bit more than you think on the subject. Also, instead of trying to insuate some bit of dishonesty on my part (think I'm trying to sell a wideband here? :roll: ) or naiveness, you should give me a little credit for taking the time to post this and save some people from wasting money on useless and potentially dangerous tuning/diagnostic tools. Do you have any idea what the response curve looks like for an o2 sensor? I doubt it. Do you know how the PCM uses the output voltage of the o2 sensor? Until you read my post, probably not.
 

·
Premium Member
Joined
·
1,154 Posts
im not sure about code in mustang ecu's but i think i may know why they aren't accurate at WOT. typically, at WOT, ecu's go into open loop mode and follow a different function for injection and ignition. i think this gets implemented by several manufacturers (of engine computers, not cars) as pretty much a guessing game that fluctuates a lot. this may cause the o2 sensor voltage to bounce around a bit, creating an appearance of an average voltage to the a/f meter, which may not be interpreted accurately. just a guess...
 

·
Registered
Joined
·
13 Posts
Discussion Starter #6
Jeremy Smolik said:
im not sure about code in mustang ecu's but i think i may know why they aren't accurate at WOT. typically, at WOT, ecu's go into open loop mode and follow a different function for injection and ignition. i think this gets implemented by several manufacturers (of engine computers, not cars) as pretty much a guessing game that fluctuates a lot. this may cause the o2 sensor voltage to bounce around a bit, creating an appearance of an average voltage to the a/f meter, which may not be interpreted accurately. just a guess...
No, this has nothing to do with it. The PCM simply reads off the voltage that the o2 sensor PRODUCES chemically. This is unique in that it produces its own voltage, instead of acting as a variable resistor and changing the voltage dropped across it that is supplied by another source. The PCM is not in the loop in the a/f gauges I have seen. They typically read the voltage directly off the o2 sensor. The bouncing around is the way the o2 sensor is supposed to work at stoich, a la 14.7 a/f ratio for emissions. At wot the PCM probably ignores the o2 because emissions are pretty irrelevant at WOT.
 

·
Registered
Joined
·
7,270 Posts
OK, answer this if you will. I purchased a Blitz Boost controller and plan on cranking the PSI up when I'm at the track. Stock boost holds at 11psi stock and periodically spikes at 15psi. If I crank it up to say 17-20psi, how do I know if I'm running to lean? I don't want my engine to go POOF!
 

·
Registered
Joined
·
13 Posts
Discussion Starter #9
drizz- that's what a dyno tune is for- knock sensor + dyno + wideband o2. I can't believe anyone would start cranking up boost without checking on a dyno & wideband.
 

·
Premium Member
Joined
·
1,154 Posts
CobraBri said:
No, this has nothing to do with it. The PCM simply reads off the voltage that the o2 sensor PRODUCES chemically. This is unique in that it produces its own voltage, instead of acting as a variable resistor and changing the voltage dropped across it that is supplied by another source. The PCM is not in the loop in the a/f gauges I have seen. They typically read the voltage directly off the o2 sensor. The bouncing around is the way the o2 sensor is supposed to work at stoich, a la 14.7 a/f ratio for emissions. At wot the PCM probably ignores the o2 because emissions are pretty irrelevant at WOT.
i understand all that. what i'm saying is, no matter what, you really can't take the pcm out of the loop. yeah, the gauge does not connect to the pcm. but, the o2 sensor voltage changes as exhaust gasses change, which is caused by the pcm's decisions. whatever the pcm may be doing to injector pulse and timing during a WOT open loop function may result in an electrically misleading signal out of the sensor. i may be completely wrong, but i just wanted to clarify. AFAIK, some ecu's in open loop will try to sneak in a rich mix every few pulses to be safe.
 

·
Registered
Joined
·
11,093 Posts
A cheap A/F meter is only that, cheap. Its not accurate. When the car is at WOT (wide open throttle), the 02 sensor is no longer adjustnig the fuel mixture of the car which is why it does not have to be as accurate . It does measure towards the ends of the scale.


When the car is at WOT, it goes to a default fuel map which gives the engien maximum fuel per say.
 

·
Registered
Joined
·
113 Posts
drizze99 said:
OK, answer this if you will. I purchased a Blitz Boost controller and plan on cranking the PSI up when I'm at the track. Stock boost holds at 11psi stock and periodically spikes at 15psi. If I crank it up to say 17-20psi, how do I know if I'm running to lean? I don't want my engine to go POOF!
EGT in the EX. manifold.
 

·
Registered
Joined
·
449 Posts
The way a narrow band sensor works makes it almost useless for tuning. You can argue that it helps you to know if the engine is rich or lean, but personally it doesn't help me to see a bunch of lights wildly bouncing back and forth. The only thing my air fule gauge ever helped me with was determining that an O2 sensor was bad.

A stock PCM doesn't look at what the air fuel ratio is it just looks to see if it is above or below the stoich point and then adjusts the fuel mixture accordingly. Most people have seen this graph from a NB O2 sensor:

So you can see that around the stoich point very small changes in ARF produce huge, wildly flluctuating voltages, which makes tuning a hit and miss operation. If you are trying to tune with a NB it can be done if you are careful, but skip the gauge and use a good digital volt meter hooked to the O2 sensor.

