lean condition worse under load?

B6/7 S4/RS4
#1

Hi everyone. I’m hoping to get some help tracking down a lean condition. I believe it’s a vacuum leak, most likely caused by this little divot in the head right by the #3 intake port in this picture:

http://audirevolution.net/addons/albums/images/276529851.jpg

I caused that when I was struggling to get the IM back on and accidentally dropped it, and a corner landed right in that spot and made the dent. It is fairly small, but it goes all the way across and I think the photo makes it look smaller than it is. I’ve tried confirming that this is the source of the vacuum leak by spraying propane under the IM on that bank while watching the fuel trims in VCDS. It’s kind of hard to do since I don’t have direct access to that side of the intake ports, but if I spray under the manifold, regardless of whether I’m spraying from the front or from the back, I can see the fuel trims for both banks going down to adjust for the extra fuel. I’ve already re-checked all of the IM bolts and none of them are loose.

To give some background info, I pulled the engine and did the timing job not long ago. Before I reinstalled the IM, I put a small dab of permatex #2 non-hardening sealer over that dent, and then used a new set of aftermarket (paper) IM gaskets. It seemed to be running perfect for at least 2k miles after that. I didn’t check fuel trims at that time and I can’t say I fully trust my butt dyno, but I wasn’t getting any cels at all and the power seemed fine.

The thing that seems weird to me, is that everything I’ve read online says that a vacuum leak should be more lean at idle, and less lean under load. For the long term fuel trims VCDS is telling me that adaptation (idle) is about 7% and adaptation (partial) is about 15%. If I understand those numbers correctly, that means that my engine is going more lean under higher load/rpm, which points to a fueling issue instead of a vacuum leak. Is that correct?

another possible issue I have is that my fuel pump makes a juddering noise which I have heard is fairly common. Shortly before I did the timing, I replaced the fuel pump and filter with brand new genuine parts but it still continued to make that juddering noise, although it only happens on startup and goes away after driving a 1/4 mile or so. I’ve seen a lot of conjecture over on audizine about this juddering noise possibly being a sign of a failing pump, but nothing definitive. It would be odd if this pump is the cause since it’s new.

soooo… sorry this is post got so long btw but can anyone more knowledgeable help me out here? Is it possible that this is just a vacuum leak even though it gets more lean under load?

these are the codes I’m getting:

17536 - Fuel Trim; Bank 1 (Mult)
P1128 - 001 - System too Lean - Intermittent - MIL ON
17538 - Fuel Trim; Bank 2 (Mult)
P1130 - 001 - System too Lean - MIL ON
16891 - Idle Control System RPM
P0507 - 001 - Higher than Expected. - Intermittent
17544 - Fuel Trim: Bank 1 (Add)
P1136 - 001 - System too Lean - MIL ON
17546 - Fuel Trim: Bank 2 (Add)
P1138 - 001 - System too Lean - Intermittent
18359 - Radiator Fan 2 (V177)
P1951 - 001 - Movement Restricted / Jammed - Intermittent

TY in advance for any assistance!

#2

A few things. As you have already figgured out AZ is not really full of super helpful people any more.

To start. Your car has a lean code on both the driver and passenger side. So that would probably make the thought that its the one side bump not stand up.

If you dropped your intake manifold I and your getting a change in fuel adaption when adding propane to the surounding air it might be a cracked intke manifold. That would cause issues.

If its a lean at part load or wot it can still be a vac leak. 15% lean at part throttle is correcting a lot. and if its on both banks it could be an issue with the fuel pump or even the fuel filter as the fuel filter has the fuel pressure regulator in it. I would try hooking up a fuel pressure line and gauge in just before the fuel rail and watch that. That will tell you a lot right there. Its not hard to do and it would be a good thing to look into

#3

Thanks for the help, Justin. I gotta get ahold of a fuel pressure tester and I’ll check on that next.

as far as dropping the IM, it didn’t drop far at all so I doubt it hit hard enough to crack anything but I’ll keep that possibility in mind. I was trying to get it into position and there was a hose or something in the way, so I was holding it just like maybe 6 inches above the head with one hand while trying to move those hoses out of the way with the other hand when I dropped it, so again it only fell a few inches but it was at an angle and the corner hit right there where there’s a small dent. probably nbd, I hope. I can also post a few logs I made of my maf readings and fuel trims if those will tell you more

#4

Oh and I follow you on the thought that the leak I suspected probably wouldn’t cause both banks to go lean. My thinking was if that cylinder is sucking in a lot of unmetered air, then maybe all the other cylinders would be getting more of the metered air than the ecu is expecting, resulting in all of them showing lean. But I didn’t know if that reasoning was sound or not.

#5

No its not going to have that effect.

Not to say you couldnt have an issue on the one side and from what you said you didnt really drop the intake manifold that far but when both banks are effected like this its always good to look over the intake manifold really well.

