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Running lean and detonation

mustangpegasus51

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If it was a vacuum leak your LTFTs would go down when you accelerate and up when you let off again.

This might be something like a fuel pump issue as described here:
 

Kong76

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If it was a vacuum leak your LTFTs would go down when you accelerate and up when you let off again.

This might be something like a fuel pump issue as described here:

Yea I was leaning that way. I dont know how to check pressure. There is no shrader valve. Like to know what the pressure is when engine is under load. I think I have plenty of fuel at idle. Numbers look normal.
 

mustangpegasus51

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You can check fuel pressure with a scan tool. FRP is pressure at the rails. Compare that with the desired FRP (you may need a more advanced tool to get desired FRP PID) and that will help you diag fueling. There's also a PID for the low pressure fuel system but I don't know it off hand.
 

Kong76

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You can check fuel pressure with a scan tool. FRP is pressure at the rails. Compare that with the desired FRP (you may need a more advanced tool to get desired FRP PID) and that will help you diag fueling. There's also a PID for the low pressure fuel system but I don't know it off hand.
Ok will do. Thanks for the help. Sucks knowing the car has more in it and I can't enjoy it.
 

mustangpegasus51

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Oh I'm with you bud. My 'stang has been in and out of shop since June for hesitation and low power issues. Finally noticed around late August that my rail pressure at idle was like 3000-4000 psi, when it should be 400. The rail pressure gets normal-ish under load, but all this business is causing the fuel trims and AFR to get all whacked out. My throttle position also has mad dead spots.

Brought this up to dealer and they said they found codes from me using a scan tool, reset the computer and called it a day. Car still runs like crap. Going back this week for a ride-along if I can with their tool.
 

Kong76

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Oh I'm with you bud. My 'stang has been in and out of shop since June for hesitation and low power issues. Finally noticed around late August that my rail pressure at idle was like 3000-4000 psi, when it should be 400. The rail pressure gets normal-ish under load, but all this business is causing the fuel trims and AFR to get all whacked out. My throttle position also has mad dead spots.

Brought this up to dealer and they said they found codes from me using a scan tool, reset the computer and called it a day. Car still runs like crap. Going back this week for a ride-along if I can with their tool.

Well I'll follow your lead..lol
 

accel

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Bluemustang

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Have you considered it may be the tune and nothing is wrong with the car? Probably not what you want to hear, I realize. Just another suggestion nevertheless. Might be worth exploring.
 

Kong76

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Have you considered it may be the tune and nothing is wrong with the car? Probably not what you want to hear, I realize. Just another suggestion nevertheless. Might be worth exploring.

Yes that has crossed my mind several times. I do believe the timing on the Ford tunes is way to aggressive for our Ca 91. I have been adding boostane to try and compensate. The pinging does diminish some. I will have to make a decision on going back to stock. Still have another full bottle of Boostane though..lol
 

accel

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Have you considered it may be the tune and nothing is wrong with the car? Probably not what you want to hear, I realize. Just another suggestion nevertheless. Might be worth exploring.
with this tune some detonate on 93 and some do not detonate on 91. So there moght be something specific to a car.
 

mustangpegasus51

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@Kong76 did you ever get your issues figured out? In trying to get to my issues the fuel PIDs ended up being a red herring; apparently in this vehicle the port fuel injection system holds pressure in the rail for some reason. The full writeup is at my servicing dealership but the buyback was approved before I was planning to return for service and grab the document.

If you have the service manual the reference values sort of match up; however WHY they wouldn't just program the desired FRP to reflect what it should be is beyond me. Either way, if you haven't been able to look at fuel system pressure in the low-pressure system yourself, it might be easier just to go to the dealer and ask them to perform Pinpoint Test HC.

For anyone looking for updates from me, I got approved for buyback as of today! I'll do a bigger writeup when the excitement wears off, I'm just so happy to have a properly working car soon.

However TL;DR guessing my issues were in fact my throttle body. My OBD detective skills caught that my TPS temporarily fails pinpoint test DV16 (this involves popping and releasing the throttle with key on and the ignition off.) Throttle position would drop to around 6% (default throttle position for this car is 7.84%) before snapping back to an in-spec value. There was also a delay between the APP and TPS when moving throttle in KOEO, but am unsure if that has something to do with the car being off.
 

Kong76

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No I did not. My scan tool does not read fuel pressure. More than likely going back to stock.
 

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