Toyota technician explanation wanted: '75 &'76 distributors with vacuum retard (1 Viewer)

[Roadnoiz40]

I have a 1976 FJ40 that has a build date of 9/75. These two years had vacuum retard canisters on the distributor ( instead of vacuum advance) from the factory. The ignition at this point in time was moving to total electronic. They had a "box" but the distributor still had points. I have the factory Toyota manuals that give no explanation of why these two years came with the vacuum retard canisters. Is there any Toyota technician with intimate knowledge of why? Was this to pull timing advance out of the ignition for some reason? Were the centrifugal weights over-advancing the timing and this was an easy fix? "Splane Lucy" share your knowledge please.

 

[Downey]

Ok, I've read comments here on Mud that will not agree with me, but I will tell it as the Toyota techs explained it to me. When a Landcruiser is under hard/full acceleration, the engine is demanding about 40 degrees of advance spark. Most dizzys only give about 24 degrees of mechanical advance, but the Landcruiser dizzys gives about 32 degrees of mechanical advance. The vacuum advance then makes up the difference demanded (only on demand). Normally you'd set your static timing at 7 or 8 degrees advanced so that you'd get 32 degrees of mechanical advance, plus the 8 degrees you put in, equals the 40 degrees demanded, Then vacuum advance works as needed with your mechanical and static timing. Now what Toyota did (as part of the emissions system) was to give you vacuum retard- - -my theory is to take away spontaneous performance that causes emissions (probably not the best/honest/most technical explanation you are going to get here though).

 

[ToyotaMatt]

@4Cruisers

 

[FJ40Jim]

Oh hey, I'm a Toyota tech.

Yes, you've got the basics. The 69-76 vac retard dissys have a bunch of mechanical advance (17*), and then the computer can pull back that timing thru vacuum to reduce NOx at high speed, high load, high temps.

 

[Dizzy]

I found that 15 degrees of static advance actually caused trouble getting a hot 2F motor restarted. It was like the cylinder pressure was working against the crank's position. Fuel burns at a given rate, but cranking an engine is about as slow as it gets, it burns faster when hot, and, I had the spark creating cylinder pressure too far ahead (15 degrees) of the power stroke. That got me wondering about how I could build the engine to work well at below-idle rpms that take it super slow, yet full of torque, around obstacles. So, I wonder if the factory vacuum retard actually helped the Land Cruiser idle-up that rock, or deal with a rich (or lots of throttle), hot, and low rpm condition that is part of pulling the rig behind you thru a tough section of trail?

 

[FJ40Jim]

I wonder if the factory vacuum retard actually helped the Land Cruiser idle-up that rock, or deal with a rich (or lots of throttle), hot, and low rpm condition that is part of pulling the rig behind you thru a tough section of trail?

Read the post above yours. Vac retard is a (poorly engineered) emissions control method.