Question From A Stang Newbie

Discussion in 'SN95 4.6L Mustang Tech' started by Leakyvert, Apr 22, 2014.


  1. Leakyvert

    Leakyvert New Member

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    Okay so I'm more mechanically inclined then the average person been working on my own cars as long as I've been driving. But I never owned or worked on a stang before, still learning the in's and outs.

    My girlfriend drives a 03 gt vert that she purchased used with some after market bolt-on parts.
    I've identified only CAI, cat back, and trick flow throttle body so far while working on it. Not sure if there are other parts installed.

    Before we met and not long after owning the car she had something with the cooling fan fail and the car overheated and needed work. Not long after that she developed codes P0174 and P0171 (lean condition both banks) and a coolant leak in the intake.

    I replaced the intake manifold and gasket thinking it would fix the codes as well (made sense leaking intake would let in more air)

    But codes remain and I'm working on troubleshooting them. Biggest question I have for you is whether or not the bolt-on's listed above could allow enough extra air into the engine to throw these codes? If so a tune would fix this?

    I have a live data obd device on order so I can look at long term fuel trim and O2 voltages but I'm open to guidance from people smarter than I. Thank you!
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  2. Nightfire

    Nightfire Mustang Master

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    Disconnect the battery, then see if codes still exist.
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  3. Leakyvert

    Leakyvert New Member

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    Batt was disconnected during entire intake manifold swap. Code returned in a matter of days.
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  4. Mattstang04

    Mattstang04 Active Member

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    Those bolt ons really shouldn't affect anything like mixture. Maybe the front O2 sensors are cooked. :shrug:
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  5. 91TwighlightGT

    91TwighlightGT Active Member

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    You probably still have a vacuum leak somewhere. I rarely see lean codes from bad O2 sensors, they usually throw codes for voltage if they are bad.
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  6. Leakyvert

    Leakyvert New Member

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    that's my biggest suspicion as well. I'm making an impromptu smoke machine this weekend to see if I can find the probable leak.
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  7. Leakyvert

    Leakyvert New Member

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    Reader came today. GF was in a rush so I was only able to get long and short term data at idle for about 20 seconds.


    Bank one Long term was 25%
    Short term bounced around between -1 and 9
    Bank two long term 25%
    Short term between -.8 and 6 (this bank almost always lower than bank one if that matters)

    Idle bounced around 800-100 rpm

    Guess with long term that high this is looking like a vacuum leak. Ordered parts to make an impromptu fogger. Hoping to try to smoke the engine, and possibly exhaust this weekend and see what I find.
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  8. COramprat

    COramprat Drone Driver Mod Dude

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    Or a leak at the intake manifold. What intake manifold did you use?
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  9. Leakyvert

    Leakyvert New Member

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    New Ford PI intake with the basic felpro gasket. I should have run a bead of RTV on the heads though they were a little pitted. So if there is a leak at the manifold it's probably there but very small. I'd personally lean toward one of the old brittle vac line broke during the install.
    #9
  10. wmburns

    wmburns SN Certified Technician

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    Only if the bolt on leaks! Never ever try to fix a vacuum leak with a tune. It will never really work because the amount of air entering the leak isn't the same all the time.

    Also look for exhaust leaks.
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  11. Leakyvert

    Leakyvert New Member

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    Oh I would not tune it to fix the code. Not unless I was certain the bolt on's were causing it. Like I said I'm new to working on cars with performance parts. I know at a certain point certain parts require you to tune, I was just unsure when that point was.
    #11
  12. COramprat

    COramprat Drone Driver Mod Dude

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    I have a lean condition that throws a code at idle. Very rarely and only if it is idling for a while, like stuck in traffic. I think my midpipe may be the cause since it had the flange welded where it attaches to the header due to rust. I may just replace it. But it is only on bank one. With your being 1 and 2 I'm not sure yours is an exhaust leak unless the midpipe is junk.
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  13. Leakyvert

    Leakyvert New Member

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    Was able to spend some time today giving the car a once over and logging some data. Heres what I've gotten:


    RPM idle ~750 RPM
    STFT 1: -1.6 and 3.1
    LTFT 1: 24.2
    STFT 2: -6.0 - 2.0 always lower than bank 1
    LTFT 2: 25.0


    RPM ~1500 RPM
    STFT 1: 5.0 - 8.0 with a peak of 11 (should have held the rev longer for it level out better)
    LTFT 1: 24.2
    STFT 2: 3.0 - 8.0 peak of 10
    LTFT 2: 25.0

    RPM ~2500 RPM
    STFT 1: 3.0 - 8.0 peak of 10.0
    LTFT 1: 24.2
    STFT 2: pretty level at 3.0 with a peak of 9.0
    LTFT 2: 25.0

    Revs above idle were held for around 10 seconds.

