View Full Version : Opti vacumn reading?

04-20-2012, 05:49 PM
if you measure vacumn at the blue nipple on intake elbow should it = vacumn from the intake manifold?

I get 18 at manifold. 18 at bottom of hose with 2 check valves that goes to bottom of Opti BUT only 4" of vacumn when reading from the blue nipple.

new opti and vent harness

does the opti itself restrict vacumn or would my reading suggest new opti cap is not sealing?

anyone have a vac gauge and can read theirs to see wtf, thanks

FSM states "until needle slowly reaches manifold vacumn"...which suggests it should eventually read 18" at blue nipple...not 4"

04-20-2012, 06:15 PM
There is a check valve AND a flow orifice. Orifice = reduced vacuum.

04-20-2012, 08:04 PM
There is a check valve AND a flow orifice. Orifice = reduced vacuum.

I understand the 'check" valves ....but when I measure vacumn at the end of that line it reads exactly what the vacumn is direct from intake manifold. The line with 2 valves is the "draw" vacumn into Opti. The other vent hose has no valves and goes from bottom of Opti to rubber air duck reads 4" there suggesting the "Opti" itself is not holding vacumn

My ? is should the measured vacumn at blue nipple read the same as the draw side after check valves.

In my case it does not

18" in and 4" of vacumn out.

FSM says vacums should "slowly" climb to what intake manifold vacumn stops at 4"

04-20-2012, 10:46 PM
I don't think you should be getting 18" going into the opti, but I have not actually measured vacuum there. I would expect the blue valves to restrict and lower the vacuum before it gets there.
I have tested vacuum where the blue elbow connector is on the intake elbow and get a maximum of 8" back toward the opti at any engine running throttle level. I also tested with a vacuum tester at the same spot (engine not running) and was able to pull vacuum through the hose, into the opti and back to the check valves. It held vacuum.
You could test the seal of the opti by using a vacuum tester.

04-21-2012, 02:29 PM
You could test the seal of the opti by using a vacuum tester.

I did my Mighty Vac hooked up to draw side of Opti with other line 'slowly" bleeds off to 0. It holds 4" while engine running but won't go higher. The 2 valve line leading to the Opti builds and holds solid at 18"

My old opti would not even let vacumn build up.

should the Opti be 100% sealed?

Since the engine vacumn system is tied into opti I would think it should hold vacumn otherwise a "leak" in the system would effect motor.

I am chasing a stumble under load problem and while this opti not holding vacumn issue may not be related...I want to know if it should be 100% sealed.

would have to pull it and rtv or dialectic grease on inner seal.

I would think the rear bearing on Opti would prevent 100% seal has to spin???

04-21-2012, 06:52 PM
I do not believe it seals 100 percent. I have messed with several opti's on the bench trying to achieve a 100% vac seal and not been able too. The housing it's self has the screen behind the optical sensor I can never get to seal as well as the shaft seal. I can pull vacuum on it but it won't hold vacuum.

04-22-2012, 12:03 PM
yeah I bench tested the Opti with Mighty Vac and it will bleed off vacumn. The biggest hole obviously is where the 4 pin connector plugs in.

I just skimmed some dialectic grease on cap seal and bolted back togeather and 4 pin plug seal. opti is venting but getting = manifold vacumn will never happen as FSM suggests.