Another_User

I will never turn to the dark side and buy an LSX intake. Is the method I propose using to eliminate EVAP without removing the system a good idea? Will it still vent out the EVAP vent, and just not allow purged vapors into the intake?

HumpinSS

iTrader: (1)

I removed mine but its still hooked up to the manifold. I just removed the solenoid or whatever the hell that is

Another_User

Ok, cool. I will buy some plugs tomorrow, then I can cap it off and know for sure if the problem is my EVAP solenoid. Since the problem was far less with it forced closed (or as closed as it would go), I suspect it is leaking. But, if I disable it that will work for me. I will post an update tomorrow.

jimmyblue

iTrader: (11)

Back in the old days (not the good old days, they
didn't have evaporative emissions crap back then)
the evap system was a charcoal filled cannister, a
vacuum line to the tank and a vacuum line to the
carb base or manifold.

The gas tank fumes on your warm sunny California
day would exit via the tank-cannister line and the
charcoal would adsorb the vapor and hold it (some).
But there's a limit and the cannister needs to be
purged with fresh air, and that air is sucked into
the cannister and then into the intake when the
car is running.

Of course a vacuum line and checkball or three just
don't cut it in the modern age so we have, what,
a few solenoid valves, way too many obscure
sensors, a man-week of code and a steenkin' SES
light? That's progress.

In the good old days a vented cap and a breather
up in the axle arch seemed to work out fine.
That was before the EPA started making smog
and Spiro Agnew was President.

Another_User

Well, I completely capped it off and unplugged the EVAP solenoid. No good. Still got the same thing. I don't get it... It can't be a bad injector because both sides do it at the same time. Oh well...stumped again.

Silverhawk_02TA

My best guess is that it's not really a rich condition at all. I think that the O2's locking at .900 is a false signal, and I think that your overall crazy O2 signals are another symptom of your problem. At this point I would suspect the O2 monitoring circuit inside the PCM itself. Again, I'd try to get some time with a wideband (from a buddy/on a dyno) to check what your AFR really is when this problem happens.

Maybe it's God's way of telling you to ditch the MAF?

Another_User

See, I don't know about that O2 thing. If that were the case it would not only happen with the MAF plugged in. Is it possible that at some odd point in my new MAF table (but just at one point) it is not properly metering airflow because of the lid? I have tested and shown that this trim thing happens with and without ported MAF ends. The MAF signal doesn't go crazy, so I can't see it being the actual MAF itself...

Silverhawk_02TA

Maybe and maybe not. I'm sure there's a ton of stuff going on that none of us have a clue about. Electronics sometimes do wierd **** for seemingly no reason (this is the voice of experience, I've been an electronics tech for 6 years). We're talking micro-miniature SMT and BGA components and construction here, so it doesn't take a whole lot to produce transient faults and wierd operation.

The problems you're having are intermittant, and happening at steady state operation. Hence, the MAF freq is roughly the same between the good and bad spots. This alone would seem to rule out an "odd point" in your MAF table. Also, I would expect to see the logged MAF airflow quirk at the same point your trims dive. Keep in mind, the MAF signal is in Hz, and the MAF airflow PID reading is derived by the PCM from referencing the MAF table. If it was off in one spot, you'd definitely see it in the logged MAF airflow. Of course, anything is possible, so it wouldn't hurt to rescale the MAF table and see if it produces positive results.

jimmyblue

iTrader: (11)

I think it would be a good exercise, just to log MAF
frequency and see if it shows any "sports" that
might kick the airflow measurement around. Back
to the EMI / glitch angle. The MAF frequency
-should- be stable, smooth and continuous. But
if it hiccups and it's the main airflow term it might
mess things around.

If you log 12 or fewer PIDs you chould get higher
data rate (6 or less, even more) with a better
chance of actually seeing the freak, if there is one.

Another_User

I'll do it again, but trust me, I have logged with only a few PIDs hoping to catch something like that. It doesn't appear to exist. Interesting enough, I have looked at my logs with my MAF table unmolested (very lean), you don't get the weird STFT dips. Very odd.

dr.mike

Here's a little experiment to try while logging MAF frequency.

http://67.43.173.134/StupidWidebandTricks.htm

Still working on it.

