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· Premium Member
Z3's 3.0L and 2.8L
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2,640 Posts
Discussion Starter · #1 · (Edited)
Well, here it is, finally published. After 2 years of learning and 1 year in the writing here is the "How to" for reading OBD2 engine diagnostic logs.

These are the secrets to what I've been doing when I've been looking at everyone's OBD Fusion data logs.

Version 1.5 is now loaded. It has a better reading structure and a few additional sections.

Thank you to everyone who has let me learn on their OBD Fusion logs. It's been a real learning curve.

Enjoy

Regards

NZ00Z3
 

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· Premium Member
Z3's 3.0L and 2.8L
Joined
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2,640 Posts
Discussion Starter · #3 ·
Yes, that's a lot of information. Which you need to understand what is going on with the logs.

I had been calling it a mini novel for some time now.

Have already thought of 2 more sections to add, so, the next version is in draft.

As with all such documents, they go through a life cycle and get refined over time. Need some feedback to help with that.
 

· Banned
2004 325ci
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1,473 Posts
Well, here it is, finally published. After 2 years of learning and 1 year in the writing here is the "How to" for reading OBD2 engine diagnostic logs.

It may not be perfect or even correct, but these are the secrets to what I've been doing when I've been looking at everyone's OBD Fusion data logs.

It is version 1 so there will be errors and corrections need. Gentle prompts to them are appreciated. I feel that it's better to get this out there and get peoples feedback rather than me study it to death looking for all the errors. This document represents a significant number of hours of work over the last 2 years. Just as well that I'm retired.

I have a few more case studies in draft. These will be added to the next version. I feel that the case studies are very good at letting people learn from real life engine problems.

Thank you to everyone who has let me learn on their OBD Fusion logs. There have been successes and failures with mis-diagnoses. It's been a real learning curve.

Enjoy

Regards

NZ00Z3

Time to relax with a glass of red wine.
Dang... It probably took so long because you were busy answring all my swap questions.
 

· Premium Member
Z3's 3.0L and 2.8L
Joined
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2,640 Posts
Discussion Starter · #6 ·
Version 1.5 has been added to post #1. It has a better reading structure and a few additional sections.

Thank you to those who have provided feedback.
 

· Banned
2004 325ci
Joined
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1,473 Posts
OK NZ I have a great idea. We're partners now OK? You keep writing great documents Like How to read ODB2 .. and I'll start selling them. We'll give 'em the first page .. then sell them the rest !!
We're gonna strike it rich man!!
 

· Premium Member
Z3's 3.0L and 2.8L
Joined
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2,640 Posts
Discussion Starter · #9 · (Edited)
LOL, thank you for the complements. I'm pleased you like the "How to".

In the copywrite section I have written,

"This document has been written by a car enthusiast with the help of car enthusiasts, for car enthusiasts. It is provided free of charge to all car enthusiast to use, share, distribute and copy in any non-commercial use or undertaking."
To me, this is the essence of why the E46Fanatics forum is so successful. People willing to share their knowledge and support others to learn as they work on their cars. I have learnt a tremendous amount from this forum since joining in November 2016. These documents are me giving back to the forum.

So, sorry, I do not accept your business offer.:ROFLMAO:
 

· Banned
2004 325ci
Joined
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1,473 Posts
LOL, thank you for the complements. I'm pleased you like the "How to".

In the copywrite section I have written,

"This document has been written by a car enthusiast with the help of car enthusiasts, for car enthusiasts. It is provided free of charge to all car enthusiast to use, share, distribute and copy in any non-commercial use or undertaking."
To me, this is the essence of why the E46Fanatics forum is so successful. People willing to share their knowledge and support others to learn as they work on their cars. I have learnt a tremendous amount from this forum since joining in November 2016. These documents are me giving back to the forum.

So, sorry, I do not accept your business offer.:ROFLMAO:
Dang!! ... Well its good that I was just razzzing you then !!! But I really am impressed. I looked at your info today ..and found out you are in New Zealand!! What happened .. did you get shipwrecked?? I can send someone (laughing).
 

· Banned
2004 325ci
Joined
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1,473 Posts
Its unfortunate but I had a bunch of great high school friends long ago & we basically razzed each other constantly .. Its kid of the way Guys show appreciation/fondness for each other here. The habit has stayed with me for a lifetime...but I should not assume that is true in NZ
 

· Premium Member
Z3's 3.0L and 2.8L
Joined
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2,640 Posts
Discussion Starter · #12 ·
The habit has stayed with me for a lifetime...but I should not assume that is true in NZ
It's not a problem Dan. Kiwi's don't mind a bit of Razzing, especially at the expense of Aussie, Plus our open minded colloquial sense of humour tends to get us into trouble in the USA. I often have to delete 1/2 written posts, when I realise that the humour might get misinterpreted in the USA. So, I come across a bit dry at times.

