96-00 454 Running Rough

[scons96]

I have a 1999 K2500 with the L29 454. I replaced the 34 gal. fuel tank, fuel lines, upper intake manifold gaskets, and the cap and rotor in the truck. I also replaced the small vacuum line going to the fuel pressure regulator as it was dried out and brittle, and I replaced the PCV hose. Before doing that, the truck ran fine, but it had an extended crank time after it sat for anywhere between 5 minutes to 10 hours. I would park it when I got home from work and in the morning it would start right up like a champ. After replacing the aforementioned parts, the truck now starts right up every time regardless of how long it has been sitting, but it runs ROUGH. I looked at the live data on a scanner and bank 1 is showing extremely lean. Bank 2 is pretty much normal. I'm fairly positive it is a vacuum leak of some sort on bank 1 somewhere, but I'm not quite sure where it could be. I sprayed carb cleaner all around the intake everywhere I could to see if I could locate the leak that way, but no such luck. Any advice would be greatly appreciated. Thanks!


-Sean

 

[stutaeng]

You can spray a bit of carb cleaner in the inlet tube and look at your fuel trims on bank 1. If the O2 sensors are working correctly you will see some activity on your graph.

It could be an O2 under-reporting and that's a good way to check. If you see no activity after spraying the carb cleaner it's the O2 sensor.

You don't have lean codes? P0171? What is the fuel trims % on bank 1?

 

[scons96]

You can spray a bit of carb cleaner in the inlet tube and look at your fuel trims on bank 1. If the O2 sensors are working correctly you will see some activity on your graph.

It could be an O2 under-reporting and that's a good way to check. If you see no activity after spraying the carb cleaner it's the O2 sensor.

You don't have lean codes? P0171? What is the fuel trims % on bank 1?

There are no codes for anything. Not even pending codes, that's the frustrating part. Bank 1 fuel trim was hovering between +30% and +50%

 

[stutaeng]

There are no codes for anything. Not even pending codes, that's the frustrating part. Bank 1 fuel trim was hovering between +30% and +50%

Is your CEL light bulb burnt out? But no code? Um, that's strange?!

15% fuel trims or more triggers CEL light is what I understood... didn't even know it went to 50%!?

 

[stutaeng]

If O2 data seem right, I'd do an injector balance test. Doesn't say you have tested them or have been replaced? 1,3,5,7 are bank 1, I think?

Maybe one one of those is
faulty and is is not pulsing? That's why bank 1 is lean?

 

[81nascar]

I've got one of those motors.. in my 98 GMC... I think before anything you really need to go recheck all of your work including the intake ,cap and wires along with injector wires etc... If it was fine before, then that is logical approach. Propane works pretty good for vac leaks. I had that starting issue as well. Ended up being the pressure regulator, Though I have seen leaking injectors cause that as well. They just bleed off as it sits.

 

[Schurkey]

Any misfire results in false "lean" indication.

When it was my '97 L29, it was a cracked spark plug porcelain.

 

[scons96]

Well I guess what I'm going to do first is go back and double check all my work which will probably mean taking the upper intake back off so I can have a look at the cap and rotor again. I did plugs and wires when I first got the truck in September so I'm not worried about those. Thanks for the suggestions fellas!

 

[454cid]

Make sure you use a good cap, like an ACDelco.

 

[81nascar]

If you take the intake off again do yourself a favor and grind that casting line on the back of the upper intake flush. That little bit makes all the difference and It makes it much easier to get to the cap and distributor with the intake on...