AFR fluctuation normal?

[Hoffbrohaus]

I have an Innovate MTX-L AFR gauge I installed to troubleshoot issues. I recently hooked it up to the laptop to log. Now my gauge may be off because of the electrical connection but I have been troubleshooting a lumpy and low idle issue.

Should my AFRs move this much between 13.5 and 15.5? If not is this an indicator of anything specific or I just have to run through the list - intake leaks, o2, fpr, injectors, etc.

Here are my AFRs at idle when cold


and when warm

[mazzo]

Please forgive me if I am asking a stupid question, but isn't M20B25 by default should be 3 bars for fuel pressure and M20B27 be 2.5 bar? if 1 bar = 14.7 psi then we are suppose to see a much higher number, or am I reading something wrong?

[ak-]

Your graph doesn't look too off I'd say. After the o2 heats up and ECU acknowledges, AFR's usually bounces consistently from 13.00 to 15.00 up and down.
I'd think your AFR's should be richer at cold start up though.
Have you grounded your wideband where the ECU grounds as advised? That cleared up false readings on my megasquirt/wideband setup in tunerstudio.

Please forgive me if I am asking a stupid question, but isn't M20B25 by default should be 3 bars for fuel pressure and M20B27 be 2.5 bar? if 1 bar = 14.7 psi then we are suppose to see a much higher number, or am I reading something wrong?

You're correct on the fuel pressure part of your statement, but his graph is of an air/fuel mixture reading with the ratio of 14.7 being a stoich mixture - where all the oxygen is consumed and all the fuel is burned.

[george graves]

What's the x-axis time scale?

[Hoffbrohaus]

Your graph doesn't look too off I'd say. After the o2 heats up and ECU acknowledges, AFR's usually bounces consistently from 13.00 to 15.00 up and down.
I'd think your AFR's should be richer at cold start up though.
Have you grounded your wideband where the ECU grounds as advised? That cleared up false readings on my megasquirt/wideband setup in tunerstudio.

I did not ground it where the ECU grounds, I will try that but last night I followed the Bentley procedures to check the stock o2 and struggled to get any voltages from it, so I'm thinking a new o2 may be in order. I am looking through all the POs paperwork today to see if it was ever replaced. 7 owners though

What's the x-axis time scale?

Time in seconds, looks like it samples every .08192 seconds.

[mazzo]

Thanks for the explanation, I did mis-read the graph, hahahahaha!! :)
Hoffbrohaus, good luck fixing the issue!