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Old 11-02-2016, 06:22 PM   #1
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Checking crankcase pressure under boost

I have oil leaks from both the front and rear of the crank in a viggen motor that was rebuilt not that many miles ago. Before I go through the work of pulling the transmission off to get to the rear main, I want to make sure this isn't just excessive crank pressure.

I've done the glove over the oil filler neck trick, it definitely pulls a good vacuum at idle. And I've pulled off and blown through the various check valves, which seem ok. That's all I can test without making boost. I put the car in the air, cleaned it off, and ran it for a while to see if I could get it to form any new drips, but it doesn't seem to leak at idle, part of why I think it only leaks on boost.

If I had access to a dyno, I could just hook a vacuum gauge into the pcv system and see what happens on a 3rd gear pull. Sadly not an option.

Is there anything else to check before I give up and replace seals?
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Old 11-03-2016, 10:36 AM   #2
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You can do it while driving. You don't want to see much more than ~1 psi of positive pressure max under acceleration, so you'll need a low pressure gage. McMaster-Carr carries pressure gages that will read vacuum and a couple PSI pressure.
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Old 11-18-2016, 04:45 PM   #3
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I bought "Actron CP7802 Vacuum and Fuel Pressure Tester Kit" from amazon, hooked it to the crankcase side of the pcv vacuum lines, ran it out the hood onto the windshield tucked under the wiper, and drove around with a gopro on. The gopro part wasn't really necessary, just prefer to keep my eyes on the road.



Result is pretty conclusive. Never goes above atmospheric pressure (zero on the gauge) on boost. Always strong vacuum the rest of the time. Looks like I'm replacing seals.

Last edited by jerrit; 11-18-2016 at 04:48 PM.
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