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Old 03-30-2010, 09:15 PM   #1
Bad Noodle
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Default maf 5v Spike / car stumbles / during rain ???

So while driving if I start spooling, the maf registers a 5v spike around 5psi and the car stumbles like I popped a intercooler hose. No codes get thrown, just a smash your face into the steering wheel stumble...

I've only had this happen in the rain. I'm stumped ...

Log looks like:
Code:
   Time     Load     rpm       FbKC    PSI       mafV     thrttle    AFR
  5359     0.68      2448     0          -6.51     2.2        14.06    14.29
  5531     0.74      2474     0          -4.66     2.6        18.27    14.07
  5672     1.29      2554     0          0          2.74      40.36    14.17
  5843     1.33      2648     0          0.45      2.82      38.76    15.21
  6000     1.57      2710     0          1.04      3          38.47    15.67
  6187     1.66      2784     0          1.7        2.98      39.63    14.46
  6343     1.73      2895     0          2.38      3.14      38.91    12.5
  6500     1.8        3005     0          3.05      3.2        38.91    12.61
  6687     1.93      3102     0          3.75      3.22      37.89    12.14
  6875     1.97      3226     0          4.34      3.38      36.43    11.25
  7031     2.1        3338     0          4.76      3.44      34.98    11.17
  7234     2.08      3488     0          4.85      3.48      33.96    10.91
  7422     2.03      3591     0          3.97      3.46      30.62    0
  7578     2.06      3718     0          3.4        3.56      29.75    10.73
  7718     3.37      3444     0          3.6        3.44      29.46    10.58
  7922     3.34      4299     0          5.68      5          56.78    10.83
  8093     3.92      3319     0          1.89      3.7        22.92    10.08
  8265     1.36      3833     0          -3.59     2.8        15.8      13.45
  8422     0.65      3450     0          -8.45     1.94      8.82      12.54
  8656     0.32      3353     0          -9.56     1.96      8.24      11.61
  8750     0.27      3282     0          -10.18   1.82      7.81      12.01
  8906     0.25      3053     0          -10.06   1.72      7.23      11.01

mods - vf39 with all the fixins and a blow-thru setup.
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Old 03-31-2010, 07:58 AM   #2
Bad Noodle
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Good morning smart people
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Old 03-31-2010, 09:53 AM   #3
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Check your grounds and electrical connections, a little water could be getting in and screwing with your connections. If not that maybe a post maf leak, thus metering all the air but your engine not seeing much of it. Maybe the maf has gone bad?

This is where i would start looking, hope it was of some help.
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Old 03-31-2010, 10:55 AM   #4
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My MAF did that once when it got wet in the rain. Is your air filter wet at all? Mine was soaked when it happened.

I cleaned the MAF and it was better, but still not perfect, always ran a bit rich after that. I ended up swapping MAF sensors, still have the old one in my garage.
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Old 03-31-2010, 12:35 PM   #5
Bad Noodle
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Thanks for the info guys

Today is nice and sunny and it seems like everything is doing better. Still stumbles a little, but I it should be fine once everything "dries" assuming water got in somewhere. I'll have to check all my electrical connections to make sure water isn't getting somwhere around the shrink wrapping.

I'll take out the maf and clean it as well. It was pouring like hell yesterday all day so I wouldn't be surprised if it's a little wet. Might have to change the location of the filter
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Old 03-31-2010, 02:08 PM   #6
bren wrx
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wet or bad maf or maf wiring

most of the time when i see this the maf wiring is frayed or there is a bad connection
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Old 04-01-2010, 05:38 PM   #7
PhatBotti Tuning TKR
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probably just an anomaly much like your AFR reading 0 at 3500rpm.

if it is really happening it should be evident in your AFR. if its not visible in the log try upping your g/s a crap ton at 5v to make the car really really rich and see if it shows in the logs.

what bov are you running?
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Old 04-01-2010, 08:06 PM   #8
Bad Noodle
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Update, 2 sunny days later, everything is back to normal. My guess is that there is some kind of exposed wiring for the maf. I soldered the wires like a mofo and coated them with liquid electrical tape, then shrink warped them. Must have missed a spot where the water gets in during the drain...
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Old 05-10-2010, 11:16 PM   #9
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The MAF is a hotwire style sensor. It measures how much current is needed to maintain the 'hot-wire' at a given temperature. More air passing over it means the wire cools down more so it adds more current to keep the temperature of the hot-wire the same. When a drop of water or moisture hits this hotwire, the sensor thinks a LOT of air has passed over it since the temperature of the hotwire dropped like a rock and it adds current to compensate. Hence the spike in perceived MAF voltage.

Change your air filter and make sure it is sealing well to the airbox.
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Old 05-10-2010, 11:20 PM   #10
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i had a problem with oil and water in my intercooler pipes when it was really cold out. that causes the exact same thing to happen to me. dried the pipes out and cleaning the MAF really helped.
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Old 05-11-2010, 10:08 AM   #11
the suicidal eggroll
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Quote:
Originally Posted by ThaFlyinSoundman@aim View Post
i had a problem with oil and water in my intercooler pipes when it was really cold out. that causes the exact same thing to happen to me. dried the pipes out and cleaning the MAF really helped.
Unless you're running blow-through, condensation or oil in the intercooler pipes won't affect the MAF.
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Old 05-11-2010, 10:20 AM   #12
bren wrx
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Quote:
Originally Posted by MRF582 View Post
The MAF is a hotwire style sensor. It measures how much current is needed to maintain the 'hot-wire' at a given temperature. More air passing over it means the wire cools down more so it adds more current to keep the temperature of the hot-wire the same. When a drop of water or moisture hits this hotwire, the sensor thinks a LOT of air has passed over it since the temperature of the hotwire dropped like a rock and it adds current to compensate. Hence the spike in perceived MAF voltage.

Change your air filter and make sure it is sealing well to the airbox.
bingo.
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