That's something I hadn't considered, but entirely possible as the truck has been running like this for god knows how long. Any idea how I could test?

 

Well my dad had an 03 suburban and it was runnin rough was pretty slow and trans was slippin with only 15,000 on his new trans. So we dropped unbolted the y pipe from the manifolds and just let it hang and she drove like a brand new rig. So i would unbolt the y pipe and see how it runs then go from there. That would be the best way to test it

 

I replaced the coolant temperature sensor (the one in the intake manifold) last night. No change (but what the heck, it was a $5 part and I can cross that one off my list). SES light is still on as well.


While I was in there, I took the air filter housing off and watched the injector spray pattern with a bright LED light. Both injectors have a really lousy spray pattern. Lots of dripping and dribbling. You can see drops of gas running down the barrels of the throttle body. So I guess that's contributing to the problem. Time to replace the injectors.


I got an O2 sensor but haven't had a chance to replace yet.

 

Low fuel pressure will cause the spray pattern you describe...have it checked before you spring for new injectors. Also clogged fuel filter. You could also add injector cleaner for a couple of tankfuls to see if it helps. What code is giving you the light? Reset 'em and see which ones come back.

 

Too late on the injectors, they're on their way. But I recently replaced both the in-tank pump and the fuel filter, so it's probably not them. Will report back.

 

Well, sometimes it's the simple things ...

I discovered after taking the plastic cover off the passenger side firewall that the timing wire was disconnected. After reconnecting it, it runs like a different truck. Tons more power, idles like it should -- and best of all, the check engine light has finally turned off.

I need to drive it to get a handle on how improved the fuel economy is now, but I'm betting a lot.

 

The wire you found disconnected allows the ECM to advance the timing for the distributor, when setting the timing you disconnect the wire to set the timing. After the timing is set the wire should be reconnected.

You should disconnect the negative terminal from the battery for at least two minutes and that will clear all codes and reset the ECM, after the engine is ran for a few miles the ECM will reprogram itself.

 

I will do that, Richard. Thanks for the tip.