77 dies while running

[n2deep]

Thank you. This is a great manual.

[LostxSoul]

My '77 has a similar issue. I changed the fuel filter, some fuel lines, etc. just because they needed it but in reality my issue was solved when I pulled the cold start connection from the thermotime switch at the cold start valve. I have to get a multimeter to test for sure but when I pull the switch that leads from the thermotime to the cold start valve AFTER I start it up (Approx 8-10 seconds) it'll idle well enough to hold indefinitely without stalling. You may want to try that and see if your problem is solved.

From what I've read on this forum it's supposed to kick fuel in based on coolant temp for about 8 seconds instead of having an old choke to help on cold starts. I've ruled out replacing the cold start valve ($80 special order) because some people say they rarely get stuck open. More often than not they will be stuck open because of a bad thermotime switch which tells it to stay open. Thermotime switch introducing extra un-metered fuel could cause the stall from what I understand.

Anyone may correct me if I'm wrong, as I don't want to mislead anyone. This is just what I've gathered from my research on my issue. I've attached two pictures as well to show what I'm explaining. Let me know if I've mislabeled anything.

Fastwoman, could tapping on the thermostat housing cause the Thermotime switch or coolant temp sensor to act up? That seems plausible in my opinion but I'm a relative noob when it comes to these cars.

[n2deep]

With time off today I got back to working on this problem. I unplugged and cleaned the cold strat connector, unplugged and checked the thermotime switch connector and temp sensor. The cold start connector was the only one that was a little corroded. The other two are clean like new. Also today I found a few vaccum lines split and broken that went to something I dont recognize. Sorry. It is located in front of the fusible link relay bracket. It has both electrical wiring and vacuum lines to it. Anyway I reapaired the vacuum lines and the problem has gone away or went back to hiding. Can any body tell me what I fixed, if anything?

[FastWoman]

n2deep, you fixed the vacuum lines to the heater/AC system that are used to open and close doors, stopcocks, etc. One of the lines pulls your idle up when the AC compressor comes on. I doubt any problem in this system would cause the symptoms you've described -- certainly nothing that would instantly kill your engine after it's been running well for a while.

Lostxsoul, yes, I would think tapping on the thermo housing could trigger a malfunction with the thermotime switch too. I don't know whether that would be enough to kill an engine, though. I also question whether a bad thermotime switch would cause an engine to run for a while and then spontaneously die. My own theory is that tapping on the thermo housing caused the thermistor in the coolant temp sensor to open up, giving it an infinite resistance, signaling EXTREME cold, and triggering a very rich running condition that might kill the engine.

[n2deep]

n2deep, you fixed the vacuum lines to the heater/AC system that are used to open and close doors, stopcocks, etc. One of the lines pulls your idle up when the AC compressor comes on. I doubt any problem in this system would cause the symptoms you've described -- certainly nothing that would instantly kill your engine after it's been running well for a while.

Lostxsoul, yes, I would think tapping on the thermo housing could trigger a malfunction with the thermotime switch too. I don't know whether that would be enough to kill an engine, though. I also question whether a bad thermotime switch would cause an engine to run for a while and then spontaneously die. My own theory is that tapping on the thermo housing caused the thermistor in the coolant temp sensor to open up, giving it an infinite resistance, signaling EXTREME cold, and triggering a very rich running condition that might kill the engine.

That's interesting. Thanks. I guess I.m back to the drawing board. Although I could not get it to die as before. It will wait till I'm at a busy intersection. Should I just replace the coolant switch?

By the way, unrelated but I have always had a vacuum leak somewhere for the vent controls. At one point I had the defrost working for 5 minutes and then it quit.

[FastWoman]

Replace the thermotime switch? Dunno... Probably not. I think I'd do more diagnosis. I'd keep a multimeter and a can of starter fluid with me and have an action plan for what to measure/check when the engine dies next. Practice these measurements so that you can work quickly and methodically.

First thing, use your method of choice to determine whether your ignition is generating a spark.

Second, pull the small vacuum line off of the intake manifold near your brake booster vacuum line. Remember the small line that goes to the vacuum valves? The line that you fixed? That one. Pull the small hose off, and shoot some starter fluid into the hole. Then try starting the engine. Does it fire up for a second or two, but then not run after that? Then the problem is probably a failure of the system to deliver fuel.

Keep the the spring clip removed from your cold start injector, so that you can pull the plug easily. When your engine dies, try pulling the cold start injector plug and seeing if you can fire up your engine. If you can, then you probably have a faulty thermotime switch.

I'd have the trim over the driver kick panel removed, so that you can easily get to the big ECU connector. Write down on a card which contacts to probe to test for continuity in the coolant temp sensor. when the engine dies, TURN OFF THE IGNITION SWITCH FIRST, remove the ECU connector, and take that resistance measurement ASAP. If you have no continuity or have a dead short, that's your problem. If it checks normally, plug your ECU connector back in and try firing up your engine. If your engine fires up, then you can't really conclude much. If it DOESN'T fire up, even when the coolant temp sensor checks normal, the problem is not your coolant temp sensor.

Also make sure you have power to the ECU connector when the ignition switch is on. Note again: BE CERTAIN THE IGNITION SWITCH IS OFF WHENEVER DISCONNECTING OR RECONNECTING THE ECU CONNECTOR FROM THE ECU!

Try jiggling connectors to see if that gets your engine going again. Try disconnecting and reconnecting your ECU connector -- but again, ONLY WITH THE IGNITION SWITCH OFF! Also try jiggling the big connector on the bottom of the air flow meter.

That's all that occurs to me right now. I'm sure others will chip in. My point is, prepare yourself to conduct a lot of essential tests very quickly and efficiently, so that next time the engine dies, you can rule lots of potential issues out. The alternative approach is to just start replacing things you suspect MIGHT be at fault. You can simultaneously go broke and lose your sanity doing that.

[n2deep]

Thanks FastWoman. Excellent advice. I'll report back whatever I discover.

[240260280z]

Some items to check:

- low voltage Wires to the distributor and grounds to distributor

- bullet connectors ~ 1' of wire into the harness downstream from the temp sensor

- ignition unit in passenger kick panel over heating (transistors)

- bad condenser/cap shorting

Watch the tach when the car dies. If it drops to 0 then the problem is electrical.

Also check for spark immediately after the car dies... no spark means elecrtical