Blue/black Smoke only after Idle
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Northstar Engines and System Technical Discussion Discussion, Blue/black Smoke only after Idle in Cadillac Engine Technical Discussion; Hey guys...so I've been reading a lot about smoke on the site here, but I'm still not convinced I have ...
  1. #1
    digitalcaddie is offline Cadillac Owners Fanatic
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    Blue/black Smoke only after Idle

    Hey guys...so I've been reading a lot about smoke on the site here, but I'm still not convinced I have a solution to my problem. When I sit at a stop light for a good 60 secs or longer and then take off, I get blue/black smoke just for a second or two. Any suggestions on what's causing this? My oil consumption is 1qt every 1-1.5k miles which does not appear to be excessive and the engine does not burn any coolant so I *HOPE* I don't have a headgasket problem. One post said replace the fuel pressure regulator which they claimed was "easy" but where exactly is this part located? Several other posts say that WOTs cure smoke problems, but I get into enough I think. I haven't done one of the "2nd gear only WOTs to 70mph" but I suppose I could try a couple of those on the interstate tonight after work. Any suggestions would be greatly appreciated.

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    PhantomCadillac is offline Cadillac Owners Fanatic
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    Re: Blue/black Smoke only after Idle

    The secret to the WOT is to keep it in 2nd gear take it up to 6 grand and let it back pedal to 4 grand and repeat 2 to 3 times.
    It will clear the carbon off the pistons going to 6 grand and letting it back pedal to 4 grand will shake the piston rings and take the carbon off of them.
    You will probaly see a reduction in oil consumption too.
    And maybe and increase in mpg.
    Just remember to look ahead and behind for those in society that give tickects for that.

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    misfit6794 is offline Cadillac Owners Connoisseur
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    Re: Blue/black Smoke only after Idle

    Blueish smoke out the exhaust would mean that you are burning oil. But since you are only losing a quart every thousand miles, which is completely normal, I don't think its that. Definetly sounds more like carbon build up, there is a write up in the tech tips section about cleaning your throttle body, this might help a little. I wouldn't worry about headgaskets yet. Im not sure a fuel pressure regulator would have anything to do with it, but i may be wrong. It is extremely easy to change and will be on the top right hand side of the engine, right before the fuel rail. Theres also a write up for that in tech tips.

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    jadcock's Avatar
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    Re: Blue/black Smoke only after Idle

    A bit of blue smoke after idle and/or startup is a classic symptom of valve guide seals. There's a lot of vacuum at idle, and oil more easily gets sucked down into the valve seal. When you take off, that excess oil gets burned off quickly and you notice a puff of smoke. Valve guide seal problems are almost unheard of with these engines, but there are going to be some out there I'm sure. This is nothing any WOT procedure can help you with (if it IS the valve guide seals). This is a mechanical breach and can only be fixed by replacing the seals. A high mileage type oil may help, but I wouldn't count on a quick fix from oil alone.

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    misfit6794 is offline Cadillac Owners Connoisseur
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    Re: Blue/black Smoke only after Idle

    jadcock A bit of blue smoke after idle and/or startup is a classic symptom of valve guide seals. There's a lot of vacuum at idle, and oil more easily gets sucked down into the valve seal. When you take off, that excess oil gets burned off quickly and you notice a puff of smoke. Valve guide seal problems are almost unheard of with these engines, but there are going to be some out there I'm sure. This is nothing any WOT procedure can help you with (if it IS the valve guide seals). This is a mechanical breach and can only be fixed by replacing the seals. A high mileage type oil may help, but I wouldn't count on a quick fix from oil alone.


    see, some of us know what were talking about. I woulda never guessed vavle guide seals.

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    digitalcaddie is offline Cadillac Owners Fanatic
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    Re: Blue/black Smoke only after Idle

    OK...so a little bit of follow-up. At lunch I went out and did a couple runs up 6000rpm in 2nd gear, engine brake back to 4000rpm and then floor it back to 6000rpm (its pretty impressive that the car can do 90mph in 2nd gear!!). After that I went and got a sandwich and didn't see any smoke after sitting at traffic lights so it appears like hammering the throttle *MAY* have taken care of the problem. I'll keep an eye on things this weekend and keep ya all updated.