..and found out you are in New Zealand!! What happened .. did you get shipwrecked??
No, my ancestors came out here by their own choice, to seek a new beginning in a new world. They did well, it's a nice place down here and looking at the world today, I don't want to be rescued.
 

· Registered
2001 BMW 330 ci
Joined
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274 Posts
Well, here it is, finally published. After 2 years of learning and 1 year in the writing here is the "How to" for reading OBD2 engine diagnostic logs.

These are the secrets to what I've been doing when I've been looking at everyone's OBD Fusion data logs.

Version 1.5 is now loaded. It has a better reading structure and a few additional sections.

Thank you to everyone who has let me learn on their OBD Fusion logs. It's been a real learning curve.

Enjoy

Regards

NZ00Z3
This is priceless!
 

· Premium Member
Joined
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12,528 Posts
Feedback:

Section Ignition Timing: "The timing retards to -15 degrees to enrichen the mixture during the operation of the SAP. "
I would say the reason for -15 deg retarded ignition is for creating an after burner condition and in combination with the SAP enriched oxygen to heat up the CAT faster. The Author intention of using the words "enrichen the mixture" in the Cat but most readers are thinking the mixture in the normal combustion chambers.
 

· Premium Member
Z3's 3.0L and 2.8L
Joined
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2,640 Posts
Discussion Starter · #16 ·
Thank you for your feedback.

This is the wording I've out into the next draft version.

The timing retards to -15 degrees to creating an after-burner condition and in combination with the enriched oxygen to heat up the CAT faster. The mixture going to the combustion chamber is enrichened by the DME. The retarded timing means that not all of the fuel is burnt in the combustion chamber and some flows into the exhaust. This mixes with the SAP enriched oxygen and burns in the exhaust manifold.
This wording lines up with the charts in the Narrow Band Pre-Cat O2 sensor section, where there are 2 cold start charts. One with the SAP connected and one with it disconnected. The disconnected chart shows a rich mixture. I take it that this rich mixture has been created by the DME by adding more fuel and retarding the timing. This means that not all of the fuel is burnt in the combustion chamber and it flows over into the exhaust for SAP air mixture and combustion.

Is this correct?
 

· Premium Member
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This wording lines up with the charts in the Narrow Band Pre-Cat O2 sensor section, where there are 2 cold start charts. One with the SAP connected and one with it disconnected. The disconnected chart shows a rich mixture. I take it that this rich mixture has been created by the DME by adding more fuel and retarding the timing. This means that not all of the fuel is burnt in the combustion chamber and it flows over into the exhaust for SAP air mixture and combustion.

Is this correct?
I don't know if the DME has to enrich more fuel just for heating the CAT faster, or it enriches more fuel to keep the combustion burning properly with a cold engine. IOW, if x grams of fuel is perfect for cold engine idling, then does the DME need to have x + a grams, more fuel for fast heating the Cat? I don't know, but even with just x grams of fuel, the extra -15 degrees retarded ignition will provide the after-burner flame and some unburned fuel for heating up the Cat. This can be proved by comparing the injectors pulses length during SAP activation and after it turned off.
 

· Premium Member
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One mystery about these charts is that I have not seen the relationship between the pre-Cat O2 signal trending and the STFT trending. It seems to be random but we know for sure the DME uses the O2 signal to drive the STFT. Do you have any charts that show the relationship?
 

· Premium Member
Z3's 3.0L and 2.8L
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2,640 Posts
Discussion Starter · #20 ·
One mysterious about these charts is that I have not seen the relationship between the pre-Cat O2 signal trending and the STFT trending. It seems to be random but we know for sure the DME uses the O2 signal to drive the STFT. Do you have any charts that show the relationship?
This is a really hard question to answer.

The O2 sensor signals are oscillating at between 1 to 3 cycle per second. OBD Fusion is refreshing between 5 to 7 seconds. So the O2 sensor charts are just a generalisation of what the signals are doing. We look at the max and min values. While I have learnt to pick a car running on E10 with a 0.75 max Voltage. I can't pick anything else for our steady state logs.

During a drive log, the narrow band O2 signals vary quite a lot. You can pick the changes with the total fuel trims. But because things are moving very fast, it's hard to do diagnostics with a drive log.

Wide Band O2 sensors are a bit easier to read. They have an offset either rich or lean. That is the average point reference is either above or below the reference point. Still learning about wide band O2 sensor signals, so have no firm conclusions.
 
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