2002 Envoy

[Brenda Warwick]

My 2002 GMC ENVOY won't start and I've changed the fuel filter and the camshaft sensor and the camshaft sensor 

[Jsdirt]

Just so we're clear ...  it's cranking, but not starting?

 

You need 4 things in order for an engine to run: fuel, air, timed ignition, and compression - the trick is figuring out which one of the 4 is missing.

 

First thing I do in cases like this is listen for the fuel pump to run as soon as the key is turned on. If you don't hear that, you'll need to track down why (fuse, relay, wiring, bad pump, etc.). Next, I listed to the sound of the engine while it cranks over - if the starter sounds like it's speeding up and slowing down, there's a potential compression problem (valve train, head gasket, piston rings, etc.). It should crank evenly, with a steady cadence.

 

If that checks out, I get something flammable (brake cleaner, carburetor or throttle body cleaner, propane, etc.) and spray it into the throttle body while someone cranks the engine over. If it fires up and runs even briefly, you've eliminated 3 elements: spark, compression, and air. In that case you would have a fuel issue. If it does nothing, my next step is to see if there is spark. I usually just use an incandescent test light connected to ground, remove one coil and lay it on top of the engine where it won't fall while it's running, then fire it up, and get the sharp end of the test light inside the coil (or plug wire on older vehicles), and slowly pull it out - should be a bright and loud spark jumping to the test light all the way outside of the coil, or wire. If you have spark, now you need to see if you have fuel (and fuel that will burn!), air, and compression.

 

There's literally 1,000+ things that can cause a crank, no-start condition. Doing these tests will help narrow that down significantly. Let us know what you find.