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Old February 15th, 2017, 07:35
Spydie Spydie is offline
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Join Date: Feb 2017
Location: Michigan
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1990 4.0 auto misfire at 1700rpm

About to pick up a 1990 comanche with a 4.0 auto in it but am leary as it has a slight misfire at 1700rpm. The engine was just rebuilt by an actual engine machine shop so its not a garage build. The engine was bored out .020", over sized pistons, new rods, has cleggs stage 1 cam and cleggs stage 2 head. The engine has maybe 50 miles on it after the rebuild so its still in its break in period. Am wondering before i get this, what might the general causes be? Would like to know how little or big of an issue it might be.

Edit: When i went and looked at the truck the engine would only misfire once. Owner says its a crap shoot on if it will happen or not any given day
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Old February 15th, 2017, 11:29
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old_man old_man is offline
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Join Date: May 2003
Location: Loveland, Colorado
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Re: 1990 4.0 auto misfire at 1700rpm

My bet would be on an injector that dried out and is clogged, but before I bought anything I would do a wet/dry compression check. I would take my endoscope and look down the cylinders.

An oil assay should show you if there is any metal in the oil.

A question would be if they used any breakin lube on the cam before starting it up. The assay should show that up as long as they haven't done an oil change.
Tom Houston - Former Colorado Chapter President , Terminal Adrenaline Junkie, and Rocket Scientist
Loveland, Colorado My teardrop build
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