348 hard start at hot some times

Welcome!

Head down to the 348/355 section and do a search on hot start, idle, and hard start. Also, learn how to pull ECU codes. If you don't know how to do this, you may have some very helpful information waiting in your ECU that will point you to the problem.

Is your problem due to the starter not turning, or does the starter turn but the engine fails to start?

If your starter fails to turn, this is a very common issue due to lack of current reaching the starter. You can either do a lot of electrical connection and wiring work, or you can do what many of us have done, and install a relay.

If you starter is turning, but the engine will not start, you have either a fuel, ignition, or air issue which could be a lot of things. The good news is that many of these are relatively simple to fix.

And yes, if you haven't done the fuel filters, might be a good idea. Fuel pressure can definitely cause hard start (if the starter is turning), and there is a known issue with rubber clogging them up from failed seals in the tank.

Let us know what you find.

 

IIRC, they also got overly-fancy (IMO) with the clutch/flywheel design and went to a two-mass damped arrangement -- so when the (damping) grease gets old, hot (thin), and less effective, the one mass can oscillate with respect to the other mass and confuse the ignition system (so no spark) -- and the starter motor gear mesh action can drive this oscillation more than just normal engine running.

Per John's thought (to better identify the root problem) -- does it run perfectly at all other times? (Something dodgy in the fuel system shouldn't only give trouble during warm restarts.)