TBI: No Vacuum at Port A

[1987 GMC Jimmy]

I was doing some vacuum repairs today (MAP tube melted) and noticed that I got no vacuum reading at idle from the A Port on the TBI. I've used this port to hook my vacuum gauge to many times to get my vacuum reading with no problems. I'd always get a strong reading here, which was roughly about 19" of Hg. Well, I wondered if I had gone crazy so I tried to see if this was a ported source by blipping the throttle and watching the gauge. Nothing. Am I missing something here, or is something broken? The line is clear, and there's nothing coming straight from the port on the TBI. Gauge works fine, and I get 18-19" at every other manifold source. If this is ported, how in the world did I use this thing for a manifold source with no problem? And why would the evap canister be hooked up to a ported source if this is the case? This is weird. I know this port is the one I used because the line is long, it's away from the engine, and it's easy to hook the gauge up to.

 

[bucket]

It has to be plugged up somewhere? With melted plastic perhaps?

 

[1987 GMC Jimmy]

I sucked on the port, and it wasn’t blocked.

 

[1987 GMC Jimmy]

Tried again in the light of day and I did get a ported response on the gauge. That’s still weird, though, because I swear I’ve used this port for my manifold reading. Maybe I’m just going bananas.

 

[yevgenievich]

does it match this one:

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[1987 GMC Jimmy]

It’s only three ports. Doesn’t have the right manifold port. I guess that corresponds with what I’m seeing now.