Idle issue

Discussion in '2005+ Mustang GT 4.6L Tech' started by Clown9, Apr 12, 2018.

  1. Clown9

    Clown9 Junior Member

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    I do not know if this makes a difference or not but after recently shutting the car off I tested the AC volts from both the battery and the Alternator and they tested at .0231 and .024 respectively.

    Sadly enough my tuner (Bama Revx) does not do the things you mentioned from TPS voltage onwards. In the video Fuel Rail Pressure is bottom left.
     
  2. 07gts197

    07gts197 forum member

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    Thats why I got an ELM327. Its an awesome tool.

    The pid on the bottom left is fuel pump duty cycle not fuel rail pressure.
     
  3. 702GT

    702GT S197 Fanatic

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    The FRPP T-body is way too massive for a NA car. The FRPP Manifold is also huge. You're sacrificing a grip of low-mid power for virtually no top end gain. You have huge air volume and low air velocity, and no cubic inch to back it up. That setup needs a blower huffing into it to make use of it.

    Regardless, the T-body would be a possible idle issue component. The movement of a t-body that large would have to be extremely small at idle and have huge effects if the movement weren't tight enough. Abormalities in TPS voltage alone would cause significant idle hunting. Particularly if having alternator issues as well.
     
    46addict likes this.
  4. Clown9

    Clown9 Junior Member

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    I get what you are saying. Which I will add, I have plans to add a blower later on *but* the rpm wasn't dipping and jumping until recently.
    I was driving with the whole setup for months without any issues.
    As far as the alternator goes I have no clue...
     
  5. 07gts197

    07gts197 forum member

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    I highly doubt thats the case unless he got a crap tb from the factory but we wouldnt know unless the pids I mentioned were monitored. And frpp stuff isnt known for their problems like the BBK tb’s. But that does bring up a point, the op could back probe the tps to monitor for changes in throttle plate position maybe causing this problem.
     
  6. Clown9

    Clown9 Junior Member

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    How would I go about backprobing the tps?
     
  7. 46addict

    46addict 13726548

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    Did the surging go away when you bumped up the idle to 800? In your video it seems like it did.

    And can you log "fuel press drop across inj" and see what you get for that at idle?
     
  8. 07gts197

    07gts197 forum member

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    No if you watch the idle rpms it moves around quite a bit and the needle jumps a lot too.

    Op either you can use wire piercing probes with your multimeter or push the probes into the back side of the connector, with the car idling and the tps plugged in, until the probes make contact with the back side of the contacts on the harness. Its not invasive and will directly monitor tps voltage. This test will determine if the throttle plate is moving around causing your erratic idle narrowing down possible causes. Its a crap shoot right now without more datalogging capabilities and physically being under the hood checking everything in person.
     
  9. Clown9

    Clown9 Junior Member

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    Alright, I decided to just go ahead and get the forscan elm stuff and this is what it came up with.
    Posting uploaded video since it wouldn't let me upload the fls or csv file.

    Might I also add, I did not know which settings to pick from. And I say that because both TPS readings seem to be waaaay off or I just completely picked the wrong settings

     
    Last edited: Apr 16, 2018
  10. 46addict

    46addict 13726548

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    The TPS voltage is supposed to read somewhere between .95 and 1.30 with throttle off. You can do this with the key on/engine off and verify that voltage increases with pedal input all the way to 5v at WOT. If voltage fluctuates while holding throttle steady, you know there is a problem. Another thing to check is fluctuations when you move the TPS wire around.

    Are there any driveability issues while driving? Are we sure this is not a fuel pressure/delivery issue?
     
  11. Clown9

    Clown9 Junior Member

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    How much fluctuation are we talking about here? I'm going to guess there has to be some
    Also after some reading up there is two sensors whose sum needs to equal 5V. Those being TP1 and TP2 in the video. In the video their sum is like 5.1x volts. Is that a problem?

    No issues with driving other than car kinda hangs when trying to go from a stop then after a second or so of pushing on the pedal it goes and I mean it goes.
    I don't know if that's just me pussy footing the pedal tho
    Also I might add, in the video Fuel Rail Pressure and Voltage are both monitered in the video, albeit only sitting at idle
     
  12. 46addict

    46addict 13726548

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    Yes I see you logged FRP but the numbers are small and blurry from my end. Also looks like a 4 digit number so if it logged in kpa I will need a psi conversion because I don't know metric.

    With a VMP tune there should not be any throttle hang. But as 07gts197 said we are all just taking guesses here without being in the car.
     
  13. Clown9

    Clown9 Junior Member

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    So what exactly do I need to datalog and in what units?

    Just doing a quick conversion FRP was anywhere from 38psi to almost 41psi
    Fuel rail voltage was from 2.68Volts to 2.83Volts
     
  14. 07gts197

    07gts197 forum member

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    The tps voltage should not fluctuate while idling. It looks to me like the tb is opening and closing slighly. The maf voltage reflects that with varying voltages. I doubt the problem is there. I would datalog app (absolute pedal position) to see if that pid is fluctuating too.

    Im not sure what that etc pid is, maybe engine coolant temp but if it is the voltage should not jump around there either.

    Edit: I just looked over a log I took recently and act_ect is for the throttle position actual and mine doesnt bounce around like that.
     
    Last edited: Apr 16, 2018
  15. jpbaily1

    jpbaily1 Junior Member

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    I am having similar issues and will be "trolling" this thread for the solution. :) THX
     
  16. 46addict

    46addict 13726548

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    I asked about fuel pressure because I saw in your other video the pump duty cycle was showing .24. This translates to 48% in percentage value which is high for an idling engine. I think mine was at .15-18. The throttle hesitation could be from a dirty in-line fuel filter and/or a dirty pre-filter attached to the fuel pump which would explain the high duty cycle.
    But it could also be a bad throttle position sensor. Usually people replace the whole TB when diagnosing throttle related problems.

    As for TPS voltage, there should not be any fluctuating at all if the throttle is staying in one position.
     
  17. 07gts197

    07gts197 forum member

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    More datalogging needs to be done with different parameters to figure out the cause. The erratic tps signal seems to be the symptom not the cause.
     
  18. Clown9

    Clown9 Junior Member

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    Which parameters?
     
  19. 07gts197

    07gts197 forum member

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    Fuelsysobd2, stft1, stft2, ltft1, ltft2, iat, ect, app, total number of misfires, fuel pump, fuel rail pressure, battery voltage, cylinder head temp and spark advance. Include the parameters you already have up.
     
  20. Clown9

    Clown9 Junior Member

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    Here are the goods
     

    Attached Files: