Mazda 3 Running Lean
- ajherrera58
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I have already replaced the fuel pump and injectors and they seem to have made a slight change in terms of the O2 signals and they now look how they're supposed to at idle, but there's still something clearly wrong.
I have done a volumetric efficiency test and plugging my data into an online calculator I'm getting really horrible scores like 50% - 60% range. Looking at my MAP sensor at idle, it stays pretty constant which should mean the engine's okay mechanically but I'm really not sure what I should do next. Judging from this does this scream MAF sensor?
Are there any other tests I can run? I'm just confused on where to go next, any help would be greatly appreciated.
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This does scream air measurement issue, OR unmetered air. Being a Mazda 3, I'd have a careful look at the air intake boot between the MAF and the throttle body. They like to split at the accordion and open up when the engine torques under load.
Otherwise, I'd suspect a MAF problem. What's the highest voltage you can get out of it while at WOT through 1st gear?
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- ajherrera58
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What's your Maf reading at idle?
That should be near 2.0 g/s.
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- ajherrera58
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ajherrera58 wrote: I'm not sure about actual voltage unfortunately my scan tool doesn't measure that but under those conditions I can get like 100 g/s I think maybe the highest I've seen is 101, 105?
Eh, that's not terrible? I threw that into a VE calculator and got a decent result:
Still doesn't explain the lean.
As for the intake tube, I actually have a cold air installed by the previous owner so no problem there.
Oh, really? :huh: I know CAI's are supposed to be an upgrade, but that only works if they allow the MAF to measure correctly. I'm guessing the old intake plumbing is long gone?
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How about fuel pressure reg? Fuel filter?
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- ajherrera58
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As for the CAI I haven't had a problem with it for the lifetime of the car like it sorta just came out of the blue so I don't know about it causing a problem now? I have double checked it though, everything's tight, all the airflow should be going through the MAF. But yeah old intake plumbing is long gone
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- ajherrera58
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ajherrera58 wrote: I did this a little while ago using this calculator and using the parameters from the scan tool I wasn't getting anywhere close to those numbers.
Would you mind doing another WOT run through 1st gear for us? Capture the data if at all possible, or just record the highest values. We mostly need the highest MAF value and the engine speed during peak airflow. It'd also be useful to know what the upstream O2/AF sensor is doing at WOT.
For arguments sake, say it was a VE issue what exactly would I do next?
Then you'd start looking into plugged cats, restricted intake, like that. Still, none of those will account for the lean trims you're seeing. There's a genuine fueling issue at work.
For your fuel trims to be equally lean across all loads, you've got a few options. Ethanol fuel, though I doubt you'd make that mistake at the pump. :silly: A stuck open purge valve, which you could eliminate by disconnecting the vapor line from the purge valve and capping the end. Then there's the MAF, which we'll hopefully address with another VE test.
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- ajherrera58
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Anyway, it sure looks like your MAF is done. Only other things I'd investigate are debris in the MAF itself, or anything that might cause the MAF to incorrectly measure.
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- ajherrera58
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Also side note, is it weird for my MAP sensor to automatically turn to 99 kPa for every test? And in terms of throttle position do those values at WOT look normal? Thought they might be higher? Thanks
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what are the STFT and LTFT at idle.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
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"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
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