Changed air filters...LTFTs went up ~8%?
06-28-2004, 09:53 PM
#1
Changed air filters...LTFTs went up ~8%? Car is an '82 Z28 with an '01 LS1, running IROC induction snorkel shaped like a Y with two square panel air filters.
I wasn't thrilled with my oil analysis data showing silicon in slightly higher than normal quantities, so I removed my Green cotton/gauze filters and installed a new set of Fram paper filters. I put ~80 or so street miles w/ these in place, car felt fine so I left it at that.
Tonight I was using EFILive to capture some data for spark tuning, happened to look at my LTFT values and they had gone to 5.5 in most RPM/KPa areas, to as much as 10 in the 2400+ high KPa areas. Still balanced to within 2% of each other like before, just much higher...I had the suckers tuned to zero to -0.8%/-1.2% in every driving cell previously.
Changing from cotton to paper filters has evidently had some effect on my MAF. All my VE table tuning to date has been w/ the Green filters in, so I have nothing to compare against as a baseline. My theory is that the paper filters flow more air, or straighter air, than the Green cotton ones...more air is entering the engine than before, and the PCM is having to add fuel to compensate. Any other ideas?
I carved up the data I captured into FTC groups again, and added fuel as indicated by the LTFT data...then did the necessary smoothing at the FTC boundaries. LTFTs responded correctly, so later this week I'll do a 50+ min driving capture to finalize the VE table.
Any ideas on the whackiness of filter changing greatly appreciated. Could it be that brand new Fram paper filters flow more air than freshly cleaned + oiled Green filters??
I wasn't thrilled with my oil analysis data showing silicon in slightly higher than normal quantities, so I removed my Green cotton/gauze filters and installed a new set of Fram paper filters. I put ~80 or so street miles w/ these in place, car felt fine so I left it at that.
Tonight I was using EFILive to capture some data for spark tuning, happened to look at my LTFT values and they had gone to 5.5 in most RPM/KPa areas, to as much as 10 in the 2400+ high KPa areas. Still balanced to within 2% of each other like before, just much higher...I had the suckers tuned to zero to -0.8%/-1.2% in every driving cell previously.
Changing from cotton to paper filters has evidently had some effect on my MAF. All my VE table tuning to date has been w/ the Green filters in, so I have nothing to compare against as a baseline. My theory is that the paper filters flow more air, or straighter air, than the Green cotton ones...more air is entering the engine than before, and the PCM is having to add fuel to compensate. Any other ideas?
I carved up the data I captured into FTC groups again, and added fuel as indicated by the LTFT data...then did the necessary smoothing at the FTC boundaries. LTFTs responded correctly, so later this week I'll do a 50+ min driving capture to finalize the VE table.
Any ideas on the whackiness of filter changing greatly appreciated. Could it be that brand new Fram paper filters flow more air than freshly cleaned + oiled Green filters??
06-28-2004, 10:20 PM
#2
TECH Senior Member
... the flow of the air filter shouldn't matter... the MAF should be capturing the airflow and teling the PCM how much air is coming in... you're sure there isn't a leak post MAF?
is it a stock MAF or aftermarket?
seems odd that a filter would affect the MAF ... unless the MAF was having issues to begin with.... (or if during the change a leak developed between the MAF and intake manifold...)
is it a stock MAF or aftermarket?
seems odd that a filter would affect the MAF ... unless the MAF was having issues to begin with.... (or if during the change a leak developed between the MAF and intake manifold...)
06-29-2004, 08:07 AM
#3
Stock MAF, and I believe you're right about it having issues to begin with...keep reading.
Earlier this month, I cleaned and carefully oiled my Green filters before the road trip to Indy. The LS1 swap just completed back in March, so this was it's first long road trip. On the way to Indy, I got DTC P0101 on a long uphill in 6th gear. I cleared the code, started downshifting to 5th on the long uphills, no further DTCs. I figured I was just lugging the engine on the uphills in 6th gear.
