AEM AFR trouble....

[drl911]

Cross post from "engine building"

I had successful first start after rebuilding top end of my '86 3.2 (now 3.3) with complete change to Megasquirt MS3pro and distributor-less ignition. Then the following....

I tested the AEM wideband sensor by removing it from the exhaust and wrapping it in a wet rag of gas. Within a few seconds the gauge in dash and in TunerStudio software indicated 10 AFR. When I removed the rag it started to climb back to 17+ out of range lean. So gauge is working correctly. Re-installed sensor back into exhaust, started engine and still 17.8 (out of range) even though exhaust/tune was purposely rich.

What am I missing?

random thoughts....
new pistons/cylinders/rings, possible oil blow and masking AFR as lean?.... but sensor tip is dry
currently running without air filter in garage because I still don't have the supercharger back yet.
AEM gauge in dash and TS match values exactly so I believe it is wired correctly to MS3, but not 100% sure of wideband settings in TS (wideband normal?)
__________________

[racing97]

It can cause inaccurate readings depending upon where the Lambda Sensor is located it should be near the collector at the end of the primaries.

regards

[drl911]

It's always been mounted in the header extension pipe just before entering M&K 2in/2out.

[jpnovak]

Does it always read 17.8 for about 10-20 seconds and then start reading correctly?

The WBO2 sensors need time to heat up. ONce they reach operating temperature they usually function normally. As the sensors age and get coated with soot they take longer to warm up.

You don't say what happens after startup.

[dicklague]

i read her that the AEM is the best thing since sliced bread......is it not true?

[drl911]

Originally Posted by jpnovak

Does it always read 17.8 for about 10-20 seconds and then start reading correctly?

The WBO2 sensors need time to heat up. ONce they reach operating temperature they usually function normally. As the sensors age and get coated with soot they take longer to warm up.

You don't say what happens after startup.

Always 17.8 on Tunerstudio (but also "O2 out of range" message) even after 5+ minutes of running in garage. It worked fine in gas rag.

It has been suggested in my "engine building" thread and on MSextra that excessive rich can cause mis-fire and mess with oxygen reading of O2 sensor. I haven't gotten it completely straight in my head yet, but will try to lean it out tomorrow and verify ignition (LS2 coils packs wired directly to MS3pro).

[911pcars]

Upon power up (Ign ON), the WB circuit should go through a standard startup routine, then read the A/F ratio when the engine starts. Sounds like a glitch in the electronics.

Here's the AEM Users Forum. Your answer should be found there.
Wideband UEGO Air/Fuel Controllers | AEM

Sherwood

[Vereeken]

I have zero experience with AEM but it is a wideband.

"02 out of range" indicates an open circuit.

I assume you have it installed after the headers and before the exhaust in an upright position (or at least not in a downward angle).

If you can get it to read rich with your rag test I assume you did that with the WBD02 out of its bung.

If you install it in the bung again you ground it again. They should get ground from the wire not from the exhaust I hope so that to me is what seems different.

It might be an open ground/short to ground which does not occur when you do the rag test in your hand.

Does this thing come with auto-calibration? How does it return to 20.9 AFM zero reading.

['78 SC]

The sensor only detects oxygen so any misfiring (due to mixture or ignition issues) or exhaust leaks that allow oxygen to break though will appear as extremely lean AFR. For example, an ignition miss appears as a lean condition even though the mixture is good.

I have the same gauge in my track car and it is extremely useful, but its internal model assumes good combustion.

If you have access to a shop with a multiple gas analyzer (O2, CO2, hydrocarbons) that would allow you to see the whole picture.

[drl911]

Originally Posted by 911pcars

Upon power up (Ign ON), the WB circuit should go through a standard startup routine, then read the A/F ratio when the engine starts.

It is doing this start up procedure fine as usual, then reading 17.8 stable after the engine starts with no change.

[patkeefe]

I had a sensor go bad and that is what it did. I think there is a verification procedure somewhere either in the AIM manual or online.

[drl911]

Thanks Pelican support for the valued input.

Problem solved!

This 12v power supply to 3 coil packs was disconnected.
It was actually only running on 3 cylinders last night.... and the O2 sensor is on the header extension on the side that was not firing. Sensor is fine and doing its job.

On to the next hurdle..........