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    Re: Blue/black Smoke only after Idle

    Have you read the Technical Archives at the top left of this page regarding oil consumption?

    BTW, you are not in second gear when you reach 90. The shifter may be, but the trans has shifted to third, then goes back to second when you back off the throttle.

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    digitalcaddie is offline Cadillac Owners Fanatic
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    Re: Blue/black Smoke only after Idle

    Following the WOT instructions from PhantomCadillac appears to have taken care of my problem. I was driving around all weekend and didn't see any smoke under any circumstances. That's a relief since the car has 145k miles on it, but is still running GREAT and I don't feel like dealing with a major problem right now.

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    Re: Blue/black Smoke only after Idle

    Quote Originally Posted by Ranger View Post
    BTW, you are not in second gear when you reach 90. The shifter may be, but the trans has shifted to third, then goes back to second when you back off the throttle.
    Actually, he is still in 2nd gear at 90. On an SLS, or any LD8 powertrain, 2nd gear is good to about 93 MPH (2nd = 5943 RPM at that speed).

    The same RPM (almost 6000) on an L37 powertrain is only 78 MPH, however.

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    Re: Blue/black Smoke only after Idle

    Appears that a little WOT work may have cleaned things out a bit. In regards to rpm vs. speed, remember that a small engine needs to maintain higher rpm for power delivered (normally aspirated). The N* 280 C.I. engine is a small, sophisticated engine. Bigger than a riceburner 4, yes, but a lot smaller than some of the 400+ c.i. stuff out there. An old drag racing axiom was "There ain't no substitute for cubic inches". It was true in 60, and it's true today. Witness the proliferation of HUGE crate engines.......Wait 'till someone takes a RWD late STS and stuffs a 572 into it........(Yeah, I know.....off the thread, but it's fun to dream....)

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    digitalcaddie is offline Cadillac Owners Fanatic
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    Re: Blue/black Smoke only after Idle

    Yea...I'm pretty sure it was still in 2nd since the needle on the tach only dropped once. It does shift into 3rd gear eventually even though the shifter is in '2'. Does the computer override the shifter to protect the engine from too high rpms?

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    Ranger's Avatar
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    Re: Blue/black Smoke only after Idle

    Now you guys have me doubting myself. You may be correct. I'll have to pay more attention next time I do it. Yes, regardless of shifter position, the trans will shift to protect the engine. Try putting it in 1st one time and nail it. It will shift into 2nd in no time at all.

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    jadcock's Avatar
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    Re: Blue/black Smoke only after Idle

    Ranger, try it on your DHS. 2nd gear should be good until about 92-95 mph (depending on the exact shift point that your car has). 1st gear on your car should be good to over 50 mph (6000 rpm in 1st = 51.6 mph). Again, that's only for LD8 powertrains (3.11 final drive).

    Theoretical maximum speeds-in-gear for LD8 (3.11), assuming 6000 rpm max:

    1: 51 mph
    2: 93 mph
    3: 152 mph
    4: 224 mph

    Theoretical maximum speeds-in-gear for L37 (3.71), assuming 6500 rpm max:

    1: 46 mph
    2: 85 mph
    3: 138 mph
    4: 203 mph

    That's right, both cars have a theoretical top speed of over 200 mph, if the engines were strong enough to push the cars to redline in 4th gear.

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    Re: Blue/black Smoke only after Idle

    I tried first gear once just to see what it would do. The engine winds up to 6000 RPM pretty fast and shifts well before 50 MPH.

  16. #15
    jadcock's Avatar
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    Re: Blue/black Smoke only after Idle

    Larry, the previous owner of your DHS must have slipped a 3.71 transaxle in under ya.

    My '97 SLS would wind out to about 50 in 1st. I can verify that over 90 was attainable in 2nd as well.

    I'd be interested to know what your DHS tops out at in 2nd gear.

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