Troubleshooting help
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Northstar Engines and System Technical Discussion Discussion, Troubleshooting help in Cadillac Engine Technical Discussion; I have an 02 Deville I am trying to get through CA smog test. I have a data scanner I ...
  1. #1
    don_k is offline Cadillac Owners Member
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    Troubleshooting help

    I have an 02 Deville I am trying to get through CA smog test. I have a data scanner I use, and found what I thought was lazy 02 sensors. They would indicate lean condition with little variation for significant periods. I replaced the sensors and now they seem to work properly other than at closed throttle, where they once again show a lean condition with very little variation. My first thoght was a vacume leak during high intake vacume conditions. I checked idle map and found 30 kpa/9 in merc idle pressure. My thought is if there is a significant vacume leak my map readings should be higher. Help - suggestions.

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  3. #2
    postman2000's Avatar
    postman2000 is offline Cadillac Owners Fanatic
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    Re: Troubleshooting help

    Any check engine light or codes? If not then why are you concerned with passing emissions? I think you should be ok...

  4. #3
    don_k is offline Cadillac Owners Member
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    Re: Troubleshooting help

    No lights or codes, but all readiness tests in the computer must be successfully completed to pass. Right now the cat converter test and the evap emissions test heve not completed. I don't know yet if this is related to the lean idle condition, but this condition is not normal. My idle fuel trims are both really high (ltft - +28% and stft are still showing +10% or more). Something is not working correctly.

  5. #4
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Troubleshooting help

    Have you cleaned the TB and checked for a ripped plenum Don? A plenum rip will usually set two DTC's, but can't hurt to check it.

  6. #5
    don_k is offline Cadillac Owners Member
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    Re: Troubleshooting help

    Ranger,
    I have sprayed carb cleaner around the area where the throttle body bolts to the intake, is that the area? When I sprayed the solvent there was no change in rpm.

  7. #6
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Troubleshooting help

    Spray it around the rubber coupler between the TB and the manifold at the 6:00 position while flexing it with your finger. If it has a rip, that's where it will be and flexing it will open it up enough to get a response from the spray.

  8. #7
    don_k is offline Cadillac Owners Member
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    Re: Troubleshooting help

    Ranger,

    Thanks for stearing me in the right direction. I could not get a response to spraying solvent around the plenum, but the symptoms w/02 sensors going lean at idle and closed throttle decels supported a vacume leak. I removed the plenum (along w/the intake and injectors) and found a 1 inch+ rip in the 6:00 area. It was not real visible until I pushed on the area where there was a visible line in the 6:00 area. I replaced it and now the 02's are normal.

    Thanks again for the help!!!

  9. #8
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Troubleshooting help

    Those damned things are a real PITA. I suspect mine is on borrowed time at 93K.

  10. #9
    CadillacLuke24's Avatar
    CadillacLuke24 is offline Cadillac Owners Connoisseur
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    Re: Troubleshooting help

    Did they make them out of higher grade rubber in the aftermarket units? That's kind of a hosejob.

  11. #10
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Troubleshooting help

    Not sure if they are available in the aftermarket.

  12. #11
    don_k is offline Cadillac Owners Member
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    Re: Troubleshooting help

    I bought mine from the dealership, but I did find aftermarket units available on the internet. My dealership had them instock and time was a major factor in my decision.

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    CadillacLuke24's Avatar
    CadillacLuke24 is offline Cadillac Owners Connoisseur
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    Re: Troubleshooting help

    I guess rubber gets old. Glad you found your problem!

  14. #13
    Ranger's Avatar
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    Re: Troubleshooting help

    It's not so much that the rubber gets old as it is the combination of EGR and PCV gases settling in the low spot of the plenum after shut down and deteriorating the rubber. Just have a look inside your manifold with a flashlight next time you clean the TB. It's rather ugly in there.

  15. #14
    don_k is offline Cadillac Owners Member
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    Re: Troubleshooting help

    I was surprised at the amount of visible oil in the plastic intake and the gasket interface between the head and intake. I own a 90 vette w/lt5 that I found pooling oil in the intake and installed a catch can in the pcv line that collects the oil befor ingestion into the engine. I am seriously considering doing the same for my northstar.

  16. #15
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: Troubleshooting help

    Make sure of the type of PCV your engine has - 2001 or 2002 saw the change from a rattle-type PCV valve to a fixed orifice in the right (rear) cam cover.

    Think of how long/how many miles it took for that amount of oil vapor to condense in that manifold - would running a catch can system to the bracket in front of the radiator be worth it ....... yes, if you could actually pour oil out of the manifold center distribution log, that's one thing.....but condensed vapor on the interior of the passages ?????

    What is your present oil consumption ?? If the engine is not consuming greater than one quart per 1,500 miles (2,000 to 3,000 would be better) then according to GM your oil use is about in the design window of ~2,000 miles/quart.

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