Hi, I am a professional certified mechanic, with an engineering background, and 35+ years experience. I will do my best to assist you. Also keep in mind I don't know if you are a pro or a novice, so feel free to add any additional info at any time.
Hi, I work on these LT1 5.7L, and the L99 4.3L V8's they used in these cars a lot. If the fuel pump is failing when it does, just turn the ignition off, and back on quickly and listen for the fuel pump. You can actually hear it if it is operating like it should. Normally on one of these Roadmaster's when the fuel pump fails it will idle all day, and the pump will act up normally while driving down the road, then the engine will die. Once that happens it wont start no matter what for at least an hour. Then it will fire right back up and run perfect. The cycle repeats over and over, and it will take longer for it to restart, and the pump eventually fails.
There are a few inherent problems in this model that cause the symptoms you are having. One is a ground connection that attached to the front of the drivers side cylinder head. This ground is where several critical ground wires from the ECU, and other parts of the electrical system grounds. For experienced electrical techs that have worked on these a lot Roadmasters are well known for loosing connection here, and it causes the engine to die. Normally the engine will restart. What happens is where the electrical connector crimps to the wire the connection starts going bad. The solution is to locate this bundle of ground wires, and clean them, then solder the connectors to the wire, and reattach it all. Look for the ignition coil bolted to the front of the drivers side cylinder heads, the ground cluster normally attaches at the base of one of the coil mounting bolts if it is all still like it was out of the factory. You will probably have to remove the electric emissions air pump to get to the ground.
Other than this problem the optispark distributors, and ignition modules are bad about failing. The opti uses a Mitsubishi optical trigger, and they get dirty, and have more trouble triggering at lower speeds, so the engine dies. There is no definitive test for this. The ignition module is also suspect, and can cause this problem. It is riveted to a bracket attached to the ignition coil on the front of the drivers side cylinder head. The opti, and the ign module, or the ground connection will not register any trouble code. If it was mine I would start off with the ground connection. And make sure the optispark distributor has it's two vacuum hoses attached. The earlier opti spark didn’t have vacuum hoses, and water would find its way inside, along with and crud the water had in it. This would eventually crud up the optics on the opti spark, and cause misfires. These hoses are on the drivers side, one taps into the duct from the throttle body to the MAF, the other taps into the intake manifold, drivers side about halfway back, on the side. One last thing is if you replace the optispark distributor, the early and late opti units do not interchange, and ebay is your best price source, search for “optispark”. Go over all of this and if you have any more questions at all, I am here to help. Good luck with it, have a great day, and Thanks for using Just Answer.
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