today i after 5 hour's of smoke test for intake manifold and fuel pressure test map test maf test and PCV test and i think i found why my car runs lean i have found a crack in exhaust manifold its about 3cm chick this picture out



your help is most appreciated please advice me does the crack through the lean code P0171?

 

do i have to wild it is it possible ? or i replace it by new one thanks in advance.

 

Do you recall looking at my other post I linked for you about 0171 codes?

Let's refresh:
"For the H3 a code P0171 may mean that one or more of the following has happened:

There could be a vacuum leak downstream of the MAF sensor, a possible cracked vacuum or PCV line/connection;

The MAF Sensor is dirty or faulty,
[The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.];

Failed or faulty oxygen sensor (bank 1 since I5s only have one, sensor 1=upstream);

Sticking/plugged or failed fuel injector;
Low fuel pressure (pump going bad);and,
Exhaust leak between engine and the upstream oxygen sensor (I5s are known to break exhaust manifold bolts)."

Notice the bold print last item?

That crack is likely a cause for the CEL, but it doesn't explain why you said the truck runs poorly at RPM.

Cast manifolds can be welded, but the larger the crack the more difficult. Since full fusion penetration in welding thick cast material is not going to occur (it could be done through a certain process but this is not a welding metals forum and I am not going there), the downside is any weld will likely fail over time, especially with the vibrations the I5 puts out.

I can weld, but if it were mine, i would look for an aftermarket replacement, like MagnaFlow and others.

 

it was HO2S sensor for poor performance after the change its much better now

yes i did read the pages about 0171 codes do the same test for vacum test maf test by tech 2 map test by tech 2 and the the last inspection was exhaust manifold and i found the crack that's why i ask
great info thanks i will change and update the car info after the change

 

new exhaust manifold

 

I just started to get this code and think it could be two things, one I removed the PCV line to this intake and just put a small filter.


Or maybe somewhere under this mess there is a crack in it.

 

Curious as to why you put a small filter there? The air flow is going out there. They have a little kit at autozone that comes with a drill bit and a couple of little fittings you can plumb into your cross pipe and run 1/2" heater hose.

You know the rule; undo what you just did and see what it does

 

Well my thinking behind this is that the PCV valve is made to send all the built up blowby emission and oil vapor back into the intake system and to be burn out in the cylinder. If i just install a filter over the PCV valve it pretty much doing the same thing and I wouldn't have to drill into the intake and run a line into it. But you do have a point Widespread Hummer.

 

I can assure you the lack of vacuum in the secondary PVC line (the one you put the filter on that is supposed to be tied to the intake) is causing your CEL, it basically reads like a leak.

BTW: There are two PVCs, the primary goes into the intake manifold from the other valve cover and handles about 70% of the load, the secondary kicks in at heavy throttle to WOT.