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Does anyone adjust the "Cold Offset" for long tube headers?
How does this work aor what is the theory behind the Cold Offset table? I notice on the stock tune the cold offset goes from 75 down to 50 when the colant temp passes 100 C. Does this mean that my fuel trims will shift depending whether the tuning was done at 90 deg C vs 105 C?
That table is only used to offset O2 crossovers for (about) the first 30 to 90 (or so) seconds that the engine is running. After that, it is ignored by the ECM.
Thanks
Can you explain to me what exactly that means?Quote:
Originally Posted by LazMan
Sure. Its easier to understand on the first Gen4 calibrations, such as the 2005 GTO. Instead of a table, it had a single crossover value, a max temperature, and a timer.
Whenever you started the engine the computer is in open loop and uses the preset fueling tables in the open loop section of the tune.
However, when the engine first enters closed loop, if the temperature of the coolant was below the indicated temperature (284F), the O2 crossover (typically 450mv) would be added to the offset value (in this case 100mv) for the amount of seconds indicated (200 seconds).
This way, when the engine first enters closed loop, for the first 200 seconds (2 and 1/2 minutes or so) O2 crossover was 550mv (slightly rich) and then went back to stoich (14.7 or whatever) after the 200 seconds.
In newer tunes, they replaced the single crossover value with a crossover table which has different values depending on the temperature of the engine. They *hid* the Cold Time value. Rest assured that once the engine warms up and enters closed loop, the Cold Offset Table does NOT continue to be used after more than a minute or three.
(Ive included an image from a 2005 GTO calibration for reference)
Thanks LazMan!
I've been chasing a "stumble" that only happens for about the first 60 seconds or so after a cold start. My 2011 Camaro has the single table you mentioned (but the 2005 image you showed really helped) and shows a 300mv add at 61, 82, and 102 coolant temps.
Maybe the 300mv is too rich with my current mods?
Sick_WS6, It could very well be, depending on what mods you have....but...
...I would think that in those 60 seconds you'd still be in cold loop. I should have said above "That table is used for the first 60-90 or so seconds that the engine IS IN CLOSED LOOP"
Want to post your tune and mods and I'll take a quick look and make some suggestions. :)
Current tune file attached.
Car is an L99 Camaro converted to LS3 style cam, Lingenfelter GT11 cam, longtubes and cats...pretty much it. Let me know if you see anything that stands out. Like I said, just does it right after startup
I made a cold start log sunday morning, and the car didn't stumble and I saw nothing. But it did it to me this morning leaving the house, at noon leaving for lunch, and then just now leaving work on the way home. :shrug:
It is hard to say without a log, it would have been nice if that cold start you did log would have had the stumble ... but ...
What you describe sounds to me like lean stumble. Two possibilities: a. stumble in cold loop, or b. stumble in open loop.
a) It could be when you first go into Closed Loop. You go into closed loop quickly, at anything above 95 degrees, possibly before the O2 sensors are truly ready due to the long-tubes. I made a change to the table to wait to change to Closed Loop until the engine is a bit warmer.
b) You have decimal values in the "minimum AFR" table which means that AFR can be lean (less than stoich) during start-up. This is done on newer stock calibrations to help the cats get up to operating temperature a bit sooner and meet 2012 emissions standards, but with your cam it could be the source of your stumble. I changed to values to what is stock on 6.2L engines.
Both these changes are stock-like for other applications, and I feel confident suggesting them. They wont cause any issues with fuel consumption or any harm of any type that I can conceive of, and just may well solve your problem.
If the stumble continues, I will suggest a few other changes.
Both seem logical possibilities LazMan. I had thought about bumping up the closed loop ECT enable but hadn't thought about the minimum open loop EQ table.
I'll flash this tonight and see how it goes the next few days.
Thanks!
Here are two more that come from the 2010 Camaro 6.2L V8 M6. Also stock values.
File 02a has richer fuel values where I suspect your stumble is - I know its in the "Park/Neutral" values, but I thought you should bring it up to 6.2L stock.
File 02b has less timing retard during warm-up. The higher timing retard on the 6.0 auto is also there to help warm up the cats, easily tolerable with the original milder cam.
Make these two, plus the prior two changes and I think you will have good results.
-Laz
I was just looking at a 2010 file that I have. I see no reason not to try these changes also.
I didn't feel the stumble this morning or at lunch, but got a slight hint of it leaving the office about an hour ago.
Thanks Laz.