Help please with my 1997 Express 2500 5.7. I've had it 3 years and it's been running fine.

The current issue is when I go to start it, while it's cranking it will not fire, just cranks, BUT if I slightly release the key toward run, it will fire slightly and then slowly catch and will idle. Then when driving no problems accelerating, smooth and powerful, when you get up to cruising speed, say 50mph, it kind of pulsates, almost feels like a TC lock up problem, but then will smooth out mostly in a few minutes.

So, I just changed the ignition switch, no help, I've done basic tune up stuff in the last year, all new cats and O2 sensors, Premium gas and regular Seafood or Techron. No codes, none. New air filter. New gas cap. Fuel pump sounds fine and the last time the pressure was checked it was OK.

Any ideas are appreciated, Thanks, Frank

 

Ignition module? See if it will fire if you spray a little brake cleaner on air filter. Make sure it's the extremely flammable kind or you will start feeling stupid. If you are sure it's the spark check ground on the coils