Ken Cemo

Their are 2 vacuum hoses for the Optispark (Harness # 12555323 ). One is a vent that goes to the air intake duct. The other hose with its filter and check valve goes to the intake manifold.

What is the purpose of the second hose. I understand how vacuum is used on a distributor for timing. What is the function of intake manifold vacuum in this application?

'97 Camaro SS

DrewHMS97SS

The vent system was added to remove ozone from the distributor. I hope someone more technical will answer, but I believe the vacuum from the intake is pulling the ozone out and the other line is allowing clean air in (from the air intake elbow).

Injuneer

As noted above, it is a “ventilation” system. Early (1993-94) “unvented” Opti’s had a lot of problem, including rust buildup that could blind the optical cam position sensor. Mine started acting up at about 50,000 miles, and was full of rust. The vent system was added in 1995, when the drive mechanism was also revised.

The high voltage discharge inside the cap generates highly corrosive ozone. GM added the vent system to remove the ozone. Filtered air, which has also passed through the MAF sensor is pulled out the elbow inserted in the rubber intake elbow, pulled through the Opti by vacuum from a full vacuum port on the intake manifold. The line from the Opti to the manifold incorporates a check valve and a flow restrictor.

Courtesy of Shoebox

Ken Cemo

Thanks for the explanation and clarification. I am still trying to figure out the "Starts and Runs Great for 5 Minutes" problem. At least now I can put those vacuum hoses out of my mind.