when it’s cold it runs great. once it warms up, it starts to hesitate, and bog down. and then we get a strong smell of gasoline while we are driving. there is no check engine light except for rarely and it only shows a code 12 (no distributor reference pulse/diagnostic mode code). we’ve replaced the fuel pump, fuel filter, distributor, egnition coil, spark plugs, spark plugs and wires, and the spark control sensor. we have no clue what could be causing the problem and we have ran out of options for what it might be.
Are you sure that’s the only code you’re getting? It will list codes sequentially, so make sure the second code is also code 12 - if it’s not, note down all of the codes it’s flashing and post here.
I’d be looking at the fuel injectors to see if they’re sticking open. If the engine is running rich, that’s OK at startup because it needs to run rich anyway. But if it can’t lean out once it warms up then you’ll get a poorly-running engine and if it’s bad enough you’ll smell gas because it’s not all being burned.
Wouldn’t hurt to test for vacuum leaks either.
@shadowfax has the right idea. Since this truck has a throttle body fuel injection you can SEE the fuel spray pattern by removing the air cleaner. It should be a nice cone shape spray from each of the 2 injectors.
Chevy OBDI code 12 is the start and end code. Each code is repeated 3 times. So, if all you get is 6 code 12s, there’s no stored diagnostic codes…
Make sure the fuel pressure regulator diaphragm in the throttle body isn’t leaking.