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Old 04-24-2018, 10:45 PM
Witsend Witsend is offline
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Default P1391 code 2000 Jeep Grand Cherokee

Intermittent loss of signal of Crankshaft sensor or Camshaft sensor after installing a new Crankshaft sensor for P0320 code.(No Crankshaft reference signal at ECM . Jeep initially runs ok cold but as it warms it starts missing on acceleration and then looses all power on acceleration and runs rough at idle and sets P1391. The new crank sensor is an economy brand I suspect was bad out of box.
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Old 04-25-2018, 12:10 PM
ToltecasChavez ToltecasChavez is offline
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Happened to me a few times. One time, one of those aftermarket sensors came with some plastic sheet on top of the sensor and didn't realize it afterwards. I always install new mopar crankshaft. They are ridiculously overpriced, but better safe than sorry.
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Old 04-25-2018, 02:27 PM
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where are you are scoping the cam and crank signals?

back probing at the ECM?

also, just looking at the crank signal does this jeep use a hall effect sensor? if so, make sure the ecm is not faulty and stops sending a 5v power to the sensor when that also gets hot.

Last edited by tech25; 04-25-2018 at 02:33 PM.. Reason: added question about hall effect sensors
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Old 04-25-2018, 07:02 PM
Witsend Witsend is offline
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Quote:
Happened to me a few times. One time, one of those aftermarket sensors came with some plastic sheet on top of the sensor and didn't realize it afterwards. I always install new mopar crankshaft. They are ridiculously overpriced, but better safe than sorry.
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According to instructions that plastic or paper thingy stuck on tip is a sacrificial shim that remains left on the tip of crankshaft sensor during installation that is not supposed to be removed, problem is there is no way to maintain light downward pressure on the sensor up on top to keep it seated against the crankshaft signal ring when you need to access and tighten the bolt from beneath the vehicle, and it is possible it might move or walk away slightly when tightening down the bolt and skew the desired air gap, so I ever so slightly seated the bolt against the sensor, then went on top and pressed it down once again against the signal ring, then went underneath and tighten the bolt the rest of the way.

Quote:
where are you are scoping the cam and crank signals?

back probing at the ECM?

also, just looking at the crank signal does this jeep use a hall effect sensor? if so, make sure the ecm is not faulty and stops sending a 5v power to the sensor when that also gets hot.
sensor
I checked at the sensor harness connectors back probing the signal terminals per service manual, using pins.
The second Crankshaft sensor cleaned up the pattern considerably but seemed to have sets of 4 spikes like a Hill Billy Smile missing a couple teeth and initially thought maybe the crankshaft signal ring was an issue, but a little googling and it is normal and got rid of the P1391code , But I still have a cylinder missing with all new plugs with a misfire code P0304. I take the plug out of #4 wipe off what I thought looked like a tiny hair bridging the electrode gap and swap it with #1. Drive the car and Vehicle still has damn miss but now P0301. I install one of the old plugs in #1 and now all is well.
Bad New crankshaft sensor and a bad new plug . Talk about bad luck
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