P0174 system lean (b2), 50% power after hard pull.

Discussion in '2011+ Mustang GT 5.0L Tech' started by want2race441, Jul 18, 2018.

  1. want2race441

    want2race441 Junior Member

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    2011 GT, I think the code is the culmination of an issue that's been underlying for a bit. Motor has been rebuilt, block prepped, stage 2 ported heads, stage 2 cams (vct locked out), 302 intake, JLT MAF, unk TB, Kooks long tubes, high flow cats. JLT catch cans on both sides with new PCV. Just replaced upstream b2 o2 sensor for previous CEL.
    I've suspected a vacuum leak because of "hanging revs" between shifts. However, idles smooth and didn't present with the usual leak symptoms. Figured it was just in the tune (unknown tuner, B&D in LA did the build)
    Sunday, after a strong 3rd gear pull to 7k to motor would no longer respond to anything more than half throttle. Raspy engine sound muted. Would still rev to 5k but at reduced engine power and noise. No codes. Very smooth running, just at reduced power.
    Yesterday, tried to data log (it didn't record) and the mild acceleration was noticably shuttery then CEL. P0174.

    On my to-do list. Propane vacuum leak test. Clean MAF (already cleaned tb). Record temps of both cats. Remove fuel pump and clean pick up screen.

    Likely causes of vac leaks?
    Chances the fuel pump has gone south (check valve not "checking", etc)?
     
  2. want2race441

    want2race441 Junior Member

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    Vacuum test gave no results. Other than removing the clunky foam pads left and right of the intake.

    Passenger cat was 30* hotter than driver side after just 2 minutes of idling. The pipes just in front of the cats were 147* driver side, 207* passenger side. Think I've found a clogged/blown converter. Car is no longer a CA state car and is destined for the track so off they go.
     
  3. want2race441

    want2race441 Junior Member

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    Update. Cats are fine. Plugs were a bit worn (.060 gap), and were replaced. Cleaned MAF. Found one loose header bolt. Tightened 1/4 turn. Gasket is now questionable.
    Test drive still had some shuddering while accelerating. Next test is fuel pressure voltage and inspection.
     
  4. redfirepearlgt

    redfirepearlgt forum member

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    Often times the P0174 can be caused due to a leak at midpipe or header. I had this code pop up after a clutch swap on my 13GT years ago. It would only show up on long distance drives. Found the cat was not seated correctly to the header and midpipe on the drivers side when it was pulled to remove the tranny. Problem solved. So with the cats off and retuning the aft O2's will be turned off and that problem will at least be gone. I don't believe it would be related to your other concerns. My car still ran as if there were no codes at all when this would happen.
     
  5. want2race441

    want2race441 Junior Member

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    The bolts holding cat pipe to headers were surprisingly easy to remove. Not too tight. That's been fixed.
    So the last time I drove it, turns out I had loaded a tune that came with the SCT tuner instead of the custom tune. I thought the high idle (950, tuner set to 650) and hanging revs were fixed by cleaning the MAF. Turns out, it was a different tune. The car didn't like that tune after 3500 rpm however and shuddered while trying to accelerate. Idled and revved smooth though. No codes.

    Yesterday I loaded the correct, custom tune. High idle is back as is the slow rev down (I call it 'hanging revs). I'll have that fixed next week via tuning session. I did capture something odd though, the O2 sensors are off. All four read 0.07, fixed, while driving. Is that 'safe mode'? Open loop or closed? They were reading fine with the other tune. Reacted to throttle inputs. Switch to the custom tune and they are not. Car ran fine before this issue. Tuner was B&D Racing in Van Nuys, CA. New tuner will be JPC in MD.
     
  6. redfirepearlgt

    redfirepearlgt forum member

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    Do you have any CEL's still present?

    Typically a wide band should read about +0.5VDC at 1.0 Lambda assuming it is a Bosch or similar in output span. They range from -2.0 to +1.5 vdc output. If the car is running rich you may be reading .07vdc, but you need to see what the AFR output is in Lambda on the datalogger. At normal under under closed loop at Lambda 1.0 (which should be the target) the O2 sensor should indicate 0.5vdc or close. As a reminder to other readers all GT Mustangs built 11 or later have Wide Band O2's as stock equipment on the front banks at minimum. Not sure about the rears as they only monitor the function of the Cats.

    Tuners have been known to tune cars without using the o2's but these would be very radical setups usually according to my reading on advanced tuning. Most however only turn off the rear O2's.
     
  7. Sky Render

    Sky Render Stig's Retarded Cousin S197 Team Member

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    An open loop tune that doesn't use o2 sensor feedback is called "Alpha-n," and the only engines running that are either in limp mode or running HUGE cams for a quarter mile at a time.
     
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  8. want2race441

    want2race441 Junior Member

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    I'm learning. The PIDs VVEXb1a, VVEXb2a, VVINb1a, VVINb2a are not the O2's like I thought. Those are the cams, intake and exhaust. On SCT provided tune, there is VVT control. That's why there are numbers that change with rpm and load. On my custom tune, cams are locked out, so it's the vvt control. As it would seem anyway. Therefore the 0.07 on all four lines.

    Once the engine is at operating temp, the ltft's are .95 b1, .98b2 and change a little with rpm. Bank 2 is a new O2 sensor.

    Fuel pressure and fuel voltage are two things i can't log. My SCT tuner doesn't have a usb. It's aprox 8yrs old and has what looks like an optical cable port.

    Will update once it's at the shop.
     
  9. redfirepearlgt

    redfirepearlgt forum member

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    LT's are respectable. Yes you were looking at VCt timing for intake and exhaust. You really need to take advantage of Livelink datalogging software for SCT. It is a free download. SCT tuners are limited to 20 PID's of datalogging. Most tuners want 23+ points for a remote tune. AFR B1 and AFR B2 will give you the lambda value for bank 1 and 2.
     
  10. want2race441

    want2race441 Junior Member

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    Lol. Looking back, I'm laughing at everything I had to learn in short order.

    I pulled the plugs and scoped the number 8 cylinder. It was wet. This was right before taking it the shop. My research suggested either valve guide seals or bad rings. Good compression, good leak down test. The shop tore the motor down to the block and pulled the piston to verify. Short block was fine. Exhaust valve guides and seals over 8 were toast, allowed oil into the cylinder, which spreads throughout the motor. Piston crowns are carmalized a bit.

    So, since I've paid to have the motor pulled I might as well take advantage of it. Looking at having an NA 5.2 coyote built up. See if I can make more than the 522whp the old one made. So I might have a forged internals short block for sale soon...
     
  11. LarryJM

    LarryJM forum member

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    I read a report the 5.2's have been throwing rods through the plastic oil pan. Something about balance is not what Ford expected on the 5.2's. Then another report, the extra .2 is not worth the effort and money is best spent on making the heads as fancy as possible on the 5.0.