67 GMC

Since I've owned it, my '87 XJ has had the MAP sensor and cruise control connected to a T fitting that goes to a vacuum port on the intake manifold. From other posts, I understand that it is supposed to go to the back of the throttle body. When I look at my throttle body, I just see a plastic piece. Is there supposed to be a nipple that the hose connects to? Anyone have a pic of the TB nipple?

Parsnip

The Tb doesn't have a nipple for the molded plastic hose. The hose simply pushes in through the lower port on the Tb. In your second picture, you can see the little black thing with two holes in it on the throttle body? The lower hole is the map port.

67 GMC

Oh-So that screw that's been put in there by the PO was probably just to block off the hole. Wonder why you'd do that instead of just putting the tubing in. Does the MAP tubing have an "end" on it or is it just the tubing that is put into the TB? Is it that hard plastic tubing that all the vacuum liens are made of or is it just rubber tubing?

DFlintstone

Often the hard tube breaks off in the rubber plug. I pried my plug out, found a small screw that would tread into the broken stub, pulled that and hooked up my MAP there. It's Cruisers opinion that any good manifold vac port will do. For instance if you have re-located your IAT sensor, right there is a handy port. I'm just a tad more cautious/(****), about changing the original design, thinking they may have have had some reason I don't see, to put it there center on the TB.

As long as that screw in the rubber plug is making a good seal you are likely fine. I might actually submit my first writeup on that. (there's plenty more).

One has successfully used metal brake line, my new 90 has a long looped black flex tube. You want it small/short so the vacuum drop will be quick. You may want it angled down from the MAP to eleminate any chance of any fluid laying in there that would dampen the vac. drop time to the MAP.

I think it waz 97 they simply moved the MAP to the TB.

67 GMC

Thanks for the replies. What is supposed to be installed on the intake manifold vacuum port? Just the cruise control tubing? I'm like you-if they factory had it there, it usually was for a reason.

DFlintstone

There are a number of vacuum ports on the intake. Thinking maybe you should look at diagrams, there is one in my sig. The port front of the Tb does the FPR, EGR.. IIRC. OH and that hot air intake deal on the airbox.

IIRC it's only the cruse and heater controls that use the little tube from the vacuum reservoir. That's the 'bottle", behind the RF bumper that 'holds" vacuum, for when you have the throttle plate open, and there is no manifold vacuum. There is a check valve somewhere. Following me? These things still need intake vacuum, even when the petal is on the floor and the intake is free to 'inhale" right from the airbox. No intake vacuum available at that point.

67 GMC

All the diagrams I have show that nipple on the intake manifold without anything connected. The vacuum diagram that shows the routing of most of the EVAP stuff air and vac lines, shows the TB connection. I agree with you that if you are giving throttle, the vacuum below the throttle plate would be a little different than the vacuum at the intake manifold. This would cause the MAP sensor to output to the ECU that there was more vacuum than there is. I will hook up a vacuum gauge and see what the difference is when the throttle is opened up. The reason for the vacuum reservoir is to prevent lost of vacuum to cruise and heating controls when you are accelerating. So, probably having the MAP reading that port is not the best since it is now "Tee'd" into the same line as the reservoir. Not sure where the check valve is but it would have to be between the cruise and map to allow the map to see intake vacuum and not "system" vacuum.

DFlintstone

Me thinks is there is any difference in the vac drop time from any manifold vacuum, and the manifold vacuum right where it's taken for the MAP, it's very small. Maybe the centered to to cover if you had, say a bad gasket and a major leak on #6...Idk. I only mentioned the ball because you mentioned the cruse...

67 GMC

OK-Just an update:
I made a new MAP line from an old EGR vac line I had (I put in a new vac harness recently). It had two 90 degree bends so I took a heat gun and made them straight and voila! New MAP tube into Throttle Body. I re-did the vac line from the intake manifold to the cruise too. I just used some clear Tygon tubing for that. Everything seems good now. I swear it accelerates a bit differently when I give it the gas. Might be my imagination. Idle seems smoother too. Haven't been on the highway with it yet so I'll see if anything else is impacted. There's a big difference in the diameter of the EGR vac line and the hose I had on it before. Wondering if it wants the smaller diameter tubing for quicker response to changes in vacuum.

DFlintstone

I'm sure larger causes some delay. If it were 1 inch line, for instance. I just did mine with 3/16" tubing that has about a 3/32" ID. Whatever lag that might cause, I'm gonna live with!

In the first pic, I have just extracted the broken stub by screwing a small screw into it and pulling it out with pliers.

Second is the whole business. I didn't happen to need to heat and bend it. I think the PO cut off part of the coupling to the MAP so it comes off at an angle, downward. (see the third pic).

67 GMC

My MAP tube is a little thinner but it's working. Thanks for the post.