Any one ever used an Air/Fuel ratio gauge to determine MFI ratio

[Ho Hum 74]

Folks,

I'm about to complete my 2.7 MFI rebuild (with the help of my friends Souk and Chris Streit ). My MFI runs VERY rich. I get about 220 miles out of my tank.

I have read all the literature on tuning the MFI etc. But I couldn;t help noticing the Air / Fuel ratio gauge and transducer for sale in a Performance Products catalog. What I was wondering is the following:

1. Is this a good way of indicating relative richnesss/leaness of our MFI cars under many conditions?
2. Has anyone else ever used this product? Seems pretty simple - just weld a nipple on the header.
3. Are there any other products out there that are better?
4. Does it fit into the clock position on the dash? I was thinking about nixing the clock and putting this in.

What else would help me lean the car out a little? Of course I don't want it too lean but I'd rather not have the folks behind me complain of gas fumes when I put my foot down (as they have been).

Thanks

Tristan

[Rot 911]

Why not just get the Gunson gas tester for around $130.00 and set the idle and 3000 rpm mixtures? Once you do that, it should run fine across the rpm range.

[Ho Hum 74]

Kurt,

Thanks. OK. Never thought of that. What is a Gunson gas tester?

Tristan

[Rot 911]

It measures the CO at the exhaust. Very easy to use. I used one on my '72E. Here is the review I posted here a couple of years ago: Gunson Gas Tester Review

[MotoSook]

I have not used a Gunson tester yet, but I had the use of a friend's 4-gas ananlyzer...much better than the single gas analyzer.

If the Gunson gets the job done, great, but the 4-gas seems to be a better tuning tool. We were able to make various changes that are affected by by-pass air, ignition and idle mixture screw (on a CIS..so MFI may be voodoo).

I can't imagine that a CO tester alone will provide a really good tuning...But! That's just my experience...

Tristan, we have a local track junky with a 4-gas at his shop...I bet he'll charge less than the Gunson's cost...which you may use once or twice in a great while if you bought it.

EDIT: Kurt don't get me wrong, I would like to own a Gunson tester, for the minor tweeking, but I would love a 4-gas...or one of those sniffers that MikeZ picked up for cheap....

Mike...can you track one down for me?

[Rot 911]

Souk, no doubt that the 4-gas tester is superior. However, MFI problems are usually due to an over rich or lean condition that is easily resolved if you know the CO readings.

[William Miller]

One thing the CO meter can't do is tell you what's happening when you drive. You can set the mixtures dead on when tuning at idle, but the A/F meters give a lot more info about how your mixtures are doing while you are driving. Unless you are tuning for an emissions test, watching the idle CO does not tell you what it's doing under load conditions.

I have an anilog A/F meter mounted just below the knee pad. ( It's upside down but I didn't want it sticking out.)

I was having problems with my CIS. If I adjusted CO at Idle it was running too lean during light load conditions to the point that one cylinder would drop out. (Ths was a guess until I installed the A/F meter.) With the A/F meter I can see exactly what happens with the ratios at every engine condition. Now that I have solved my problems I can see it lean out as the cold running compensation (Control Pressure on CIS) stop doing their thing ans I can watch as the acelleration enrichment functions react when I stop on it.

All of this information will help you tweek your system. I don't have MFI but I'm sure there are some adjustments that are not only at idle. If not you can see if it's owrking as designed.

I think it was a good investment. I think the analog gauges with a/f ratios are good.

[911pcars]

For in-vehicle monitoring of A/F ratios, use a wide band O2 sensor in the exhaust system (preferably two sensors) or ......

run on chassis dyno with their A/F ratio analyzer (wide band sensor) connected to exhaust pipe.

Regular, narrow-band oxygen sensors are not as accurate outside of stochiometric (14.7:1 A/F).

BTW, in my research, I could find only one source for a dual, wide-band sensor system.

Sherwood

[Ho Hum 74]

Sherwood - thanks for the info but the link isn't working. Not sure if it's my ISP or what.

[jpnovak]

I tried the link earlier, didn't work. Seems to be fine now.

