efi Megasquirt And Lc-1 Grounds

[stuff]

My megasquirt build is showing low and sometimes erratic AFR reading, and the CLT reading also waivers by about 2c and pegs the temperature meter frequently. By low AFR reading, I mean the tail sniffer used during a dyno session was reading consistently richer than my o2 sensor/megasquirt, which seems backwards. Checked for exhaust leaks, found none, and any leaks would presumably affect the tail sniffer too.

O2 sensor is an Innovate LC-1

CLT sensor is a Honeywell R300-F35-M14-C

Trawling the megasquirt forums suggests that some people have encountered similar situations and resolved it by separating the o2 sensor ground and the o2 heater grounds (grounding in different locations) which is contrary to the LC-1 manual:

5. The BLUE and WHITE wires should all be grounded to the same ground source. Optimally, these (and any other MTS device ground) will be soldered to the same lug, and connected to a single point. When this isn’t possible, connect each one to a separate lug, and attach in close proximity. Multiple lugs on the same bolt is not optimal, and can result in unwanted signal “noise.” When possible, soldering is always better than crimping. Please see chapter 2.3 for more information on Electrical Grounding Concerns.

Where do you ground your LC-1 ground wires?

[ray_]

The LC-1 can be set for different fuel types IIRC. I'd suggest checking your settings.

 

OTOH mine was acting wonky so I dumped it.

 

GL,

Edited August 26, 2014 by ray_koke

[M3M3]

I ran into similar problem with ecu and lc showing different voltages. Solution was to make sure the ecu and lc1 shared common ground and power feed.

Differences with the dyno afr not as relevant. Ecu and lc1 must be on same page.

[stuff]

Ray - fair point that I should go back and reconfirm that my LC-1 config matches what I believe it to be. Hoping it's that easy. However, the fact that's the CLT and O2 both fluctuate suggest something more fundamental, or multiple issues.

Marshall - do you have the o2 heater ground grounded at the megasquirt unit like all sensor grounds, or is that grounded differently?

If relevant, I am using the megasquirt relay board to provide power to the LC-1. Today, both LC-1 heater and sensor ground are grounded at the megasquirt, and the megasquirt is grounded on the head.

Thanks gents.

Edited August 26, 2014 by stuff

[jimk]

(I can't copy and paste links or even text nor quote anymore on here, so I attached a text file.)

If you other sensors are jumping around you probably have a ground loop and most likely from how the Lc-1 is wired.  Wire per the Innovate manual with the heater ground and the shield ground to chasis ground or where the main ground for your ecu is grounded.  Wire signal ground to the same place your other sensor signal grounds are (from your description where they are grounded at present).  I had this happen on my present system becaust the O2 sensor system does not have a separate ground for heater and signal and I placed the ground on the signal ground point.  I moved the ground to the chasis ground and all is stable.

You can sync the LC-1 to the efi system by temporarily setting the LC-1 to out put a level signal for all afrs and key on to see if the efi reads the same.  If not adjust the output voltage on the LC-1 to get the correct same on the efi system.  Do this for low afr, mid scale and high afr.  I have done this on Electromotive systems and Haltech.

Ground Loops.txt

[Colin]

(I can't copy and paste links or even text nor quote anymore on here, so I attached a text file.)

If you other sensors are jumping around you probably have a ground loop and most likely from how the Lc-1 is wired.  Wire per the Innovate manual with the heater ground and the shield ground to chasis ground or where the main ground for your ecu is grounded.  Wire signal ground to the same place your other sensor signal grounds are (from your description where they are grounded at present).  I had this happen on my present system becaust the O2 sensor system does not have a separate ground for heater and signal and I placed the ground on the signal ground point.  I moved the ground to the chasis ground and all is stable.

You can sync the LC-1 to the efi system by temporarily setting the LC-1 to out put a level signal for all afrs and key on to see if the efi reads the same.  If not adjust the output voltage on the LC-1 to get the correct same on the efi system.  Do this for low afr, mid scale and high afr.  I have done this on Electromotive systems and Haltech.

This.

[jimk]

I've been on the board quite  while and never had troubles quoting.  I select the quote and it won't paste.  I select a line, right click quote and no paste.  I doesn't work for me. So no "this".

[AustrianVespaGuy]

Hi Colin,

 

Feel free to PM me at some point, but I just went through this experience also.  Here's my thread on the issue: http://www.bmw2002faq.com/topic/154579-erratic-wideband-o2-sensor-output-ideas/

 

But to summarize, mine turned out to simply be a dying O2 sensor, and not the Innovate controller. $50 from Amazon here: http://www.amazon.com/gp/product/B000BZI4ZW/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

 

Before getting to that point however, I DID go through and clean up all of my Megasquirt grounds, and I am glad I did, as I do have much better signals now.  The main point is to bring all of the sensor grounds (including the Innovate white wire, but blue is just the heater ground so doesn't matter that much) to one of the MS ground pins and NOT to either the chassis or block!  Some of the MS wiring diagrams show this to be Pin #19, but any MS ground pin will work.  The key here is you don't want any current travelling along the sensor ground path from anything else, because that will screw up the voltage reading that MS is looking for.  It also ensures that if Megasquirt's reference ground floats at all (which it does), the sensor reference floats along with it.  Again, feel free to PM me if you'd like to hear more details or see some datalogs or whatnot.

 

-Carl

[stuff]

Thanks everyone, I moved o2 heater ground to the chassis (originally grounded with all other sensors at megasquirt relay board) and the CLT no longer spikes to indicate that I am driving on the surface of the sun. O2 sensor has also stopped spiking too.

I'm not home and dry yet though. CLT reading still waivers a few degrees, so grounding loop still present somewhere. And I will check for air bubbles trapped in the coolant neck near the sensor too.

Cheers,