hi guys, looking to hunt down a supposed lean issue on my 2007 Honda Fit.
Earlier this year, I had a pretty bad misfire from a coil problem driving to work and this eventually wound up causing the cat to fail afterward. Come to find out, this vehicle had an aftermarket cat from a PO!
Anyway, I replaced the cat because it was beginning to cause a restriction while breaking apart internally; I had this verified by a mechanic. I had the mechanic weld in an aftermarket MagnaFlow universal; due to previous owner exhaust mod which made a direct fit no longer a straight forward option anyway.
Just before replacing the cat; which had thrown a P0420 a number of times driving around with it rattling, well I also had a P0171 general lean code come up.
fast forward, I started looking at some live data with a cheap scan tool. Even though the cat replacement has kept the P0420 away and so far the P0171 has stayed off... well, I’m still getting poor fuel economy and very lean running at highway speeds; which was when I got the P0171 originally.
I’m uploading a screenshot of some data that shows the symptom while driving. It happens more at highway speeds; as the code tripped while going 74 originally... but sometimes it will stay stuck reading this way while coming to a stop after but will quickly go away. it hasn’t read this way at idle on its own so I have not suspected a vacuum leak.
If I’m reading this right, I believe the front/upstream AF sensor is reading very lean but the downstream is reading very rich:
Do I have a fixed lean upstream sensor? Of course it’s perhaps Instead an air leak somewhere or even a fuel delivery problem.
My understanding is a 4-wire AF sensor for a Honda shows negative current when lean and positive when rich; similar to a typical 02. Where as a Toyota 4-wire will read the opposite.
what will happen is if I slow down some during my commute; after it has read very lean at highway speeds, then it will read very rich from time to time and finally pull fuel and this leads to hesitation when trying to regain speed afterward; such as dropping cruise control to slow down some.
Otherwise, the car drives mostly fine and it doesn’t seem to have trouble at idle at least.
the good news: my BIL has the same vehicle and I will swap upstream sensors after I rule out some easier possibilities like ensuring vacuum Isn’t a factor or the EGR isn’t contributing. Fuel economy has dropped to barely 25MPG from usually over 30 without blinking.
Maybe a fuel delivery instead, but I think the screenshot points to an obvious discrepancy between the sensors.
side note: this engine has a MAP sensor, not the typical MAF used more recently.
Earlier this year, I had a pretty bad misfire from a coil problem driving to work and this eventually wound up causing the cat to fail afterward. Come to find out, this vehicle had an aftermarket cat from a PO!
Anyway, I replaced the cat because it was beginning to cause a restriction while breaking apart internally; I had this verified by a mechanic. I had the mechanic weld in an aftermarket MagnaFlow universal; due to previous owner exhaust mod which made a direct fit no longer a straight forward option anyway.
Just before replacing the cat; which had thrown a P0420 a number of times driving around with it rattling, well I also had a P0171 general lean code come up.
fast forward, I started looking at some live data with a cheap scan tool. Even though the cat replacement has kept the P0420 away and so far the P0171 has stayed off... well, I’m still getting poor fuel economy and very lean running at highway speeds; which was when I got the P0171 originally.
I’m uploading a screenshot of some data that shows the symptom while driving. It happens more at highway speeds; as the code tripped while going 74 originally... but sometimes it will stay stuck reading this way while coming to a stop after but will quickly go away. it hasn’t read this way at idle on its own so I have not suspected a vacuum leak.
If I’m reading this right, I believe the front/upstream AF sensor is reading very lean but the downstream is reading very rich:
Do I have a fixed lean upstream sensor? Of course it’s perhaps Instead an air leak somewhere or even a fuel delivery problem.
My understanding is a 4-wire AF sensor for a Honda shows negative current when lean and positive when rich; similar to a typical 02. Where as a Toyota 4-wire will read the opposite.
what will happen is if I slow down some during my commute; after it has read very lean at highway speeds, then it will read very rich from time to time and finally pull fuel and this leads to hesitation when trying to regain speed afterward; such as dropping cruise control to slow down some.
Otherwise, the car drives mostly fine and it doesn’t seem to have trouble at idle at least.
the good news: my BIL has the same vehicle and I will swap upstream sensors after I rule out some easier possibilities like ensuring vacuum Isn’t a factor or the EGR isn’t contributing. Fuel economy has dropped to barely 25MPG from usually over 30 without blinking.
Maybe a fuel delivery instead, but I think the screenshot points to an obvious discrepancy between the sensors.
side note: this engine has a MAP sensor, not the typical MAF used more recently.
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