P0174 & P0171

N8Dogg98 · Apr 17, 2011

So I installed MHS stage 2 NPI N/A cams last week and today got a check engine light. Upon pulling the codes it turns out I have a lean condition in both banks (codes P0174 and P0171). I have never had the car tuned, so is this just due to the PCM being confused becuase of my new cams? Will it go away once the car is professionally tuned (scheduled for May 4th)?

It sounds like I also have a very small exhaust leak coming from the passenger side manifold. I'm fairly positive it's the joint between the midpipe and the passenger side manifold. Could the exhaust leak be responsible for the codes as well? I do plan on fixing the exhaust leak soon, but is it necessary before getting a tune?

Thanks!

trombonedemon · Apr 17, 2011

N8Dogg98 said:
So I installed MHS stage 2 NPI N/A cams last week and today got a check engine light. Upon pulling the codes it turns out I have a lean condition in both banks (codes P0174 and P0171). I have never had the car tuned, so is this just due to the PCM being confused becuase of my new cams? Will it go away once the car is professionally tuned (scheduled for May 4th)?

It sounds like I also have a very small exhaust leak coming from the passenger side manifold. I'm fairly positive it's the joint between the midpipe and the passenger side manifold. Could the exhaust leak be responsible for the codes as well? I do plan on fixing the exhaust leak soon, but is it necessary before getting a tune?

Thanks!

Do you still you have oxygen sensors?

N8Dogg98 · Apr 18, 2011

trombonedemon said:
Do you still you have oxygen sensors?

No offense but this has nothing to do with the questions I asked and of course I have my O2 sensors, why wouldn't I? The car has stock manifolds and the only change was installation of cams last week. The code showed up for the first time yesterday so I assume the code is related to teh cam install and will be corrected once I have a dyno tune. I just want to be sure so that when I go to get tuned the time on the dyno is spent tuning and not fixing some other problem.

Can any of you give me an idea if this is normal to get these codes after a cam install and before a proper dyno tune?

wmburns · Apr 18, 2011

Are you aware that an exhaust leak ahead of the O2 sensors will cause a false lean DTC?

N8Dogg98 · Apr 18, 2011

wmburns said:
Are you aware that an exhaust leak ahead of the O2 sensors will cause a false lean DTC?

Will it do that on both banks? I can hear a very small leak that I think is coming from the passenger side manifold-midpipe joint. I'll probably go in there and replace the gasket soon, but would that cause the lean code to be triggered on both banks?

EDIT: I feel like a dumb ass. I looked under the hood and sure enough there was a disconnected vacuum line.

I do still hear a very small "thris... thris... thris" sound from the passenger side of the engine which makes me think there is a small exhaust leak. Strangely enough I inspected the passenger side joint between the midpipe and manifold and it looks tight as a drumb. Last time I moved the mid pipe was for my clutch install last summer and I reassembled it with a new ford exhaust gasket

I didn't notice this sound until after my new cam install. It is worth nothing that I did have a significant oil leak coming from the passenger side cam cover when I finished the cam install (I've since fixed this), could all that oil on the manifold cause any of the gaskets to fail? I wouldn't think so but figured I should ask anyways.

Regarding my tune, is it absolutely necessary to fix that small exhaust leak before I have it tuned? It sounds so small I don't see it impacting the AFR readings in the exhaust much.

NIKwoaC · Apr 18, 2011

N8Dogg98 said:
Regarding my tune, is it absolutely necessary to fix that small exhaust leak before I have it tuned? It sounds so small I don't see it impacting the AFR readings in the exhaust much.

Hey Nate, I'm only here because you linked it to DA.

FWIW, I know of dyno tuners that won't even touch your car if it has ANY maintenance/mechanical issue. If you have time, I'd try to fix it.

fiveohwblow · Apr 18, 2011

I had those EXACT codes on my 98, switched the o2 sensors and it went away....

N8Dogg98 · Apr 18, 2011

The O2 sensors are less than 2 years old. It ended up being a loose vacuum line that was throwing the codes.

Hey Nik, the thing is it's really tough to tell if it is actually an exhaust leak. I mean it may be something else that's making a similar noise. I've had an exhaust leak before at the manifold to mid-pipe gasket and it sounded much more distinctive and increased with RPM. This noise is very faint at idle and its difficult to tell if it increases with RPM. The manifold gasket looks good and tight and I don't see any areas of black soot typical of exhaust leaks... maybe it's just in my head

NIKwoaC · Apr 18, 2011

Man, I am so bad at diagnosing anything with sounds. I can feel your pain. I would never be able to tell if I had an exhaust leak by sound, unless I had a pipe completely fall off.

If you don't think it's significant, if it exists at all, it probably isn't an issue. Your tuner may actually have something to say about it, maybe you could ask him what he thinks before you put the car on the dyno.

N8Dogg98 · Apr 18, 2011

Thanks Nik. It's such a faint noise that even if it is an exhaust leak it's probably small enough to not make a noticeable difference while tuning anyways. I don't know if I'll even bring it up to the tuner.

sneaky98gt · Apr 18, 2011

N8Dogg98 said:
Hey Nik, the thing is it's really tough to tell if it is actually an exhaust leak. I mean it may be something else that's making a similar noise. I've had an exhaust leak before at the manifold to mid-pipe gasket and it sounded much more distinctive and increased with RPM. This noise is very faint at idle and its difficult to tell if it increases with RPM. The manifold gasket looks good and tight and I don't see any areas of black soot typical of exhaust leaks... maybe it's just in my head

True that. I thought I was having bad detonation a few weeks ago. Someone rode with me and said they thought it sounded more like an exhaust leak at high rpms than detonation. I got under the car, and sure enough, all 4 nuts holding the midpipe to the headers were FINGER TIGHT! I was like WTF!? I tightened them back up (using loc-tite this time), and the noise went away. You might want to check the same bolts/nuts and make sure they are good and tight. Could be a very simple solution.

N8Dogg98 · Apr 18, 2011

sneaky98gt said:
True that. I thought I was having bad detonation a few weeks ago. Someone rode with me and said they thought it sounded more like an exhaust leak at high rpms than detonation. I got under the car, and sure enough, all 4 nuts holding the midpipe to the headers were FINGER TIGHT! I was like WTF!? I tightened them back up (using loc-tite this time), and the noise went away. You might want to check the same bolts/nuts and make sure they are good and tight. Could be a very simple solution.

I probably should, but i just don't want to remove my f'n O2 sensor again. Dumb magnaflow midpipe has the O2 sensor right in the way of the front most midpipe to header bolt. Dumb... I hate it and really wish I had a tubular K member.

sneaky98gt · Apr 18, 2011

N8Dogg98 said:
I probably should, but i just don't want to remove my f'n O2 sensor again. Dumb magnaflow midpipe has the O2 sensor right in the way of the front most midpipe to header bolt. Dumb... I hate it and really wish I had a tubular K member.

Ah, didn't realize that. That is dumb. My Mac Prochamber is very easy to get to those bolts; swivel + extension = job done.

N8Dogg98 · Apr 18, 2011

sneaky98gt said:
Ah, didn't realize that. That is dumb. My Mac Prochamber is very easy to get to those bolts; swivel + extension = job done.

Had a MAC o/r H and it was easy too... once I switched to the Magnaflow catted x-pipe it was no longer easy... dammit

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