Cascade of Issues - Help

Discussion in '2005+ Ford Mustang v6 4.0L Tech' started by Nick1719, Apr 28, 2021.

  1. Nick1719

    Nick1719 Junior Member

    Hi! I have had my 09 V6 since it was new. After the warranty expired, I installed a Ford Performance Cold Air Intake and Bama tune. They too have run fine for many years. The car has ran fine until a month ago when it fuel gauge dropped to E instantly. The dealer said the jet fuel pump was bad and to tank from getting low while I wait for parts.

    Thinking of saving gas, I attempted to to switch to my fuel efficiency tune from Bama. The car wouldn’t start and I could smell gas. I swapped back over to the old tune and the car still had rough start but eventually started. The engine idle was very rough. Thinking that the tune just needed to settle in, I drove it for 200 miles. The issue persisted so I tried again reflashing the tune. The car now starts fine, but it still idles rough. The RPM goes as low as 450 and almost stalls. The whole car shudders when it’s this low. It will bounce up to 2000 without any pressure on the accelerator.

    The car drives normally after a few minutes, but this problem re-occurs on start-up with it being much worse on cold-start-up.

    The check engine light only gives errors for “system too lean” on both banks.

    Any suggestions? Thank you in advance.
  2. Macman45

    Macman45 Resident Geriatric

    Tune is trash, and pump may be failing. No idea what a "jet" fuel pump is. I'd wipe that crap tune off, wipe to stock and do a KAM reset, and see. If its still bad do a fuel pressure check at the rail. If bad, its the pump. no one around here likes BAMA tunes
  3. Nick1719

    Nick1719 Junior Member

    Gotcha, I’ll check those out. I asked the service tech at the dealer what they meant by jet fuel pump and he said it’s the one that moved fuel from one side of the saddle fuel tank to the other. First I heard of it.
  4. Juice

    Juice forum member

    Did you fill it after this happened?
    Transfer pump bad does not explain the fuel guage dropping suddenly. That sounds more like a fuel pump and fuel level sensor problem, not a transfer pump.
    If it was running fine with rhe Bama tune, tune is probably not the issue. Both banks lean means not enough fuel. I would start with verifying fuel pressure. A new fuel filter is cheap. (Mine was full of nasty sediment, and the car still ran fine)
    Load the known good tune and leave that alone. Check one thing at a time.
    Check the air intake for leaks between maf sensor and throttle body.
    Last edited: Apr 29, 2021
  5. Nick1719

    Nick1719 Junior Member

    Yeah, I’ve kept the tank at least 1/2 full since it happened. The dealer said the pump and sensors were ok, but I’m not sure how much I trust them because I moved so it’s their first time working on my car. I will leave the tune as is as check on potential causes.
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