1973 Emissions Modifications

[The_Eagles’_Nest]

I just bought my second Imperial which is a 73. It has far more emissions controls than the 72. I want to target the OSAC and evap system for improvements. I was thinking of doing a direct connection from the carburetor to the vacuum advance, and then t-ing that to the OSAC on the side that is opposite from normal and using a 72 charcoal canister with the purge valve connected to the OSAC valve.

My thinking behind this is to make the evap purge behave more like a modern car and eliminate the OSAC from effecting ignition timing.

Thoughts?

 

[CBODY67]

The OSAC situation is easy to do, as many others have previously done.

Why does the '73 canister not purge "like a modern car does"? All canisters operate their purge functions related to coolant temperature (vacuum through a thermovacuum switch, so no purge happens during warm-up) and vacuum bias.

Respectfully,
CBODY67

 

[saforwardlook]

OSAC delays vacuum advance by 25 seconds and it starts all over again any time you let off the throttle and accelerate or cruise again. It is a terrible control device since it really hurts fuel economy and produces a less responsive feel on light to moderate accelerations. The increase in nitrogen oxides by getting rid of the lousy valve would be offset by less CO2 emissions that affect climate change according to the scientists. Get rid of it is my view.

As far as canister purge, was that originally tied to OSAC controlled cleaning of the stored vapor/fuel or did it just occur whenever vacuum advance was taking place in 1973 systems? Is your Imperial a federal emission system or a California one (federal emissions had underhood green/white emission labels/decals on the inner driver fender and the California cars originally had blue/white labels?

 

[The_Eagles’_Nest]

OSAC delays vacuum advance by 25 seconds and it starts all over again any time you let off the throttle and accelerate or cruise again. It is a terrible control device since it really hurts fuel economy and produces a less responsive feel on light to moderate accelerations. The increase in nitrogen oxides by getting rid of the lousy valve would be offset by less CO2 emissions that affect climate change according to the scientists. Get rid of it is my view.

As far as canister purge, was that originally tied to OSAC controlled cleaning of the stored vapor/fuel or did it just occur whenever vacuum advance was taking place in 1973 systems? Is your Imperial a federal emission system or a California one (federal emissions had underhood green/white emission labels/decals on the inner driver fender and the California cars originally had blue/white labels?

My idea is to connect the vacuum advance directly to the carburetor and tee the opposite than normal side of the OSAC valve, then hook up the opposite side of the OSAC to the purge valve on a 1972 charcoal canister. This would prevent purging at idle and during acceleration.

This also removes the OSAC from interfering with ignition timing since everything is now switched.

The OSAC was not used in the purge system but I am thinking it can be repurposed to be used to make the evap system similar to a modern car where it does not purge at idle or acceleration. Since the OSAC delays a vacuum signal why not repurposed it to the purge valve on a 1972 charcoal canister.

 

[The_Eagles’_Nest]

The OSAC situation is easy to do, as many others have previously done.

Why does the '73 canister not purge "like a modern car does"? All canisters operate their purge functions related to coolant temperature (vacuum through a thermovacuum switch, so no purge happens during warm-up) and vacuum bias.

Respectfully,
CBODY67

The 1972 is not controlled by temperature, it works off of vacuum signal from the distributor. The 1973 purges all the time regardless of distributor advance. It does not have a control valve on the canister.

 

[saforwardlook]

The 1972 is not controlled by temperature, it works off of vacuum signal from the distributor. The 1973 purges all the time regardless of distributor advance. It does not have a control valve on the canister.

One of my questions was whether the canister purge was performed before the OSAC valve or teed in after it in case my wording wasn't clear.