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Join Date: Jun 2008
Location: SE Pa.
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AFR Gauges, tailpipe exhaust analyzers and the Gunson Gas Tester

I have had an AEM AFR for a few years.

This was a revelation to me when I got it - it's so nice to be able to see what your mixture is as you drive. It makes tuning and troubleshooting the CIS much easier.

Here's the thing - it has failed. I was pulling what little hair I have out until I figured out the problem wasn't a CIS component, it was a faulty gauge. (although I did manage to identify and fix some actual component problems).

Now I'm thinking that I should have some kind of "tailpipe sniffer" to keep the AFR honest. I see that the Gunson Gas Tester is back in production - is this the one to get? Is there anything better out there that isn't thousands of dollars?

I haven't heard back from AEM yet about getting the AFR fixed. If I need to replace it, what's good? I see a bunch of options on the market now.

A coworker swears that his Innovate is the best, but he needs to pull the O2 sensor once a month for "free air" calibration.

Thanks Guys!
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1981 911 SC
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Old 08-29-2019, 04:11 AM
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Counterclockwise?
 
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What is your gauge doing?
Mine is sporadic. It always goes through the start up numbers fine, but then sometimes it just shows straight lines or 1.00
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Old 08-29-2019, 08:37 AM
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The problem started with gauge readings sporadically going high or low. Now they are pretty consistently low (Like 10.2 -11.3 when warmed up).

I use the narrow band output to my Lambda ECU, so this drives my frequency valve to 9% or so - making the car run very lean, even though the gauge is showing rich (Like 12.5 with the sensor lead connected, when it's likely actually around 18. )

I had some other issues (WUR problem) which are currently corrected, so it wasn't obvious to me that my readings were false. I was trying to correct a very rich condition that wasn't there.

I contacted AEM and got this advise:
-Key on engine off: should read 14.6 – 14.7 initially, after about 30 seconds it should read dashes across the screen.

-sensor unplugged: should read 14.6 to 14.7

If the gauge stays in the 14.x range, the gauge is not detecting a sensor. In that case, I’d recommend inspecting the harness to verify it has not come into contact with the exhaust or been damaged in any other way.

If you still cannot find any issues, you likely have a bad sensor.
My gauge goes to 14.8 with or without the sensor connected, then goes to dashes either way, so the AEM Rep. tells me the gauge is faulty. He has not provided a return authorization yet.
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Old 08-29-2019, 09:18 AM
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Quote:
Originally Posted by Porchdog View Post
I see that the Gunson Gas Tester is back in production - is this the one to get? Is there anything better out there that isn't thousands of dollars?
The Gunson isn't an oxygen sensor. It measures CO in the tailpipe. I think it is kind of expensive for what it is, especially if you considering that it is useful for testing mixture at idle only, and takes some 12-15 minutes for a reading - which corresponded well to my wrenches 5 gas analyzer at 50x the price, however.

AEM is generally considered one of the best AFR gauges these days, I think. Innovate was one of the first on the scene, but complaints about their need for frequent free air calibrations (and failing) are not rare. I have no idea why they would need that and the AEM with the same sensor doesn't, but there you are.

I don't (and haven't) used either.

Many seem to view selling a Bosch LSU 4.9 sensor as an opportunity to gouge you, seriously and deeply. I paid $79 shipped for the genuine article on Amazon; other than it having a "NASCAR" flash on the box, I have no complaints.
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Old 08-29-2019, 03:03 PM
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I have an AEM wideband and find it very useful and it has lasted....it is the sweep hand analog style.

The senders can be very sensitive to fuel...like lead if you've ever gassed up with that or some other additives....
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Old 08-29-2019, 04:53 PM
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AEM has had a large number of their Gauges that have failed , two for me . They are not very helpful when it come to admitting the fault . When it works it is the best . Just no long term quality
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Old 08-29-2019, 05:55 PM
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Quote:
Originally Posted by icarp View Post
AEM has had a large number of their Gauges that have failed , two for me . They are not very helpful when it come to admitting the fault . When it works it is the best . Just no long term quality
FYI...my analog gauge has been in place 4 years now...are you referring to the digital reading ones?
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Old 08-29-2019, 06:53 PM
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yes digital ones
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Old 08-29-2019, 08:35 PM
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Quote:
Originally Posted by Reiver View Post
FYI...my analog gauge has been in place 4 years now...are you referring to the digital reading ones?
They are all digital internally.
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Old 08-29-2019, 08:39 PM
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the best one out there from mmy years of experience with it in the Daytona-Sensors WEGO IV

VERY VERY GOOD QUALITY. ACCURATE data gatheirng etc,

Have had mine running faultlessly of 15 years. Great product, great company, and sadly a well kept secret.

WEGO™ III & WEGO™ Single Channel Displays | Daytona Sensors™

Highly recommended.

AEMS are well known, but unreliable and lack useable features.....it is more than just readouts.
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00 Saab 95 Aero wagon stick
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03 Boxster
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Old 08-29-2019, 08:44 PM
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Quote:
Originally Posted by dicklague View Post
They are all digital internally.
To a point yes....but not identical.
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Old 08-29-2019, 09:32 PM
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Are you sure the narrowband output works with the Bosch K-Jet box?

I have always wanted to see a scope trace of a narrowband O2 sensor feeding the K-Jet vs a narrowband output from an AFR gauge. It has been theorized that the K-Jet may not work well with with a “modern” narrowband output.

I tried it once using a PLX gauge with terrible results. Kept going lean no matter what.
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Old 08-29-2019, 10:10 PM
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AEM wants about the same price as a new gauge to evaluate mine - so I'm buying another.

Given my recent experience I will be reconnecting the narrow band to the Lambda. I guess I need to weld another bung or two into my exhaust.
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Old 08-30-2019, 04:06 AM
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AEM gauge

I have had a AEM air / fuel gauge installed in my SC for 4 years, however, I have 2 bungs in my cat bypass - one for CIS sensor and one for AEM sensor. It has worked flawlessly.

Dave
Old 08-30-2019, 07:29 AM
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Quote:
Originally Posted by tirwin View Post
Are you sure the narrowband output works with the Bosch K-Jet box?

I have always wanted to see a scope trace of a narrowband O2 sensor feeding the K-Jet vs a narrowband output from an AFR gauge. It has been theorized that the K-Jet may not work well with with a “modern” narrowband output.

I tried it once using a PLX gauge with terrible results. Kept going lean no matter what.
The proper ECU function does not only rely on the provided 0.2-0.8 voltage by the the sensor. IIRC the impedance based on the temperature of the "hardware" narrowband sensor also affects the ECUs behavior and how it recognizes the signal.
The Innovate LC2 Software i.E. offers a setting where you can choose between "zero volt" or "High impedance" which will be provided to the ECU if a sensor error occurs.
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Last edited by AndrewCologne; 11-11-2019 at 08:32 AM..
Old 11-11-2019, 08:26 AM
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