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Old 02-21-2018, 11:43 AM   #1  
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Monitoring engine health with OBD datalogging

I want to try to use OBD datalogging to catch problems with aging injectors/sensors/etc. as they develop, before they're bad enough to trigger a CEL. The idea is to randomly datalog my drives to build up a history, and then watch for deviations from the baseline.

Anyone have feedback on good parameters to measure? Iíll be using Torque Pro with a generic OBD Bluetooth dongle.

Fuel trims and cat temp are two fairly obvious examples. Another might be ignition timing. I'd imagine any of those would have to be compared against IATs, throttle, measured load, etc. But that bridge can be crossed later.

I canít be the first to think of this. Anyone heard of others doing it? What do tuners monitor when they do remote tunes?

Any thoughts welcome.
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Old 02-21-2018, 11:44 AM   #2  
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It's really too bad we don't have a real oil pressure sensor, that is probably the most important that we cannot monitor. We cannot monitor fuel pressure either which is also a bummer.

Timing doesn't help much because the knock sensor is not reliable. I'd go with g/sec air at idle, and LTFT over time. If idle gets too far off from 5.5 g/sec or fuel trims build, something is up.

Cat temp isn't awful, but the sensor is kind of slow so it won't tell you a ton except for long-term cat failure.

IAT's are so-so since the stock intake is pretty darn good, however, if you go FI, different story.

If you already own the logger then do airflow at idle, and fuel trims, but not a ton of useful information on the rest, unfortunately.

Last edited by Kane; 02-21-2018 at 06:46 PM. Reason: Translating for cranky 9K.
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Old 02-21-2018, 06:47 PM   #3  
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Old 02-21-2018, 07:42 PM   #4  
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Thanks, Kane.
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Old 02-21-2018, 08:54 PM   #5  
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Quote:
Originally Posted by 9krpmrx8 View Post
It's really too bad we don't have a real oil pressure sensor, that is probably the most important that we cannot monitor. We cannot monitor fuel pressure either which is also a bummer.

Timing doesn't help much because the knock sensor is not reliable. I'd go with g/sec air at idle, and LTFT over time. If idle gets too far off from 5.5 g/sec or fuel trims build, something is up.

Cat temp isn't awful, but the sensor is kind of slow so it won't tell you a ton except for long-term cat failure.

IAT's are so-so since the stock intake is pretty darn good, however, if you go FI, different story.

If you already own the logger then do airflow at idle, and fuel trims, but not a ton of useful information on the rest, unfortunately.

F**CKING LOL

Kane you are the man
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Old 02-24-2018, 01:53 PM   #6  
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So, few questions/comments on this.

"g/sec air at idle" refers to the MAF reading at warm idle, correct? And if I see a deviation, that might be a reason to check the MAF sensor? What else would be worth looking at if that happened?

Understood about cat temp. Long-term failure (in this and other parts) is exactly what I'm looking to increase my odds of detecting.

What about O2 sensor readings? I know O2 sensors fail gradually; could I expect the logged values to change over time?

I brought up IATs and those other parameters not to suggest that they'd be interesting on their own, but because I thought they'd be necessary context for things like ignition timing. Correlating everything might be more trouble than it's worth, though. Maybe another day, when I have a ton more time on my hands...

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Old 02-24-2018, 02:58 PM   #7  
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O2 sensor failure manifests as inconsistent readings or slow response. There is an OBD code for slow response, and I *think* there is one for inconsistent readings also. So you don't really need to monitor the raw output yourself.

Cat temp, coolant temp and fuel trims get you 90% of the info necessary to detect a problem. Oil pressure/temp would be the other 10%.
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Old 02-25-2018, 03:52 PM   #8  
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Quote:
Originally Posted by iamfodi View Post
so, few questions/comments on this.

"g/sec air at idle" refers to the maf reading at warm idle, correct? And if i see a deviation, that might be a reason to check the maf sensor? What else would be worth looking at if that happened?
vacuum leak

understood about cat temp. Long-term failure (in this and other parts) is exactly what i'm looking to increase my odds of detecting.

What about o2 sensor readings? I know o2 sensors fail gradually; could i expect the logged values to change over time?
fuel trims will also alert you to this.

i brought up iats and those other parameters not to suggest that they'd be interesting on their own, but because i thought they'd be necessary context for things like ignition timing. Correlating everything might be more trouble than it's worth, though. timing has always been the bane of our engines, too hard to accurately gain insight with odbii only.

maybe another day, when i have a ton more time on my hands...
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Old 02-25-2018, 05:15 PM   #9  
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Bit late ...but here are the parameters I monitor when tuning etc :


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