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Old 10-29-2005, 05:49 AM   #1
Patrick Olsen
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Question (long story) MAF sensor going bad in wet weather or ???

For a while I've had issues with smooth power delivery on my car. I've always kinda figured it had to do with the Cobb heads and cams, that perhaps the engine was seeing enough extra airflow compared to stock that the ECU was a bit "confused". It pulls timing in the midrange, and throttle response can often be herky-jerky (result of the aluminum flywheel probably, but it doesn't seem that others have the same problem).

I've noticed a few times that in wet weather the herky-jerkiness is even more pronounced (fortunately it's been a pretty dry year out here on my side of the island). About a year ago while out at night with some friends and family the car actually quit on me - trying to climb a hill on the highway it just wouldn't go. We pulled over, fiddled around with it a bit, didn't see anything obvious, and then started it back up and it was OK initially. For the rest of the ride, though, it continued to buck every once in a while - very pronounced at 65mph or so, like throw you against the seatbelt bucking - and then it would be fine for another couple minutes. I datalogged with my pocketlogger and it looked to me like the front O2 sensor had died - the bucking seemed to correspond to the O2 sensor pegging low, and then it would "come back to life" and the car would be OK. So, I replaced the O2 sensor and things were back to normal (normal being not really "right", but at least it wasn't dying on the side of the road). Note that it never threw any CEL codes other than the "normal" misfires on all 4 cylinders.

Fast forward about 8 or 10 months. I had noticed a couple times in wet weather (not even really raining, just kinda grey misty weather) that the "normal" herky-jerkies were a bit more pronounced. Hmmm... Then last weekend we had a day where it rained all day long. My roommate and I went out to grab some dinner and on the way home the car did the hard bucking thing just a little bit, enough that I was worried. Sure enough, we got off the highway and onto the main surface street heading towards our neighborhood and the car just fell flat on its face. I was having to give it way too much gas to do even 50mph, and throttle response was extremely slow to non-existent. Stopped for a stop light and the car just wouldn't go, so we're stuck in the middle of the road (in the dark, and raining, on a road with people doing 50+ mph zipping by on either side ). We were waiting for the light to turn red again so we could safely get out and push the car out of the way. After waiting for a minute or so, I tried starting it again, and sure enough I was able to get it going. The last few miles home were rough, but it made it. I pulled the codes with my pocketlogger and it threw a P0102 MAF sensor signal low. Interesting, never seen that before.

I left the car parked over night, and the next morning (dry weather) tried to start it up. Still no joy, immediately stalled, and again threw the P0102. So, I unplugged the MAF sensor and limped it around so I could get it on a lift to install some new rear lateral links (note that "limp home mode" doesn't work too well with a significantly modified engine ). About noon or 1pm I was done with the suspension work and decided to try the MAF again. Plugged it in, car started right up. I've now been running "normally" for a week with no additional P0102 codes, just the standard misfire codes.

I have an Injen CAI on the car, which puts the filter in the fender. There are some small openings, but nothing that (in my mind) would allow the intake to be sucking in heavy streams of water that would make the MAF want to **** itself. Even on the day it died on me and threw the P0102 codes I never drove through any deep standing water, just regular wet pavement and moderate rainfall. And even if there's no rain, just a kinda damp day, it still seems to be affected (although I've only seen the P0102 code on that one day). I don't want to just blindly buy a new MAF sensor, since that's a cool $355 or something like that. Clearly something's not right, though, and I'd appreciate some thoughts on what I should look at to try to resolve this.

Thanks,
Pat Olsen
'97 Legacy 2.5GT sedan
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Old 10-29-2005, 10:53 AM   #2
Legacy777
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Does sound like the MAF. I had issues where my car would just lose power while driving. Sometimes I could rev the engine and get it back. Other times it would die, especially if RPMS were low. One day it died, and I couldn't get it back running. It sputtered, choked, and just wouldn't run. I waited a few minutes, started it up, and everything was fine. However the code confirmed it was the MAF sensor.

Replaced the sensor and everything was fine.

I attribute its demise to the open pod style intake filter. I had it on the car for probably about 3 years and no problems. I've seen other similar failures in which people had the open "pod" style filters. The MAF sensors just don't like them.

Is your MAF sensor the black JECS sensor?
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Old 10-29-2005, 01:38 PM   #3
Patrick Olsen
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It is black, but I don't know what a JECS sensor is. Is that the brand?

