P0174, Lean Bank 2 solved


Xcentric

GT Owner
Mark II Lifetime
Jul 9, 2012
5,213
Myakka City, Florida
This may never happen to anyone, but it's an interesting bit of diagnostic sleuthing.

I took my GT to my GT tech after repeated CEL and P0174 codes. This code indicates a lean condition in bank 2 (driver side). When the PCM detects the lean condition, the response is to go full rich. Too rich is not good, but too lean can be really bad. Full rich is a safety measure. The engine ran fine, but eventually the plugs would foul.

My GT has a pulley and tune, Accufab TB, and FRPP/Borla long tube headers and muffler.

Diagnostic steps:

- Verify no vacuum leaks with smoke generator
- Verify correct flow from fuel injectors
- Verify operation of O2 and MAF sensors
- Verify compression and leak down
- Test circuits from PCM to Bank 2 O2 sensor 1
- Perform visual inspection of exhaust valve springs

At this point, it's important to note the difference between OEM exhaust manifolds and long tube headers.

The OEM setup has O2 sensor 1 sampling the oxygen content of all four cylinders in the bank.

The long tube header has O2 sensor 1 sampling only cylinder 7 (see bung location in the image).

This means that cylinders 5, 6 and 8 could be too lean or too rich and that condition would not be detected!

So, what could be wrong with cylinder 7 to cause an apparent lean condition?

At this point, the tech swapped and rewired the O2 sensors to sample from cylinder 8. Sensor voltage and A/F mixture returned to normal! (He demonstrated this to me and Howard on his laptop...pretty cool).

Next, he put some rubber gloves over the exhaust outlet tips and blew smoke into the exhaust system. Smoke leaked from the slip-fit header connection, which is adjacent to O2 sensor 1.

The tech determined that the header was drawing enough external air at the slip-fit connection to fool the O2 sensor in the cylinder 7 tube into a "too lean" reading. The O2 sensor in the cylinder 8 tube is well downstream of the slip-fit connection (see image) and is not affected by the leak.

At this point, the rewired O2 sensor may be the final solution. We're seeing if Borla will supply a bank 2 header under warranty.

An unusual problem to say the least.

One takeaway for anyone with headers is don't count on the PCM to let you know if you have a lean condition on six of the eight cylinders. This should be obvious if you look at the O2 sensor locations, but I never thought anything of it.

Very happy to have the GT back in the garage! :)

17253_xlarge.jpg
 
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twobjshelbys

GT Owner
Jul 26, 2010
6,053
Las Vegas, NV
Great detective work. Your tech really knows what he is doing!
 

DakotaGT

GT Owner
Mark II Lifetime
Dec 9, 2012
1,694
Sioux Falls, South Dakota
Great post! Nice job. Satisfying, even when it's not my car!
 

Howard

GT Owner
Mark IV Lifetime
Apr 26, 2007
1,135
Florida/North Jersey
Sarasota Ford. Highly recommended. And they will be certified for NFGT service.

Howard
 

soroush

Ford Gt Owner
Mark II Lifetime
Aug 8, 2007
5,256
great post thanks for the info.
 

NorthwoodGT

GT Owner
Jun 12, 2009
1,215
Michigan
wow, that's great info. would it have made sense if Borla put the O2 sensor in the collector and supplied a harness extension? I can see this set up could give erroneous information. good find
 

STORMCAT

GT
Mark IV Lifetime
Le Mans 2010 Supporter
May 25, 2006
7,549
Ft. Lauderdale
Interesting,, thanks for sharing.. !!
 

PeteK

GT Owner
Mark II Lifetime
Apr 18, 2014
2,268
Kalama, Free part of WA State
Great sleuthing. Shows the importance of spending time on diagnostics, not just "throwing parts at the problem."
 

Sinovac

GT Owner
Mark II Lifetime
Jul 18, 2006
5,832
Largo, Florida
Thanks for sharing that Gary. I'm glad you got it figured out.
 

mmlcobra

GT Owner
May 25, 2013
1,215
Guess I'm going to Sarasota Ford based on your post.
Thanks,
Mark
 

acolvin

GT Owner
Mar 25, 2015
14
Ewa Beach, HI
Brilliant! Thank you for sharing.
 

texas mongrel

GT Owner
Mark II Lifetime
May 3, 2009
1,661
Houston Texas
Calling the GT Guys! Remember both of our cars throwing this code at COTA? Mine has never done it again, so I'm relaxed about it and, as you thought, I suspect it was a bad tank of gas or similar
 

Beach-GT

GT Owner
Mark II Lifetime
May 8, 2006
887
Seminole Florida
O2 bungs and plugs are available from Stainless works and others. I'd weld in a bung up near the Flange and plug the current bung.
 

2112

Blue/white 06'
Mark II Lifetime
Xcentric, Is the vacuum leak (for lack of a better description) in the slip joint present at start up or only when things get really hot?

I was not excited about having a slip joint when I first got my headers, but when I saw how much movement occurred between different operating conditions, I understood it as a necessary feature. (I have the version with it's own small muffler on each side).

