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YOUR RESEARCH996 emissions
Leading reported evidence
Check when plugs were
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
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Read evidence and context
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Performed · outcome unconfirmed · Original poster
They were visually checked when plugs were changed and no cracks or issues.
Leading evidence: 'Check when plugs were' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check when plugs were' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed · Original poster
Coil packs were changed within last 10k miles, but this was 6-7 years ago.
Replace spark plugs, spark plug tube seals and o2 sensors
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
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Performed · outcome unconfirmed · Original poster
changed spark plugs, spark plug tube seals and o2 sensors.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
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Performed · outcome unconfirmed · Original poster
They were visually checked when plugs were changed and no cracks or issues.
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Suggestion
When you changed out the four O2 sensors, did you disconnect the battery to reset the DME to default values?
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Generation: 20261026T135432Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
1998 3.4 996. bank 1-3 reading high emissions and bank 4-6 on border line. o2 sensors reading 1.15 and 0.85 Mass Air Flow 17.5-18.00 reading on PIWIS. changed spark plugs, spark plug tube seals and o2 sensors.
What is causing the o2 imbalance and should I be concerned?
The MAF sensor reading seems right. Maybe cleaning it would help. How many miles and how old are the coil packs? When you changed out the four O2 sensors, did you disconnect the battery to reset the DME to default values? Are you getting a CEL and any codes?
Some other MAF information here -
https://www.renntech.org/forums/topi...m-please-help/
What emsisions are high? HC (hydrocarbons)? NoX? CO2?
Are all readiness monitors set to complete?
What are the intake air temperature and coolant temperature readings when this is going on?
What are the long term fuel trims of both banks?
O2 sensor readings do not make sense. The #1 sensors should cycle between 0.1V (or a bit less) to 0.7V (or a bit more) every second or so at idle.
The #2 sensors should read a pretty consistent 0.6V to 0.7V. A voltage reading in this range indicates a lack of oxygen in the exhaust gas which is an indication the excess oxygen being supplied to the converters is being consumed by the converter in processing exhaust gases.
I assume you used the right plugs? They were gapped correctly? And the coil to plug connection was good for each plug?
Any large or substantial imbalance between the two cylinder banks is always cause for concern. The imbalance can be due to a difference in fuel supply. The fuel line to one of the banks is pinched. Or an injector is leaking or is weak/lazy and the DME adjusts fueling of all injectors of that bank which can have the "good" cylinders acting up. It can be due to an air leak confined to that bank.
There has been at least one case I know of a bad MAF caused one bank to behave considerable differently compared to the other bank. What probably accounted for this is the normal variation possible between cylinder banks had one bank more sensitive to the improper fueling conditions brought about by the failing MAF and this accounted for misfires confined to one bank.
Coil packs were changed within last 10k miles, but this was 6-7 years ago. They were visually checked when plugs were changed and no cracks or issues.
This is an early 996, so only has 2 x O2 sensors before cats. No codes or lights on dash. Battery was not disconnected.
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