Jamie

[Randy Webb]

You might also try just putting in a stock lambda sensor and measuring that. Might be cheaper.

[Ho Hum 74]

Randy,

Like this? http://www.speedshop.org/store/scripts/prodView.asp?idproduct=15

[Randy Webb]

I would use a datalogger -- I like to see the trace.

[911pcars]

I'd opt for something other than a one-wire sensor they sell. Use a 3 or 4-wire sensor if you choose that type of system.

Sherwood

[kanihitit]

My .02

One wire sensors aka factory O2 sensors are not sensitive enough to do serious tuning/tweaking. If you are going to tune with a factory O2 you do not need a 70 gauge. If you have DVM it will do the same. Factory 02 tuning can get you in the ball park but widebands help get you in the bleechers.

As mentioned earlier, a wideband setup is a powerful tool for extracting the most power out of your car at different engine loads. Many people have identical mods on their cars but some cars seem to make more and more power while others languish. Tuning is always the overlooked variable.




PS. I would like to suggest that you tune your car with a wideband on a dyno. Driving on the street and trying to tune your AFR is very very dangerous. Dont ask how I know.

Speed Safely

[William Miller]

Mine is a 3 wire.
I had a debate going at one time with Charlie in the NOVA Gang.
I still cannot understand why a narrow band is said to be not accurate.
I can imagine that the wide ban is probably an improvement, but what I have seems to work well. Can some with some documentation clue me in?

I certainly would like a data logger but it would really be useful if it could log several functions at the same time. A/F, control pressure, tempature, vacuum, rpm's.

Even without it over an extended period of time you sort of log the data in your own head. You get used to what is normal and what's not.
As I said above you can watch on the gauge how the various oparts of the system are effecting the A/F.

Remember mine is a K-basic cis with no computer. It would be intresting to watch a A/F gauge in action on the K-lambda and later computer controled cars. Although they probably do such a good job managing the A/F that the meter probably doesn't move much.

Problems with Dynos is that If you experience a symptome when driving you may not be able to duplicate that on the machine.

I think all of these have tremendous value and limitations. Some cost more than others.

[rs911t]

I would use a datalogger -- I like to see the trace.

I bought a Lambda Boy with analog outputs I plug into the DL-90. Nice way to produce AFR-to-RPM graphs.

[MotoSook]

That Lambda boy is expensive! Wow! I think Tom Tweed has a A/F meter/logger that has a starting price below $300. If I recall correctly, it can handle something like 5 inputs, and log 45 minutes of data.

Such a tool would be great for frequent tuning and analysis, but for street or track car that is set and leave until something else changes...an anolog gauge and a 3-wire should be adequate.

I'd like on like Tom Tweek's, but I'm also going to put an analog gauge in the car.

Anyone wanna buy a kit from me?

Greg, can't you direct wire an O2 sensor to the DL-90? I wish I had a DL-90

[ttweed]

Originally posted by Souk
I think Tom Tweed has a A/F meter/logger that has a starting price below $300.

Starting price is $349 for mine, but I got in on a group buy and saved a little (10%). It's an extra $99 for the aux. input cable if you want to log 5 inputs. It's an invaluable tuning aid. Their website is here. Good support and a great product.

Sherwood- I'm interested in why you think a dual channel AFR instrument is better? I have only seen that used with before-and-after cat converter systems. Are you talking about putting a bung on each header and monitoring both banks of cylinders simultaneously?

TT

[cowtown]

Originally posted by William Miller
I still cannot understand why a narrow band is said to be not accurate.
I can imagine that the wide ban is probably an improvement, but what I have seems to work well.

The narrowband is accurate in terms of showing the stoich. point (cleanest burning mix), it's just that it won't show other mixtures. We want to set up out cars to run closer to 13:1 or maybe even 12:1 for maximum power under acceleration, and maybe 15:1 for cruising. The NB sensor can't show these. It just reports "rich" or "lean" in a sort of binary way.

The NB sensor is fine for showing you that you're not running lean, though. I use a generic NB with an Autometer gauge on my 930 engine, just to be sure it's not going to blow up under boost. But I'm saving my pennies for a WB setup.