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Cad-Deville 1991 4.9L 300K miles
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74 Posts
Discussion Starter #1
Hello, I failed emmissions on 91 Cad Devile 4.9. The Cat is only 1.5 years old and I replace 2 fuel injectors. Cleaned EGR 2 years ago and looked fine 1.5 years ago. I do not have any codes E091 transaxle..What shouuld I check.
 

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Cad-Deville 1991 4.9L 300K miles
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74 Posts
Discussion Starter #3
MODE Idle Fail Reading Standard
HC ppm 2240 should be standard 220
CO% 2.56 should be or less 1.20

MODE High Idle Fail Reading Standard
HC ppm 299 should be standard 220
 

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Super Moderator
2010 DTS
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87,415 Posts
If the vehicle has failed as a result of high CO and HC, the CO failure should be diagnosed first. If the "Service Engine Soon" or "Check Engine" light is on it should be diagnosed prior to any emissions diagnosis. CO Failure is the result of an excessively rich air fuel mixture. The following is a list of the most common causes:
- Defective Oxygen Sensor
- Inoperative Air Injection System (if equipped)
- Leaking or defective Fuel Injectors or FPR
- Restricted air filter (especially if high CO is present only at high RPM)
- Vacuum leaks resulting in improper MAP sensor operation
- Defective air mass or air flow sensor
- Malfunctioning fuel evaporation system or purge valve
- Defective Catalytic Converter
- Defective thermostat (cooling system), thermostat stuck open
- Oil contaminated with fuel, excessive miles between oil changes

HC Failure is the result of incomplete combustion. Any item that causes incomplete combustion can result in high HC. The most common causes are:
- Worn spark plugs
- Defective spark plug wires
- Worn distributor cap and/or rotor
- Improper ignition timing, usually over advanced
- Vacuum leaks
- Engine mechanical failure, low compression, worn valves, excessive oil consumption
 

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Cad-Deville 1991 4.9L 300K miles
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74 Posts
Discussion Starter #5
Thanks I will start working on this weekend. I have a question starting with the CO failure which I will work on first as advised. I do not have a "service engine soon" or check engine light" and the only code is E091. Would the absence of code eliminate some of the items like (catalytic convert, oxygen sensor?)on this list as the least likely. If so please tell me where you would start?
 

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Super Moderator
2010 DTS
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Hard to say with no codes. Might check the EGR tubes down in the TB and see if they are carboned closed. The absence of codes should eliminate those things that are monitored.

P.S.
We don't know what those codes mean unless you post the definitions along with the codes.
 

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Cad-Deville 1991 4.9L 300K miles
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74 Posts
Discussion Starter #7
I changed oil replace Oxyg. sensor and took it to the test after driving for about 15-20 minutes. I am almost there failed MODE Idle Fail Reading Standard HC ppm 300 should be standard 220
Any advice I am almost there maybe drive around a little more.
 

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Cad-Deville 1991 4.9L 300K miles
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74 Posts
Discussion Starter #8
Thanks again I changed all of the spark plugs, wires distributor cap and put new oil, 95 octane drove car for about 15 minutes adn passed easily.
 
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