Subaru engine sensor oil leaks and loom oil contamination.
https://www.clubsub.org.nz/forum/index. ... have-avcs/
This is a known issue and is referenced in my AVCS faq.
I had thought the issue was confined to preFL DAVCS cars because thats where most instances appear due to the extra exhaust cam and avcs sensors, below the heads.
However I recently saw a post on FB regarding an 04 WRX cam sensor issue which prompted me to do some more research that led to the ClubSub post linked above.
Definitely worth reading that forum post, however if you have a short attention span,
here’s a few observations to consider...
The loom can be contaminated all the way to the engine harness and ecu, but also other sensors on the engine.
So the focus here is the inlet cam position sensors on the upper rear of each head, but the issue also affects exhaust avcs cam position sensors, avcs oil control valves, oil pressure switches, eg also those related to ALVS on H6 etc.
The oil can harden loom wiring causing continuity issues.
Therefore its useful to check the extent of the contamination around all terminations on the loom.
It it’s not too bad, the affected sensors can be modified with sealant, remove plug seal, and or use bullet connectors etc to isolate the sensor from the loom.
This could save you a bunch doing the sensor mods as new oem replacement cam sensors can be quite expensive.
I did some research and some fixes include:
Pulling apart the sensor connectors and coating the individual wire crimped terminals with epoxy resin,
Using epoxy resin in the sensor plug (in place of the internal rubber seal),
Applying 3bond to seal the metal sensor transducer to the plastic sensor body, around the circumference of the join.
Also measure up for new oil and heat resistant oring:
This will likely be a metric oring and you’ll need to extrapolate the oring outer diameter and oring section width dimensions.
Causes and prevention.
As for causes of the issue, and prevention, the primary candidates are oil ingress due to leaks from faulty or worn sensors and their seals an orings...
The oil enters the loom via gravity, osmosis, heat or potentially excessive crank case pressure.
The sensor plugs and loom is water and potentially airtight meaning the oil has no choice but to penetrate the loom.
Therefore keeping the engine very clean along with regular inspections will help to spot leaks early before the loom and plugs become inundated with oil.
Equally important is checking crank case pressure as part of regular health checking, in paticular ensuring the PCV isnt stuck.
A quick way to check for PCV or compression related excessive crankcase pressure issues is to get a spare oil cap, tee a fitting for a hose to a boost gauge into the cap, and make a few pulls over 3k rpm. If you go positive pressure, youve confirmed the issue.