LTFT +25 only when K&N installed. Logs and cfg included

[JamieGallien]

I'm a total noob to HP tuners, but not to engines so here goes.

2000 Yukon 5.3/A4. The only programming change done is to disable the EVAP codes and unplugged the EVAP solenoid on the intake. The only mod is on a whim years ago I removed the MAF from the stock airbox, removed the airbox, and installed a spare cone-style filter that I had directly to the inlet of the MAF.

I disabled the EVAP the line back to the tank is broken and I don't want to drop the tank again. It was causing rough idle and stumbling to the point the engine would die due to unmetered air coming into the EVAP purge valve. After disableing the EVAP the truck runs as well as ever, BUT...

In the course of scanning the engine just to see how everything looked I noticed that my LTFT are running +25 which would tell me that there is an air leak somewhere that the engine can't completely compensate for or possible MAF problems among other less likely things. I have a spare MAF handy so I was going to swap, but when I removed the K&N the STFT started pulling fuel to the point that the LTFT settled to +1 to +2 which I would consider normal. I went ahead and swapped MAF just for curiosity sake but the problem is still repeatable and the numbers are the same for each MAF (which I assume are both good).

In my log, the filter is OFF just before 19:18:06, ON at 19:20:00 OFF again at 19:24:42. I repeated this several other times. Watching the MAF signal I can see that the filter is some restriction, which I would assume would cut airflow and require less fuel lower LTFT. Removed I would assume more airflow and more fuel higher LTFT. It seems completely backwards to me.

Another strange thing I notice you can see in the logs just after this point. By simply touching the metal of the MAF (either one) the LTFT changed dramatically. 19:26:18 I touch it, 19:26:42 hands off.19:28:42 touching, 19:29:12 hands off. Are these things that static sensitive or what? Blowing a noobs mind here.

Please edjumacate me! and Thanks!VCM Scanner.cfg VCM Suite.cfg filter on and off.hpl

[GHuggins]

Mafs pick up air flow = anything changing air flow across it's sensing element will change it. It was probably just seeing more air with the filter removed thus better fuel trims - air filter back on - air not seen flowing past sensor due to filters shape? = +25 fuel trims... Just to literate things better, if you have access to one of the newer duramax's, just pop the tip of the air filter up a little - goes into rep just from airflow difference while cranking You'll also want to verify that your purge valve isn't leaking - which doesn't sound like it is, depending on how you bypassed it (plugged off backside or intake side?)

[JamieGallien]

I understand the concept you are explaining, and thanks for the reply, but my numbers are acting OPPOSITE of what they should.

Air filter on = less airflow which SHOULD = lower trims/less fuel.

That's not what's happening. With the filter ON I'm seen +25 (max increase in fuel) and with it OFF I'm seeing 1-2 (less fuel).

Isn't that the exact opposite of what should be happening?

[JamieGallien]

Could having the filter attached directly to the MAF be causing airflow flucuations? Like in this example? http://www.masterenginetuner.com/sen...liability.html

[1955]

[QUOTE= but my numbers are acting OPPOSITE of what they should.[/QUOTE]


Have you had any progress with this? I have a similar issue with +25 ltft with a kn filter, when that and evap delete are my only mods. Would love to know what you did to fix/compensate.

Thanks

[jtrosky]

You could always adjust the MAF table so that the increased airflow will cause more fuel to be added in order to keep the mixture correct. Modfiying the MAF table is how you adjust the A/F ratios while in closed loop.

THen again, I'm a novice, so I'd like to see this confirmed by a more experienced tuner before taking this advice! :-) But I think what I just said is correct! :-)

[GHuggins]

You could always adjust the MAF table so that the increased airflow will cause more fuel to be added in order to keep the mixture correct. Modfiying the MAF table is how you adjust the A/F ratios while in closed loop.

THen again, I'm a novice, so I'd like to see this confirmed by a more experienced tuner before taking this advice! :-) But I think what I just said is correct! :-)

[JamieGallien]

Have you had any progress with this? I have a similar issue with +25 ltft with a kn filter, when that and evap delete are my only mods. Would love to know what you did to fix/compensate.

Thanks

All I can figure is with the K&N direct on the MAF it's directing an out of whack amount of air over the sensor, causing it to overdo fuel to compensate. I put the factory airbox back on, which solved the problem, until I can get a pipe between the MAF and K&N to smooth out the air before it hit the MAF sensor.

ANOTHER thing....if the MAF/K&N aren't mounted to something and you're still using the factor bellows pipe between the MAF and the throttle body, and little bump or motion of that rubber bellows pipe will change the airflow reading enough to cause surges. It acts like an accordion bellows, pulling air in and out.

[JamieGallien]

You could always adjust the MAF table so that the increased airflow will cause more fuel to be added in order to keep the mixture correct. Modfiying the MAF table is how you adjust the A/F ratios while in closed loop.

THen again, I'm a novice, so I'd like to see this confirmed by a more experienced tuner before taking this advice! :-) But I think what I just said is correct! :-)

You are correct, but I was having a mechanical problem, i.e. the physical placement of the K&N was causing a screwed up WAY WAY high reading that was not real. I put the factory airbox back on until I can get the K&N mounted correctly, farther downstream from the MAF>