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Old 04-24-2018, 02:29 AM   #1
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Limp mode, no codes ?

Had the car at NHMS over the weekend and had the car go into limp mode twice during separate sessions. Both times I pulled off line, turned off key and it re started with full power restored. Checked with PS2 and no codes stored. Run this car for 3 years with no engine issues. 2002 chassis w/ '99 3.4, where to start looking?
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Old 04-24-2018, 07:25 AM   #2
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who did your tune?
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Old 04-24-2018, 08:56 AM   #3
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Hey Quad, I read your thread and saw that Softronic reflashed yours and cured your problem. Mine is not the same time dependent issue as the first time it was about 20 min and the second time closer to 15 min. Jorge at ECU Dr. in FL flashed mine to row specs and raised the limiter a bit. I would think if it was a problem with the flash, it would have showed up some time ago. My current theory is a bad servo at the throttle body, but not confident in that. I'm going to check the output from the pedal as well.
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Old 04-24-2018, 09:08 AM   #4
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the issue w the flash may not be that it is causing the limp mode, but rather that it is not reporting it - no cels. this behavior may not be obvious even after several years of operation.

otherwise, is it limp mode or failure to go into open loop, or cams not switching over, or resonance flap not activating?
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Old 04-24-2018, 09:14 AM   #5
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Feels like the throttle got disconnected. Engine drops to idle and throttle pedal has not effect. Shut if off and the ecu resets and all works as it should.
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Old 04-24-2018, 09:21 AM   #6
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ok, that's not limp mode, at least not what i've experienced. when i had a bad MAF and the ecu decided that it couldn't trust it, i got a cel and limp mode - limp mode felt like the engine was lugging or surging over about 4000 rpm - the ecu uses the throttle position to set fueling.

what you have sounds like no gas - fuel filter? fuel pressure regulator? start drawing lots of fuel at high rpm and crud plugs filter and engine dies. or fpr not regulating fuel pressure. if it happens fast enough car may not throw a code. meebe just a matter of checking vacuum fitting to fpr.

also, there was a person on here that was having something similar with a flash from ecu doctors and it was a screw up in programming the rev limiter. probably not your thing, however, as you've been running w this flash for a while.
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Old 04-24-2018, 10:18 AM   #7
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Feels like a switch got thrown and disconnected throttle body from the pedal. Won't come up off idle until I shut it off and restart to "re boot" the ecu.
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Old 04-25-2018, 05:31 AM   #8
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Didn't happen to me on a Porsche, but in a Chevy truck I had the same issue. For me it was the fly by wire control. I was told the fail to idle is the answer to the old Audi 5000 issue where they would accelerate uncontrolled because the failure mode was WOT. I would look there first based on what you wrote. I had an 84 911 that had fuel pressure regulators fail, but the symptoms I had were it stalled when the throttle was pressed. It got the air, but the regulators weren't pressurizing to give it enough gas. Mechanic took a while to figure it out because he told me he had only seen them fail open causing flooding not fuel starvation.
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Old 04-25-2018, 11:41 AM   #9
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Had you changed any of the motor mounts to solid or semi solid. It was one of the side effect I had at track when I changed to Wevo's
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Old 04-25-2018, 03:43 PM   #10
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No change to motor mounts. They are wevo semi solid, but have been there all along. Leaning toward throttle body electric actuator.
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Old 04-25-2018, 07:06 PM   #11
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Using a durametric or PST2 check the voltages of the two pedal sensors, one should always read half of the other. I've seen the same issue you are having with this code:



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Old 04-26-2018, 02:24 AM   #12
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Paul, was code 2135 stored in the dme? A friend hooked up his PST2 at the track and no codes were stored.
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Old 04-26-2018, 05:32 AM   #13
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Yes the code was present, but it results in the exact issue you are having. It can be anything that changes the 2 to 1 relationship between the 2 sensors. This includes at least the pedal sensor, the 6 wires to the DME, and connector 4 at the DME (7.8 DME).
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Old 04-26-2018, 05:48 AM   #14
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I have the pin out details and will test the wires between the potentiometer, the throttle body and the DME. Leaning toward the throttle body based on shop owner's input. He said the potentiometer has two circuits that send inverse voltage to the TB and the TB has similar circuitry. And if the DME sees any annomolies will close the TB until restart.
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Old 04-26-2018, 05:53 AM   #15
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Yes that is exactly what I would do next. It is important that the 6 wires from the pedal sensor to the DME all have the same resistance.
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Old 04-26-2018, 07:51 AM   #16
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Not looking forward to crawling under the dash to access the potentiometer harness connection ;-/
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Old 04-26-2018, 08:57 AM   #17
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Borrow a PST2 and check the voltages first?

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Old 04-26-2018, 10:40 AM   #18
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Will a durametric show the voltage at the pedal?
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Old 04-26-2018, 11:29 AM   #19
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According to their website yes. What is important is the voltage that the DME sees from the two pedal potentiometers while Car is running.

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Old 04-26-2018, 02:49 PM   #20
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Thanks Paul. Hope to have time to get into this over the weekend
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