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Old 03-02-2015, 09:50 AM
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Error code 1391

I drive a 99 Grand Cherokee Larado with a 4.7 V8. I changed all the plugs and ignition coils about 3 weeks ago to correct a missfire. Seemed to work and then I noticed what seemed to be excessive lifter clattering when it was cold, worse when going up hill but it went away at temp. After reading up I thought it might be the 10W40 I had them put in at the last oil change. So I had it flushed and 5W30 put in. It didnt work. And now last nite it started sporadically missing while on the highway and the check engine light went on. The code is 1391 and internet says its cam or crank position sensor or worse. Any tips on figuring this out?
Its has 146,000 miles on it without much trouble.

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Old 03-03-2015, 09:28 AM
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Re: Error code 1391

I think the 1999 4.7 has a single overhead cam on each side. That would mean NO lifters. So the clatter you heard may be engine knock brough on by a timing issue which could be related to a cam or crank position sensor.

Changing the spark plugs may have improved firing if the old plugs were in very bad condition, but not sure either would produce engine knock. Your error code may be right on with the position sensor, but then again sometimes an error code only points us in a certain direction.

10 W 40 oil in an older high milage engine might not be so bad, but if you live in a very cold climate, that thick oil when the engine is cold could make for hard start ups and a lack of a good oil supply during warm up.

Please follow up with your progress. That could help others along the way.
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