Pat
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Old 10-29-2005, 01:41 PM   #4
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Make sure you don't have any way that air can enter the intek post MAF. And even though you are getting a MAF CEL, I would replace you plug wires and plugs.
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Old 10-29-2005, 05:14 PM   #5
Subie Gal
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i had the same code at one time...

ended up being a bad ground off of the MAF

check all of the wiring.....

Jamie
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Old 10-30-2005, 12:27 AM   #6
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Quote:
Originally Posted by Patrick Olsen
It is black, but I don't know what a JECS sensor is. Is that the brand?

Pat
Yes the black one is the JECS brand sensor.
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Old 10-30-2005, 11:22 PM   #7
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Pat,

You can get JUST the sensor portion, the part number is 22794AA000. Should be about $50 on www.subaruparts.com . Buying it now gives you the updated sensor, I ran Peaty's old Reactive filter short ram pod intake filter, and it didn't blow the sensor. I was impressed by that. I'll be running a Cobb CAI in a few weeks, and it will put the new meter to the test.

-Gagan

Last edited by joltdudeuc; 10-31-2005 at 09:39 AM.
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Old 10-30-2005, 11:25 PM   #8
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Very true, check the contacts on your plug wires, and especially the coil pack. Mine was very badly coroded. Some battery cleaner and a wire brush will get the coil contacts back to workable shape.

-Gagan
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Old 10-30-2005, 11:28 PM   #9
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I have a '99 RS, I'm not sure if we have the same MAF setup. do you have pics of the housing? I'll know if you need a 98 RS one or the 99RS one.
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Old 10-30-2005, 11:33 PM   #10
Patrick Olsen
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Here's what the MAF looks like:


Quote:
You can get JUST the sensor portion, the part number is 22794AA0)0. Should be about $50 on www.subaruparts.com .
Is that ) supposed to be a 0 or what? That's really good news if I can get just the sensor.

Pat
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Old 10-31-2005, 12:43 AM   #11
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I don't think you can get just the sensor for that early type of MAF. If it was the 99...yeah, you definately can for that one. I've been seeing a couple on Ebay now and again for substantially less than retail. I believe the early EJ series used the same MAF for all models......I can't confirm that though.

In the meantime, you may try a prefilter type insert prior to the MAF to help it out.

Jay Storm
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Old 10-31-2005, 08:47 AM   #12
Legacy777
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Yeah, you can't get just the sensor, you have to buy the whole thing, and it's around 300 bucks. I know....I bought one
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Old 10-31-2005, 09:38 AM   #13
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Yeah, you have the same MAF as the 98.

wow... there is only the whole assembly listed. Wonder why the 99 is listed for $125, and we were paying $250 for it...



-Gagan

Last edited by joltdudeuc; 10-31-2005 at 09:44 AM.
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Old 10-31-2005, 09:39 AM   #14
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LOL, yeah, that's supposed to be a zero
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Old 10-31-2005, 09:48 AM   #15
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Pat, your part number is 22680AA160
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Old 10-31-2005, 10:15 AM   #16
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Quote:
Originally Posted by Storm
I don't think you can get just the sensor for that early type of MAF. If it was the 99...yeah, you definately can for that one. I've been seeing a couple on Ebay now and again for substantially less than retail. I believe the early EJ series used the same MAF for all models......I can't confirm that though.

In the meantime, you may try a prefilter type insert prior to the MAF to help it out.

Jay Storm
Jay,
Not true. Some of the Legacies used a MAF manufactured by Hitachi. That's why Josh asked if it was the JECS unit. But I believe all the Imprezas and later Legacies have all used the JECS unit.

Pat,
You should be able to look on the side of the MAF and see the manufacturer right by the part number. But based on your picture (the Hitachi units are metal) I am pretty sure you have the JECS unit. I've got a good used one from one of my parts Legacies. PM me and we can work it out.

As a side note, I have the 02 sensor issue. It reared it's ugly head again last week when it got cold and wet.It is strange how it does seem to coincide with wet weather. Last time replacing it remedied the issue. This time I limped around for a week since we were pulling my engine on Saturday. The plugs got so bad from richness that the car wouldn't even idle on it's own. I tried to clean it using methods that have been suggested from time to time. Ran fine yesterday afternoon. This morning (cold and wet) no go. It barely got me to work. Looks like another new 02 sensor is in order...
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Old 10-31-2005, 11:55 PM   #17
Patrick Olsen
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Quote:
Originally Posted by Subie Gal
i had the same code at one time...

ended up being a bad ground off of the MAF

check all of the wiring.....
Jamie - What ground did you find was bad? The wiring from the MAF all goes into a harness that runs along the firewall, so I'm not sure where exactly it's grounded. I cleaned up the four grounds on the strut towers, figuring the MAF probably connects to one of those.

