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  #1  
Old December 15th, 2017, 20:21
Blindtheft Blindtheft is offline
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P0351 - Random Limp Mode

I'm chasing my tail and would appreciate any insight.

Patient: 2001 XJ, 4.6 stroker, Viper coil pack mod

Symptoms: Without warning on maybe a dozen occasions over the past couple of weeks the CEL (always p0351) has illuminated and limp mode is triggered immediately. To be clear, I mean there is a steady (not-flashing) CEL and it loses almost all power. It feels like you're giving it gas while also mashing the brakes. Has happened at freeway speeds and while idling. In every case, shifting to neutral and restarting immediately eliminates all issues for a day or so.

Treatment: Nothing happens when wiggling the harness or wires at idle. We've checked grounds, which all seem to be in good shape. I swapped another coil pack in, which made no difference. I have a tune, so really don't want to replace the PCM. Any other ideas?

My horn has never worked. Any chance the clockspring is shorting out and causing this somehow?
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Old December 15th, 2017, 23:02
RCP Phx RCP Phx is offline
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Re: P0351 - Random Limp Mode

Bad spark plug/gap
Bad spark plug wire
Bad coil
Bad wiring(back to the PCM) and/or connections(specially resistance to ground)
Bad PCM
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Old December 16th, 2017, 11:00
RCP Phx RCP Phx is offline
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Re: P0351 - Random Limp Mode

I read thru your other threads. Did you have "Chris" reflash your system? Was he trying to compensate for the undersized injectors(23 lb)? Was any work done with the timing curves? Another far out thought would be something messing with the flexplate/flywheel reluctor.

Some specs on your build might help? I have a 2000 with a Russ P motor and it runs great!
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Old December 16th, 2017, 12:59
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Tim_MN Tim_MN is offline
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Re: P0351 - Random Limp Mode

Quote:
Originally Posted by Blindtheft View Post
.... My horn has never worked. Any chance the clockspring is shorting out and causing this somehow?
Yes.

While the symptoms are non-typical for a faulty clock spring shorted to the TPS, the diagnostic is pretty simple, remove the horn fuse.

Unplugging a faulty Clock Spring or removing the Horn fuse in your fuse block will remove the 12 VDC supply to the clock spring. Once the clock spring short circuit is temporarily disconnected, you should be able to reset the trouble code, and confirm a diagnosis of a faulty clock spring.

CAUSE: The Switch Sense circuit in the Clock spring in the steering wheel hub has shorted to 12 volts battery voltage from the horn button circuit. When the Switch Sense Circuit shorts to the 12 volt HORN circuit the 5 volt TPS signal voltage is driven high. This is because the 5 volt reference voltage used by the Cruise Control “Switch Sense” circuit and the TPS are shared inside the PCM. The TPS has direct input to the Transmission Control Unit.

Shutting off the engine and restarting is essentially re-booting the systems, strongly suggesting a TCM issue, or an intermittant 12 volt short circuit to the 5 volt CCD Bus.
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Last edited by Tim_MN; December 16th, 2017 at 13:07.
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