Question about 1991 Cadillac DeVille

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1991 deville idling very ruff

I have a 91 deville/4.9 v8 pfi. sometimes it will start and run fine. sometimes it will start and run very ruff blowing black smoke. sometimes it will start and idle fine for awhile then run very ruff. durring these ruff running times it will set no codes. i have replaced the pvc valve, egr valve and cleaned the throttle body and tubes, replaced the tps, and idle motor and adjusted them, replaced the map sensor and oxygen sensor, installed delco plugs ( the old ones had black soot on them but looked good) and checked for vac. leaks and bad fuel. i have monitored a fuel gauge while it was idleing ruff and it held 36 psi. the last time i drove it, it set an e47 code, lost data between ecm and bcm but the car ran fine with this code. i am starting to suspect the ecm because when i first start it the car wll run fine, then about 1 or 2 minutes it starts idling very ruff. i read somewhere that the ecm runs in open loop mode for the first minute or two after start then the ecm starts controlling the fuel/air mixture. i am at the end of my rope. help!

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Hi you should change the coolant temp sensor this is a white sensor on top of the intake and is part ot the computer system.

Posted on May 19, 2010

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My 1991 deville 4.9 is running ruff, stalls, hesitates, bucks n jerks when pressing the gas. the fuel pressure is 36psi koeo, while driving it ranges from 35-40.5 psi. I gave it a tune up. so what am i missing? help, car is in great shape just is not runing good at all.

Posted on May 12, 2011


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Posted on Jan 02, 2017

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