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Re: 1991 GMC runs poorly after engine is warm
I see it’s your first post, so welcome to the message board.
Let’s address the check engine light first.
Being you said the truck run ok for a year, until a week ago, my guess is there is an O2 sensor on it, but you just have not found it. I’m assuming the check engine light just started going on as the problems started.
Did the check engine light just start coming on as the problem started in the last week?
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