No start

[Adam Thompson]

99 Yukon 350. Came home last night shut it off went about my day. Went to go to the store today wouldn’t hit. Had a spare ICM threw it in and it tried to start actually backfired REALLY hard from all the fuel dumped in the exhaust which makes me think this is spark related. I currently don’t have my diagnostic tools with me, so where should I start?

 

[OR VietVet]

Right where you think. Check for spark at the plugs. If you have no special tools, just get a screwdriver, pull an easy to get to plug wire and put the screwdriver end in there and get close to metal ground area and while cranking the engine look for spark. You want to see a blue spark-strong. Orange spark-weak. You can also go to a shrader valve spout on the fuel rail and depress the inner needle and see if fuel spouts out. If the cranking rhythm is normal then you likely still have good compression. You need those three things....spark, fuel and compression to start the engine. Report back with what you find.

 

[willxfs]

I would pull the distributor cap and check the contacts including the rotor contacts. A month ago my rig wouldn't start and would backfire. It was bad corrosion on all the contacts of the distributor cap.