I have been researching this forum and others trying to find an answer to my issue with my 98 Ram 1500 5.9. When I first bought this truck at the beginning of this year I had the stalling while driving issue. I took it to the shop long story short it received a tune-up, replaced belt, fan clutch, rotor, and the crankshaft sensor. She drove very well until she would not start during the hottest parts of the day. I live in Florida so it's hot most of the day. So here is my issue, She will start in the morning and evening and sometimes when she is parked in the shade. She will crank but not start. I have put in a new starter, new battery terminals, and still she will not start during the day. Maybe it's something that we have overlooked and are having a duh moment if someone could help with this it would be fantastic. I love my truck but she is being moody.

 

Heat issues like that are frustrating because they can be hard to track down. Usually they boil (pun intended) down to either a fuel problem or an ignition problem. When it won't start, you need to use an ignition spark tester to make sure you are getting a strong spark to the plugs. You can get a tester relatively cheap from an auto parts store and connect it to the main coil wire. You should have a strong spark at the coil. Anything less means you have a bad coil or a fault in the system that sends signal to the coil. Even if you had a traditional tune-up (cap, rotor, wires, & plugs), you still need to continue on as it isn't unusual to get bad parts off the shelf. If it's strong at the coil, move the tester to the end of each of the ignition wires. If you have a weak or nonexistent spark at the end of the wires, you probably need new wires. Be warned, a weak coil may throw a good spark at the coil, but can lack enough strength to take it down to the plugs. If you've got strong spark at the end of the wires, check your plugs.

On the fuel side, you need to rent a fuel pressure tester and familiarize yourself with how it works. You'll need to check the pressure when its cold and then compare it to when it is warn and not starting. Any difference here would indicate an issue with the fuel pump module. Another test to perform is to time how long it takes the pressure to bleed off after the key is turned off. It should a very very slow bleed off. Rapid bleed off could indicate one or more leaking injectors that could be flooding the engine when it is hot. The only reliable way to fix that is to replace the injectors.

One more thing, find someone with a data capable scanner and have them monitor the data stream when its cold and hot. It's possible that one or more sensors are failing when the engine is hot, but not consistently enough to throw a code.

Finally, just for giggles, take the fuel cap off when its hot and see if that makes any difference. If it does, you've got a problem in your Evap. Emissions system goofing things up.

It's not a simple list of things to try, but it has worked pretty good for me on no-start conditions on my other vehicles.