96 Chevy 3500 5.7 Bank 2 Lean P0174

[Jbarry14]

1996 Chevy K3500 5.7L. I am getting a code for only bank 2 being lean. Originally, I was getting codes for both bank 1 and bank 2 being lean. I had low fuel pressure too. I replaced the fuel pump, and fuel filter. I also replaced the O2 sensors and cleaned the MAF sensor. When the truck is idling and I unplug the MAF sensor wiring, the truck kills. I get mixed answers with people saying that should not happen and others saying that is normal. The live data of the MAF sensor looks to be in spec at idle. After cleaning and replacing those parts, It seemed to be ok for a couple days. Then the check engine light came back on. The truck runs a little rough and the idle is off. Now I am only getting the code for bank 2 being lean. The LTFT for bank 2 is at 25%. When I had the fuel pump replaced, the shop put a camera down the intake and saw that my FPR was working perfectly. They also told me the injectors have been replaced and updated to the new style. I am thinking I might have a vacuum leak somewhere. I am hoping I do not have an intake gasket leak. I did inspect the air intake piping and that all looks good. I sprayed carb cleaner around those areas with the truck running and I did not get any idle change. Where else could I look or what else could I start troubleshooting?

 

[Brian Shanahan]

1996 Chevy K3500 5.7L. I am getting a code for only bank 2 being lean. Originally, I was getting codes for both bank 1 and bank 2 being lean. I had low fuel pressure too. I replaced the fuel pump, and fuel filter. I also replaced the O2 sensors and cleaned the MAF sensor. When the truck is idling and I unplug the MAF sensor wiring, the truck kills. I get mixed answers with people saying that should not happen and others saying that is normal. The live data of the MAF sensor looks to be in spec at idle. After cleaning and replacing those parts, It seemed to be ok for a couple days. Then the check engine light came back on. The truck runs a little rough and the idle is off. Now I am only getting the code for bank 2 being lean. The LTFT for bank 2 is at 25%. When I had the fuel pump replaced, the shop put a camera down the intake and saw that my FPR was working perfectly. They also told me the injectors have been replaced and updated to the new style. I am thinking I might have a vacuum leak somewhere. I am hoping I do not have an intake gasket leak. I did inspect the air intake piping and that all looks good. I sprayed carb cleaner around those areas with the truck running and I did not get any idle change. Where else could I look or what else could I start troubleshooting?

I would expect the intake gasket to have a leak in that bank. A quick way to check is to spray around the intake base with carb cleaner while running. Another check I would recommend is the o2 sensors on that bank. They can get clogged up and give an incorrect reading. I personally upgraded my fuel injection to the multiport system for just under $400. The difference is night and day and it also comes with a new pressure regulator on the system. If the popets n the spider system get dirty at all they can and will fail.

 

[Schurkey]

Use the scan tool to check the misfire counts. I bet you find a cylinder on Bank 2 that isn't running right.

Rough idle, lean codes go hand-in-hand with misfire. Mind you there's other things that can cause those problems, but misfire is likely.

You should be able to check (larger) vacuum leaks indirectly by looking at idle speed vs. IAC position. If the idle speed is normal or high, and the IAC is nearly closed...the combustion air is coming from somewhere it shouldn't be.

You replaced the fuel pump and filter. What is the fuel pressure now? A new pump that's connected to faulty wiring can still produce low pressure.

 

[Jbarry14]

Use the scan tool to check the misfire counts. I bet you find a cylinder on Bank 2 that isn't running right.

Rough idle, lean codes go hand-in-hand with misfire. Mind you there's other things that can cause those problems, but misfire is likely.

You should be able to check (larger) vacuum leaks indirectly by looking at idle speed vs. IAC position. If the idle speed is normal or high, and the IAC is nearly closed...the combustion air is coming from somewhere it shouldn't be.

You replaced the fuel pump and filter. What is the fuel pressure now? A new pump that's connected to faulty wiring can still produce low pressure.

From what I was told by the shop who is doing the smoke test for me, there are no misfire codes. That same shop also replaced the fuel pump and fuel filter and they inspected everything including the wiring. Pressure is at spec now and no pressure leaks down like before. Pump was bad and had a bad check valve. I am going to assume I have a intake gasket leak on that bank causing the lean code. Pretty much everything else that could cause the lean code has been replaced.
MAF sensor cleaned and functioning properly
MAP sensor working properly
O2 sensors replaced
Fuel Pump and Fuel Filter replaced
Previous owner replaced FPR and injectors with new style and were just inspected and working perfectly
Plugs and wires replaced recently

I should know in a few hours if I have a vacuum leak.