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1992 F-150 Top End Misfire

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Old 04-17-2017, 09:05 AM   #1
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Default 1992 F-150 Top End Misfire

I am a little new to posting on forums, I hope I am doing this right.
I recently did a tune up.
I replaced the following items:
Spark Plugs
Spark Plug wires
Distributor Cap and button
Oil and filter (10-W30)
Rear Fuel pump
Belt
tensionor pulley

Before I did the tune-up, she was not running bad. She had a misfire every now and then. The rear tank fuel pump was weak, now since the replacement, the rear tank works flawless. Idle was good, top end power was good.

The problem I am having since the tune-up is, she has a nasty top end misfire. At 60 or 65, when i ascend an incline, she starts to misfire really bad. So bad in fact, it jerks the entire truck. My knowledge of the way this truck works is amateur at best. I suspect that I may have cracked the white insulation on one of the spark plugs is the issue. She still idles well (seemingly better than before the tune up).

What I would like to find out is, if the misfire still happens after the spark plug replacement, where would I start next as far as solving the misfire?

Thanks.
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Old 04-18-2017, 09:03 AM   #2
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I would suggest a clogged catalytic converter. But I don't know how you could verify that w/o just changing it.
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Old 04-20-2017, 06:29 AM   #3
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Quote:
Originally Posted by Myron's View Post
I would suggest a clogged catalytic converter. But I don't know how you could verify that w/o just changing it.
Thanks for the input. I did consider the clogged cataylic converter and the fuel filter. I changed the fuel filter. It still had the misfire. Then I took it to the shop, the mechanic told me that when i replaced the spark plugs, I cracked the spark plug on cylinder 5. I also found out the my truck has a straight pipe?
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Old 04-21-2017, 10:09 AM   #4
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You don't say what motor you have but cylinder 5 is easy enough to get to on either a v8 or a 6.
A cracked plug would do that.
If that doesn't work, get a gauge and test the fuel pressure. A new pump doesn't guarantee good pressure.
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