Whilst tinkering to get the car going, I spotted this laying on top of the intake manifold. It wasn't connected to anything.



Can anyone tell me what it is?

Cheers everyone!

 

Not that it's a lot of help, but it appears to be a vacuum line.

 

looks the heater control valve vacuum line to me, but it could be a vacuum line for something else

 

The previous owner removed the aircon, EGR and EFE, if that helps.

The car's not driveable, so I can't fully confirm if there's anything (apart from those!) that doesn't work...

 

It is either the vacuum line that goes from the vac sensor near the brake booster to the vac fitting on the rear of the carb OR the vac line that goes to the heater diverter valve from the HVAC harness. More likely the first.

 

Is that vac sensor different from the MAP sensor, bolted to the bulkhead behind the brake booster? Because that's definitely connected by a 6mm (4mm?) rubber line to a vacuum connection on the top of the intake behind the carb...

It does sound suspiciously like what you've described here: https://www.thirdgen.org/forums/cool...-diverter.html

It is a hard, thin plastic line. If the AC was removed, would it be left lying spare? More importantly, is it a vacuum leak?? Where should it connect if it was?

Cheers, you're giving me some leads here!

 

Looks to me like the MAP sensor line.

Find the MAP sensor: if your car is still American-style left-hand-drive, it will be right by the brake booster, a thin flat thing about 4 x 10 x 1 cm w a 3-wire plug and a vac line. Blow through that and see if air comes out the thing in your hand. If it does, that end plugs into the back of the carb.

 

Does it go into the loom? Most likely for the hvac system.

 

HVAC system isn't in "the loom"; it has its own little harness, that goes into the firewall right below the heater hoses. Eeeeeezy way to differentiate between things that are part of The Car (one harness), The Engine (another harness all its own) and The HVAC (yet another individual harness, installed on the production line as part of the optional equipment). Other options (cruise, radio, etc.) all have their own little harnesses that are specific to themselves and part of themselves, that maybe plug into The Car harness to get power or other important signals, and also sometimes include vacuum lines.

If it goes into "the loom" (the BIG harness that runs across the back of the engine behind the distributor, it's for the MAP sensor.

 

Just found this:

https://www.thirdgen.org/forums/attachments/carburetors/295796d1443567407-1984-l69-overall-poor-map-sensor-vac-line.png

I have a spare vacuum connection right there on my carb! For some reason I thought it was supposed to be spare...

When I've got the intake back on, I think I'll have to remember to connect that up. Please tell me that won't be a sufficient leak to be the reason it wasn't idling...

Thanks for all the advice guys!

 

For the purposes of this discussion VAC = MAP.

The VAC line should connect to the right rear base plate of the carb.

The rear vacuum port on the manifold (behind the carb) is for vacuum operated accessories. That vac line goes to the rear and tees to the HVAC ducts and the vacuum reservoir (and cruise if equipped).

 

That vacuum line connects to the back of the carb and the line comes from a harness directly behind the engine. So, exactly what naf said.

 

The Vac Line Fitting That Connects To The Carb Is Smaller Then The One Shown In Post #1

 

I'll bear that in mind GT, but that vacuum connection on the back my carb is suspiciously vacant so it's still my primary suspect. I'm heading over to the car shortly, so I'll use SK's blow through test and then see if the vacuum line fits the vacant connection.

On my car, that vacuum connection on the intake manifold behind the carb doesn't seem to connect to any accessories - it just runs to a round-fronted black plastic box about 15cm/6" long mounted high up on the firewall... I actually thought THAT was the map sensor!

 

That is the vacuum reservoir for your car. The line should also be connected to the HVAC duct system. If it isn't, your system will stay in the default, defrost, mode. If you did not have cruise control, there will be no other connection to it.

 

Oh dear, nothing T's into that vacuum line at all.

I have a sinking feeling the HVAC system is another thing the previous owner FUBAR'd...

 

If it has bends it, than a hard plastic vacuum line is bent when its made. It travels freely following a specific route with no pressure forcing it to move from side to side.
It is made to only go to one specific spot.

 

Thanks for the tip - I'll be careful not put too much force on it and see where it 'wants' to go.

 

Well, it's definitely the MAP sensor vacuum line - I disconnected the other end at the sensor itself and blew through the line (glad no one was watching!!) and felt the air come out the other end.

Plus the line only really wanted to extend as far as the back of the carb.

Thanks everyone, mystery solved!

Incidentally, a second hard vacuum line comes out of my vacuum reservoir and heads into the bulkhead just behind the engine on the passenger side. I assume this is the vacuum HVAC connection instead of something else T'ing into the line from the manifold?

Haven't managed to change the intake gaskets yet - the previous owner saw fit to use rtv along the whole length of each gasket. I had to pry the damn thing off! It left quite a mess that took a good couple of hours of scrubbing with meths, rags and carb cleaner to tidy up. Grrr!

 

This "could" be it.