2001 Cadillac DeVille Lean Misfire Fix

2001 CADILLAC DEVILLE
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ROWLANDRT
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2001 Cadillac DeVille V8-4.6L VIN Y @ 85K miles. Replaced Ho2 sensors, cleaned MAF and replaced air filter. Sensors showed normal wear. Cleared codes and engine runs rough at idle but smooths out at higher RPM. Codes returned. Checked all vacuum lines and EGR all are fine. Do have loud air intake sound near intake manifold? But all looks well.

Ideas and recommendations?
Feb 23, 2007 at 9:45 AM
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CHEVY22
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which 02s were replaced ?? and was the pcm reset after that , are the codes current ???
Feb 23, 2007 at 9:53 AM
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CHEVY22
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hmm , let me think about this , the p0171 is bank one lean and you have a random misfire code , im wondering if you have a new part that is bad
Feb 23, 2007 at 10:10 AM
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ROWLANDRT
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Replaced the following; Heated Oxygen Sensor (HO2S) Replacement Bank 1 Sensor 1
. Heated Oxygen Sensor (HO2S) Replacement Bank 1 Sensor 2
. Heated Oxygen Sensor (HO2S) Replacement Bank 2 Sensor 1

PCM reset and codes are current.
Feb 23, 2007 at 10:12 AM
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ROWLANDRT
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Used after market sensors from Oxygensensors.com. I had same thought that one of the sensors may be bad? But local mechanic seems to think there may be a air leak in throttle body?
Feb 23, 2007 at 10:18 AM
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CHEVY22
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yeah there is something wrong here , if the ho2s are all known good which at the moment we have no idea , have you checked the fuel pressure yet spec is 41-47 psi
Feb 23, 2007 at 10:18 AM
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ROWLANDRT
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Fuel PSI and electrical check fine. MAF seems to be OK but don't want to go there yet.
Feb 23, 2007 at 10:24 AM
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ROWLANDRT
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Meant to use both 0171 & 0174 codes in subject! Just noticed I used 0171 twice.........
Feb 23, 2007 at 10:28 AM
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CHEVY22
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the throttle body leak really isnt a problem with the caddys , if everything else checks i would fall back to the 02 bank one sensor one , go to gm and get one , when i was at the dealer i would see 02's that were aftermarket bad and reading wrong , you sound like you know what your doing , and youve done some good diagnosis

again my opinion without actually seeing the car suspect b1s1 random misfire lean bank one ??? makes sense
if you had a tech 2 scanner you could watch them and see for sure

thanks jim
Feb 23, 2007 at 10:30 AM
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CHEVY22
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same difference fuel trim lean bank 2,,ho2s related , and i use this loosely most of the time
Feb 23, 2007 at 10:33 AM
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CHEVY22
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any way gms procedure for this condition , is check fuel pressure spec , check wiring to h02s , chck for split or laking vaccum hoses , replace h02s related
Feb 23, 2007 at 10:38 AM
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ROWLANDRT
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Jim,

Same thought process hear. Not bad for a shade tree mechanic who started rebuilding engines at the age of 13 on his first car which was a 57 chevy, eh.

Thanks,
Ray
Feb 23, 2007 at 10:39 AM
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CHEVY22
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hey man , i started at my uncles harley shop at 13 , and look who i work for now , the big guys ,hope i helped dude , you will get this im sure and im almost sure of the failure when the codes are gone hit me up

thanks

jim
Feb 23, 2007 at 10:48 AM
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ROWLANDRT
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Will do............
Feb 23, 2007 at 10:50 AM
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ROWLANDRT
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All,

Final fix was remove and replace plenum duct. It was cracked.....go figure. Replaced plugs as well and runs great....... :D

Thanks...
Feb 28, 2007 at 11:07 AM
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SERVICE WRITER
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Poetry in motion!!
Feb 28, 2007 at 11:21 AM
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CHEVY22
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good deal , cheap fix

good lucj

take care

thanks , jim

oh and if you are happy with the info please leave some feedback we all donate out time here helping people for free
Feb 28, 2007 at 11:25 AM

Suggested Repair

Replace the cracked intake plenum duct. Spark plugs were also replaced; after that the lean and misfire codes cleared and the engine ran normally.

Conversation Summary

A 2001 Cadillac DeVille with about 85,000 miles set P0171, P0174, and P0300, idled roughly, and made a loud intake sound. Oxygen sensors, the air filter, vacuum lines, EGR, fuel pressure, and electrical checks did not solve it. The expert suspected an aftermarket oxygen sensor or an air leak. The owner later found a cracked plenum duct; replacing it and the spark plugs fixed the problem.

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