Another_User

Very interesting. I have gone back to my stock VCM and added in all my changes manually to make sure there is no residual junk from changing my tune over and over (I usually do this every so often anyways). I am going to use my stock MAF table and log some trims and dynamic airflows and frequencies and see what happens.

Another_User

Another update:
I found what I would call an "ugly spot" in my MAF tables (including stock). It looks like I am actually running rich where it says I am. Basically, right in that frequency range the MAF airflow is only a hair leaner than the rest of the table. Basically using a stock table it would go lean-barely lean-lean-super lean, barely lean being my problem area where my trims go crazy. I have generated (another and hopefully better than my initial try) MAF table from scratch. It looks good, and matches up very nicely, so hopefully it will at least come close to doing the trick!

Another thing I was working on, I managed to kill all the EGR DTCs (even ones that I don't ever show a code for) and now my EGR test says complete. Woohoo! So if I ever have to get a scan for emmissions, it should be clean (I guess).

Another_User

So much for the new MAF table. What a waste of time. What the heck can be driving my trims rich only with the MAF plugged in without making the MAF frequency go crazy, because the MAF frequency seems fine. I doubt my airflow is actually changing significantly because my MAP stays steady, so the MAF seems to be metering right. If it were blowby getting sucked into the PCV it would happen with the MAF disabled, but it doesn't. Grrrr....WTF?!

Another_User

Are you guys out of ideas too?

jimmyblue

iTrader: (11)

I wonder whether having the MAF in/out, maybe
changes the dynamic airflow / cylAir calculation
(maybe its sampling / smoothing or whatever) and
makes for more twitchiness in the presence of bad
or glitchy airflow data? Like running off the MAP
alone might be applying more filtering to the data
as a precaution? Just this afternoon's wild idea....

Now, the MAF may be a lot more finicky an instrument
than the MAP sensor. The MAF needs 12V power to
run and in the past I observed a pretty strong line
dependence of frequency output (heater power being
V**2 to first order). If you had some sort of deal
where the MAF was seeing its power supply drop
out and come back, bounce around, that might make
for some peculiar frequency output. But then, if that
were the deal you should be seeing it in the logs.

It sounds more like spurious trimming than spurious
mixture, to me. How about the block-chassis ground
voltage? Wonder if there is a ground offset, maybe
intermittent? Something that might offset the O2s
to the point where their output can't be made to cross
switch threshold by mixture, so whacked trims result?

Silverhawk_02TA

Like I said before, and jimmyblue just mentioned, you are probably not having an actual rich condition at all driving your trims down. The O2's signals are maxxing for another reason. At this point you should be looking at the PCM, and possibly other chassis wiring issues.

Another_User

But why wouldn't they do this in SD? It makes the O2s being the culprit hard to believe. The PCM...ugh....I hate that idea. Wouldn't that show in the logs?

Another_User

I had another thought. IAT. Could my FRA! mod possibly be the culprit. One thing I noticed is that it normally does that screwy thing early on from a stop, or after a hot start. Could being able to pull cooler air from the front, and hotter air from in front of the radiator be responsible? Is there a difference in how the IAT is factored between SD and MAF?

Silverhawk_02TA

I think the O2's themselves are fine. I would say it's probably an issue with the O2 signal processing circuit inside the PCM. I think this is also the reason your general O2 waveform looks so demented. Even one component a little bit out of tolerance in that circuit could cause issues, and with the complicated interdependencies of an electronic device as complex as the PCM, it's quite possible that plugging in the MAF results in an errant induced voltage or extra load that just pushes it over the edge.

The MAF airflow reading is independent of the IAT sensor reading. The DA calc relies heavily on the IAT, which makes SD operation very dependent upon it as well. IAT only indirectly affects MAF operation through the DA calc that's used to filter the MAF reading during throttle transients. Also, I've seen your logged IAT when your trims take a ****, and it is steady.