When I got home after a GREAT 3 days of road racing, drag race spectating, and auto-x spectating (www.fbody-event.org) I changed the oil and swapped in the Fram paper air filters. Shortly afterward I got P0200 (injector circuit voltage) and found one injector with an 8 Ohm variation compared to the rest...in went my backup set of injectors, no further P0200.
I made one ~40 mile work commute last week with zero issues, great performance, all is good. A few short hops as well.
Then yesterday, I hooked up the laptop to grab some data prior to spark map tuning and saw my LTFTs abnormally high. I bumped my VE table as described above, drove it to work this morning, and just as I came off the highway I got a noticeable misfire and P0101 came back.
Given the problems onset right after oiling my air filters, I'm inclined to go after the MAF. I really went out of my way to not over-oil them, applied all oil to the "dirty" side of the filter panels, etc...ah well.
I'll report back w/ my findings on the MAF. Lots of saved EFILive logs I can go thru to compare relative MAF readings before and after the filter oiling also...
Earlier this month, I cleaned and carefully oiled my Green filters before the road trip to Indy. The LS1 swap just completed back in March, so this was it's first long road trip. On the way to Indy, I got DTC P0101 on a long uphill in 6th gear. I cleared the code, started downshifting to 5th on the long uphills, no further DTCs. I figured I was just lugging the engine on the uphills in 6th gear.
When I got home after a GREAT 3 days of road racing, drag race spectating, and auto-x spectating (www.fbody-event.org) I changed the oil and swapped in the Fram paper air filters. Shortly afterward I got P0200 (injector circuit voltage) and found one injector with an 8 Ohm variation compared to the rest...in went my backup set of injectors, no further P0200.
I made one ~40 mile work commute last week with zero issues, great performance, all is good. A few short hops as well.
Then yesterday, I hooked up the laptop to grab some data prior to spark map tuning and saw my LTFTs abnormally high. I bumped my VE table as described above, drove it to work this morning, and just as I came off the highway I got a noticeable misfire and P0101 came back.
Given the problems onset right after oiling my air filters, I'm inclined to go after the MAF. I really went out of my way to not over-oil them, applied all oil to the "dirty" side of the filter panels, etc...ah well.
I'll report back w/ my findings on the MAF. Lots of saved EFILive logs I can go thru to compare relative MAF readings before and after the filter oiling also...
06-29-2004, 12:32 PM
#6
Update: I hit Radio Shack during lunch, got an aerosol can of electronics contact cleaner and a bag of long q-tips. I hosed down the interior of the MAF, the filaments & resistors, and the screen.
I then soaked down a q-tip and cleaned the interior surfaces of the MAF body...didn't touch the filaments & resistors.
The filaments/resistors were a dull color before, they're shiny silver now. The interior of the MAF turned several q-tips black before it was clean.
I'll get loose at 4pm and put it back together and take a test spin to see if it made any difference good or bad.
I then soaked down a q-tip and cleaned the interior surfaces of the MAF body...didn't touch the filaments & resistors.
The filaments/resistors were a dull color before, they're shiny silver now. The interior of the MAF turned several q-tips black before it was clean.
I'll get loose at 4pm and put it back together and take a test spin to see if it made any difference good or bad.
06-29-2004, 08:00 PM
#7
Update: cleaning the MAF with Radio Shack electronics cleaner was a clean kill on this problem. Nice smooth ride home w/ the previous binary flashed, LTFTs are back to slightly negative right where I left them.
There were no solids or visible liquids caked on the MAF thermistors, they were just discolored. Spraying w/ the Rat Shack stuff shined them right up, and the q-tips removed the black dried-up film from the MAF's interior nicely.
There were no solids or visible liquids caked on the MAF thermistors, they were just discolored. Spraying w/ the Rat Shack stuff shined them right up, and the q-tips removed the black dried-up film from the MAF's interior nicely.