For those of you using the AEM wideband, do you ever notice momentary upspikes towards a lean AFR? I'm trying to figure out if what I'm seeing is an artifact (perhaps due to electrical noise) or a true misfire condition. It's shown on both the guage as well as the output line which I have logged in real time with the e01:





The bottom axis is time (20 seconds long) and the vertical axis is A/F ratio (11 on bottom, 19 on top.) See those brief upspikes overlying the normal cycling of the wideband? So you see it sometimes happens once every 8-10 seconds. Here's a normal tracing with no events:


Sorry for the ugly cell phone pics.

If this is a misfire, it's not something I can sense at idle. I don't hear it or feel it. And when I'm accelerating, I feel like there *might* be a misfire, but it's almost below my threshold to detect because of the feel of the prokits/18s that make the car feel bumpy already. I just can't tell. I think a misfire could explain the p0420 (cat efficiency down) I just got 10 minutes ago (even though I have a relatively new cat). I just put a bottle of G2P in my tank immediately before the code popped up, I wonder if that could cause an p0420 code during this tank of gas.

TIA!

I have an AEM and I hate it... buying an LC-1 first couple hundred $$ I get. I've got the one that has multiple, rotary selected outputs - and it switches spontaneously on me from wide to narrow, freaking my MS out. That and despite all wiring being triple-checked, it outputs an AFR 1-1.5 higher than MS is seeing, depending on the outside temp (WTF ?!) I've never logged any lean spikes like you're describing though - possibly a different controller though.

No experience with the AEM, but experience with O2's, lol. How old/what condition the sensor? Cracked wire possibility?

O2 sensor was just installed this summer. No cracks or anything in wires. IIRC, I've always seen this spike.

It was only after failing smog (isolated high HC, which indicates issue with ignition, e.g. missing combustion), that I searched for reasons why the car was misfiring. I found out the TPS had wandering voltage - fixing this solved all my drivability issues and the misfiring that was perceivable.

I've:
-Changed the coil.
-Changed the plugs (NGK BKR7E, gapped for boost).
-Checked wires. Had only 2 extra spark plug wires, so switched with my nology wires on cylinder 1&4, and then switched with wires on 2&3.
-Wiggled a bunch of wires, while looking at the real-time log.

None of this prevented the upspikes from continuing to occur. Oddly enough, for all of today, I haven't seen one spike at idle. It was happening a lot yesterday. Only difference between yesterday and today is, today is hot. Also, I'm on day 3 of a G2P bottle in my tank.

I noticed the same thing several months ago, but it was due to incorrect dwell settings causing a slight misfire at idle that caused the problems you were seeing. Ever since I corrected it the problem ceased. I’ve noticed it several times in the past with the PCM when cold around 15.0:1, part of the problem was due to bad spark plugs... my PCM never gave a misfire code. Its been gettin cold, this was taken in 50*F. Here is a short log my AEM readings with MS.

Thanks for your input :thumbsup

Interestingly, this phenomena seems to go away after driving the car for a bit. The spikes seems to occur frequently when I first start her up, maybe once every 10 seconds at idle. Then when she's been on the freeway or a bit, there are no spikes if she sits idling for several minutes. I think this rules out electrical interference.

The Nology's met resistance specs at 300ohms/foot, variance <10% across them.

Wideband GND and 12+V source were double checked and fine.

I wonder if it's occuring b/c the sparkies are cold in the beginning, which are already BKR5Es (one range cooler), or perhaps the injectors are "sticky" until the intake mani warms up a bit. hmmm

Originally posted by ez
I wonder if it's occuring b/c the sparkies are cold in the beginning, which are already BKR5Es (one range cooler), or perhaps the injectors are "sticky" until the intake mani warms up a bit. hmmm

I hope you meant to say BKR7Es - the 5's are one range hotter. With my MS, LC-1, and BKR7Es (NGK 4644) my idle is a bit off on a cold start too.

Originally posted by ez
I wonder if it's occuring b/c the sparkies are cold in the beginning, which are already BKR5Es (one range cooler),

Interesting to note that if we see that on a dyno, first thought is blowing out spark.

(+2 on what Dave said)

If it was blowing out the spark, you wouldn't see anything in your logs but you would feel the lost power.

I've used A LOT of widebands, and I hate to tell you guys, but the momentary spikes are caused by the AEM and the PLX widebands. The old school PLX boxes don't do it, but the popular SM-AFR does. There's nothing you can do about except pick yourself up a different wideband... I prefer Innovate.

It's not going to hurt anything though. All it will do is reset your EGO Correction back to 100% and it's a little annoying. Also, I've seen a lot of AEM and PLX wideband gauges read about 0.5 off from their analog outputs.

Originally posted by dougie2
If it was blowing out the spark, you wouldn't see anything in your logs but you would feel the lost power.

Only if it was continuous. A quick lost spark in a cylinder (which happens as you get close to the threshold of blowing out your spark consistantly) will generally not be noticeable except on the log.

Originally posted by bullettdsm
A quick lost spark in a cylinder ... will generally not be noticeable except on the log.

That's what I was wondering. Essentially we can have misfire events and not even know they are occuring until seeing it on a sensor log.

Originally posted by dougie2
I've seen a lot of AEM and PLX wideband gauges read about 0.5 off from their analog outputs.

I've noticed this with the AEM.

Originally posted by CODE4
I hope you meant to say BKR7Es

Yes you are right, that's what we call a brain misfire that showed up on the log.

BTW - all the events I'm noticing are happening in vacuum. She feels strong under boost, and I run so rich under boost that it probably would cover up the phenomena if it occured :)

Originally posted by ez
Interestingly, this phenomena seems to go away after driving the car for a bit. The spikes seems to occur frequently when I first start her up, maybe once every 10 seconds at idle. Then when she's been on the freeway or a bit, there are no spikes if she sits idling for several minutes. I think this rules out electrical interference.

Now that you mention it, other hot starts may be leaner then others depending how far off the PCM’s estimation are. That blip in the AFR may be a slight lean mixture where the PCM is trying to catch up with the correct PW percentages to achieve stoch. Here is another log I’ve had for some time where I had the blip in AFR before going sequential on a hot start with MS. This would only happen if my after start enrichment were off (if AFR > 14.7:0), as they slightly were in this log. The PCM was much like this, if not identical. The AEM is picky; make sure you have a good ground (i.e chassis ground).

Now that MS developers have added 02 sensor %error for MS2/MS3, it makes closed loop hot starts much better for AEM users as it ignores the signal for 30 sec (GEGO remaining at 100 for 30 sec). Not so much for the LC1 users because they already have it built in. (Outputting a 14.7 signal) In this log, dwell was 4.53 with ADV of 12.2. The IAT was on the manifold, so I was battling heat soak issues. It’s now on the IC pipe. You can see the slight lean spikes incrementing GEGO. I couldn’t feel or hear a misfire though. I have an LC1 on my other car and it preforms about the same as the AEM, but the readings are somewhat smoother.

what is your setup?