Hey folks, long time no see for alot of ya. Got a problem with my DD that I need a little help with. Its a 2002 Silverado 1500 5.3L for those unaware.

So for about a year almost now Ive been chasing an issue with 2 engine codes, P0171 and P0174. Both are system too lean for the left and right banks and they only crop up under WOT above 4000rpm and you can hear the engine tick or ping when it does it.

I have troubleshot the issue a bit and have nearly replaced the ENTIRE fuel system. I started with the fuel filter, then the fuel pump, followed by new injectors (well new to me, they came off a wrecked 2004 escalade with only 52k on the clock) and new intake manifold gaskets (which i torqued down right this time), and finally today i replaced the fuel pressure regulator. I even borrowed the MAF from my father's 07 silverado classic (because i was told it could be the MAF) since its the same part and i still have the same issue.

I've gone though just about every possible thing I can think of and the issue still remains. I don't want to take it to a dealer but I'm dead out of ideas. The only other things I think it could be are a vacuum leak somewhere or the vent tube the the PCV valve. If its vacuum im not sure how to really test that though from a visual inspection, everything I can see looks to be in good shape (no worn or damaged hoses anywhere that Ive been able to locate). Now the PCV tube did crack in half at one time and when it did the engine ran terrible so I repaired it by connecting the two pieces with a bit of 3/8"id braided tubing, which helped but the engine does have a very tiny stumble that comes up once in a while which im thinking might becoming more pronounced at higher rev's maybe.

Anyway this is where I am, I'm stuck and I'm hoping any of you can help.

 

Are there any exhaust leaks? These engines are known for broken exhaust manifold bolts that can allow outside air into the exhaust, throwing off the O2 sensor readings which can cause a lean code to be triggered.

 

I would also inspect the flextube that connects your MAF to your throttlebody. Ive seen them crack on older vehicles, however, not on a 2000+ vehicle yet... But it could happen. Most times I have dealt with lean on both banks, its because there is a vacuum leak somewhere between the MAF and the cylinders. Could be a leak at the PCV, or where the upper and lower intakes mate, or where the TB mounts on the intake, the bushings on the throttle plates pin, or the gaskets where any sensors plug into the intake, or even a cracked plastic intake..? Its a minor leak, and thats why it only shows up under high vacuum situations.

You can usually get an upper intake gasket set and go change them all, maybe the old gaskets are cracked or pinched, or swelled with oil and causing a vacuum leak.

When you take it apart, you will be able to see the soot where the rubber gaskets should be clean. You can check for cracks in the plastic intake with solvent, it loves to sneak through small cracks easy. So wet a rag and wet down one side of the intake, and check in 5 min too see if the wetness came through to the other side. Also check in the grooves that the gasket sit in for little bits of plastic from the casting that may be interfering with the mating of the surfaces.

 

If you do end up pulling off the intake plenum, check/clean your knock sensors. If there is corrosion down there, replace the knock sensors and the harness!

 

I had both knock sensors go out and it did not effect anything.

 

I'm not saying they are affecting his current condition, just that while he's in there, it is very easy to inspect things and correct any potential problems that may exist.

 

Funny enough what started this whole thing was I had the intake manifold off to replace both knock sensors since one went to hell and i figured i might as well replace both. I even RTV sealed the the plugs in place to keep the water out since the one that went bad was practically floating in water. But about 2 weeks after replacing them the codes came up and it started the whole knocking/pinging thing.

Ill check the exhaust manifold bolts to be sure. Its reading the issue on both banks so its not likely but hell i'll check anything at this point. Another ironic point, i did have to replace one of the O2 sensors about 2 months back since it threw a code for that as well (i think it was the downstream passenger side one but i can remember right off hand).

I had heard that the issue could be caused by more air getting in than out so i do suspect the intake a little bit. Ill try the wet rag trick and see what happens. If its that simple I'll put a new cold air intake on tomorrow (justified expense, am I right )


EDIT: Just remembered my dad's 07 silverado classic has the same intake tube as my truck so i borrowed his just now and did a WOT drive up the road.....no change. So i guess no early Christmas CAI gift for me, LOL.

Based on reading Ohsofly's suggestions again I really think its the PCV valve and tube so I'm going to give that a go. I would borrow the one off the 07 but its actually shaped differently on that truck.....go figure.

 

Ok, after some searching, its impossible to find a factory formed PCV tube. Oreilly and Autozone dont carry it (at least the websites dont)....and im afraid to ask what the dealership wants to overcharge. Any ideas on where i can get a new tube or if a generic bit of tubing would work?

 

I have found my local dealership to be pretty good on pricing for parts like this. Wouldn't hurt anything to ask.

Other than that, you could probably get some metal tubing and bend it appropriately then use some rubber hose to couple it up at the ends.

 

Hmm, didnt think of the metal tubing, but not a bad idea. I did take your advise though and asked the dealership down the road what they would charge. Surprisingly it was alot less than i thought. Only $23.04 after tax and it came with the tube, the heat shielding foam already installed, a new pcv valve installed and the bit of rubber tube that connects to the intake manifold.

So i changed that out and ran the truck. Its running smoother but its still having an issue so I'm thinking there has to be a vacuum leak somewhere else or the manifold might be cracked (god i hope not). I've been told there are tools to test for vacuum leaks so I'll look into getting one of those and troubleshooting there next. If that doesn't pan out then I'll wait till after the first of the year and take it in to the shop.