chk engine - lean code - 1996 STS
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Cadillac Seville / Cadillac Eldorado Forum Discussion, chk engine - lean code - 1996 STS in Past Cadillac Vehicle Discussion; fantastic...chk engine came on today. ran the codes. forgot the code but the definition was "system running too lean bank ...
  1. #1
    donavo is offline Cadillac Owners Connoisseur
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    chk engine - lean code - 1996 STS

    fantastic...chk engine came on today. ran the codes. forgot the code but the definition was "system running too lean bank 2"
    it said "service emmission system" on the dash when the light went off.

    any suggestions? i dont think its a vacuum leak cuz the engine is not idling on high rpm. idles at like 600-700 when warm.

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    maeng9981's Avatar
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    Re: chk engine D:<

    P0174? List all the codes with the definitions on here, they are needed for proper diagnostics. I don't think P0174 will set Service Emissions System.

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    donavo is offline Cadillac Owners Connoisseur
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    Re: chk engine D:<

    actually u got it right. i just went and scanned the codes. that was the only one. and when it came off it said service emission system. this happened b4 i think with the same code even. if i remember right, the thing tht fixed it was an oxygen sensor. but when it was "fixed" i assumed i would get better performance since the engine wouldnt b lean n e more (its running about 25% lean right now). but it didnt change. now the code came up.

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    maeng9981's Avatar
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    Re: chk engine D:<

    Might want to start from something obvious like vacuum leaks, exhaust leaks and such (that would only affect the bank 2). Which HO2S was fixed? Have you used AC Delco HO2S?

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    Re: chk engine D:<

    you have a vacuum leak somewhere -
    take off the beauty cover and spray carb cleaner around the area -
    when the idle speed increases - you found your leak

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    donavo is offline Cadillac Owners Connoisseur
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    Re: chk engine D:<

    Yeah that's what I did basscatt. Nothing happened though. Also yes. I used acdelco oxygen sensors. I've sprayed the whole compartment a few times alrdy with the beauty cover off. No rpm increase at all.

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    Re: chk engine D:<

    did you check around the back of the intake - there is a little "trap door" that's the backfire pressure relief valve - it is spring-loaded to keep it closed - but could open out if there was an engine backfire

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    Re: chk engine D:<

    Yeah lol. I had a vacuum leak b4 this ended up changing the whole manifold and throttle body. That's where they tested them to b leaking. With these replaced ones it seems so far they're good. I changed them less than a month ago and b4 having them put in I checked that particular spot thoroughly. I think I mentioned this in that last thread. Idk what it could b this tine. Maybe the parts I got r faulty (they're used). But after spraying them many times while the engine idled with no rpm spikes, I don't think they're leaking

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    Re: chk engine D:<

    Did you spray the backfire relief valve behind the P/S pump?

    Check plastic vacuum lines for split type of cracks?

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    Re: chk engine D:<

    Ill check the lines but I'm not sure which lines to check. Some r for liquids. But ill check em again. Also, do I end up getting more performance in the end when the system isn't running lean n e more?

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    Here is a pic of my code scanner readings and monitoring of what was going on. This was taken while in cruise control.
    Attached Images

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    Re: chk engine - lean code - 1996 STS

    That is still showing some sort of lean trim. I assume you still have the PXXXX Bank 2 lean code.............when you changed the intake manifold, did you use new gaskets ??? I ask because lean codes on one bank only are pretty rare, and they're restricted to very few places - the intake gasket(s) being one, a leaky fuel injector O-ring seal is another. Hopefully it's not a cracked intake manifold at a bolt boss on the left (front) side of the manifold..........but your spraying fluid should show that up.............

    Your engine should be showing 1985 rpm at 60. TPS looks good, MAP = .57 X 15 = 8.55 psi absolute: that's good manifold vacuum for 60 mph cruise. The timing is 4 degrees BTDS higher than mine at the same conditions, but that's because you have the higher compression 10.3:1 engine (mine is 10.0:1 and calibrated for 87 octane fuels). I don't like that long term fuel trim. Funny thing is, with lean mixtures your calculated long term mileage from fuel flow should be higher - Most STS in good condition give 23.5 - 25 mpg on the highway at steady 65 mph.

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    Re: chk engine - lean code - 1996 STS

    Hmm. Yes I used the old gaskets. They looked ok. And spraying didn't reveal n e leaks. One issue I have is how u said timing is ok....that threw me off. I showed it to a few experienced car knowera and they all said timing should not b in the negative....they were surprised the car was running. Now obviously I don't even have the slightest clue what all that means but if timing is ok then ill go with ur word. So apart from a cracked manifold, what else could b the problem? Ill attach another picture of a different reading. (Btw idk if that pic I took was when the car was running on a level ground. That's y the rpm might not b as accurate as ud think)

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    donavo is offline Cadillac Owners Connoisseur
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    These r not in cruise control. If these don't make n e thing clear, let me know in what condition u want me to scan it in. Idling, 50 or whatever. Anything to help u diagnose it.
    Attached Images

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    Re: chk engine - lean code - 1996 STS

    2000 rpm @ 70 mph sounds more like a LD8/3.11:1 config.

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