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Does anyone know what can cause a lean code to trip? I filled up with a tank of 93 the other week and the car threw a lean code. Engine sounds healthy and the turbo is putting out around 19-21 psi of boost on the current tune. Car does not idle rough. I reset the code and it hasent come back. All I/M monitors have gone to a ready state. I had the same code trip about 1 year ago and when I reset the check engine light it did not come back for some time. I'm thinking maybe a bad tank of gas was the problem. The only other possibility I can think of is maybe an intake leak.
 

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Does anyone know what can cause a lean code to trip? I filled up with a tank of 93 the other week and the car threw a lean code. Engine sounds healthy and the turbo is putting out around 19-21 psi of boost on the current tune. Car does not idle rough. I reset the code and it hasent come back. All I/M monitors have gone to a ready state. I had the same code trip about 1 year ago and when I reset the check engine light it did not come back for some time. I'm thinking maybe a bad tank of gas was the problem. The only other possibility I can think of is maybe an intake leak.
According to this video a fuel quality issue is a good possibility.


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Hello All,

I was hoping I might get some input on a little issue that has popped up with my car. I tend to be over-verbose, so I'll try to keep concise...

2018 Mustang Ecoboost base model (100A...no options), M/T
34k miles on the odometer currently
Completely stock except for:
K&N Re-usable Air Filter
SP-542 spark plugs

About 4 weeks ago, my girlfriend mentioned that she smelled "gas or something" while sitting in the passenger seat while I took her to work. I didn't smell anything at the time, but I also have a markedly ineffective nose...I tend to not smell things as easily as others--which is both a blessing and a curse. Anyway...fast-forward to a week or so later, and I noticed (while idling in the driveway and waiting for the car to warm up a bit) what seemed to be a fairly strong exhaust-like smell (while in the cabin).

Now....since then, I have noticed this happen several times. If I switch the AC so that it recirculates the cabin air, it seems that the smell goes away. It is much more noticeable when the Air Recirculation is OFF, and I'm at a stop and idling. This caused me to suspect an exhaust leak. As of last week, though, I hadn't gotten any codes yet.

Then...this morning while on my way to work...I went WOT for a few seconds in 4th gear while passing an 18-Wheeler and--about 2 or 3 seconds after letting off the gas, my CHECK ENGINE light came on. Note that I did not hear any strange noises or notice anything else amiss. The car seemed (and still does) to be pulling strong and everything seems to be working just fine. Once I got to work, I scanned for trouble codes with Torque Pro and got a P0171 (LEAN CONDITION BANK ONE).

After googling/researching a bit, most of the info I was seeing seemed to suggest un-metered air entering the system somewhere around the intake...but I didn't see anything mentioning a possible exhaust leak. I did check my hoses and everything SEEMS to be tight.

I decided to take the car back out for a few minutes just to drive around and see if I noticed anything else off. I did a little driving on and off the freeway, at various speeds and gears, and didn't notice anything weird, but--after I stopped and got gas--I scanned again and now (in addition to the P0171) it was showing a "pending fault" for "Misfire On One Or More Cylinders" (I apologize, I didn't write down what the actual code was and don't have it in front of me now).

I drove back to work, worked for a couple of hours, and just drove the car again about 2 miles down the road to the Post Office, scanned again--and now I am only showing the P0171 code (not the "pending" fault for misfires). I did not clear any of the codes, so that seems weird to me (maybe something to do with it being a "pending" fault..?)


All of that said...

1. Is there a chance this could be due to an exhaust leak (as opposed to something being loose in the intake)?
2. Do you think it is safe to drive the car like this for another two days? (I have no way of dropping the car off at the dealership before then)
3. Is there anything else that I maybe should check myself, that I'm not thinking of?
4. Related to the exhaust leak question...is there a way to check for an exhaust leak myself? I got advice from someone who recommended plugging a shop-vac with blower capability to the exhaust pipe, and coating my exaust w/ soapy water, and then turning on the blower and checking for bubbles. No idea if that is genius or idiotic.


Any and all advice welcome; Thanks much!!!!

