Q: Truck misfires when the engine warms up - 1995 Chevrolet C3500

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When I bought this pre-owned truck, it had 145,000 miles on it. The truck has a 454 and a 4L80-E transmission. During a long road trip, it started misfiring. I figured this was caused by low-quality gas but it wasn't as it kept misfiring even when I put quality gas in. I had the fuel filter replaced and the previous owner said the fuel pump is almost new. The truck starts immediately and runs fine for a while. When the engine warms up though, the misfiring occurs. The truck has no trouble developing and cruising at high speed though. The engine has power. The dash isn't showing any lights on either. Temperature gauge is at 175. What kind of repairs do you suggest?

If the heat sensitivity is a good clue, this could well be the ignition control module, which is quite heat sensitive on the big block Chevy’s. Would check fuel pressure (while running) as well to make sure you’re getting enough fuel. Engine temperature seems low, as well as the thermostat may not be staying closed enough to get to design running temperature. A YourMechanic professional can help with the misfiring issue and make all necessary repairs.

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