E38 LS7 EQ_RAT and EOILTS Issues

[hapnermw]

Apart from the EQ_Ratio units showing up as lambda, I can't see any other problems.

EQ Ratio is directly proportional to AFR, so EQ Ratio should track AFR.
Lamba is inversely proportional to AFR, so Lambda should inversely track AFR.

Or am I missing something? (It happens, often :( )

Regards
Paul

Actually, Lambda is proportional to AFR. EQ is inversely proportional to AFR.

Lambda is the ratio of AFR/AFR Stoich - EQ is 1/Lambda. Lambda > 1 is lean; EQ > 1 is rich.

Having EQ reported as Lambda is completely wrong.

I'm assuming this hasn't been caught earlier because everyone has been using the AFR PID for tuning.

See http://en.wikipedia.org/wiki/Air-fuel_ratio

[Blacky]

Me-><-Math
I'll fix the PID to be correct

Regards
Paul

[Blacky]

Ok, so I'm going nuts here...

Wiki says:
http://en.wikipedia.org/wiki/Air-fuel_ratio
To calculate AFR from a given lambda, multiply the measured lambda by the stoichiometric AFR for that fuel.

The SAE specification says:
(see image)
To obtain the actual A/F ratio being commanded, multiply the stoichiometric A/F ratio by the equivalence ratio.

Which one is correct? What am I missing?

Regards
Paul

[hapnermw]

Ok, so I'm going nuts here...

Wiki says:
http://en.wikipedia.org/wiki/Air-fuel_ratio
To calculate AFR from a given lambda, multiply the measured lambda by the stoichiometric AFR for that fuel.

The SAE specification says:
(see image)
To obtain the actual A/F ratio being commanded, multiply the stoichiometric A/F ratio by the equivalence ratio.

Which one is correct? What am I missing?

Regards
Paul

Lambda = AFR/AFR Stoich so AFR=AFR Stoich*Lambda
EQ=AFR Stoich/AFR so AFR=AFR Stoich/EQ

The SAE spec is in error. Somewhere it must say that EQ=1/Lambda. EQ is proportional to fuel so it doesn't make sense that increasing EQ would increase the air/fuel ratio - increasing EQ must decrease AFR.

[joecar]

Paul,

In the SAE document:

if 0.95 was Lambda, then 14.64 * 0.95 = 13.9 would be true (gets richer with Lambda < 1).
if 0.95 was EQR then 14.64 * 0.95 = 13.9 would be strange (should have gotten leaner with EQR < 1).

So the SAE paper seems to be treating EQ_RAT as Lambda, or it could be a typo in the paper (as said by hapnermw).

In Heywood ("ICE Fundamentals") on page 71: φ = FAR/FARs and λ = 1/φ = AFR/AFRs

so from those 2 we can then deduce: φ = AFRs/AFR = FAR/FARs = 1/λ or λ = AFR/AFRs = FARs/FAR = 1/φ

[joecar]

There is an updated SAE J1979 paper:

...

Differences from SAE J1979 APR2002:
...

• Appendix B – Consistent use of "LAMBDA" instead of "EQ_RAT" for external test equipment to display equivalence ratio for PIDs $24 to $2B, $34 to $3B, and $44
...

[Blacky]

That'll teach me for blindly trusting the specification
SAE spec -> <- Me

Not sure why I never got the updated doc, have to check my subscription. Joe where did you get/find the update?

Regards
Paul

[joecar]

I searched the web for "SAE J1979" and it showed me a site where the update could be purchased, and it showed a list of changes since the 2002 edition...

SAE J1979 Edition: 07 Chg: Date: 05/00/07

<hmmm.... when I went to that same link last night it showed what changed since the 2002 edition>


I don't actually have the document itself.

[Blacky]

I just updated our subscription with SAE, the new documents are on their way...

Regards
Paul

[gmh308]

I just updated our subscription with SAE, the new documents are on their way...

Regards
Paul

Hey Paul, Any further feedback on this?

Does the GM ECM run on Lambda as a base unit or EQ Ratio or ..... AFR no less?

Every PID I have seen looks to be lambda, but is usually, if not always labelled EQ_Rat or EQ Ratio or something similar.

And the actual value is always lambda. Via EFILive and alternate scanner device/s.

Cheers