disty vac advance, on mpfi cars

[archemitis]

this goes out to anybody with the mpfi pre 87 system. i think even the ea81t should be the same, as far as this question goes.

where should i get the vac from? i cant find a port on the throttlebody, and right now i have it plugged in after the tb, so i think im gettin retarded when i hit the throttle. i have more power at 3/4 than at full throttle.

mcbrat? anybody?

[archemitis]

ok, after reving, staring at a vac guage, and sucking on alot of bad tasting hoses. i figured out a vac source, before the throttle plate. but i got two hoses coming off my disty... and they both advance....

[GLCraig]

Are you sure that both connections on the dist. cause it to advance? Typically the inner is for retard and the outer is for advance.

[archemitis]

after some more screwin around, ya it looks like the one underneath is a retard, mabye it hooked to a knock sensor?

[WJM]

is it EA82? I know that on my turbo 86 its only got one port on the disty...and there is a metal line right at it that gives it vac...or whatso...and there is a little rubber line connecting the vac unit to the metal line. I dont know where the line goes....but I could trace it.

[archemitis]

i found the same sort of thing on my motor(junkyard, so i never saw it in its factory state). there was a metal line, coming off the tb, going over to the egr, or some solenoid, with a t that i got vac from.

makes a huge difference. that backwards hookup stuff, is backwards.

[Guest taprackready]

Archemitis, your gonna hafta dig in your manual. I looked in mine and found info on Non-turbo cars which may help but its not turbo related.

 

"the thermo vacuum valve (TVV) controls vacuum to the distributor according to the temperature......the TVV receives ported vacuum when the engine is idiling and manifold vacuum when the throttle is opened up after the engine is warmed up to operating temperature"

 

On several other web sites regarding all sorts of turbo imports (not chevys) including Pugs it seems that vacuum advance is largely controlled by how much turbo boost there is. Less boost more timing, more boost less timing. Too much boost and timing together might detonate your engine. Most of the advance would be in initially to reduce turbo lag, and reduce as RPMS/boost get higher. Not sub specific but maybe helpful anyway.

 

Bill