    Also gave the engine and vacuum lines a once over to look for anything obvious. Found nothing but given my (very limited) understanding of reading this data doesn't the Lt trim not moving point more toward a fuel delivery issue?

    Attached Files:

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  14. wmburns

    wmburns SN Certified Technician

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    Your LTFT are off the charts on both banks. Since there isn't a real difference between idle and load, IMO that lowers the likely hood of this being a vacuum leak. Instead the focus should be on a cause common to both banks. For example:
    • Bad MAF
    • bad Fuel rail pressure sensor
    • bad fuel pump
    Suggest monitor the MAF flow and confirm that it changes. Also monitor the fuel pressure with the ODB2 scanner. Verify that it changes some with motor load. Cross check the PCM fuel pressure to an external gauge (disconnect and plug the FRPS intake vacuum line for this test).
    Last edited: May 2, 2014
    #14
  15. Leakyvert

    Leakyvert New Member

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    Planing on doing these tests plus forcing a rich condition on the O2's using carb cleaner to check their voltages. When you say "disconnect and plug the intake vacuum line for this test" you're referencing the vacuum line on the FRPS correct? Thanks.
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  16. Leakyvert

    Leakyvert New Member

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    I was able to spend a short amount of time yesterday logging some data:
    WOT test:
    Rpm ~4k
    Calc Load: Peak 99.6%
    Air Flow rate from MAF: Peak 132 g/s
    Throttle Position: Peak 92%

    Again correct me if I'm wrong but this ruled out faulty MAF correct?

    Other info: Fuel rail pressure showed high 40's to mid 50's PSI even at idle Peak (during WOT)was 59 PSI. Have not had a chance to get a reading from the rail, will later today as well as force O2 voltages.

    Possibly related or unrelated?? : I'm using an ELM327 Wifi scanner paired with my iphone to log data. Last time I plugged it in I logged all data while stationary in the driveway, I noticed while the scanner was plugged in the odometer showed only "------" while engine was running and that removing the scanner returned it to normal. I chalked this up to something to do with the scanner talking to the car and dismissed it. Then yesterday same thing with the odo however after I took it on the road about 30 seconds into test drive I look down and no odo OR speedometer (???) About a minute into the drive speedometer and odometer returned to function normally. Once again removing the scanner returns all functions to normal. This has never happened accept these two instances with scanner attached. Data log shows vehicle speed as 0mph until right around the time speedo returned during drive, and the computer showed a PENDING code p0720 (output speed shaft sensor circuit) I can only assume the scanner is doing something the car does not like but I thought I should mention it for total diagnostic transparency...

    I will report back later with more data.
    #16
  17. wmburns

    wmburns SN Certified Technician

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    The FRPS numbers look reasonable. Won't know for certain until cross checked.

    For the MAF, you need to cross check the reported flows at various motor loads. IE, is it "reasonable" at idle? It might help the rest of us to report in US units.

    One thing to look at is some CAI's change the location/index of the MAF from the stock location. This could cause the MAF to read incorrectly.
    #17
  18. Leakyvert

    Leakyvert New Member

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    Okay so seems ford did away with the fuel rail mounted schrader valve sometime in 2003. What's the procedure for checking fuel pressure on these cars? Seems I'll need to buy an adaptor of some sort?

    Attached Files:

    Last edited: May 3, 2014
    #18
  19. Leakyvert

    Leakyvert New Member

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    Okay update here. Spent Thursday evening installing the stock air intake and stock upper plenum just to rule them out as suspect, did this while neg terminal was unplugged and did an idle re-learn when all was done (ten minute idle then 2 min AC max idle).

    This morning I replaced the fuel filter, again to rule out as suspect and also as good preventative maintenance (who knows how old the one in there was...) put a piece of vacuum line on the end of the old one and gave it a "blow test" and it seemed very clogged (lots of resistance when blowing through it) Plugged my scanner on for the first time since idle re-learn and parts swap and LTFT is perfect!

    Right now my biggest question is has enough time passed (maybe 50 miles or so) for LTFT to be effected if the problem still exists?

    Thanks for all your guys help thus far.
    #19

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