The Stovebolt Site Forums The Shop Area Engine Shop '73 dies after running for 30 minutes

Chevy, 1973, 1/2 ton, 2wd, longbed, dual tanks, automatic, original 454 (rebuilt within the past 3 years). So this truck fires up nicely and runs strong through all the gears for a grand total of about 30 minutes. Then it starts idling rough and stalls out. I limp it home, after having to start and rev multiple times (depending upon how far from home I got). After letting it sit for an hour or so, I can crank it up and drive it off, with no problems, for another 30 minutes. Just started this about 6 months ago, previously was a daily driver. I have replaced the fuel filter, to no avail, but that is it. Don't want to get too involved before I get some advice. Any and all is welcome. Thanks in advance.

Well, it's either running out of fuel or has an ignition problem. An ignition problem can occur after the components have time to warm up.

What does the truck do when you give it more gas while driving it when the problem occurs? Does it bog? If it does, I'd shut off the ignition key and pull over. Work the throttle and see if the carburetor is empty or not by looking to see if it's squirting fuel still. If not, you've got rust/debris in the tank or possibly a bad fuel pump.

Of course it could be ignition. Easiest way to figure that out is to trade a distributor and coil out of another good running truck. If that is not available, possibly the condensor or ignition coil is bad. A condensor is very cheap and easy to replace. I've seen bad "New" condensors.

Good luck.

Fuel tank vent blocked ?.

Although it could be any of the above mentioned problems, I would suspect the coil first. When the insulation gets bad, the coil starts shorting out as the windings expand from heat. I would check the gas cap first to make sure it is vented, and then try a different coil.

Before you start tearing into the fuel or electrical system, apply a wet rag to any section of metallic fuel line that is near the carb. The "heat soak" issue has caused a number of vehicles to exhibit the same symptoms. The E10 fuel which we all now are forced to use, has a very low "phase separation" temperature (128 degrees F). When under-hood temps rise, the incidence of this phenomena increases. Once you cool the line the vapor lock will dissipate and fuel pressure/flow will return.

This issue has surfaced in both engines that are operating and those that have been shut down for 15-20 minutes. The key is to keep engine bay temperatures under control and shield lines that come in close contact with the exhaust system as well as the cooling system. Adding an electric pump on a momentary switch, in addition to the mechanical pump and adding a pusher fan with a timer that runs 10 minutes after shutting down the engine, has eliminated the problem.

Can't say that slapping a wet rag on the line will solve your issues.....but it's easy, quick, cheap and might identify your problem without having to drag out the toolbox.

Dave

Heat causes gasoline to boil in the fuel lines and cause vapor lock. This is nothing new. And cooling the fuel lines helps. However, E10 is more volatile than the gasoline these engines were designed. And this is the time of the year when refineries are switching to winter blend fuel and volatility is more common during the transition period. Phase separation is caused by alcohol's affinity for water. Phase separation occurs when the gasoline water content exceeds the maximum amount of water the fuel can dissolve, and the excess water drops out of the solution to form a gasoline layer and a water layer. Phase separation is temperature sensitive, but cooling the line will not fix the problem. Only keeping water out of the fuel supply will fix phase separation.

As I mentioned before.....apply a wet rag to any metallic fuel line close to the carb if you experience the same symptoms as MattMeese. I'm really not interested in a debate about why it will or won't work; just wanted to share something that I've discovered WORKS to get fuel flowing.

Dave

appears it might be in electronic module.. they can brake down when hot and cause a problem like this... I had one that did but not as quick or often, would be ru nning fine and just shut down or it would skip beats at time on start up, all kinds of weird things.. it broke down a lot at hi way speeds, just shut off like it was running out of gas, then it would pick back up it would always start up easy though..

this was in my 52 with a 235 and mallary electronic dist, no points.. may not be your deal but if it starts up easy I would not think it is a fuel issue but..

put a close pin on the fuel line........lol

good luck

Thanks for the advice. Gonna try some ignition troubleshooting, as well as the wet rag idea. Will update once it is solved.

I haven't seen a case of vapor lock in years. That 73 with the 454 might have a return line on the pump also. You need to figure out which system is failing before you can properly repair it,
Scott

Hook a gage on fuel pump discharge and tape it to the windshield and watch the pressure. If a bad fuel pump filter etc you will see pressure drop just before engine shuts down.

If the cold rag trick works for vapor lock problems the old timey solution was to wrap the fuel lines - especially the metal ones - with aluminum foil.

From sounds of things I do not believe you have water in fuel problems. Water willsettle in fuel bowl and make for a hard start.


Dan Bentler








.

Joker, I believe that there were still points in '73, so no ignition module unless the distributor was replaced with an HEI.

First and foremost. The next time it dies, pull the air cleaner and look down the throttle plates. If you see fuel when you move the throttle lever, it is electrical. If you dont see fuel its fuel related.

If its ignition related it could be any of the following: coil, plugs, wires or ignition switch
If its fuel related it could be any of the following: vapor lock, plugged fuel filter, plugged carb passage, bad float, bad needle & seat, bad dual tank valve.

I think in '72 they went to HEI. It could have been a mid year change. My 71 had a problem that sounds similar. My problem was the second tank still had some scum in it and needed to be cleaned better. It kept clogging my filters. My fuel pump diaphram was brittle too and needed to be replaced. Old fuel ines can look OK but be breaking apart from the inside. If they are getting hard and not too flexible, you might want to replace them now too.

Hey, perhaps you have some debris in your fuel tank that is getting sucked up against the fuel line thus blocking flow, which is why after letting it sit for a while (the debris will float away from the fuel line) allowing you to fire the engine again. This happened to my truck once, it is a real pain. Good Luck