Another_User

I will take a look when I get home, I don't have access to HPTuners right now. I am pretty sure I logged the occurrence in the log I have in this thread if you have a chance to look at it. I have not tried another stock MAF, but I have trouble believing it is the MAF when the frequency and calculated airflow is stable. I have tested and had the same trimming issue with stock ends and ported ends. Very mysterious...

Silverhawk_02TA

He's in FTC 2 when it happens. I have to agree with Another_User, I don't think the MAF itself is the problem. The MAF readings are steady.

Another_User- Do you have convenient access to a wideband O2? I'm interested in whether or not your O2's are locking at max because of an actual rich condition, or because of some other problem, perhaps something internal to the PCM. Which brings up another question: Do you have a buddy you could swap PCM's with?

Another_User

Eeeeew...the PCM. No, not really. Is this something I *might* need to do a complete reflash with my stock BIN for? I don't have a wideband...unfortunately it isn't in the budget right now...

jimmyblue

iTrader: (11)

I wonder whether you have some sort of intermittent
electronics issue with the MAF. Like EMI or something
(I read that in the Helm manuals, the MAF or the PCM's
reading of it can be bothered by electrical noise, like
from injector harness or plug wires). The HPTuners log
can only show you the data that comes over the OBDII
and that is "decimated" by a factor of 8 (12.5mS main
data cycle but 100mS report cycle) so you might just
not see the thing that really set off the problem unless
you catch a lot of these events. You might look at the
MAF frequency and see if there is anything twitchy
about that. Like supposing you were at a MAF frequency
that was close to your ignition or fuel injector pulse
freq, maybe you get an occasional funky beat.

Or something.

Silverhawk_02TA

I really don't know.

Maybe it's just bad MAF karma, considering your avatar and all...

Another_User

So, are you ready for this? I think I may be on to something...but I am not sure what exactly to do. Any ideas? Here is my log and a pic:
http://users.adelphia.net/~someoneelse/05MAY05.hpl

Silverhawk_02TA

I can see where you're going and why, and I was thinking the same thing at first, but after mulling it over awhile, I think what we're seeing here is Commanded EVAP reacting to your trims, and not your trims reacting to Commanded EVAP. Keep in mind that I'm not 100% on EVAP operation, but here's my thoughts:

If you look at your STFT's and compare it to Commanded EVAP, you can see that they mirror eachother perfectly. I think Commanded EVAP changes with fuel trims so as not to throw off fueling by letting in too much fuel vapor. You'll notice that when your STFT's drop to -40, the Commanded EVAP % drops from around 50 to about 30. When the PCM is pulling fuel using trims, I believe it is also telling the EVAP system to cut back on the amount of fuel vapor it's allowing into the intake. I think that if the EVAP system itself was causing the dive in trims from allowing in too much fuel vapor, you would see the Commanded EVAP % rising when your trims drop, instead of falling. Also, I'm not sure that even if the purge solenoid was stuck all the way open that the additional fuel vapor would be enough to result in STFT's in the -40 range. I am also unaware of any difference in EVAP operation in MAF vs. SD mode.

But, like I said, I'm not exactly well versed on EVAP system operation. I hope I'm wrong, because it'd be great to be able to narrow it down to the EVAP system.

Another_User

I need to do some more testing, but if you notice that I locked out the EVAP purge and I did not get any strange trims. I need to do a long test run to be sure. I really think they are somehow related, because that is the only other way that fuel could get in my engine without injector pulse width changing.

jimmyblue

iTrader: (11)

Since you've taken the car way outside any emissions
protocol anyway, why not say "screw the EVAP" and
call it weight reduction?

Another_User

The thought has crossed my mind. I am still trying to figure out the "why." If it is my problem I will probably end up removing it (if it is not a repairable issue). Actually my car ran and idled a lot better with it disabled. I just get nervous modifying anything that carries fuel.

Silverhawk_02TA

Hopefully you're right. Keep in mind that there is a comprehensive set of DTC's that monitor EVAP malfunctions (not that they are infallible). Also, with the Commanded EVAP % dropping from 50 to 30, it should be allowing less fuel vapor into the intake, not more. At this point, I'm not convinced that you are having an actual rich condition at all. I think your O2's are locking at .900 because of some other type of malfunction.

But anyhow, like you said, do alot more logging and see if the problem recurs.

sevanseriesta

iTrader: (34)

All I want to say is that I do not understand more then half of what you two have been talking about. But I am going to read all of this about another 30 times While I am looking at My hp tuner.

I have a question about 02 sensors and how to tell if they are bad. I do not think mine are bad but mine do not look like yours. Mine Run right on top of each other is that bad or good. Your at the top are kind of inbetween each other. Do you kind of know what I am saying?

I hope that you guys do get this figured so I can go in and compare this to other logs and least I will know what the problem is if I ever see it. I definently will not for get this post

Silverhawk_02TA

They can be out of phase with eachother. But generally a good O2 waveform at cruise looks something like a sine wave.

WS6snake-eater

JIMMY, What exactly does the EVAP do? You had mentioned deleting it for weight reduction, would that affect fueling? How would one go about tuning it out of the PCM?

Another_User

EVAP is an emmissions system that recirculates fuel vapors back into your engine so that it does not just go right out into the atmosphere. The system replaces things like vented gas caps, which cars used to have. The system is now "sealed", which is why you will get a check engine light if you don't put your gas cap on tight, or your gas cap is bad. Removing it should only affect your emmissions...but I don't really think it is something that could be tested for if you removed it. Weight reduction gains would be minimal...maybe around a pound or so I would imagine...there is not much to it. You can tune out the codes. With HPTuners you can also disable it on a temporary basis through the VCM controls. Unfortunately they have not really setup a way I know of to disable it permanently via the PCM. The only way I can think of is to remove it and disable the codes.

If anybody looks at the second log I posted for information, please watch the EVAP PIDs because I was turning things on and off while I was testing, so it does not fully reflect a real situation while only your PCM is in control of everything.

Another_User

I just found documentation that says that EVAP (not GM specific) will not purge during a MAF failure. That would be consistent with my problem. Everything I have found also shows that EVAP should not purge at idle, which mine does. I suspect that there is some table in the PCM that needs modification after a cam installation. I am going to take my test drive tonight with EVAP purge disabled. What long term problems could I run into if I leave my EVAP system intact, but disable it's ability to purge? Will it build up pressure, or should it be fine left alone?

Another_User

Update: I did more logging and found that one time at idle I still got high negative trims, but not as high as before. This was with the purge disabled. I did some testing and shut the purge valve and the vent valve and monitored the fuel tank pressure, and it looks like the fuel tank pressure decreased pretty rapidly, particularly if I decellerated a lot. I am thinking that I may have an EVAP purge valve that is partially stuck open. Any input guys?

Silverhawk_02TA

I can't find an option to disable EVAP purge in the editor, so you'll have to do it manually unless you want to supress it with the scanner every time you drive anywhere. Just pull the wiring harness off the purge solenoid (I'm assuming that's where it is. I'm too lazy to go out and look). I've been running SD for months now (without the EVAP purging I guess) with no ill effects. The EVAP system itself is what pressurizes the lines, and does this so it can detect leaks. If you're worried about it, just pull the lines, plug the manifold side, and put a breather filter on the fuel tank side.

Good luck, and keep us posted on what the log shows!

Another_User

Can I get away with plugging the manifold and plugging the purge valve and disconnecting the harness to it? Will the vent still operate properly? It seems to me that it should vent both directions, right? Or is there some info I am missing?

HumpinSS

iTrader: (1)

buy and lsx intake and you will have to remove it . Mine is gone