Help, complete drop in LOAD during WOT

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  1. #1
    Member Array raetza's Avatar
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    Default Help, complete drop in LOAD during WOT

    I've been fighting this nasty little problem for a while and need some help. My car is an 06 Mustang GT with a forged/stroked 3V and a KB 2.6, Comp Cams Stage II Blower cams, 80 lb injectors, return fuel system running E85.

    Problem I'm having is under load doing WOT pulls while tuning my MAF curve, the car suddenly falls off like I let off the throttle. I have logged everything I can think of to find a corresponding event...and nothing. Spark is constant, Throttle angle remains at WOT, A/F is good...as I said it feels as if I let off the throttle ...but didn't. Load suddenly drops like a rock. The only way to recover is to let off the throttle and then get back on it.

    Any ideas anyone?

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    I know when i was trying to get my maf curve that adjusted i was having a similar problem. I was doing the runs in 3rd gear. I did notice the sound of the exhaust changed for a fraction of a second a few times. On the datalog it showed the load decreased (not sure exactly what drops like a rock means) to less then 200%, the spark increased a few times. On the graph it looked like there were a couple of spikes. We figured out to be a slight loss of traction.

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    Member Array raetza's Avatar
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    When I say "Drops like a rock"...I mean the load goes from 1.945 to 0.30 instantaneously...just as if I had completely let off the throttle....but I didn't. When I do let off for a bit and then get back on it...it recovers. TP ABSOLUTE remains constant for the event.

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    Could the blower bypass be malfunctioning? Does it happen at the same point every time?

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    Member Array raetza's Avatar
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    Thanks for the input .... I actually had considered disconnecting the bypass and keeping it closed....just for a test. I haven't done that but guess that I will. It actually FEELS like the throttle is closing...but I have logged every PID I can find that has anything to do with throttle and none of them ever show that the throttle is coming off of WOT until far after the drop in Load (when I actually let up).

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    Quote Originally Posted by raetza View Post
    When I say "Drops like a rock"...I mean the load goes from 1.945 to 0.30 instantaneously...just as if I had completely let off the throttle....but I didn't. When I do let off for a bit and then get back on it...it recovers. TP ABSOLUTE remains constant for the event.

    Have you adjusted the load with failed maf tables? And on another note what gets scaled for a motor exceeding 1.999 load? Motor size?

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    Member Array raetza's Avatar
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    Thanks for the input....but yes I have modified the load for failed MAF table. Can I log a failed MAF condition?

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    Member Array raetza's Avatar
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    It's not the KB bypass. I tied it shut and the event still occurs. I'm all but convinced that the throttle is being commanded shut and I'm not logging the correct PID to show it....or the correct PID(s) to shed light on why.

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    Have you logged Torque source?

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    Premium Member Array Eric Brooks's Avatar
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    Check the screenshot for the parameter to see what the PCM is commanding the throttle to do. 82 degrees = WOT

    Name:  Parameter.JPG
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    Email me your tune file and I'll take a peak at it if you want ( eric at brooksspeed dot com)

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    Member Array raetza's Avatar
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    Name:  LOG1.jpg
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    Name:  LOG2.jpg
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    Eric, thanks for the input. I was logging TP ABSOLUTE previously as shown in LOG1. I logged ETC COMMD TA in LOG2. Both events appear to show the throttle position remains WOT until I let off...which is well past the event (loss of LOAD and MAP).

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    Member Array raetza's Avatar
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    @VistaBlue08. I relogged last night with TQ SOURCE and it remains a ZERO for the entire event ... so it doesn't seem to give any hints. Thanks, Alan

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    I had this issue with a 2003 Mustang GT. it turned out that there was a problem with the coils, as they all cut loss in power during WOT.

    but the RPM didn't drop to zero as it only dropped to 2rpm and stayed there.

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    Member Array raetza's Avatar
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    Anyone have any fresh ideas for me on this? I was convinced that I had S/C belt slip...but have now discounted this as a possibility. I am fresh out of ideas on what to look for! :(

    Again, for review...I have logged the following:
    1) LOAD and MAP (both inferred) drop suddenly while WOT with a sudden loss of power. Let off of the throttle and get back on it and it goes again for a bit until the same event re-occurs.
    2) SPARK remains constant through the event until LOAD drops, then it increases
    3) No indications that I have logged show the throttle coming off of WOT until I release it (after the power loss)
    4) Injector Pulse Clockticks remain constant until the power loss, at which time they drop
    5) A/F (set currently at 7.4 for high load on E85) go richer than my Wideband will measure (< 6.7) at the time of the power loss
    6) My Boost gauge drops from 15PSI to under 0 instantaneously at the time of the power loss
    7) Airflow through the MAF decreases almost in half at the time of the power loss
    8) Belt is not slipping
    9) Tires are not slipping
    10) KB Bypass is not opening (I tested by tying it shut)
    11) If I remain WOT after the power loss, the car struggles along as you would expect it would with A/F being hugely rich. Boost will NOT return until I let off the throttle for about a second and then stab it again.

    Thanks to anyone with ideas!

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    Premium Member Array Eric Brooks's Avatar
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    The MAF counts fall resulting in everything else you see. Your boost is going someplace.

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