MJ
 

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Any and all advice welcome; Thanks much!!!!

MJ

I also forgot to mention--and this is probably relevant--that a couple of weeks before all this started, I ran over a concrete median-type thing that was in front of my parking space (not realizing it was there) and bottomed out the car. At that time, I didn't see any obvious damage to the hard parts of the car, but a couple of the plastic bolts that holds on the plastic shield had broken and the shield was hanging a bit loose in the middle.


I'm thinking a might have broken/knocked something loose and that might be causing my theoretical exhaust leak (if that would even cause a P0171 code....).

Thanks!

MJ
 

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A lean fuel condition may exist if the engine is sucking in too much air and/or the fuel system is not delivering enough fuel. If bad enough, a lean fuel condition may cause lean misfire, a rough idle, hesitation or stumble when accelerating, and/or poor engine performance.

Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow (because the EGR differential pressure sensor that monitors EGR flow is faulty and is under-reporting EGR flow).
If the problem is not enough fuel, the underling cause may be a weak fuel pump, restricted fuel filter, leaky fuel pressure regulator or dirty fuel injectors.
 

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Check your hot and cold side pipes from inter cooler. You mentioned that you went over a concrete barrier, which might have caused one of the pipes to the intercooler to come loose. Keep us posted.
 

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As others stated check your charge pipes, intake connection to the turbo, and one other thing that can get overlooked. I have heard of some owners having the stock downpipe "donut" to start to have an exhaust leak and can cause air to be sucked into the downpipe, the o2 sensor sees the extra air and trips the lean code.

It's more likely on the intake side, but check the downpipe too.
 

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Update:

I have checked all the tubes I was able to reach...the first thing I noticed was that the tube leading away from the intake and toward the turbo was obviously loose (not so obvious at first glance, but it was basically on there crooked so that it looked tight from the top (I couldnt' even tell till I felt around the rim with my fingers. I tightened that up, then checked all the hoses from the front of the turbo and forward, and everything seemed to be okay. Then it started raining before I could try to get a sense of the downpipe connection.

The first thing I notice after tightening the intake tube is that the exhaust smell was still there after I started the car up. The car had been off for several hours before I did this, and I got the impression that the smell was strongest when I stuck my head down into the engine bay near the turbo/downpipe. If it stops raining at any point, I'll probably go back out and try to inspect the downpipe itself.

It seems to me that everything for this code seems to point to that loose intake hose, but I don't see how that cause me to smell exhaust fumes unless I ALSO have an exhaust leak. Can one have something to do with the other? Or maybe I just happened to have an exhaust leak AND just happened to have a loose intake tube at the same time?

I'm currently out of town for work and nowhere near a dealership, which is the main reason I haven't taken it in yet--likely will be this weekend before I can make it happen. If I do have an exhaust leak, is there any chance I'm doing irreparable damage to my car by driving it 12 miles per day til then? If this were an older car, I wouldn't even ask, but with these modern cars with all their sensors and negative feedback protocols and whatnot, never know.
 

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Update:


I'm currently out of town for work and nowhere near a dealership, which is the main reason I haven't taken it in yet--likely will be this weekend before I can make it happen. If I do have an exhaust leak, is there any chance I'm doing irreparable damage to my car by driving it 12 miles per day til then? If this were an older car, I wouldn't even ask, but with these modern cars with all their sensors and negative feedback protocols and whatnot, never know.

Also...I'm wondering--now that I tightened that one loose hose, should I go ahead and clear out that code and see if it comes back? Or is that a bad idea?
 

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Update:

I have checked all the tubes I was able to reach...the first thing I noticed was that the tube leading away from the intake and toward the turbo was obviously loose (not so obvious at first glance, but it was basically on there crooked so that it looked tight from the top (I couldnt' even tell till I felt around the rim with my fingers. I tightened that up, then checked all the hoses from the front of the turbo and forward, and everything seemed to be okay. Then it started raining before I could try to get a sense of the downpipe connection.

