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P0351 - Random Limp Mode

Blindtheft

NAXJA Forum User
Location
United States
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?
 
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
 
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!
 
.... 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.
 
Last edited:
I was away during the holidays and have otherwise been occupied, but am now back to chasing my tail. UPDATE:

It's getting worse. I can't make it more than 3-5 miles without it being triggered.

I pulled the horn relay out of the passenger footwell panel. This was to cut power to the clockspring in case it was shorting out or something. No change.

Replaced PCM with one that has no tune. No change.

In every case, shifting to neutral and restarting immediately eliminates all issues for a day or so

This is no longer true. Upon occasion, even putting in park, removing the key, and restarting doesn't eliminate the issue. Clearing the code with a code reader still has a 100% success rate so far, but the CEL and symptoms do come back within a minute or two upon occasion.

I have new plugs on order. My current set are the NGK (3459) ZFR5N and about a year old. They look okay to me and are gapped to .35 (stock).

I don't imagine one of my Magnacore wires is bad. I'd be getting a misfire code as well if that were the case, yeah?

This all started following a Jiffy Lube oil change in case that helps trigger any suggestions!
 
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!

The tune came well after I sized up the injectors. I believe Chris did give me 6 degrees or so of advanced timing, but honestly I pretty much just let him do his thing and didn't take notes. And he's a hard man to reach... Regardless, issue continues with a new PCM.

What specs would be useful do you think? I keep a list of work done to date:

1. Armor – bumpers, transfer case skid plate, rock rails, and gas tank skid installed
2. Oversized wipers installed
3. Headlight switch replaced
4. Wiring harness for headlight switch replaced
5. Headlight relay installed
6. CCV/PCV elbows and grommets replaced
7. Breather valve hose replaced
8. Fuel cap replaced
9. Valve cover gasket replaced
10. Lift gate struts installed
11. Dynomax catback exhaust installed
12. Rear sway bar removed
13. Cut and folded rear quarter panels
14. Napier fender flares installed
15. Quick disconnects for front sway bar installed
16. Rear bump stops installed
17. Remote door lock programmed at dealership
18. Air filter replaced
19. Oversized oil filter installed
20. Stroker motor installed
21. Serpentine belt replaced and tightened
22. Water pump replaced
23. Idler pulley replaced
24. Thermostat replaced
25. Spark plugs replaced (three times so far)
26. A/C compressor mounting bracket replaced
27. A/C charged
28. Headliner and armrest replaced
29. Floor mats replaced
30. Injectors replaced with 4 hole
31. Braided brake lines installed
32. Brown dog motor mounts installed
33. Odyssey battery installed
34. Brass battery clamps and wing nuts installed
35. Upgraded alternator lead, battery cables and ground wires installed
36. D44 installed in rear
37. RE lift 3.5” installed
38. Rear locker installed
39. Currie steering installed
40. Emu steering stabilizer installed
41. Ball joints inspected
42. Oil changed
43. Radiator flushed
44. Transmission flushed
45. Brakes bled
46. Fenders trimmed and tucked
47. Center console latch replaced
48. Center console brace installed
49. Headlight bezels replaced
50. Radiator cap and all hoses replaced
51. Stereo replaced
52. Speakers replaced in rear
53. Hood lamp replaced
54. Black magic brakes and new calipers and rotors installed up front (147,000)
55. Cibie headlamps and Osram 70/65w bulbs installed
56. Front amber side marker lights installed
57. Tires and wheels 32 x 11.50 (3.75" backspacing) and keyed lug nuts installed
58. Alignment at 4Wheel Parts
59. Bump stops replaced in front and again in back
60. Spring (coat hanger) installed in lower radiator hose
61. Temp sender unit replaced (150,000)
62. OBD II app interface installed
63. Thermostat replaced again (150,000)
64. Thermostat housing replaced (150,000)
65. Radiator cap replaced again (150,000)
66. Evap leak troubleshoot
67. Flushed cooling system again and repeatedly (150,000)
68. Bar pin eliminators installed in rear
69. Rotated tires (153,000; 164,950)
70. Correct speedo installed
71. Replaced braided brake lines, brake flush (153,000)
72. Replaced oil pressure sending unit (153,000)
73. Changed gear oil front and rear (153,000)
74. Cleaned idle air control valve
75. Replaced interior, license plate, and under hood lights with LEDs
76. Dash cam installed
77. Washable air filter installed
78. Compression test performed
79. Misfire troubleshoot
80. Replaced injector pigtails
81. Throttle position sensor
82. Crankshaft position sensor
83. Viper coil
84. Magnacore spark plug wires
85. Camshaft position sensor check (toothpick test)
86. Change injectors again
87. Liftgate struts again
88. Rubber pcv hose fittings
89. O2 sensors
90. Tune
91. Water pump – Hesco (161,000)
92. Serpentine belt (161,000)
93. Flush block, heater core (161,000)
94. Thermostat (161,000)
95. Thermostat housing (161,000)
96. Radiator (161,000)
97. Washer fluid reservoir hole plugged
98. Replace shock boots
99. Fan clutch – ZJ (161,000)
100. Lubricate doors
101. Replace wipers again
102. Replace license plate holder - front
103. Shackle relocation brackets
104. Ballistic comp shackles
105. Oil pressure sending unit (165,000)
106. Remove old alarm
107. Deaver leaf springs (165,000)
108. DPG Off-Road rear spring bump stop plates
109. Replaced coil pack (165,000)
 
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