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914World.com _ 914World Garage _ Testing vacuum on MPS?

Posted by: burlybryan Apr 13 2021, 07:53 AM

Does it need to be energized to test vacuum or can I just bench test it with vac hose (properly clamped) and a mityvac? I have a few on hand and while all test correctly for resistance on the appropriate pins, I'm not able to get any vac with my mityvac. Am I missing something or are the diaphragms all toast?

Posted by: 914werke Apr 13 2021, 07:57 AM

if you can apply say 5 or so #'s of vacuum on the port & it doesnt hold (at all or drops to 0 in a period of time) its toast.

Posted by: brant Apr 13 2021, 08:05 AM

its that simple... if your mighty vac is working correctly... they must be all toast

I believe Paul Anders said 15Hg of vacuum?
but would have to go check to be sure
brant

Posted by: BeatNavy Apr 13 2021, 08:22 AM

QUOTE(brant @ Apr 13 2021, 09:05 AM)

its that simple... if your mighty vac is working correctly... they must be all toast

I believe Paul Anders said 15Hg of vacuum?
but would have to go check to be sure
brant

Yes, 15 in Hg is the standard test, simulating idle vacuum on a stock engine. I've read a couple of specs about how much it can leak (e.g., < 5 in Hg in a minute, or < 5 in in FIVE minutes), but if it won't hold any vacuum it's done.

http://www.tangerineracing.com/mpsdiaphragm.htm

Here's Brad's page: https://members.rennlist.com/pbanders/manifold_pressure_sensor.htm#MPS%20Diagnostics

Posted by: bob164 Apr 13 2021, 08:43 AM

Double check you gauge and connections to make sure these are valid readings. Pull a vacuum on a vacuum cap first then work up from there.

Posted by: 914werke Apr 13 2021, 08:50 AM

15Hg=7psi approx

Posted by: burlybryan Apr 13 2021, 09:14 AM

Got it. That's what I thought. I can pull vac with the mityvac on my skin, so I think it's fine.

Thanks.