New guy with a problem

[Whitedog]

Greetings and salutations to all here. I have been searching to solve a problem on a van and you guys seem to have a lot of information here.

Van is a 2003 Chevy 210000 miles 6 liter engine. Van was running rough at low idle so I did a tune-up on it and no change. I cleaned the idle air control valve and changed the fuel filter. I change the mass airflow sensor with no change. I read codes and had a code for gross vacuum leak and found the evap canister was broken underneath. I replaced that and no change. Also had codes for both Banks running lean and when its running rough it is running very rich. You can smell it in the exhaust in the side of the van is actually covered in soot. He doesn't run rough all the time just most of the time.

Searching here I found I should check the intake gaskets, EGR valve, the throttle body and fuel pressure. To check the intake gaskets I think I can spray water at the base of the intake while running to see if things change. Does this sound right? I may have clean the throttle body but I do remember it's been awhile. But I will check that anyway next chance I get. I also have a fuel pressure gauge to check fuel pressure. I have also heard about the fuel pressure regulator so I can pull the vacuum line off of that to check for fuel there correct? The EGR valve I don't know how to check other than pulling it apart and looking.

So what else does that leave me? The spark plugs were Platinum plugs with new wires.

Before I changed the evap canister the long term fuel trims were maxed out, but afterwards they were OK until I revved it and then one went to 22. O2 sensors were e okay but not great in my opinion but I'm not good at judging that. The front O2 sensors would cycle up and down but not consistently and smoothly but each cycled just like a mirror of the other. That is something I can check again with my torque app. Something I just thought of is if it's running rich at the exhaust pipe how can the O2 sensors be saying that it's running lean? The three codes were P0455 for the gross leak, P0171 Bank 1 lean and p0174 for bank 2 lean.

What else do we need to know to help get the van running right again? Thank you for your time helping me with this problem.

[BR3W CITY]

This is your first post, and your chasing all sorts of different things. Take a breath for a second, and lets actually pinpoint and identify whats going on.

When you searched and found those items to check, did you then search those things to find out what actually needed to be done? Might seem overly simplified when I state it like that, but following up on that search (with terms like "checking fuel pressure", or "finding vacuum leaks") would have already got you to some of the info you need.
Don't get me wrong, we're happy to help...but with so much info being tossed in one post, you gotta follow up on some of your own leads/research.

Do not spray water on your intake gaskets, you're thinking of the soapy water on air leaks thing for tires etc.

Carb cleaner/starting fluid/ether can be used on the intake sparingly. An intake leak is vacuum, so it will suck in the combustible fluid and cause a small surge in idle.

Pull the vac line off of the FPR and see if it changes. If not, or you can't tell, put the gauge on it. Less than 55-60 (ideal 58) will not work unless its an flex fuel truck.

If its DBC, make sure the throttle body isn't caked with crap, and that it opens and closes normally with getting hung up. Also make sure no ones' drilled out the little air bleed hole.

Here's how a lean code runs rich; you need to consider the way the system feedback cycle works.
A vacuum leak causes air to enter the system AFTER both the MAF and the throttle body. That air is unmetered and not the result of the TPS change, so the computer isn't expecting it.
That "extra" air mixes with the existing fuel charge (what the computer is expecting for fuel), resulting in a leaner mixture than is called for in the VE tables.
The 02's see the lean mix and try to fatten the burn with extra fuel.
Back up on the intake, the MAF and TPS, STILL don't see the change because the air is entering after them in the system.
System now is running with the extra fuel to try and compensate for the unmeasured air, but it doesn't have said measurments, so it ballparks over-rich to comp.
Now you have too much fuel in the mixture, but sensors still seeing the mixture as lean because of the air. Hence, black pipes, but lean codes.

Its also worth checking that you don't have one or more massive exhaust leaks before the 02's.

[Whitedog]

Thanks for the reply. Right now my biggest problem is I can't get to the van until Monday so I can test these things. I have been searching and searching and I can't find anything about the EGR valve. Right now I think the order of March needs to be first check for exhaust leaks because that is easy. Next hook up fuel pressure gauge and check fuel pressure. Then check the fuel pressure regulator. Next check the throttle body, then check for intake gasket leaks.

Does that sound about right?

We also need to look at fuel trims and O2 sensors again.

[Whitedog]

I have seen people find vacuum leaks using water so I know that it works, but after reading your post again, I remembered something. Sometimes, the change in engine is difficult to notice, so watching the O2 sensors when using ether will show that it's being sucked in and burned because the front sensor will go rich. I don't know what water would do to the O2 reading.

[BR3W CITY]

Water will lean it out, thats why you want to use something combustible. You never want to induce a lean condition when troubleshooting, because you can create knock (showing up as Kr* in a scanner).

[Whitedog]

Originally Posted by BR3W CITY

Water will lean it out, thats why you want to use something combustible. You never want to induce a lean condition when troubleshooting, because you can create knock (showing up as Kr* in a scanner).

Ah. That's good info. thank you for that.

I drove it today and STFTs stay right at zero. LTFTs are around 10. Front O2s are all over the place, rear O2s may stay steady or they may fluctuate with 2/2 more likely to stay steady. (By steady, I mean it moves a bit, not flat lined)

[Whitedog]

Couldn't find a definitive vac leak, fuel pressure I didnt check because it runs great off of idle and at WOT.

So I threw an IAC at it. My thinking was that it runs great off idle and WOT, there isn't a vac leak, O2s respond as they should to ether, and it has a new MAF. I skipped the EGR valve because I'm lazy and the IAC was only $65.

It has been running great, so we will see what happens. Thanks again.