[MalcolmV8]

Has anyone have any experience with a wideband in a really tiny diameter exhaust with a small engine? I'm not sure if that matters but I'm tuning a 4 wheeler (Yamaha 350 Raptor) which is a single cylinder 350 CC 4 stoke motor. This one's been modded, bored, stroked etc. and I was trying to get really precise on the tuning and installed an AEM wideband on it.

The problem is after dialing in the carb (re-jetting it) on the wideband I noticed it over heats and swapping out plugs I noticed it's completely lean. Spark plugs come out looking brand new clean like the engine was never ran its so lean.
I called AEM tech support but they are stumped as they never work with small engines apparently.

Here you can see the wideband placement in the pipe about midway down before the muffler.



I guess it's back to old school tuning the carb by feel and reading plugs but wish I could have used the wideband to get more precise. Any ideas?

[LeadHead]

What was the wideband reading?

[MalcolmV8]

Idle low to mid 14s, part throttle around high 11 to mid 13, WOT is mid/high 10s to low 11s. Plug looks brand new like it's never been in an engine it's so lean.

[cgrey8]

Ah, so the WB is reporting a rich burn when the plug is presenting as though the burn is lean. I would've guessed the WB was reporting lean. Interesting...

[MalcolmV8]

Yup I've seen the other way around a lot. Never seen wideband show rich when motor was actually lean. Either a faulty unit or something with the setup in a tiny engine/exhaust.

[LeadHead]

That shouldn't matter. Is there any way you can get another wideband to compare? People use widebands all the time to tune single cylinder engines.

[MalcolmV8]

I could but I've mostly given up on the wideband at this point and just tuning by feel, throttle response and reading plugs. I've noticed as I change jets the wideband readings may shift a little in generalizations but overall its pretty worthless for showing what's happening. For example at WOT it just pegs at a solid 10.0 AF even though I'm on the leanest possible jet to go WOT without it popping and missing.

[cgrey8]

I'm trying to imagine how this could happen. When the engine behaviour and plugs are consistent, but the WB is reporting something else, that's just odd. So I'm beginning to think this isn't a physics or chemistry phenomenon.

It leads me to wonder if there's some electrical issue involved. The fundamentals of how WB signals work is based on direction and amount of current flow between the O2 and HC sensors. With zero current flow, the WB controller interprets this as a stoich burn (lambda = 1.0). Current flow in one direction or another is interpreted as a rich or lean burn. The amount of current flow is a linear correlation with lambda. Therefore if there's some ground-loop that causes an additional current flow to exist, this could alter the WB controller's interpretation of the signal and do so in non-deterministic ways as the engine revs. Or this could just be a distraction...

But to rule it out, can you report back if the WB controller and/or laptop were being powered by something other than the ATV's battery (or the internal laptop battery)? If you were using an inverter that wasn't using its 12v- as ground OR were powering the laptop and/or WB controller from a power source that derrived its power from 120VAC, then I'd start suspecting an unfavorable interaction there. If you want to retry this, try grounding the laptop's case (e.g. a USB outside case) to the ATV's frame. Even if the laptop isn't powered, grounding the laptop is not a bad idea although not as likely to fix anything since there's no "loop" to arrest.

Ditto if the WB controller is being powered by a 120VAC->12VDC converter. Ground the 12VDC neg to the ATV frame. Although this one isn't nearly as likely given you have convenient 12vdc from the ATV battery.

[MalcolmV8]

Chris,

The setup is much more simple than that. No laptop, no inverters. It's an AEM EUGO wideband / gauge in one. It's a very simple setup with a key on power source and the ground goes directly to the battery negative terminal. My volt meter says the voltage at the battery is a pretty consistent 13.8 volts with the engine running.

Something interesting I observed yesterday while checking temps with my IR temp gun. The exhaust only shows around 240 ~ 260 F along side the motor and right at the cylinder head it shows 360F. That's extremely low for exhaust temps. It's an aftermarket stainless steel exhaust.
My son has the same quad but his has the factory mild steel exhaust and his shows 560F along side the motor and right by the head just reads OL (over load) as in to hot for my IR gun which has a max reading of 605F.

I can't imagine the SS exhaust actually contains heat within that well. I'm thinking the more likely explanation is that the IR reflection the gun is picking up is just way off due to the shiny SS surface. I just thought that was interesting while trying to look for differences between the two.

Malcolm

[LeadHead]

A simple test would be to power the wideband by a separate battery. Those small engine electrical systems are often very noisy and poorly designed.

[decipha]

prob wouldnt hurt to filter the ground by hooking it to the frame / chassis as well

Ive had issues before on single cylinder measureing where it just wouldnt read anything useable, i attributed it to slow exhaust flow, is there any way you can add an additional length of pipe on the exhaust just to test

[MalcolmV8]

A simple test would be to power the wideband by a separate battery. Those small engine electrical systems are often very noisy and poorly designed.

That's a good idea. Very possible it has a crude / noisy electrical system.

prob wouldnt hurt to filter the ground by hooking it to the frame / chassis as well

Ive had issues before on single cylinder measureing where it just wouldnt read anything useable, i attributed it to slow exhaust flow, is there any way you can add an additional length of pipe on the exhaust just to test

I would think hooking the ground to chassis ground would introduce all the noise from the ignition system. Hence battery negative terminal in a car. Of course nothing to loose at this point in testing it.

If I still had the old exhaust I wouldn't have minded cutting up and welding on it etc. However this nice new stainless steel unit I just installed I would prefer not to mess with.

I think you reasoning of slow flow sounds logical. Small cubes, single cylinder, really not much flow. Very possible why it won't work right.

[decipha]

no the ground to chassis will actually filter the signal, just dont tie the ground to the ignition ground lug lol

you should never hook anything to battery ground other than a chassis and engine block ground wire so ad to prevent ground loops and interference

[MalcolmV8]

no the ground to chassis will actually filter the signal, just dont tie the ground to the ignition ground lug lol

you should never hook anything to battery ground other than a chassis and engine block ground wire so ad to prevent ground loops and interference

That's the exact opposite of all the grounding documentation for the MS3-Pro and Megasquirt products. I've been reading their documents and forums a lot lately as I've started using and reselling their products. They have a lot of documentation and info on how to ground ignition coils, injectors and other electronics such as widebands, data loggers etc. Definitely a lot of good reading and info.

I also took an in person tuning training class earlier this year too and they had a whole section dedicated to grounds and it was pretty much on par and the same as the Megasquirt documentation.

You are right ground loops can be created and there are guidelines to follow.