1978 dies at idle...after highway speeds

[Turley]

Total noob here....
Working on a 79' that dies at idle, but only after running on the highway for 15-20 min. If you fire it up, and drive around town, it'll run all day.
Hit the highway for 20 min or so, get off said highway, say approaching a stop sign, car will die. It will eventually restart, but run very rough the
entire time, needing to blip the throttle to keep it running. It's an automatic, so this gets tough on the tranny & brakes. Lately, even this won't help, it'll just die. Let the car sit for a couple hours, it'll restart fine and run fine.
I'm thinking some type of timing issue? The vaccuum advance weights
down in the distrib. not releasing properly when kicking down from highway speeds?
The car belongs to a buddy, and I'm getting off on working on it. I'm gonna have to get one of these cars, and working on his is very cool.
BTW, the temp gauge doesn't read high at all. Car is not overheating.
Fuel system/Carb issue? I'm at a total loss, and hoping to get some guidence. Thanx for any input!

Jack

[89IROC&RS]

this definatly sounds like a fuel delivery problem. for whatever reason it seems like the fuel bowls in the carb are going dry and the carb i surviving on the high rpm of the engine pumping the nessesary fuel. when it slows down the fuel pump isnt moving enough gas and the car stalls out. im not a carb guy though so this is just a guess. it could also need a new mechanical fuel pump, but if that were the problem, i would have thouht it would stall out in around town driving as well. my money is on some sort of carb fuel metering problem. but being a fuel injection guy, i cant really offer too much help in daignosing it.

[Turley]

Yep, I'm more familiar w/fuel inj myself, which may be one reason why this is so frustrating. Appreciate your input, and will hit the shop manual for more diag testing. Thanx for your input.

Jack

[89IROC&RS]

no problem, if you figure it out let me know, im curious as to what the problem is.

[Doc Blazer]

The symptoms are consistant with fuel vapor lock. Vapor lock occurs when the fuel lines get too hot. Trace your fuel line and look for places that are too close to heat source manifolds block etc. Reroute line to gain more distance from heat source or install heat shield. You can use aluminum foil shiny side down for a temporary heat shield just to see if this helps. Also may be able to move fuel lines away from heat source. A small increase in distance could mean a temp drop in fuel line. It makes sense to ck for this before taking things apart. Good luck.

[grizzer]

Originally Posted by Turley

Total noob here....
Working on a 79' that dies at idle, but only after running on the highway for 15-20 min. If you fire it up, and drive around town, it'll run all day.
Hit the highway for 20 min or so, get off said highway, say approaching a stop sign, car will die. It will eventually restart, but run very rough the
entire time, needing to blip the throttle to keep it running. It's an automatic, so this gets tough on the tranny & brakes. Lately, even this won't help, it'll just die. Let the car sit for a couple hours, it'll restart fine and run fine.
I'm thinking some type of timing issue? The vaccuum advance weights
down in the distrib. not releasing properly when kicking down from highway speeds?
The car belongs to a buddy, and I'm getting off on working on it. I'm gonna have to get one of these cars, and working on his is very cool.
BTW, the temp gauge doesn't read high at all. Car is not overheating.
Fuel system/Carb issue? I'm at a total loss, and hoping to get some guidence. Thanx for any input!

Jack

Does the car still have the original exhaust? If so, you may want to look at the CAT. They had a tendency to "plug" and if it plugs up when hot it doesn't let the exhaust flow thru. which make sthe car stall and run bad until the CAT cools dowen and lets flow resume. Run the car and when it stalls check the temp of the CAT if it is glowing and smells try replacing.
Good luck Hope this will help a little