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Old 03-08-2010, 11:03 AM   #1
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MAF WAI question, any tricks to bypass, reuse etc?

1995 Mazda B2300 (Ranger 2.3) 5 speed, 2WD.

I replaced the whole air filter assembly with a high flow filter connected to the intake tube with a PVC pipe. But the MAF sensor is molded into the filter housing. So I just unplugged it and have been driving 2 days without the MAF. It hunts for idle on startup, but otherwise seems to run great. I don't know if the better throttle response is from unplugging the MAF, or from the new intake setup.

The problem though, is that now my Scan Guage reads 9999mpg. So if you're looking for the magic bullet, just unplug your MAF for an instant 10k mpg! Other readings are still available like Load, air & water temp, open/closed loop, TPS, etc.

I thought maybe the MAF unplugged would shove me into open loop all the time, but in reality it actually stays in closed loop mode now, whereas I used to have to keep an eye on it and drop the throttle once in a while to keep it in closed loop.

I guess my question is, has anyone bypassed their MAF in their WAI? Or is there a trick to fool the MAF with resistors or something? My reading is suggesting that the unplugged MAF will result in a lean condition, which is really a good thing anyway, correct? My engine's not high compression, turbo or anything like that, and actually needs to run hotter. I was planning on a hotter thermostat anyway.

It would be nice to read my mpg in real time, but if I get a few extra mpgs out of the mod and have to gauge it by the gas pump, then so be it.
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Old 03-08-2010, 11:20 AM   #2
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I can't say for sure but if I had to guess, you are running on an internal fuel map since it can't calculate the mixture needed. the default for most engine control units is a rich mixture as a lean mixture has very detrimental affects.

the reason that your scangauge is reading 9999 is because it doesn't have enough information to calculate an actual figure (this is speculation).

it could be using just the oxy sensor to calculate it and in that case is still in closed loop (since you have feedback). that again is speculation.

I would think that your vehicle would be throwing codes like mad since you have unplugged the sensor. another possibility is that the computer sees it as a huge resistor (infinite resistance) in series with the system. I am not exactly sure how a MAF sensor works as I have a MAP and IAT on my setup.

an assumption that I could make at this point is that you are using more fuel than you think and that it will show up in your fills (at least over time).

you could purchase a MAF sensor from a junkyard out of a wrecked vehicle and cut a hole or slit into a silicon boot (most aftermarket intakes use them) and you could silicon seal it into place if needed.

good luck on your experiment.
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Old 03-08-2010, 11:30 AM   #3
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I agree, that the engine is probably running rich, if anything. The reason that the scangauge reads 9999 is that scangauges base their calculations on how much fuel is being used by how much air goes into the engine. Running lean is not a good thing, unless you like the possibility of holes being blown in your pistons. I'm shocked that you do not have a your check engine light lit with this disconnected. My 1981 Buick will complain if any sensor is unplugged, and it has a very basic computer system.
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Old 03-08-2010, 11:32 AM   #4
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Well, I just came from a half-day of research on Ford MAF sensors, and the basic summary is that with it unplugged you end up with a lean condition. How lean, I don't know.

You're probably right on the O2 driving the closed loop situation. I was under the assumption that being basically without the MAF that I'd be running on a default map and therefore in Open Loop all the time.

I will fill up tomorrow and see how the week goes.
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Old 03-08-2010, 11:41 AM   #5
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Haha, well I didn't say the CEL wasn't on. It's been on for miles upon miles, but the only codes I have are for the evap canister that I can only get at the dealer for $200, which apparently doesn't do anything anyway. I blocked off the EGR when it started acting up too.

At this point you're safe in assuming that I'm not particular adverse to the idea of holes in my pistons. Then I can move on to something with decent gas mileage to begin with. Like the Saturn, and my wife can go shopping for her daily driver. Muwahahahahaa!
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Old 03-08-2010, 12:02 PM   #6
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I assume your state (or area) doesn't have inspections? or if they do, they don't involve emissions?

most evap canister failures are not the evap canister. usually a cracked hose or the gas cap thing. I actually had a bad gas cap. the seal was cracked all over the place and it wouldn't seal.

you know you could fix the little stuff on that truck and sell it, use the money to buy a saturn (or similar) and you don't have to move on from it once it dies.
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Old 03-08-2010, 12:11 PM   #7
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Correct, MI doesn't have emission related inspections. If I wanted to I could remove my catalytic converter completely. Michigan does some weird things. Ever since moving here from the west 6 years ago, I've learned that nobody here has the right to tell Arkansas jokes.

I actually need a pickup quite often in the warm months, so I'm committed to this little Mazdarati. And I kinda like it. I'm just saying I'm not out much if I break it. I'd rather enjoy the experimenting and progress toward better mileage, it's fun for me.
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Old 03-08-2010, 12:35 PM   #8
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that's cool. it is good to have something for "truck duties".

my state has emissions but it is just the CEL check. if the check engine light is on, it don't pass. if it is off, they check to make sure it is in the READY state and you are good to go (emissions wise).

ended up spending quite a bit on an EGR valve recently to pass this year.
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Old 03-08-2010, 02:13 PM   #9
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Quote:
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my state has emissions but it is just the CEL check. if the check engine light is on, it don't pass. if it is off, they check to make sure it is in the READY state and you are good to go (emissions wise).
LOL, that sounds like an easy one to get around... Wire the CEL in tandem with the oil pressure idiot light.
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Old 03-09-2010, 10:53 AM   #10
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Originally Posted by Jay2TheRescue View Post
LOL, that sounds like an easy one to get around... Wire the CEL in tandem with the oil pressure idiot light.
Yeah I'm pretty sure there is more to it than that.. If his car is OBD-II, then it's more likely than not that they have to verify that the car is working properly by hooking up to its computer, not just checking a light on the dash. The point about the CEL is that no matter what, if the car has a CEL, it will not pass emissions because the OBD-II computer can't successfully complete a certain number of tests and in the state's eyes, it fails emissions. Getting around the light bulb issue isn't enough to pass emissions, they're not THAT stupid.. Now if the car is a '95 or earlier and isn't OBD-II and they literally have that requirement, maybe it would be that simple but it's unlikely.
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