Intermittant starting

[ButchH]

97 XLT with V6, 165K on 2nd engine - roughly 1 out of 4 starts it won't start. It just cranks. No spark at plugs. If you try few hours later it will usually start. Using 2 different Ford keys. Nothing changed lately. Did this about 6 months ago and then went away. Now back. Dealer thinks may be theft system problem, The security light isn't on when cranking or when key is on. It does lite when car is off and I lock doors. Not sure if that matters?

 

[exploded99]

Since you have no spark when it won't start , and it's intermittent, you might try swapping the ecm (computer) relay under the hood with another less important relay and see if that helps.

Could be the ecm relay is getting flaky.