Mystery vacuum hose and harness wire

[kjphilippona]

I have been trying to track down the cause of my stalling problem i have been having when i come to a stop. FastWoman has been helping me get this far, tried cleaning the cold start valve and replaced coolant temp sensor, but need to post some pictures to identify where these two attach, to determine if they could be part of the problem. I think the harness attached to the thermotime switch (which has been disconnected). Does anyone know where the vacuum hose could have been connected to ?

[esmit208]

KJ

I see some discoloration on the green wire as if it gets hot or got too hot at some point or another. Is the vacuum line plugged into the bottom of the AFM? If the car had a previous owner no doubt they had an issue and that was the solution they came up with.

Having the thermotime switch disconnected can cause idling issues as well. It tells the ECU that the car is warm enough and allows the cold start valve to close. My suggestion is find a good Z mechanic and let it get sorted out properly. No point in throwing unecessary parts at it. Good Luck.

[Zed Head]

Can't really see a disconnected vacuum hose in your picture.

A description of how the engine stalls might give some clues. Does it chug along then die, does it die as soon as you hit the brakes, does it die as soon as press the clutch in, etc.

[kjphilippona]

The hose coming out of the AFM is not connected to anything just plugged off. The car dies when you come to a stop and push in the clutch. Some times it will idle down to 300 and the fuel relay under the dash goes crazy than it idles up to 1200 and then back to 750. When the car idles it is not a steady idle, the motor surges 100 or 200 rpm.

[Zed Head]

So the dieing problem seems to be related to the poor idle. Fix the idle, you'll probably fix the dieing.

Your picture shows the side of your throttle body. If you mean the small hose connected to the port in the center of the picture, that would be a ported vacuum source, maybe to your charcoal canister, or the distributor vacuum advance. What is the open end sitting close to? There is another bigger hose that goes to the charcoal canister. If that is open, you might have a vacuum leak.

The fuel relay is clicking because the fuel pump contact switch is opening when the vane in the AFM closes as the rpm drop. Mine has done that in the past before I got things tuned up (1976 model with the same AFM switch). That will go away too if you get the engine to idle right.

I think the RPM goes up to 1200 when the fuel pump turns off because the mixture leans out, then the RPM surge, the AFM opens, the switch is made and the pump turns on again. Is it running rich or lean at idle?

The thermotime switch only comes in to play during starting. Sorry esmit, maybe you're thinking of the water temperature sensor.

I would double-check all of your vacuum hoses kjp.

[kjphilippona]

You are correct the hose comes out of the throttle body, the vac hose to the canister that t's to the vac advance on distributer is connected. The other canister vac hose is connected to the intake manifold. This hose was disconnected some time ago by PO and is not located neer anything just curled up on the wheel well.

[sblake01]

Having the thermotime switch disconnected can cause idling issues as well. It tells the ECU that the car is warm enough and allows the cold start valve to close.

Actually, the thermotime switch only sends the 'open' signal to the cold start valve when the engine is cold and then only for a max of 9 seconds. Having it disconnected would actually prevent the cold start valve from opening.

[esmit208]

Actually, the thermotime switch only sends the 'open' signal to the cold start valve when the engine is cold and then only for a max of 9 seconds. Having it disconnected would actually prevent the cold start valve from opening.

Thanks, duly noted, committed to memory.

[FastWoman]

Do you have a copy of the factory service manual? It lays out pretty clearly where all the vacuum lines connect.

The part in your picture is the BCDD ("boost controlled deceleration device??"). It's a doodad that drops your engine RPM gradually when you come off the pedal, by introducing additional air. If it's like most BCDDs, it's defunct now and has no available replacement. The good news is that it's not really that necessary.

What Zed said about your fuel pump cutting off. I found on MY car that if the mixture is off, the idle can become unstable. Perhaps that's part of your problem. Or perhaps your idle is just too low. You can adjust it with the big screw on the top of the throttle body. Another possibility is that your fuel pump shutoff switch shuts off at too high an air flow. You can open up the AFM, loosen the potentiometer arm, and move it JUST A TINY BIT to pull it a bit off of the fuel pump shutoff switch. You can also try screwing in the idle mixture adjustment screw on the lower outlet side of the AFM (possibly behind a rubber plug). That will richen your idle mixture AND simultaneously draw more air past the AFM vane, thus pulling the potentiometer arm away from the fuel pump shutoff switch.

[Zed Head]

You can also try screwing in the idle mixture adjustment screw on the lower outlet side of the AFM (possibly behind a rubber plug). That will richen your idle mixture AND simultaneously draw more air past the AFM vane, thus pulling the potentiometer arm away from the fuel pump shutoff switch.

This is what I did when my cutoff switch was "on the edge" with the same thought in mind. It worked until I went to get emissions checked. Then I failed, the idle mixture was too rich. I turned the screw back out and passed, and the idle was okay then because I had done some other tuning and it was more stable.

The problem started when I advanced my timing. The engine needed less air to maintain RPM at idle. The first thing I did was to adjust the stop for the contact switch in the AFM. It's a very simple mechanism and you can bend the wire with a pair of pliers or a crescent wrench.

I could have just set the timing back but I wanted bend the motor to my will...:mad:

[kjphilippona]

Well i got everything sorted out, my first thought was that the hose attached on top of the dash pot, FastWoman set me straight letting me know that no vacuum hose attached to the dashpot. I then got to thinking, the car started stalling or almost stalling after i removed the dash pot thinking it was just taking up space and looked like crap on the front of the engine. I cleaned it up and reinstalled it, no more stalling. As for the mystery hose, i looked at the shop manual and found where it was supposed to attach, the first nipple on the thermal vacuum valve. The second nipple is broken off so the hose that goes to the bpt valve is attached to the first nipple. All three components in this series are non functional, the fitting on the btm of the bpt valve is broken off and the steel line to the egr housing is plugged off. what a mess, i am glad i live in Alabama where there are no emission checks, this car would never pass.

[mayitin]

how far you are from Mobile? there is a good group of z guys there and some even have a shop for z cars.