PROBLEMS STARTING A HOT ENGINE

Usually, you see engine starting problems when the engine is cold, or was previously a used engine for sale that sat in storage. Low battery charge and other issues often make cold starts slow, hesitating and difficult. However, if your customer is having problems starting a hot engine, there are a few common culprits you can consider. Also, don’t worry about checking the charging/starting system, as the problem most likely lies in other areas (although a full charging system test is never a bad thing).

Relay Issues – One of the most common reasons for a car to struggle with starting when hot is a dying fuel pump relay. The easiest test for this is to use either a jumper to replace the fuel pump relay, or a known-good relay that you already have on hand. Just pop in the jumper/relay and start the car. If it fires right up when warm (don’t let the engine cool), you know the relay has started to fail. A good sign that the relay is the problem is if the car cranks right up when the engine is cold (or has cooled down for about an hour after running).

Vapor Lock – Vapor lock can be caused by quite a few different things, though the most common include leaking injectors, a failing fuel pressure regulator and a failed fuel pump check valve. The issue here is that fuel that remains in the rails after engine shut down is turned into vapor, creating a pressure void in the system. When you go to crank the engine, it can take quite some time for the fuel pump to make up for the void, creating slow starting situations. A leak down test will have to be performed on the fuel system to determine if vapor lock is the issue.

Computer Problems – Vehicle DME computers are generally reliable, but sometimes there can be issues. The most common issue is failing solder joints within the computer. Tap the computer while cranking the car. If it starts right up while tapping (and the car’s warm), then you have found the most likely issue.

None of these issues will cause problems requiring engine replacement. However, they can be time consuming to diagnose. Start with the fuel pump relay, as this is the most common issue, and then move down the list as you eliminate potential issues that might be causing the car not to start (or struggle to start) when hot.