Fuel trim codes back...

[Salty B.]

Last year I took out the IAC valve and cleaned it with MAF cleaner, and that seemed to fix the problem. Until it didn't as these codes started popping up again. "Fuel trim bank 1/2, permissible range exceeded" I sitll don't know what that means and seems like nobody else does either based on my searches.

So, gonna try the following:

• Clean IAC again and goddam I hate getting that thing out and back in. Cut my arms up bad. The old rubber snout thing was still in good shape, so I didn't replace it.
• Ensure no vacuum or air leaks, check all plumbing for cracks.
• Replace CCV (I have a new one sitting in a box because it looks like a pain in the ass to replace without pulling the intake which I def do NOT want to do)
• Replace O2 sensors. What should the voltage on these be reading? I have OBD Fusion and a bt interface that will show the sensor voltages. Pretty sure they're original.

Am I aiming in the right direction?

[andrewwynn]

Original O₂ very suspect. Use Bosch: i tried knock off they lasted a couple months.


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[X5chemist]

I'm with MEESTAHBIG, new sensors do wonders. Mine are approaching 174k OEM miles. It's time and easy maintenance. MPG is slightly up due to new rear wheel bearings. I think new O2 sensor would push it higher with all the maintenance done over the last three years.

[Meestahbig]

Hey, so what are the fuel trims, are the positive or negative. You can monitor them with the obd2 fusion. See if both banks are messed up, might be, but only one is throwing the code at this point. If the trims are over maybe +/-10 percent, it throws the code. The engine is either adding or removing too much fuel. If adding fuel resulting in positive trim, I'd suspect air leak or maf. If negative trim, like removing fuel I'd suspect fuel pressure, O2 sensors, leaky injectors. If it's not stalling or misfiring, you can probably rule out many things. If no other codes and fuel trim is negative, def change the O2 sensors..

[Meestahbig]

Can anyone else cite from experience getting fuel trim codes with no other errors? I had negative trims with my bad O2 sensors. When I had a huge air leak, causing engine misfires and car shaking.and sometimes unable to drive, needing a restart. It never gave me fuel trim errors. I had air leak and misfire codes, but nothing with fuel trim.

[andrewwynn]

When you get a fuel trim error it's usually dirty injectors not getting enough gas in, low fuel pressure or O₂ sensors reporting the wrong O₂.

Vacuum leaks usually throw off the values so fast you will get a vacuum leak error.

Every car I've worked on that had a fuel trim error was either weak fuel pump or end of life O₂. (upstream).


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[Salty B.]

Welp, the fuel pump and filter were replaced in January. Prior owner replaced at least one O2 sensor according to the service records he gave me, but it doesn't say if all four were replaced. Just says "Bosch OEM 02 sensors 13477 up stream $110" which was in 2019 at 166,000. At that price I'm not sure if it was all four or just one or two.

I'll inspect for air/vacuum leaks next...

No misfires, no shaking, runs strong, instant starts. No fuel smell. Weird.

[andrewwynn]

Upstream means just the precat. The only ones that affect fuel trim.


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[Meestahbig]

SaltyB we all want to know are your trims positive or negative? Do you know how to read the values from your obd2.dwvice?

The $110 to change O2 sensors would be awfully cheap for 2. Maybe only one was changed and you are getting the error on the bank that wasn't changed. That would be interesting! Got to tell us the LT trim readings.

Let's fix this!

[andrewwynn]

$110 for one Bosch would be more inline with expectation.

M54 upstream sensors are very accessible. But get some live data going see what you find