Fuel Trims VS Air
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Fuel Trims VS Air
I find this curious, was wondering if anyone could explain the association further. I start the video with the hood open and my fuel trims are acceptable (at least better than they've been). The MAF reading is slightly higher than displacement. I then close the hood, and fuel trims climb along with the MAF decrease to below ideal numbers (not on video, but I did get down to 5.04 g/s). This doesn't make sense to me. Not sure why more air with hood open would translate to lowering trims. I've checked for a vacuum leak 6 times in 5 different ways. All of those checks are obviously with the hood up. Well, it seems that with the hood up I don't have an issue..... Wondering if a hose is getting pushed/pinched/smashed when the hood closes?
Update: This was a bad MAF. I had replaced with a new MAF just prior to this but it ended up being faulty. Warranty replaced this one, and this issue went away.
Update: This was a bad MAF. I had replaced with a new MAF just prior to this but it ended up being faulty. Warranty replaced this one, and this issue went away.
Last edited by Schmidtstain; Oct 21, 2024 at 03:08 PM.
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From: Dyer, IN
I find this curious, was wondering if anyone could explain the association further. I start the video with the hood open and my fuel trims are acceptable (at least better than they've been). The MAF reading is slightly higher than displacement. I then close the hood, and fuel trims climb along with the MAF decrease to below ideal numbers (not on video, but I did get down to 5.04 g/s). This doesn't make sense to me. Not sure why more air with hood open would translate to lowering trims. I've checked for a vacuum leak 6 times in 5 different ways. All of those checks are obviously with the hood up. Well, it seems that with the hood up I don't have an issue..... Wondering if a hose is getting pushed/pinched/smashed when the hood closes?
Fuel trims and MAF
Fuel trims and MAF
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I have a feeling this is a rhetorical question, I get there is less air now that the hood is closed. But that would be the only thing. My thought was less air should equal less fuel to balance, but the trims go up
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From: Cape Coral, Florida
I find this curious, was wondering if anyone could explain the association further. I start the video with the hood open and my fuel trims are acceptable (at least better than they've been). The MAF reading is slightly higher than displacement. I then close the hood, and fuel trims climb along with the MAF decrease to below ideal numbers (not on video, but I did get down to 5.04 g/s). This doesn't make sense to me. Not sure why more air with hood open would translate to lowering trims. I've checked for a vacuum leak 6 times in 5 different ways. All of those checks are obviously with the hood up. Well, it seems that with the hood up I don't have an issue..... Wondering if a hose is getting pushed/pinched/smashed when the hood closes?
Fuel trims and MAF
Fuel trims and MAF
Didn’t you change your MAF sensor recently ??…was it the same as your old one ??…if not maybe this one sits higher and not knowing how much clearance there is between the top of the MAF and the hood maybe it’s “tweaking” the sensor when you close the hood…never seen this before…maybe try a little bit of clay or something similar to check.
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Didn’t you change your MAF sensor recently ??…was it the same as your old one ??…if not maybe this one sits higher and not knowing how much clearance there is between the top of the MAF and the hood maybe it’s “tweaking” the sensor when you close the hood…never seen this before…maybe try a little bit of clay or something similar to check.
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From: Cape Coral, Florida
We used clay a lot in the airline industry to check for clearances like main landing gear doors and other things like that…even bubble gum would work.
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Just thought of something while talking it over with my dad - in that video the hood isn't even fully closed. It's really just resting on the latch as I didn't close it hard enough. I'm not sure that ANYTHING would be even close to touching at that point. The last 2 seconds is me pressing it close manually.
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From: Cape Coral, Florida
Just thought of something while talking it over with my dad - in that video the hood isn't even fully closed. It's really just resting on the latch as I didn't close it hard enough. I'm not sure that ANYTHING would be even close to touching at that point. The last 2 seconds is me pressing it close manually.
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I'd be poking around searching for a vacuum leak somewhere. My guess is you have unmetered air entering the intake manifold somewhere.
Also possible you could have an exhaust leak before the O2s.
+10-25% Fuel trims isn't right.
This is all assuming your MAF sensor is working accordingly.
5.1-5.5 g/s is what my stock motor measured at warm idle 725 RPM.
Also possible you could have an exhaust leak before the O2s.
+10-25% Fuel trims isn't right.
This is all assuming your MAF sensor is working accordingly.
5.1-5.5 g/s is what my stock motor measured at warm idle 725 RPM.
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I'd be poking around searching for a vacuum leak somewhere. My guess is you have unmetered air entering the intake manifold somewhere.
Also possible you could have an exhaust leak before the O2s.
+10-25% Fuel trims isn't right.
This is all assuming your MAF sensor is working accordingly.
5.1-5.5 g/s is what my stock motor measured at warm idle 725 RPM.
Also possible you could have an exhaust leak before the O2s.
+10-25% Fuel trims isn't right.
This is all assuming your MAF sensor is working accordingly.
5.1-5.5 g/s is what my stock motor measured at warm idle 725 RPM.
2/3. Have heard that as well (I do have aftermarket cold air intake, figured "some" additional fuel trim normal). I did check for exhaust leak with smoke method through tailpipes (as well as carb/brake cleaner + smoke test engine)
4. New MAF as P0101 was original code (whole other thread, seems P0171/74 were driving codes instead of P0101)
5. I do occasionally see those MAF values at idle, but my idle is 795-830ish rpm usually. That is anywhere from 5.3-6.1 g/s MAF.
Melting Slicks
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From: Northville, MI
Which cold air intake are you using, Veraram, License plate area type, or -Calloway type? If isn't a true cold (ambient)air intake closing the hood would bring heated (engine) air thru the MAF, causing a drop of oxygen entering the TB
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It's the KN version, somewhere in between. It has a small 1" by 8" slit that gets cut into the top of the shroud in front of the radiator. Definitely getting less oxygen with hood closed.
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From: Dyer, IN
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Would it be reasonable to think that the intake would be at a minimum "struggling" to get air in a closed hood vs open hood scenario? If that was a potential, MAF reports lower number but the rest of the air that the engine needs could be pulled in through my theoretical vacuum leak? The unmetered air then causing the trims to go up?
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From: Dyer, IN
Thread Starter
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Tech Contributor
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From: Dyer, IN