The first thing I notice after tightening the intake tube is that the exhaust smell was still there after I started the car up. The car had been off for several hours before I did this, and I got the impression that the smell was strongest when I stuck my head down into the engine bay near the turbo/downpipe. If it stops raining at any point, I'll probably go back out and try to inspect the downpipe itself.

It seems to me that everything for this code seems to point to that loose intake hose, but I don't see how that cause me to smell exhaust fumes unless I ALSO have an exhaust leak. Can one have something to do with the other? Or maybe I just happened to have an exhaust leak AND just happened to have a loose intake tube at the same time?

I'm currently out of town for work and nowhere near a dealership, which is the main reason I haven't taken it in yet--likely will be this weekend before I can make it happen. If I do have an exhaust leak, is there any chance I'm doing irreparable damage to my car by driving it 12 miles per day til then? If this were an older car, I wouldn't even ask, but with these modern cars with all their sensors and negative feedback protocols and whatnot, never know.
With as strong of exhaust smell that you are getting, im starting to bet more toward the donut on the downpipe being bad.
 

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Also...I'm wondering--now that I tightened that one loose hose, should I go ahead and clear out that code and see if it comes back? Or is that a bad idea?
Definitely clear the code. Also, with exhaust smell, I’m with turbotiger604, you may have an exhaust leak there......any time you hit or drive over something always check for damage carefully. If you get a chance to get under it, follow the fuel lines and check them carefully also.
 

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With as strong of exhaust smell that you are getting, im starting to bet more toward the donut on the downpipe being bad.
I'm starting to think that's exactly what it is--the smell is definitely coming from that area. Is the donut supposed to be offset/crooked this much? I've only ever seen mine, and can't find may pics of this area online. One thing I can say for certain is that it already looked like this BEFORE I ran over that curb...I remember thinking it looked strange being all crooked-looking like that after I got it back from the dealership like a year ago, but they assured me it was supposed to look like this....
35644
 

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I'm starting to think that's exactly what it is--the smell is definitely coming from that area. Is the donut supposed to be offset/crooked this much? I've only ever seen mine, and can't find may pics of this area online. One thing I can say for certain is that it already looked like this BEFORE I ran over that curb...I remember thinking it looked strange being all crooked-looking like that after I got it back from the dealership like a year ago, but they assured me it was supposed to look like this.... View attachment 35644

Err, no, I mean if it seals it’s usable, but had they taken a moment and gave a dam it would have been straighter.
 

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@Itchy
That's definitely not sealed properly, looks like the nut came loose on the left side. Fill a spray bottle water then add some soap but don't shake it up, spray it all around the donut when you do a cold start and I'm sure you will start to see bubbles forming.

I would recommend removing the nuts completely on both sides of the downpipe pull it back, check to make sure the donut isn't cracked. If its good recenter it and re install. The donut should be centered and tightened evenly on both sides. Has your downpipe ever been removed? If it was the dealer it looks like the technician took the easy route and just tightened down the right nut since it's easier to get too, the back one can be a PITA.
 

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@Itchy
That's definitely not sealed properly, looks like the nut came loose on the left side. Fill a spray bottle water then add some soap but don't shake it up, spray it all around the donut when you do a cold start and I'm sure you will start to see bubbles forming.

I would recommend removing the nuts completely on both sides of the downpipe pull it back, check to make sure the donut isn't cracked. If its good recenter it and re install. The donut should be centered and tightened evenly on both sides. Has your downpipe ever been removed? If it was the dealer it looks like the technician took the easy route and just tightened down the right nut since it's easier to get too, the back one can be a PITA.
Yep, the first time I noticed the crooked-ness was after I got in an accident where my front passenger side was smashed in and they did have to disconnect the downpipe to do some of the work (thought I don't believe they replaced it--I'll check the invoice again).

I am going to do the soap and water suggestion, and then more than likely take it back to the dealership and ask them to fix this and explain why it was reconnected in such a wonky manner to begin with. I appreciate all the comments and assistance.
 

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No problem man, now that you said its been removed. I can guarantee that's what's happened, a tech got lazy on the reinstall.
 
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