gasmanstl

This gauge is advertised to be an AEM wideband O2 meter. It came installed on a car I'm having difficulties with (and have since purchase), and it is behaving in a confusing way. I wonder if it is actually an AEM, and if it is, if it needs a proprietary sensor? I have no instructions for the device, obviously.

It seems to have no markings at all, save for the +, the -, and the S, one for each wire in back.

Anybody recognize this? Doesn't look like any AEM products I see on the web.

Jim M.

It looks like a AFM (Air Fuel ratio Meter), but I don't think it's the type that will work with a wide band O2 sensor. There are no actual numbers to tell you the actaul ratio, just the colored bands.

Jim Mayzurk
93 GTS 5-spd

ZEUS+

Just a voltmeter
http://store.summitracing.com/partde...5&autoview=sku

gasmanstl

Ahhh, yes. A $25 Summit Racing NARROWband AFM...not exactly the device the PO said it was...

Thx for your help. At least, it will work with a nice, cheap sensor...the same one as brain.

If I can ever make the car run right...

Lizard928

I would not recommend running two things off of a single narrow band O2 sensor.

IcemanG17

That looks like the same AFM that in Pauls 82??

gasmanstl

Yeah, and Jim M: nice taste in stereos...that looks just like the Alpine in my red 85 euro...thank god I have one relatively well-functioning shark...

gasmanstl

But the AFM is only a voltmeter...and the brain only measures the voltage, too...do you really think 2 meters attached to a probe instead of just one could make a difference as to the measurement? I don't mean to argue - I'm no expert, by any means. But it's not like the sensor voltage has any draw from it. Am I missing something?

karl ruiter

You are assuming that both the injection computer and the meter function like voltmeters. That is, they draw essentially no current. This may well not be the case with either of them. In fact, it pretty much cannot be. (I think the sensor is resistive so the computer has to supply a current). Better try disconnecting it to see if it helps your running problem. If not, you can reconnect it once you have the car running properly and see if it causes any problems.

Jim M.

It is just a voltmeter, but I've had mine on for three years and had one in the 89GT and they have NO effect on the running of the cars! It can be seen in my avatar just above the radio.

Jim Mayzurk
93 GTs 5-spd

dr bob

Voltmeters need to draw a very slight amount of current to actually measure the voltage. Reality i that all "voltmeters" actually measure current in the end anyway. Better quality digital meters are typically rated in the many tens of thousands of ohms-per-volt range. If you want to find out how much of a draw this meter is putting on the sensor, hook up your milliamp-capable DMM in series with the lead from the sensor. Knowing how many volts the sensor is generating will tell you something about the meter itself. As part of this same exercise, put your milliamp-capable DMM in series with the fuel brain and see what that draws. Hopefully, the current through that is pretty low too. It's the total current draw that is important. If the new meter adds significantly (and this is percentages based on the impedance of the sensor itself...) to the total current draw, the lower voltage to the brain will result in a slightly richer mixture. Watch the actual loop voltage with the car running, and connect and disconnect the new meter while you observe the sensor voltage. If your meter is fast enough, you might see how the meter causes the voltage to drop, then see the brain compensate by richening the mixture slightly to raise the sensor voltage again. An oscilloscope would be the weapon of choice for observing this, since most common (inexpensive) DMM's don't update fast enough to see the changes.

gasmanstl

That's very interesting. Here's a question: I have seen it asserted that narrow-band sensors are very non-linear in their response, and that the computer essentially uses the information in a digital, rather than analog, manner; that is to say, sees it as "1" or "0." (Either "rich," or "lean.") That there really isn't a bunch of fancy-resolution-maintenance going on to attempt to keep the sensor at 0.45 volts, which is my understanding of where it should normally live in a perfect world. I wonder what you say to this? I am having a total-cluster**** learning experience with my LH 2.2, and EFI in general...now just trying to understand the way the thing works better. If you wanna share my misery, check out https://rennlist.com/forums/showthre...ferrerid=22139

123quattro

You are correct in that narrow band sensors are basically a digital output. You are either above or below stoich. Typically they are switching the mixture relatively quickly so that it is basically 14.7 while the sensor is controlling the mixture. Trying to infer an A/F ratio from a narrow band sensor is useless. That gauge won't give you any information. If you really want to know what's happening, install a wideband sensor in addition to the current narrow band being used for control. I'm not sure about others, but an AEM can be made to mimic a narrowband. In that mode, it can be used for measuring A/F ratio and directly replace the stock sensor completely.