Mystery vaccuum line
 

Can anyone tell me what the vaccuum line that goes from between the two middle oil injectors to the back of the upper intake is for? On an '87 TII.


Thanx

I have no idea. What I do know is, that there are four nipples on the back of the throttle body on a 87. The bottom one goes to the water thermo valve a couple of inches away. It is a vacuum coming from the back of all the throttle plates. The one you refer to is the second one from the top. It joins the one above it and the one below it, in the black plastic looking spacer between the throttle body and the manifold. I repeat, all three join together in the black plastic spacer looking thing. After they all join together, the path leads to a quarter inch hole IN FRONT OF ALL THE THROTTLE PLATES. I took the throttle body and the spacer apart to find this out. All three lead to the FRONT of the throttle plates. I have no bloody clue why. If you discover how this bailywick works, let me know.

thats also on my n/a

Hey HAILERS,

Yeah, I saw that, doing the TB mod. Wierd. Maybe RETed will chime in. I'm always looking for another vaccuum line to get rid of.

I think it goes to the throttle body, and in specific the front of the throttle plates, to provide filtered, atmospheric pressure air to the so called *vacuum* line that goes on top of your oil injectors. Thats for the large nipple on the back of the throttle body. The other two must be providing filtered, atmospheric pressure air to two other items. If you have your oil injectors, then you need the large line at least. I know that is not the line you inquired about, but all three of the top nipples are tied together in the plastic spacer, going to no other place except the quarter inch hole IN FRONT of the throttle plates.

If you follow that nipple, you will see it is a part of the intermediate housing. I you follow the path away from the throttle body, then it goes into the intermediate housing and exits as TWO holes, about .040 in size. One .040 hole goes to the injector air bleed for the primary injector for the fwd rotor and the other goes to the air bleed for the primary injector for the aft rotor. The .040 holes exit about in the middle of the air bleeds. So the path is from the middle of the air bleeds on one end and the other end is at the FRONT of the throttle plates. Something to do with supplying filtered , atmospheric air to the middle of the air bleeds. Thats the path. Why I don't know. Same principle that is used for the air nipples on the oil injectors. On a side note, I noticed on the n/a intake I was looking at, had a paper gasket to mate to the *block* and I definetly remember having a metal one on my running 87na. I looked at my spare parts, and sure enough I have a spare metal gasket for this intake. They must have made both, metal and paper, maybe for different years.

Basicaly the same situation exists on a 87n/a except the hose goes to the front of the throttle body and is located in the center of the three nipples that are there. The larger one that goes to the oil injector nipples is just below it. If I pinch the line, it cuts off air to the engine and effects the idle. Same for the larger one. So these lines are a part of the idle circuit also(part of their function anyway). They supply some of the idle air. Cut off the supply of air FROM the throttle body, and your idle goes down or to pot. Oh yeah. It did occur to me if someone had a peculiar idling problem, he might want to make sure these lines are hooked up proper and functioning. EDIT....I just took the air bleed out, and noticed that it had a grooved area isolated to the .040 hole mentioned in the above post, and that this groove itself has a .040 hole that is dead even with the bottom of the pintle of the fuel injector.

Thanx HAILERS,

Damn, Dude, you are tenacious! I think I'll do away with the orange solenoid and run a line from the PD to the lowermost vaccuum nipple. RETed said you could do this on another thread, but that the vaccuum source had to be after the TB. Wonder what would be the best source for the vaccuum line to my Greddy boost control, pre or post TB?


Thanx, Gregg

I'm a newbie, but I'd say post throttle body also. Maybe tee into your boost(pressure) sensor or the line that is now going to the air bypass valve. Got together with Irv a few months ago and decided the fpr solenoid is on the whole a useless piece of equipment unless you have a problem with hot start difficulty. As the man said, just ditch the thing and run the vacuum line from the fpr to a vacuum source on the downstream side of the throttle body. I still don't know the whole story on why the Mazda folk run a hose to the middle of the bleed airs on the primary injectors and the nipple on the oil injectors. One thing I did figure though is that if you cap off those lines, then you deprive the engine of a source of air during the idle phase, so if they are capped off the idle will be effected and steps will have to be taken to add air to get the idle back up.

Thanx, man,

Think I'll just leave well enough alone and hook it back up, don't want to add any idle probs.
Happy New year!

Gregg