Teammates,
In updating the projects on the Rebel as to my own cold air box for the intake and
having having swapped the LS1 intake manifold with the LS6 version, as you recall I pur the Rebel
back onto the same chassie dyno as was used in the first baseline testing.
Though there was an increase of HP, it was not what the claims I had heard about, it was more
like a 13 HP gain at the rear wheels and not the 20 plus some have said.
In lookng at this I find that since this is a stroked 373 cube engine, that the PCM code had been modified
by a product called the Powerloader. In short the flash memory of the PCM is replaced with modified code, much
like we did with C4's but there it was replacing the code in a E-prom of the ECM.
With OBD II mandates, the PCM functions a lot harder to monitor more functions then the ECM had to do and thus
where diag tools like the Diacom Plus worked well for the ECM, it cannot work with OBD II.
Too bad, in finding a replacement diag tool, I bought Autotap, a Diacom Plus it's not, but workable enough to
trap the engine functions as I did different types of driving, with engine at different levels of water, oil and air
temps.
True to what I thought, allowing more cooler air to be pushed into the intake via the cold air box and the fact the LS6
manifold alows more air and has a bit larger runners, the Rebel was not running as strong as it should, even though
the tests at the drag strip showed a 3 MPH gain and clipped off .6 tenths from the E.T.
I collected some engine / PCM traces mulled over them and then sent the traces via e-mail to Mark R and Craige.
In looking at the traces at times I thought it was a lean issue but other traces it looked like a rich condition, in the
end it was both.
Mark came back and said O2s showed a bit rich and as seen below Craige reported at less then WOT, running a
bit lean.
Making changes to the C5 as to PCM is much tougher, and in most cases vendors want you to yank your PCM and
ship them to them for custom coding, which is a pain in the ass.
My first shot is to attempt to fool the PCM, as to air/fuel metering by inserting a black box call ed MAF translator.
In short it has some switches and you change values so that the PCM thinks the MAF is calling for a different level
of air/fuel ratio.
To do this is not a simple flip of the switches of translator, you have to flip one switch, lets say to increase the fuel
ratio by 5 percent. Then I will have to do some tests, take diag traces and see if the levels are correct, if not make
translator changes and test, keep doing that until the ratio is correct or as Craige states go to a good dyno and do it
via whats seen at the tailpipes.
So as you can see, everything we learned doing Diacom diag's on the C4 is a help but you gotta keep learning
for in the C4, the O2s gave good idea how engine was running but now with OBD II, O2s are montiored differently
and require a new way of thinking.
Below shows you an example how much better it is when you can collect engine traces and have others review
them far from where you live and even in never even see the car.
So when I do these techie team e-mails it's to get you to grasp onto the importance to keep learning and keep
letting other teammates know what your seeing with your Corvette and mods you are doing.
One last thing the further tests on the cold air box has shown a constant lower IAT reading and the only time it
goes about 85 degrees is when the car is sitting idling, once car is moving the ramming of cold air mantains
a much cooler IAT temp.
Thanks to Mark R and Craige showing me I was not nuts all together and both rich and lean conditions is in fact
what is going on.
J.R ( Dang, give me a Holley carb and a few fuel jets :-))
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John,
Just took a look at the three runs. It seems that under other than WOT you
are running a slight bit lean. If you were to use a MAF Translator, I'd
imagine you'd only have to adjust the base setting one position rich. That
may bring your O2's a bit higher, and you'd probably end up either 2% or 4%
leaned out on the WOT setting. Remember... get the base setting (and values
of your LTFT's inline) before messing with the WOT setting, which correlates
to your O2 sensors.
If you have access to a dyno that has wideband 02's then you can calibrate
your O2 sensors to the actual a/f mixture reading from your tailpipe. If
you go with the general consensus that .875 - .90 is ideal, than you are
running a tiny bit rich when WOT.
The slight bit of KR that showed up is probably nothing to worry about,
maybe even false knock. It happened at only 23% throttle, and not while you
were accelerating quickly... (possibly lugging second gear at @ 10mph.) I
wouldn't worry about it, especially since you've got no KR at higher
throttle during hard acceleration.
Overall, you're not too far off. Definitely better than most cars I've seen
who are starting off on this journey. Have you thought about having Mallett
update your PCM? I don't have experience with them personally, but I'd bet
they can map your PCM to be right on the money, and that would save you the
hassle and expense of the MAF Trans.
Hope this helps,
Craige