PLX Wideband Wiring

s300 and SManager software questions & answers
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kraquepype
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Joined: Fri May 11, 2018 10:43 am

PLX Wideband Wiring

Post by kraquepype »

Hi! I've been having issues with my PLX setup and wanted some input since the PLX AF gauge has a good reputation here.

I originally started with just the air/fuel module, and that worked well for a few years. I added a SM-PRO module inline with my SM-AFR module for oil pressure monitoring, and since I got the SM-PRO it killed my multi-gauge - the touch screen does not respond, the display is blank and only the outer LEDs light up.

I figured my gauge died on its own, and I got a new DM6 gauge display for it. Installed it and after a day it started to do the same thing!

My PLX modules have power spliced from the ECU, everything else is wired up as per PLX instructions. The DM6 gauge serial and power is connected to the SM-PRO, a serial cable connects the SM-PRO and SM-AFR, which is the last module and has the termination jumper.

I found that the SM-PRO case was not flush with the 3.5mm jacks for the serial connections, and I'm thinking maybe those loose connections over time did something to the gauge. I'm trying to work through the issue w/ their support but knowing the good reputation PLX has here I wanted to go over my setup in case theres something I'm missing.

Many thanks
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Spunkster
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Re: PLX Wideband Wiring

Post by Spunkster »

I'm not familiar with any issues like this so the best thing to do will be to continue with the support form PLX Devices. They should be able to help you with this.
kraquepype
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Re: PLX Wideband Wiring

Post by kraquepype »

Thanks - as far as power goes, is going off the ECU power / ground acceptable?
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Spunkster
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Re: PLX Wideband Wiring

Post by Spunkster »

It should be.
kraquepype
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Re: PLX Wideband Wiring

Post by kraquepype »

One weird thing I noticed is that with the ECU fuse disconnected on my car, I still get 8-9V coming from the ECU power line. This goes away with the ECU unplugged completely. I have no idea why there is still some sort of residual voltage.

Car is an 89 Civic w/ OBD1 conversion harness and P28
kraquepype
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Re: PLX Wideband Wiring

Post by kraquepype »

Bumping this, I've decided to ditch the SM-PRO for now, it has been nothing but a PITA

I've setup my PLX Wideband and connected it for datalogging. I've noticed that no matter the ground, the ECU reads about .5 higher (Gauge says 14, Hondata reads 14.5 for example). I currently have a negative voltage offset to get it in line, but I would rather not.

+12 is hooked up to pin 25 on the ECU A connector (IGP2)

I've tried grounding the wideband to the ECU ground (ping 26 on A), and also to 23/24. These all still end up with the difference in reading. I ran a ground directly to the thermostat for the wideband and the difference is still there.

The analog output is connected to D10 (ELD), with the ELD disabled, ELD line removed, and the resistors removed.
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Spunkster
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Re: PLX Wideband Wiring

Post by Spunkster »

Have you tried using switched power at the fuse box and a solid chassis ground instead?
kraquepype
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Re: PLX Wideband Wiring

Post by kraquepype »

Have not tried a chassis ground, but from what I understand when it comes to differences in wideband output between the gauge/ecu, that you want as close a ground that the ECU uses as possible - the thermostat ground point should be doing that.

I'm wondering now if the gauge of the power wire is too small, since I also noticed that the ECU voltage and the voltage the PLX AFR shows are off by about 2v (ECU shows ~14v, PLX shows ~12). Next I'll try a slightly larger power wire, run it to a switched source and leave the ground on the thermostat.
kraquepype
Posts: 52
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Re: PLX Wideband Wiring

Post by kraquepype »

Ok so I got to do some testing.

Engine off, PLX AFR hooked up as it has been, the PLX AFR reads 11v, the ECU reads 12.3v
If I unhook the O2 sensor from the AFR, it reads much closer, 12.1v vs 12.3v
If I hook the PLX AFR up to a dedicated power close to the battery and chassis ground, with the O2 connected I get 12.1v 12.3, much closer.

So I'm going to give the wideband a better power source, and ground it at the thermostat. That should improve things I think.

Question: Should the O2 sensor be pulling so much current?
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Spunkster
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Re: PLX Wideband Wiring

Post by Spunkster »

The heater will draw a fair amount of current.
kraquepype
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Re: PLX Wideband Wiring

Post by kraquepype »

That makes sense.

I was able to finally get a good reading. For power I tapped into an ignition controlled source ( the clock power, since I have the gauge in about the same spot), and grounded it at the thermostat. I used a slightly higher gauge of wire than what came with it as well. Now my ECU AFR readings are only slightly off in the other direction and the voltage at the gauge is reading better.

Many thanks for the input!
SycRedDevil
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Re: PLX Wideband Wiring

Post by SycRedDevil »

I'm having a similar issue and found this thread while searching for answers. I have good power levels at the ECU, but changed to a chassis ground. The problem I'm having is after about 20 mins of idling, the AFR drops to 10, and so does hondata's AFR reading.

I have a Gen4 PLX Wideband, LSU4.9 Bosch o2 sensor and a DM6 Gauge all from PLX.

I'm not sure why, but it seems to do this when the radiator fan kicks in, but never readjusts to a regular reading. I'll start to generate -44% in multiple low speed tables. I have a thread " viewtopic.php?t=24515 " Not trying to thread jack but is there any reason that this happens? New to hondata, came from Cobb tuning in a Sti so I'm still learning.
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Spunkster
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Re: PLX Wideband Wiring

Post by Spunkster »

It could be the power source.
SycRedDevil
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Re: PLX Wideband Wiring

Post by SycRedDevil »

Spunkster wrote: Tue Nov 30, 2021 10:33 am It could be the power source.
No - Turned out to be a collective of issues. The power source was fine, but the supplied "clip" that plx gives you, obviously seated well within the PLX box. The issue was that the wire that reads the wideband was ..... not plugged in all the way I guess you could say. Running fine now.



(I'll wear the cone of shame proudly)
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