Pat
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Old 11-09-2006, 04:59 PM   #18
RUBEN
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Im having same issue how you fixed it please thanks
Quote:
Originally Posted by Patrick Olsen View Post
For a while I've had issues with smooth power delivery on my car. I've always kinda figured it had to do with the Cobb heads and cams, that perhaps the engine was seeing enough extra airflow compared to stock that the ECU was a bit "confused". It pulls timing in the midrange, and throttle response can often be herky-jerky (result of the aluminum flywheel probably, but it doesn't seem that others have the same problem).

I've noticed a few times that in wet weather the herky-jerkiness is even more pronounced (fortunately it's been a pretty dry year out here on my side of the island). About a year ago while out at night with some friends and family the car actually quit on me - trying to climb a hill on the highway it just wouldn't go. We pulled over, fiddled around with it a bit, didn't see anything obvious, and then started it back up and it was OK initially. For the rest of the ride, though, it continued to buck every once in a while - very pronounced at 65mph or so, like throw you against the seatbelt bucking - and then it would be fine for another couple minutes. I datalogged with my pocketlogger and it looked to me like the front O2 sensor had died - the bucking seemed to correspond to the O2 sensor pegging low, and then it would "come back to life" and the car would be OK. So, I replaced the O2 sensor and things were back to normal (normal being not really "right", but at least it wasn't dying on the side of the road). Note that it never threw any CEL codes other than the "normal" misfires on all 4 cylinders.

Fast forward about 8 or 10 months. I had noticed a couple times in wet weather (not even really raining, just kinda grey misty weather) that the "normal" herky-jerkies were a bit more pronounced. Hmmm... Then last weekend we had a day where it rained all day long. My roommate and I went out to grab some dinner and on the way home the car did the hard bucking thing just a little bit, enough that I was worried. Sure enough, we got off the highway and onto the main surface street heading towards our neighborhood and the car just fell flat on its face. I was having to give it way too much gas to do even 50mph, and throttle response was extremely slow to non-existent. Stopped for a stop light and the car just wouldn't go, so we're stuck in the middle of the road (in the dark, and raining, on a road with people doing 50+ mph zipping by on either side ). We were waiting for the light to turn red again so we could safely get out and push the car out of the way. After waiting for a minute or so, I tried starting it again, and sure enough I was able to get it going. The last few miles home were rough, but it made it. I pulled the codes with my pocketlogger and it threw a P0102 MAF sensor signal low. Interesting, never seen that before.

I left the car parked over night, and the next morning (dry weather) tried to start it up. Still no joy, immediately stalled, and again threw the P0102. So, I unplugged the MAF sensor and limped it around so I could get it on a lift to install some new rear lateral links (note that "limp home mode" doesn't work too well with a significantly modified engine ). About noon or 1pm I was done with the suspension work and decided to try the MAF again. Plugged it in, car started right up. I've now been running "normally" for a week with no additional P0102 codes, just the standard misfire codes.

I have an Injen CAI on the car, which puts the filter in the fender. There are some small openings, but nothing that (in my mind) would allow the intake to be sucking in heavy streams of water that would make the MAF want to **** itself. Even on the day it died on me and threw the P0102 codes I never drove through any deep standing water, just regular wet pavement and moderate rainfall. And even if there's no rain, just a kinda damp day, it still seems to be affected (although I've only seen the P0102 code on that one day). I don't want to just blindly buy a new MAF sensor, since that's a cool $355 or something like that. Clearly something's not right, though, and I'd appreciate some thoughts on what I should look at to try to resolve this.

Thanks,
Pat Olsen
'97 Legacy 2.5GT sedan
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Old 11-09-2006, 07:56 PM   #19
Patrick Olsen
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I replied to your PM, but I hadn't re-read this thread when I did that and was thinking you were talking about something else. Now that I think about it, though, I really don't remember what I did. I think I bought the MAF that Matt Monson offered me, but I don't remember if I installed that and it fixed the problem, or if the P0102 code just fixed itself and never came back.

And as I said in my PM, I've bypassed my knock sensor by wiring a resistor in its place. That has completely solved the herky-jerky power delivery problem I had for so long. Bypassing the knock sensor may not be the smartest thing to do, but I'm so much happier with how the car drives that I really don't care.

Pat
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