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Vacuum Circuits

Vacuum routing is slightly different between certain model years (and US/UK models). Most of this is US-centric information.

The US cars had air pumps equipped for emissions compliance. Most owners removed this system due to the fact that it would frequently break. The diverter valve and the associated plumbing is usually removed. Additionally, although the vacuum diagram seems to indicate that there is a line coming off the vacuum pump, this doesn't appear to be the case for many cars.

There are effectively two “circuits”. One is the circuit that is always under vacuum (orange line). The other is the intake pressure circuit that may be at a vacuum, but can also be under pressure (acceleration with turbo pressure).

The ignition solenoid connects the distributor to vacuum when the car is started cold (with choke) which should advance the timing.

The intake flap valve should be open under vacuum (when the car is running). When the engine is shut off, the vacuum should bleed out of the system through the air box and eventually close the flap valve.

The fuel pressure solenoid connects the fuel pressure regulator to the intake pressure circuit which will increase the fuel pressure under acceleration. The solenoid itself will force the fuel pressure regulator to drop pressure when the accelerator is not being pressed.

The purple and green lines are simply “dump” lines (of a sort).

Vacuum Solenoids

Fuel Pressure & Ignition

There are a pair of solenoids mounted under the intake plenum for fuel pressure and ignition. Lotus refers to these as part #A910E6634F.

I took some time to test and investigate these solenoids (they are identical parts, but serve two different purposes).

These solenoids are a German Pierburg part (#7.12942.00) they are not necessarily an easy part to find (right now, sourcing one is more than $50 USD each).

I tested the solenoid to see the internal routing when energized and when not. The solenoid switches between connecting the top outlet to the bottom-side outlet when energized, or connecting the bottom center outlet to the bottom-side outlet when NOT energized (polarity doesn't matter).

The least expensive replacement unit is an A/C Solenoid Valve part 1470004 or SW9000. This operates in a similar fashion to the stock unit as long as you set up the vacuum lines properly. These can be purchased for about 1/2 the cost of the Pierburg unit.

engine/vacuumrouting.txt · Last modified: 2022/04/26 09:53 by