Misfire help! - JeepForum.com

 
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post #1 of 6 Old 04-05-2013, 10:50 PM Thread Starter
swquintal5307
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Misfire help!

My 01 jeep grand cherokee 4.0 recently started misfiring and I can't figure out what it is. I figure it must be coil pack, injector, or possibly a crank sensor? I got the engine codes and they are P0320 P0300 P0301 P0306.
P0320=no crank reference signal at PCM
P0300=random multiful misfire
P0301=cylinder 1 misfire
P0306=cylinder 6 misfire

What do you guys think it is?

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post #2 of 6 Old 04-06-2013, 05:27 AM
MeBoosta
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Ummm. Cylinder 1-6 use the same coil I believe. Are there any oil leaks?
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post #3 of 6 Old 04-06-2013, 07:13 AM Thread Starter
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Ummm. Cylinder 1-6 use the same coil I believe. Are there any oil leaks?
I believe my valve cover gasket is leaking. Would that matter?
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post #4 of 6 Old 04-07-2013, 09:30 AM
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Generally an oil leak is a vacuum leak. The crank case ventilation system pulls unmeasured air from the faulty gasket and redirects it to the manifold. Chances are that your scanner would display a code for a "lean mixture"if that ever happens.

But in this case I'm thinking its your coil pack.

Here's a good way to diagnose it. Go to your local Home Depot or Lowes and see if you could find one of these "voltage pen".

Simply start the Jeep and place the tip of the pen on the ignition wire. Don't disconnect them, all you're doing is placing it against the wire, if there is current flowing through them the pen will turn red, indicating that the coil is working. If not, then I suggest you replace it.
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post #5 of 6 Old 04-07-2013, 10:29 AM
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I would verify the crank position sensor before you start throwing parts at it. The CPK tells the PCM to tell the coil packs when to fire.

Search or ask in the WJ Grand Cherokee Tech Forum here:

http://www.jeepforum.com/forum/f310/

Look and/or ask about checking and/or replacing the crankshaft position sensor and go from there.

As for a vacuum leak (oil leak), if it is an oil leak from a gasket such as the valve cover it could possibly allow extra air to enter through the intake. BUT, that air enters BEFORE the throttle body and will not generally cause a lean condition. The crankcase ventilation system is designed to work that way. What it does draw in is burned off during combustion. It is part of the pollution controls of a vehicle.

An intake vacuum leak, on the other hand, will affect how an engine runs but will not generally cause a misfire in newer vehicles.

Oh, and forget the "voltage pen". You have a system with coil packs and there are no plug wires to check for spark passing through. Also those testers are the most basic and will not work on auto electric systems. They need a minimum voltage level to detect (12 volts is too low).

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post #6 of 6 Old 04-07-2013, 10:56 PM Thread Starter
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Quote:
Originally Posted by FernBchJeep View Post
I would verify the crank position sensor before you start throwing parts at it. The CPK tells the PCM to tell the coil packs when to fire.

Search or ask in the WJ Grand Cherokee Tech Forum here:

http://www.jeepforum.com/forum/f310/

Look and/or ask about checking and/or replacing the crankshaft position sensor and go from there.

As for a vacuum leak (oil leak), if it is an oil leak from a gasket such as the valve cover it could possibly allow extra air to enter through the intake. BUT, that air enters BEFORE the throttle body and will not generally cause a lean condition. The crankcase ventilation system is designed to work that way. What it does draw in is burned off during combustion. It is part of the pollution controls of a vehicle.

An intake vacuum leak, on the other hand, will affect how an engine runs but will not generally cause a misfire in newer vehicles.

Oh, and forget the "voltage pen". You have a system with coil packs and there are no plug wires to check for spark passing through. Also those testers are the most basic and will not work on auto electric systems. They need a minimum voltage level to detect (12 volts is too low).
I replaced the crank sensor less than a year ago. You don't think it could have gone bad already do you? I'm really thinking it's a fuel issue....
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