Compare the above graph to this table of AFR vs voltage output for a wideband:
http://www.diy-wb.com/v_out.htm
So with a wideband you actually know your air fuel ratio, not just if you are rich or lean. Knowing your actual air fuel ratio not only helps you from runing lean and melting your engine it can help you tune to make more power as well.

Anyone who can solder (or who is willing to learn to solder) can buy a WB O2 sensor and put together the electronics to run it for around $200. www.diy-wb.com I am working on one of those right now, and when I am done I plan on ripping the guts out of my Autometer gauge and replacing them with a circuit that will make it work with the WB. If anyone is interested I will post back in a couple of months if I get it all to work.
 

·
Registered
Joined
·
113 Posts
This is what my feelings are on AF gauges.

Written in another topic:
http://www.srtforums.com/phpBB2/viewtopic.php?p=8569&highlight=#8569
 

·
Registered
Joined
·
4,492 Posts
Anyone who can solder (or who is willing to learn to solder) can buy a WB O2 sensor and put together the electronics to run it for around $200. www.diy-wb.com
i was trying to read that and........well im lost lol they are speaking greek to me.....if anybody in florida makes one let me know and i will pay you to make me one.
 

·
Registered
Joined
·
180 Posts
First, I wasn't trying to insult anyone (Cobrabri). For all I know you are the premier mind in high performance automobile tuning. Not likely since you drive a Ford :wink: , but hey--anything's possible!

I don't disagree that a wideband O2 is better and more accurate. What I disagree with is the statement that an a/f indicator is "completely useless." You proved this yourself in your story about your buddy's car on the dyno. It was running rich, black smoke out the tail pipe, dyno sensors said it was rich, and the a/f indicator also said it was rich. What's not accurate about that?

At WOT the computer ignores the O2 sensor. It no longer knows if the engine is running lean or rich. If I want to know if it's rich enough or not at WOT I can tap into the stock O2 sensor and get an indication of approximately where I'm at. No, the a/f indicator is not the end-all of tuning devices, but it is useful.

About the bouncing around. A/F indicators aren't really made to be used at anything other than WOT. On an EFI car, the computer is taking care of the mixture at everything except WOT. WOT is where you want an a/f indicator, and if it's bouncing around at WOT it's probably not installed very well, or it's a crummy indicator.

For those of us who can't afford the state-of-the-art in engine electronics, an a/f ratio indicator and an EGT is good enough. I know lots of guys with very fast turbo Dodges and as far as I know, none of them have wideband O2 sensors--including 3 of them who can run in the 10's all day long.
 

·
Registered
Joined
·
13 Posts
Discussion Starter #18
Mike B. said:
I don't disagree that a wideband O2 is better and more accurate. What I disagree with is the statement that an a/f indicator is "completely useless." You proved this yourself in your story about your buddy's car on the dyno. It was running rich, black smoke out the tail pipe, dyno sensors said it was rich, and the a/f indicator also said it was rich. What's not accurate about that?

At WOT the computer ignores the O2 sensor. It no longer knows if the engine is running lean or rich. If I want to know if it's rich enough or not at WOT I can tap into the stock O2 sensor and get an indication of approximately where I'm at. No, the a/f indicator is not the end-all of tuning devices, but it is useful.
Uhhm, I said my friends car had A/F ratios at ~ 15/1....thats LEAN! So, in short, the wideband said he was lean as hell (he wants 12/1 on a blown street car) but the rich/lean gauge said he was rich.

As far as it being a tuning device, I still don't buy it. A turbo/blown street car should be ~ 11.1 to 11.7 to 1 at the upper rpms. If your rich /lean indicator is accurate to +/- 1.5 points, how could it be useful to tune with?

Bottom line- If you want to tune it, take it to a reputable tuner with a dyno and wideband sensor.

Oh, no hard feelings...after all, its bad enough that your Dodge has to eat the dust of every 03 Cobra prowling the streets :wink:
 

·
Banned
Joined
·
27,026 Posts
i think its time to call Dawes Devices :wink:
 

·
Registered
Joined
·
817 Posts
Let me chime in here and say that the important concern is not whether you are running lean or not, but whether the car is approaching knock or not. Hot intake temps due to increased boost levels or hot air outside can drive the car to detonation even if your A/F ratio is perfect. An a/f gauge will not detect this. Moreover, if you have shitty gas, this will also make the car prone to detonation. The best gauge that can tell you that "something" is wrong without actually pinpointing what it could be is the EGT gauge. It is highly recommended over the A/F gauge as it responds faster and is more accurate in telling you that you are approaching the danger zone of the engine. High EGT temps can indicate a variety of things:

o Lean mixture
o Hot intake temps
o Low octane gas
o Heat soaked intercooler
o Too rich
o pulled timing

Just my 2 cents..

-M
 
1 - 20 of 25 Posts
Top