The ever present "miss"
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Northstar Engines and System Technical Discussion Discussion, The ever present "miss" in Cadillac Engine Technical Discussion; My Seville has one of the most annoying traits of any Northstar I've ever been in. When you're sitting in ...
  1. #1
    ryannel2003's Avatar
    ryannel2003 is offline Cadillac Owners Connoisseur
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    The ever present "miss"

    My Seville has one of the most annoying traits of any Northstar I've ever been in. When you're sitting in traffic, the car has an idle that is anything but perfect. It's a slight "miss" you can only feel through the seat. The tach shows no movement whatsoever, and the car runs like a raped ape. So far, it's the only Northstar (of 20 or so I've driven) that has ever had one this bad. It feels almost like a slight misfire. Shows no codes whatsoever. Brand new intake plenum boot and new CKP. Whats the deal here? Tune-up? Slight vacuum leak? It has done this since I purchased it, and does it when its cold or warm. Temp of the motor has no effect. I thought for sure it was a cracked plenum, but I guess not. It's not a big deal, it's just annoying because otherwise the motor runs beautifully.

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    Ranger's Avatar
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    Re: The ever present "miss"

    Have you cleaned the TB? Have you checked the FPR for a leak? How many miles? Might be time for plugs.

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    ryannel2003's Avatar
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    Re: The ever present "miss"

    Just cleaned throttle body, and the FPR had no leakage. Car has just a hair under 66k miles. My thoughts have been the spark plugs for awhile, though the car did have headgaskets and the water crossover done before I bought it, so I was thinking something could have been knocked loose. But that would have most likely effected performance, which is perfect. However the two times I powerwashed the motor the car was misfiring like crazy. I've done that to over 20+ Northstars without any trouble whatsoever. Could this be a link? It took about 10 minutes after that for the car to return to normal.

    I will check the FPR again. I was having hot start problems for awhile, but once my CKP started going out I chalked it up to that. Thanks for the help so far Ranger!

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    Re: The ever present "miss"

    Hot start problems point to the FPR. I have known of one or two that did not leak under fuel pressure, but add vacuum to the other side and it did. The other thing that I don't like is the missing when washed. That might point to boots or the cassette itself.

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    ryannel2003's Avatar
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    Re: The ever present "miss"

    I was actually thinking of replacing the spark plugs and boots at the same time, since they have been known to crack once they get old. I have never thought of the cassettes as a problem point, but I'm sure they could be. The FPR is a cheap part, I'll replace it anyway even if it doesn't have issues. Thanks so much for the help!

    If anyone else has a suggestion, please chime in. This car idles like a 4 cylinder, not a V8 Cadillac

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    ryannel2003's Avatar
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    Re: The ever present "miss"

    Well I have one option to check off my list. Took car to dealer today because the valet switch is broken and I can't get into my trunk without a key, so I tell my tech to check out the miss. He says he can definitely feel it, and he hooks up a Tech II to see if a cylinder is misfiring. Everything looks normal, so I tell him to go ahead and throw some spark plugs in there to see if that solves it. Well $145 later the car still does not idle correctly. I was going to get the boots but the guys there said they rarely ever go bad, and it was a waste of another $30. The motor runs great unless you're at a stop light. No codes show up. It idles much smoother in Drive than Park. I've spent every dime of my money on this car, so it's going to have to stay like this for awhile. I've gotten so sick of it I have really contemplated on selling it, but I love it too much. I just want it have a smooth V8 idle, not a 4 cylinder one.

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    Re: The ever present "miss"

    what octane are your running?
    do you get any smoke out of the pipes/odor?
    check for a vacuum leak no matter how small, make sure the hose from the brake booster to the intake has clamps on both ends and again no leaks.
    a bad motor mount will cause greater vibration so a blown front mount can make it more NOTICEABLE but not CAUSE IT (unless your just feeling the normal vib of a V8)
    when you pop the hood does it look like its bucking at all?

  9. #8
    ryannel2003's Avatar
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    Re: The ever present "miss"

    87 octane, but I'm filling it up tomorrow with 93 to see any improvement. No smoke at all, runs like a bat outta hell. When the hood was popped today, my mechanic had it in drive and was giving it gas and the motor had noticeable movement. I'll also check for vacuum leaks, as I'm sure that is what it has to be. Right now the car has me flat broke, so any kind of part that might possibly be needed will stay on hold at the moment.

    I did just remember my car sometimes has trouble starting when warm, which points to the fuel pressure regulator? Any connection there? Trying to narrow down the field here. Thanks a million!

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    Re: The ever present "miss"

    I did just remember my car sometimes has trouble starting when warm, which points to the fuel pressure regulator? Any connection there?
    Yes that points to the FPR and there is a very big connection there.

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    Re: The ever present "miss"

    could try a good system cleaner like lucas
    see if that clears it up

  12. #11
    ryannel2003's Avatar
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    Re: The ever present "miss"

    Ok so a fuel pressure regulator could cause hard hot starts and idle problems? Sounds like that could be my smoking gun. As for a cleaner, I'm going to throw the Chevron Techron that Sub is talking about at my next gas up. I did just fill up with 93 and it's a tiny bit smoother, but not Northstar smooth.

    I will get my FPR replaced ASAP. I hope thats my problem. If not, I'm going to start heavily.

  13. #12
    Ranger's Avatar
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    Re: The ever present "miss"

    Don't replace the FPR. Check it first. No sense in replacing it if it is not leaking.

  14. #13
    ryannel2003's Avatar
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    Re: The ever present "miss"

    I know this has been discussed 1000x times, but what does the FPR do? I also can no longer see the pictures you posted a few years ago, and the ones posted looked different than my 2000 did. I know you take off the beauty cover, but from there I am stumped.

  15. #14
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    Re: The ever present "miss"

    The FPR keeps the fuel pressure constant across the injectors. The fuel pump puts out 40-50 psi. That is too much at idle (high engine vacuum) so the high vacuum pulls on the diaphragm and lifts the pinle valve, returning most of the fuel from the rail back to the tank. At WOT, it's the opposite. Engine vacuum drops, and the valve closes the return line delivering max fuel pressure to the injectors that are pretty close to staying open.

    Just remove the beauty cover and locate the FPR on the rail. Pull the vacuum hose while at idle and look for fuel at the nipple. There should be none.

  16. #15
    ryannel2003's Avatar
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    Re: The ever present "miss"

    Since I'm certified idiot in Northstar problem solving knowledge, I'm going to post a picture of my engine. If someone could please show me (with a large red arrow) where the FPR is, I'll buy them something.


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