What I am getting at, is the return spring on the slip joint possibly fatigued allowing excessive movement (and a more loose fit) or a failure to return to a more overlapped location?

wow, that's great info. would it have made sense if Borla put the O2 sensor in the collector and supplied a harness extension? I can see this set up could give erroneous information. good find

This is done on GT500 Headers often and almost always creates it own issues. I think most suspect the wiring extension is the culprit.
 
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Xcentric

GT Owner
Mark II Lifetime
Jul 9, 2012
5,213
Myakka City, Florida
Xcentric, Is the vacuum leak (for lack of a better description) in the slip joint present at start up or only when things get really hot?

What I am getting at, is the return spring on the slip joint possibly fatigued allowing excessive movement (and a more loose fit) or a failure to return to a more overlapped location?

The slip joint leaks at cold start. We only ran the engine for a few minutes, so it never got hot.

Good question about the springs. I don't know the answer. The tubes look fully seated, but I can't say for sure that they are.

I will get the tubes really hot and see what I can see. :)
 

2112

Blue/white 06'
Mark II Lifetime
Just thinking outloud here, based on the sleuthing you've already accomplished.

If not the spring, maybe soot buildup is preventing proper seating? If it is just wear, would a uniform ceramic coating of the male side tighten up the fit?

I have a gut feeling Borla will say you are on your own (do they even make parts for these any longer?), so fixing what you have maybe what you have to do.

For me personally, I would be relieved the issue was with an easily (relative) accessible mechanical part rather than some electrical gremlin up stream.
 

Pete S.

GT Owner
Mark IV Lifetime
Aug 18, 2006
529
MA
Just wanted to post my most recent trouble and solution a Check Engine light which stated the typical Lean Condition codes. It was odd as it only popped on at an idle and never while actually driving. For example when I made the 300 mile drive to attend Carlisle it only appeared when I was at a traffic stop between the Fairgrounds and the Hotel. So of course I began replacing the primary O2 sensors. No change.
Returning from Carlisle rolled is onto the Race Ramp.

1. http://1fordgt.com/2017/FGT Check Engine/0001.JPG

2. http://1fordgt.com/2017/FGT Check Engine/0002.JPG

3. http://1fordgt.com/2017/FGT Check Engine/0003.JPG

After rolling the exhaust manifold heat shields on the top and checking the tightness had to crawl on my back to get at the 8 fasteners from below.

4. http://1fordgt.com/2017/FGT Check Engine/0004.JPG

5. http://1fordgt.com/2017/FGT Check Engine/0005.JPG

6. http://1fordgt.com/2017/FGT Check Engine/0006.JPG

7. http://1fordgt.com/2017/FGT Check Engine/0007.JPG

8. http://1fordgt.com/2017/FGT Check Engine/0008.JPG

9. http://1fordgt.com/2017/FGT Check Engine/0009.JPG

10. http://1fordgt.com/2017/FGT Check Engine/0010.JPG

11. http://1fordgt.com/2017/FGT Check Engine/0011.JPG

Then while at a nice local car gathering was discussing the issue with a friend and happen to ‘feel’ an imperfection on the vacuum line under the three on my finger is pointing to.

12. http://1fordgt.com/2017/FGT Check Engine/0012.JPG

So I held the I Phone in about the right spot and snapped some images.

13. http://1fordgt.com/2017/FGT Check Engine/0013.JPG

14. http://1fordgt.com/2017/FGT Check Engine/0014.jpg

And you can see the damaged hose and pretty sever degradation in several places including another rip near the clamp at the supercharger.
This is the hose off the car.

15. http://1fordgt.com/2017/FGT Check Engine/0015.JPG

16. http://1fordgt.com/2017/FGT Check Engine/0016.JPG

17. http://1fordgt.com/2017/FGT Check Engine/0017.JPG

Ordered the part from local Ford Dealership (about 30 miles out), received it and installed. No more Codes and the car getting better fuel mileage and seems to be much more “peppy”.
On a side note never had a single day not able to drive it as in-between ordering the hose and getting the new one has sealed the tear with urethane flexible cement and stiffened the hose with plastic and RTV and electrical tape. Worked fine.
Was e mailing with Shadowman thru this process and as always genuinely appreciate his kind approach and knowledge that he shares. Thanks Bill! from mid
 

ChipBeck

GT Owner
Staff member
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 13, 2006
5,770
Scottsdale, Arizona
Gentlemen,

The bitchy thing about GT headers is that slip fit 2-piece design. My headers were tight as a drum when new but eventually started leaking at the slip fit and it just kept getting worse. I eventually took them off and went back to the stock manifold. The 1 piece headers on my Shelby GT work great but I don't think there is any way to build a long tube GT header that can be installed without taking a ton of stuff apart.

Chip
 

2112

Blue/white 06'
Mark II Lifetime
I thought someone said they had Stainless Works long tube one piece headers installed?

Of course Ed Sims has, or had custom headers too.
 

fjpikul

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Jan 4, 2006
11,475
Belleville, IL
Thank you Pete that was very comprehensive. Good to know.