barely running Northstar
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Northstar Engines and System Technical Discussion Discussion, barely running Northstar in Cadillac Engine Technical Discussion; '98 Deville Low mileage (79k) Engine with start right up, but will barely run. Give it throttle (1/2 way) and ...
  1. #1
    Harry Yarnell is online now Cadillac Owners Fanatic
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    barely running Northstar

    '98 Deville
    Low mileage (79k)
    Engine with start right up, but will barely run. Give it throttle (1/2 way) and it won't change rpm for about 3 seconds, then it takes off, but won't idle when backed off unless you feather the pedal. Burn your eyes exhaust.
    Swapped MAF, ignition module; checked TPS (ohms) , glass beaded the almost new plugs, new wires.
    Tried to swap ECM, but apparently they won't swap out without being reprogramed (?).
    I'm at a loss...

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    Ranger's Avatar
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    Re: barely running Northstar

    Have you checked the FPR?

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    Harry Yarnell is online now Cadillac Owners Fanatic
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    Re: barely running Northstar

    No. Fuel pressure (engine off) was 44#. Will check with running. Vacuum line looked ok.
    The burning eyes told me that things were excessively rich.
    Oh, no codes set.
    BTW, how DO you get a OB2 ecm to swap from car to car. I've got eight ECM's sitting on the shelf from parts cars, and can't use them.

  5. #4
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    Re: barely running Northstar

    Why can't you swap PCM's? They do need to be from the same VIN (Y or 9).

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    Harry Yarnell is online now Cadillac Owners Fanatic
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    Re: barely running Northstar

    Here's the latest. Car starts instantly. Runs 'ok' for about 30 seconds, then seems to load up. Feathering the throttle is needed to keep it running and the throttle has to be at least 1/2 way to keeping it running; rpms DON"T change (about 350-400 rpm, then it really kicks in and the rpms shoot way up. It'll die in an instant if you don't feather the throttle.
    Fuel pressure is 44# at key on; 50# running. Increases to 55# with the vacuum line removed from the FPR (no fuel present at the vacuum line).
    Attempt to substitute PCM, was futile. Tried PCM's from '97 and '96 .but no start. Seems the injectors are shut off.
    This, I think, has something to do with the VATS. I had similar troubles a few years ago with a '96 STS that I swapped the IPC in, and ran into a similar situation. Had to have it rollbacked to the dealer, who did some software change(?) and it worked.
    Help me out guys; point me to another thing to check.
    I'm going to read the plugs tomorrow and do a compression check just to see what that may show.

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    Harry Yarnell is online now Cadillac Owners Fanatic
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    Re: barely running Northstar

    Oh, fuel pressure holds overnight, so no leaking injectors.

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    Re: barely running Northstar

    Check the FPR (Fuel Pressure Regulator).

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    Harry Yarnell is online now Cadillac Owners Fanatic
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    Re: barely running Northstar

    You keep mentioning the FPR. Why? Pressure too high?

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    Re: barely running Northstar

    If the diaphragm is ruptured, it may be dumping raw gas in the manifold causing it to run very rich.

  11. #10
    Harry Yarnell is online now Cadillac Owners Fanatic
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    Re: barely running Northstar

    ...but the vacuum hose is dry...

  12. #11
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    Re: barely running Northstar

    OK, then you checked it. That's all I wanted you to do. It's good and not the problem.

  13. #12
    Harry Yarnell is online now Cadillac Owners Fanatic
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    Re: barely running Northstar

    Here's an update. Ran a compression test to see what I've got and had 60-70# compression on the front bank. WTF? Thought my gauge was shot. Then I measured the rear bank; 175-185#, all 4 cylinders. I don't believe the HG is bad ; all I can think of is, its jumped time. Is that possible? Looks like I'll be pulling the cam cover for a look.

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    Re: barely running Northstar

    I have never heard that happen, but it sounds about right. yeah, pull that valve cover off and check the valve timing

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    Re: barely running Northstar

    Mine did the same thing, except I had 0 -30lbs of compression on the front cylinders. It ended up being the pin that holds the sprocket in place on the cam shaft fell out.

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    Re: barely running Northstar

    Quote Originally Posted by spin View Post
    Mine did the same thing, except I had 0 -30lbs of compression on the front cylinders. It ended up being the pin that holds the sprocket in place on the cam shaft fell out.
    Did you bend any valves? What did you do to fix it?

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