Oxygen sensor and high speed stumble UPDATE

[Scot Sealander]

David A. Cooley wrote:

> The knock you are detecting at part throttle with the aftermarket chip is
> from lack of EGR...

That could be true.  But maybe the 'part throttle' changes that the chip
maker claims to have made include more advance.


> Guaranteed that the chip people only removed the EGR
> and didn't fix the EGR timing and fuel tables to make it run right without
> the EGR...

Not a very good gaurantee.  This statement I doubt is true.  Just because of 
the algorithm used in the code.


> GM adds timing and leans the fuel during EGR so there is no loss
> of power from the EGR.  

It can stand more timing with EGR, assuming you are not knock limited.  Just 
less power lost.  The fuel is not really 'leaned'.  The 14.7 to one (stoich)
is still met for the air that is in the cylinder.  The job of the ECM is to
measure (or calculate) the amount of air in the cylinder, then add the 
required amount of fuel at the desired AFR.  The measured amount of air in the 
cylinder does not include the EGR.


> Take away the EGR, and now the timing is way too
> high, and the fuel is too lean because the part of the combustion air that
> was recirculated exhaust is now air and it needs fuel.

This is only true (in this case) if your assumptions on how things are done are 
accurate, but they aren't.  The main table may have too much timing on purpose,
or maybe it has been added.  One would have to see the file to know.


> This is why a lot of chip makers charge a fortune hoping no one knows what
> the tables contain... 

Possibly.  After figuring this particular code out, I bought a used aftermarket
chip for this app.  I'm sure that they have to sell that one as "off-road" 
only.  The "part throttle" changes do not meet emission specs, and the WOT 
changes may actually result in lower gas mileage.  I haven't actually tried it 
to see.


> it shows they have no clue as to what they are doing.

Not unusual.  But do YOU know what the chip does?   It is easy to call them 
incompetent.  You have made some assumptions that just aren't true.

Scot Sealander   Sealand at clarityconnect.com


> If you want a chip that will make the car run better, try a reputable name
> like Z Industries... Ron Zimmer has friends in the automotive manufacturer
> industry that supply info and his chips are actual dyno tested units...

I trust this kind the least!  I trust people who reverse the code, forcing
them to understand how things get accomplished.  Having a "friend" means
that you really don't understand what the code does.  Would WOT dyno testing
find the part throttle ping?