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View Full Version : question for HAL and other gurus.



jmakado
06-17-2004, 08:04 PM
hal, i read that you said that removing honeycombs on a 2g mas can create a lean condition at around 4500rpms. i have my honeycombs intact but my mas screw backed all the way out. dave and i kept having trouble with it going lean at 4500 and then the ecu dumped tons of fuel going off the chart rich until 5200 when it would go back to 11:1. i also have a sharp dip in hp and torque right before the car goes pig rich. could it be that the screw backed out is creating this lean condition, timing being pulled, and dumping of fuel? anyone feel free to chime in....i just read what HAL had said somewhere so i thought i would start with him. thanks.

sbiggi
06-18-2004, 12:41 AM
well... for one, the tail pipe sniffer wideband mac uses is going to have a delay.

So I would bet it actually goes rich at the point where the torque dips, and not exactly what you see on the airfuel curve. Due to the length of the exhaust, there is a delay in what the wideband reads.

-seth

DlandryTSI
06-18-2004, 09:05 AM
If you had dsmlink we could tell easilly if the screw on the maf was causing that. Plus the fuel curve would be straight across. Not sure why the s-afc II is causing that rich spot. The car was still below 12:1 before it went pig rich. Torque was still there and holding so I'm not sure why the car was doing that.

As far as MAC's wideband goes. The difference between that wideband and an actual wideband sensor in the downpipe w/o a cat is about .2 - .5 unless the filter on the wideband is crummy.

--Dave

jmakado
06-18-2004, 09:24 AM
i need dsmlink! i would have gone with that first, but the deal i got on the afc was to good to pass up.....i guess i might try to move the screw in a little and see what happens.

DSMtuned
06-18-2004, 09:42 AM
I might try adjusting your Ne points closer together on the SAFC II so you can get a bit more detailed tuning in the rpm range that is a bit wacky.

-Craig

hoffman
06-18-2004, 09:43 AM
Move it back.

For weeks Dave and I had been trying to figure out why my car was being such a pain. Finally it was narrowed down to the MAS and low and behold, the screw was backed out.

I swapped it with the MAS off the TSi to be on the safe side, but its amazing how one little piece of plastic messing everything up.

DlandryTSI
06-18-2004, 09:44 AM
It shouldn't matter where those points are. Where ever you specify the fuel changes it should apply them to that RPM point. All the other points were working just fine....

--Dave

DSMtuned
06-18-2004, 10:01 AM
So you guys had fuel set the same across the rpm range?

I'll try to explain where my thinking is. Lets say you have a rich spot at 5200 rpms. Your Ne points closest to 5200 rpms are at 4800 and 5400rpms. 4800 is set at 5%. 5400 is set at 9%. That means that the average that the SAFC II will place at 5200rpms is 7%, right?

So to get rid of the rich spot at 5200 you could move around your Ne points throughout the entire rpm range to gain one more. You could then have Ne points at 4800, 5200, and 5400. You could lean out 5200 and lean it out as necessary.

Maybe you're saying the exact same thing as me, but I just want to make sure.

-Craig


Originally posted by DlandryTSI
It shouldn't matter where those points are. Where ever you specify the fuel changes it should apply them to that RPM point. All the other points were working just fine....

--Dave

DlandryTSI
06-18-2004, 01:12 PM
Yes the curve was the same across the rpm band from 4k to 7k. This should prove to me that the wideband data should be the same throughout those rpm points or close to. Not going from 11.5:1 to less than 10:1 AFR then back to 11.5:1.

--Dave

jmakado
06-18-2004, 02:25 PM
ya, if we tried to lean it out at that point it would just go super lean directly before and after that point, but it would still be super rich from about 4700 to 5200 and then return. if you look at the wideband graph, it would be a fairly straight line except for that one rich area. i can't seem to find where i read that removing the honeycombs does it, but i am possitive that i read that it casues a lean condition (possibly knock) at 4500. which would explain the dumping of fuel immediatly after that point. we were able to smooth the hp and torque curves on race gas around it, but if you look at the pump gas runs you can see that it dips a fair amount aound that range. i was just "off the chart" rich during those pulls so you can't see the wideband graph. but my guess is that the same is happening on pump gas. i will move it back in and see what happens. thanks for the help as always.

sbiggi
06-18-2004, 04:41 PM
and your not maxing out your injectors? sounds like they go static to me.

-Seth

jmakado
06-18-2004, 04:44 PM
Originally posted by boostedTSI
and your not maxing out your injectors? sounds like they go static to me.

-Seth
i doubt it. the settings were all around -20 to -30.

hotrod
06-18-2004, 07:59 PM
It sounds like you may have a mis-read of air flow due to an intake resonance at that rpm. I've heard of resonant pressure waves in the intake, confusing the mass flow sensors, but off hand can find no reference for it.

Larry

jmakado
06-18-2004, 08:12 PM
Originally posted by hotrod
It sounds like you may have a mis-read of air flow due to an intake resonance at that rpm. I've heard of resonant pressure waves in the intake, confusing the mass flow sensors, but off hand can find no reference for it.

Larry
mot sure if that's the exact reason for it or not? but the mas getting *confused* at that rpm point is what i think is happening to. anyway, i'm going to screw it in more and see if that fixes the weird reading.

Jack(IAT)
06-20-2004, 02:26 PM
It sounds to me like something else is wrong. The 2G MAF is very forgiving and I have made my own 3" intake pipes using the 2G MAF's sensors and module only (the pipe was the MAF) and they worked perfect. I have also removed all the honeycombs and plastics out of them with no problems either. I highly doubt that little screw will do much of anything. Anytime I find something wrong with a DSM or 3S that makes me think it's the 2G MAF, I find it's a leak or something somewhere else. May want to keep it simple and do some leak tests and check your plugs n stuff...

Jack

KeltonDSMer
06-21-2004, 02:07 PM
Do you have a heat shield, or is the filter getting air non-symetrically from it's surroundings? I think for one reason or another there is major turbulance being created at that RPM which causes the MAS to put out a high frequency reading compared to how much actual air is entering the motor.

Do you have a way to check the air/fuel ratio while moving, for if it is turbulance that is causing the richness while stationary, it probably wouldn't happen at speed.

Mirage
06-21-2004, 08:11 PM
Originally posted by hotrod
It sounds like you may have a mis-read of air flow due to an intake resonance at that rpm. I've heard of resonant pressure waves in the intake, confusing the mass flow sensors, but off hand can find no reference for it.

Larry

Believe it or not, this has happened in one mitsu model (not sure which one) with enough frequency that they issued a service bulletin concerning this.

Seeing that this happened in such a narrow rpm range and with such specific conditions, I'll bet that resonance is what caused it.

I'll bet that if you increased boost just a little or kept the throttle at anything less than WOT, that this condition wouldn't appear or would even dissappear. Just changing those specific conditions enough to cancel that resonance would help the tuning.

I've never seen or heard about this happening with a 2g, but the model that it happened to used a 2g style MAF with some specific length for the intake hose.

Marcus Martinez
my $.02