Just want to share my experiences with the AEM Air Fuel Ratio system I installed in my mildly modified '74 a few months back. You can get them for under $160 and I think they're well worth it. If you're running any kind of modified motor in a C3, with headers, carb, intake etc, you would do yourself a big favor and get one of these.

First, there's no having to 'read the plugs'. I don't care what anybody says, this is not the most exact science, that's for sure. Varying RPM's, differing fuel pressure movements, vacuum leaks and all kinds of things play into the air/fuel ratio at any given time. What your carb is doing at idle, versus 3,000 RPM or 6,000 RPM are totally different and even the short stab on the gas changes things.

Along with a vacuum gauge (which I run, instead of a clock), you will know, instantly, what's going on with your engine. Vacuum line come off? The AFR or Air Fuel Ratio will run FULL LEAN. I know, I've started the car, after messing around with the distributor and forgot to hook the vacuum line back up. I knew instantly what was going on. AFR bouncing around all over the place? The carb was dripping fuel through the secondary venturies. Could also be a misfire from a bad plug or wire (both happened and were fixed). The AFR should be pretty steady.

Another example: Runs good AFR (12.5 to 13.5 is good for most carb'd cars) at lower RPM's, but runs 15 to 16 at 3K to 4K rpm. Way lean. Took the Holley 650 carb off. It's a mechanical, double pumper and found the jets were the tiniest jets that Holley could possibly put in: 602's. The smallest jets in the Holley Jet Kit were 64's! Put the 65's in and at 3k to 4K the AFR was between 12.5 to 13.5.

And Saturday, I went down the hill and suddenly, whenever I stomped on it good, the AFR totally pegged Full Rich 10 and the engine would nearly die. I pulled over and found out that the cheap Fuel Pressure Regulator, that we just adjusted to 6 psi, was now running nearly 9 psi! Adjusted it and everything was fine after that. I've got an Aeromotive Fuel Pressure Regulator coming in from Summit tomorrow. The good Fuel Pressure Regulators are about $100.

The AEM kit, includes a bung for the 02 sensor, that's easily welded up to your exhaust collector by a muffler shop for about $30 and AEM gives you a ten foot harness, so you're going to actually have to loop it up in the fender, you get so much cord. You won't run short. The gauge has the digital interface built into it and it just needs power. I attached it to the top of the steering column, where I can keep an eye on it.

I like the AEM better than the Innovative, as there's no periodic calibration and the AEM uses a Bosch 02 Sensor.

http://www.aemelectronics.com/?q=pro...uego-afr-gauge


It has an automatic start sequence that's pretty cool as well. It will count down, then it will say AEM U06 and set itself instantly.

 

does the AEM have data logging capability?

If so how many parameters can it log?

Neal

 

It does have a data port for logging, but I'm not sure a about the details, as I haven't tried it yet. The AEM website has more about that feature. I'm happy for now, just being able to watch in real time, what's going on with my engine, while I'm driving it around!

 

This is what I use for data logging.

Sample during some tune run's in a 1/4 mile run.


http://www.zeitronix.com/index.html

I am currently only using a PC for data logging, but you can add many choices for gauges. This is not your sub $200 setup but like "F22" States AFR measuring is a very good way to go if you like to reduce the time to tune, and get it right.

 

Good post, most of our Corvettes have true dual exhaust. The systems described above show only one O2 sensor. I suspect that means we are reading only one bank? I put bungs in both exhaust pipes and have been looking at the metering systems, but they all seem to only use one sensor or do we need dual gauges and sensors? Or do we only need to monitor one bank of the engine? T

 

I plan to run the analog version of the Autometer Ultra-Lite wideband air/fuel. They only offer the analog in 2 5/8" which match the other gauges under the cowl, or I would consider the digital (2 1/16").

 

The C4's only had one O2 sensor. My thoughts on this, unless you're a serious tuner-race kind of guy, one O2 sensor will do. After all, one carb feeds your whole engine. But I do have a solution. You can run two 02 sensors , if you have a switch between the left and right harnesses. This is something I thought about and may do as well, as my car is a street/strip car as well. I just have to make sure the system can handle switching while powered on.

As a side note, the AEM system is very sensitive! If you stab the gas pedal, you see the results, instantaneously! Because it's a carb'd car, you'll notice that it runs in a narrow range, moving around in that range, which is normal. I really like having the AFR gauge and I would be loathe, not to have it now. If you have a dead stock Corvette, you won't likely need it, hut it would help. If you have any kind of mods, I think it becomes a necessity!

 

I am running 02 sensor in each bank. See diag (right bank vs left)

Using 1 ZT2 and 1 ZT3 for the second bank where the ZT3 connects to the ZT2 and the PC connects to the ZT2 to read both banks.

Do I notice a difference in either bank, not really when everything is working, but when I remove a plug wire on one side I can tell the difference.

 

I would advise the analog version as well. The gauge is really responsive and I would guess there are a lot of digital transitions which make it hard to mentally average.

As a note, I considered replacing the gauge face with one of my own which I edited to match the look of the originals. Decided against it as the alignment was a bit tricky. I had some problems with the AEM fuel pressure gauge face not remaining oriented correctly after installation so I gave up the idea. Still it could be done for those that are interested in keeping the look. Here's what I ended up with.

 

Thanks F22 for the info. I have the same afr meter sitting on my shelf for over a year. It will get installed this spring. I will be drilling a hole in each collector so I can compare each bank and put a plug in one side as there is only one sensor. I don't expect there will be any significant difference bewteen the two banks either. I'm running a Team G SP intake and a Holley Street HP 650 w/mech'l secondaraies.