#6

I haven’t tested the fuel pressure yet but today I decided to loosen all of the IM bolts and re-torque them, even though they weren’t loose, just in case. In doing so I noticed a crack in the small vac hose that runs along the side of the IM, which was surprising since I replaced all of that hose fairly recently but I got that fixed (I just used a rubber hose as a sleeve to patch it as a temporary fix for now, I’ll have to order some of the oem stuff to replace it with). Doing that definitely fixed my shitty throttle response so I could shift a lot better, so then it felt like there was no vacuum leak anymore by the way it was driving, but my fuel trims were still bad. The went down a little bit but they’re still out of spec.

one thing I noticed after fixing this vacuum leak, is that when I would come to a stop and idle for a bit the fuel trims would seem to be perfect - the short term fuel trims in block 33 were roughly the same number as the long term idle fuel trim in block 32, except negative instead of positive so they were basically cancelling each other out. I could tell the engine sounded better at that point, as well. But after sitting at idle for a minute or two, the short term trims started going more and more positive. Then if I revved it a little bit and let it go back to idle, it would go back to running perfectly for a bit with negative short term trims cancelling out the long term, but then after sitting for another minute or two it would again start to go more and more positive/lean, even going above +20 with the short and long term combined. I reset the long term trims by clearing the codes and then it ran like shit, then I tried to unplug the maf and it still ran like shit.

Can you determine anything by the way it was idling fine after revving it up, but then going more lean after idling for a bit? I’m hoping that’s a clue, maybe indicative of a specific problem like failing o2’s or exhaust leak or fuel pressure?

#7

I should add that I also had a couple new codes pop up, which are:
16497 - Intake Air Temp. Sensor (G42)
P0113 - 002 - Signal too High - Intermittent
16486 - Mass Air Flow Sensor (G70)
P0102 - 002 - Signal too Low - Intermittent

I assume this is just because I ran it with the maf unplugged?

#8

The maf codes were going to more than likely be from unpluggiing the maf. It would be something to look into and to make sure they dont come back If you have a bad maf that can cause some issues as well.

It might not be a bad idea to unplug the maf and see what the fuel trims do. As at that point the car will be just running off the 02s and not getting any intake air feedback.

From the one post you said when you put propane around the intake the fuel trims moved. I would look deeper into to vac line siuation. There might be another crack or something off. Its a good test to do again now that you found that bad line. If the intake is on the car and bolted down you shouldnt be getting any chance in fuel trims by putting propane around the intake.

#9

Well I finally tested the fuel pressure and it’s fine. It was steady at 58 psi while running, dropped to 52 when I shut it off and 10 minutes later it was still in the 40’s so it passed the specs. my tester doesn’t have a valve to shut off one side like it says to do in the manual, but that just means it was testing for leakage on both sides at the same time and still stayed within specs. I’m thinking my issue probably is another vacuum leak and I just suck at finding them. I’ll probably go ahead and replace all of the small tubing again with stuff I can get locally, even though it didn’t last long, so at least I will know right away if that’s the issue. then if that’s not it I’m gonna have to make a smoke machine cuz I’m not having any luck using propane, the engine bay is just too cramped for that i guess.

regarding the issue with the damaged mating surface on the head that I posted the picture of earlier - even if that’s not my issue, I was meaning to ask if you think my solution would work or if you can suggest a better way to handle that (other than removing the head and taking it to a machine shop)? Would you expect a little RTV to work, placed between that damaged spot and the gasket? or would it maybe work better to fill it in with a little jb weld and smooth it down perfectly flat? that spot is just dented in a little btw, it doesn’t stick out

#10

Unless your looseing fuel pressure in the upper rpm range and thats causing the lean code I dont think you have too much to worry about.

The vac leak is going to be the bigger possibility. And a leak can come from any of the lines or even the PCV system. Check to make sure anything after the MAF is not leaking or letting in air.

The spot on the head I cant make out anything there that would cause a leak or even an issue. If your worried and want to use a little extra RTV thats fine just dont use too much the intake gasket has a small seal serface to prevent leaks.

Check all the vac ports on the intake as well.

