To those who run wideband AF gauges...

Pete Whitstone

Pete Whitstone

True Classic
What is the failure mode of the sensor?

I have a PLX Devices M-200 unit and for the past week or so, when I start the car (from either cold or hot), the gauge reads 14.67 to start with, then within about 30-40 seconds, climbs up through the teens and then shows "Lean" for the rest of the drive.

I am about 100% sure this is an instrumentation problem, not an actual lean condition - the car runs fine and the plugs look good.

The display and sensor are about 2 years old but have fairly low miles on them - maybe a couple thousand. I don't drive the car that much.

So is this consistent with the failure mode of a Bosch 5-wire heated O2 sensor? I don't want to throw $80 at something that doesn't fix the problem...:wall:

Thanks,
Pete
 
You may need to do a free air calibration....

I have an Innovate Motorsports unit that requires (too) frequent calibration. It is just a matter of unscrewing the sensor and running a cycle in free air.

That is what has cured similar sounding issues for me.

Check your documentation and FAQ's.

Ciao,
 
Unfortunately the PLX unit is non-calibrate-able

At least, according to their documentation. Which probably does not make the thing more accurate than, say, an LC1. I didn't learn this about it until after I bought it, and next time I buy, it will not be a PLX Devices, for this very reason.

Thanks,
Pete

Mark Plaia said:
I have an Innovate Motorsports unit that requires (too) frequent calibration. It is just a matter of unscrewing the sensor and running a cycle in free air.

That is what has cured similar sounding issues for me.

Check your documentation and FAQ's.

Ciao,
Click to expand...
 
Hmmm......

Does it have a protocol for fitting a new sensor? Or startup for a brand new unit?

There may be a backdoor way to get it to calibrate the sensor.

Good luck.
 
video on testing the wideband O2 sensor

[ame="http://www.youtube.com/watch?v=1mb4VmDd0ao&feature=player_embedded"]YouTube - O2 Sensor Test - How to check to see if your aftermarket O2 sensor is bad[/ame]#!
 
What angle was the sensor installed at? If the install angle is not raised enough, the sensor will fail prematurely. Could be worth unplugging it from the harness & checking the pins for corrosion. If the car was consistently running low afr's, the sensor will also fail prematurely.
 
Excellent info, thanks!

I'll try this test and see what happens. Might be the weekend before I can pull the sensor.

Thanks again,
pete
 
I can tell you that after looking at the output of the Innovate on an oscilloscope I will never use one. It was very noisy at the highest sample rate.
 
OK so a new sensor solved the issue....

The old one failed the brake solvent test described in the video.

But now I'm wondering why it died such a premature death. It's only about 2 years old or so, and probably has less than 4000 miles on it. What kills these things (aside from leaded race gas, which I have not run)?

I really don't want to buy a new one every couple years. I have noticed that my ratios under certain conditions look a little rich, for example at idle it's not uncommon for it to read in the 11s. Under part throttle cruise, or even heavy throttle, I can expect to see 12's and 13's. I rarely see 14 or above. Would a prolonged slightly rich condition do this?

If I did want to lean it down a tad, does anybody have any experience with adjustable fuel pressure regulators? Brands or features to look for or avoid? Other gotcha's?

Thanks,
Pete
 
Idle should be closer to stoic - 14's. Part throttle should be 13's - 11-12's under heavy load / WOT conditions. Continuous rich AFR's will definitely kill the sensor in short order. The fact that you only have driven 4K is probably even worse on it, since it is then subject to more rich warmup conditions than highway cruising where it could potentially clear off the buildup.

Maybe lean out your AFM flap, bump up the timing, widen the plug gap?

Check regulated fuel pressure - maybe your FPR is actually running too high pressure as it is, or leaking past the diaphragm.

Pete Whitstone said:
The old one failed the brake solvent test described in the video.

But now I'm wondering why it died such a premature death. It's only about 2 years old or so, and probably has less than 4000 miles on it. What kills these things (aside from leaded race gas, which I have not run)?

I really don't want to buy a new one every couple years. I have noticed that my ratios under certain conditions look a little rich, for example at idle it's not uncommon for it to read in the 11s. Under part throttle cruise, or even heavy throttle, I can expect to see 12's and 13's. I rarely see 14 or above. Would a prolonged slightly rich condition do this?

If I did want to lean it down a tad, does anybody have any experience with adjustable fuel pressure regulators? Brands or features to look for or avoid? Other gotcha's?

Thanks,
Pete
Click to expand...
 
The timing for this thread is actually perfect as I was just about to post a thread about my AFR gauge aswell. I recently purchased an AEM wideband with a Bosch O2 sensor and I've noticed that it reads 14.7 at idle which is good so I've read and during WOT it reads between 12.6 and 13.8 but when I take my foot off the gas the reading jumps up to 16+ so is that normal behaviour because I've taken my foot off the gas?

My X is twin carbed if that matters.

'PeteX1/9
 
Sounds about right to me...

petex19 said:
The timing for this thread is actually perfect as I was just about to post a thread about my AFR gauge aswell. I recently purchased an AEM wideband with a Bosch O2 sensor and I've noticed that it reads 14.7 at idle which is good so I've read and during WOT it reads between 12.6 and 13.8 but when I take my foot off the gas the reading jumps up to 16+ so is that normal behaviour because I've taken my foot off the gas?

My X is twin carbed if that matters.

'PeteX1/9
Click to expand...

Transient readings of a few points higher than stoich are fine under no-load conditions such as what you are describing.

You let your foot off the gas, which snaps the throttle plates shut. So at this point the engine is basically running off the idle circuits. However, it's still spinning faster than idle, and while it can't take in a huge amount of air because the throttle plates are closed, I'm guessing it is still taking in more air than if it was truly idling. So more air than idling, but only the amount of gas that idle provides, means a temporary lean condition.

With the new direct-injection engines, they are purposely running up in the 15's and 16's under very light throttle cruise conditions. So I wouldn't worry about the lean spike you are describing.

Pete
 
As Pete pointed out...

... it is normal for AFR's to spike on shifts or heavy decel

This graph of a data log is taken from my Volvo - it makes it easy to see the AFR spikes (red channel) that normally occur. Green channel is throttle position (TPS) - WOT=4.3- volts

60whllog6sess2.png
 
You must log in or register to reply here.
Back
Top