#11

how can I test the pcv valve? It was replaced with a genuine audi part relatively recently so it should be ok but it would definitely be good to test it. and ya that isn’t a very good picture, the indentation isn’t that far either but I wasn’t sure how big it would have to be for the gasket to not seal, I assumed it had to be pretty much completely flat. Now that I have all the hard plastic lines replaced I’m noticing a whooshing sound from the front of the manifold, not sure if I’m just hearing a normal sound of air moving through it or if I’m hearing a leak. It’s hard to hear anything like that since the engine is so loud. All the hoses that I can see without removing the manifold look good but I’m going to look closer around that area next

#12

well I think I just found it. Hopefully this is the last issue. I just found a broken vacuum tee in the front of the manifold, way down low where it was almost impossible to see it. one of the lines for it connects to the black electrical thing on the front of the manifold (is that the solenoid for the flaps?). To get to that I’m gonna have to put it back in service position again, I guess. sigh… I’ll let you know if that fixes it once I get it done

#13

sorry to keep making so many posts in a row, but I have a small update to what I last wrote. Someday I’ll be able to edit, some day…

So I was able to get access to the top tee and remove the hose which was going from it to the broken tee, and I capped off that spot where it connected to the top tee. I don’t think the bottom tee is going to be accessible without removing manifold and/or putting the car in service position. I’m not sure what else that tee goes to besides the black thing I mentioned, not sure if it it still leaking vacuum from there or not. Anyways, capping off that top tee definitely make a huuuge improvement in the way it runs, but the fuel trims are still too high so I’m not sure if there’s another problem of if it’s just that broken part

#14

Keep posting you get lots of member improvements after 150. It might take that many posts to get to the bottom of whats all going on.

I think I know what your talking about but feel free to take a few pictures of the parts your talking about. That way we can atleast let you know what your dealing with and what lines go where. It might help let you know if there are any other places to look for.

#15

The part circled is where it broke. The other tee, up and to the right of it, is now capped off so it isn’t leaking but the broken one is still open. Looks like it goes to the intake flap solenoid and the egr solenoid.

http://audirevolution.net/addons/albums/images/706337632.jpg

I’m gonna try to squeeze in and unbolt the egr solenoid, and hopefully that’ll give me enough access to replace that broken piece

#16

That part of the line from what I can see and what it looked like on my car is a vac source so your going to want to have that working. It supplys vacuum and your going to need that.

#17

well it was a tight squeeze but I managed to get all that stuff pulled off the front of the manifold without putting it into service position, afterall. I ended up replacing all of the vac hoses and connectors, except I originally left one of the stock hoses on. They were all basic hollow pieces except for the small hose that connects to the vacuum pod for the flap, it had something inside it. I’m not sure what it is but it looks like maybe it’s some sort of one-way valve or something like that. It doesn’t seem to be letting any air flow through the hose, though - I can’t blow through it at all from either side. Anyways I assumed it was some sort of special hose and that this stoppage, whatever it is, was supposed to be there so I originally left that hose in place. Then when I started up my engine I noticed that my IM flapper still wasn’t working, so I decided to try and replace that hose with a regular hollow piece of vacuum tube and after doing that my flapper started to work. I’ll post a picture of what the inside of the original hose looked like and hopefully someone can tell me if it’s supposed to be a special hose with something inside of it or if I just have some foreign object jammed into mine for some odd reason.

#18

http://audirevolution.net/addons/albums/images/701228015.jpg

http://audirevolution.net/addons/albums/images/229371881.jpg

here’s the hose I was talking about, is it supposed to be like this? if so, is it going to be a problem to have a regular hose on there?

#19

and btw, getting back to the original topic of this thread, that definitely seemed to be the last of my vacuum leaks. My adaptation(idle) fuel trims are now at +0.6% for bank 1 and -0.8% for bank 2. But the adaptation(partial) trim is at +18.0/bank 1 and +18.8/bank 2. Another thing I’ve been noticing but haven’t mentioned on here is a slight knocking noise that I sometimes hear at idle. It’s not always there so I’m hoping that means it’s not a rod or something really bad like that, I assumed it was just pinging or something like that either because of running lean or because of my knock sensor wiring (another issue I’ll probably post a thread about at some point but not gonna get into that right now) but I didn’t mention it yet because I know I’m already posting a lot and I figure one thing at a time. Well I looked up some videos on youtube last night to find out what an exhaust leak sounds like and now I’m pretty sure that was the knocking sound I was noticing, and I think that would explain the partial fuel trims as well. It’s a little odd that both banks are effected by the same amount but maybe I made the same mistake on both sides, I did follow the proper torque specs and used a new manifold gasket but idk… So my next plan of action is to make a diy smoke tester so I can figure out whether it’s leaking from the manifold-header connections or from the manifold-downpipe connections.

#20

Well none of the hoses should be clogged like that. you have check valves in place to make sure air flow only goes in one direction. So that hose needed to get replaced I cant even think what that might have been in the hose but you changed it and thats good.

As for the hoses all being replaced and the idle being bettter now fuel trim wise. That makes sense. Still if your part throttle fuel trims are that far off you still have a nice size leak somewhere. If you want to post video of what the knocking sounds like we can listen and maybe suggest what it might be.

If the exhaust is really leaking a good amount of air it can cause some lean issues past the 02s. So looking in to that is a good idea. If fixing the exhaust still dosent fix it getting the car smoke tested would be a good idea.

So far tho it looks like your doing a great job