Weird 4.9l issues
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HT4100 4.1, 4.5, 4.9 Discussion, Weird 4.9l issues in Cadillac Engine Technical Discussion; Ok, So i keep putting more cash into my 94 4.9l and it seems like more stuff is breaking. So ...
  1. #1
    MitchMeister- is offline Cadillac Owners Member
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    Weird 4.9l issues

    Ok,
    So i keep putting more cash into my 94 4.9l and it seems like more stuff is breaking. So I just recently replaced my TPS, do to the fact that i was getting those check engine lights. Now my car idles at around 1200rpms, and it feels like it's missing. The power is back now, but it runs like crap. The newest development is that it's starting REALLY hard, (like tries to turn over but takes two or three cranks) and the weirdest thing is that my headlights dim when i accelerate and when i brake... and today i was sitting in my friends drive way with the car running and i got a code 47? So i'm a bit confused cause i keep replacing parts (ie.. egr, tps, maf, o2, fuel pressue regulator) and nothing is fixing it. And the worse part is that it ran fine this time last summer, and it all went down hill after the fuel pressure regulator went. Any insight would be great... since i don't know where even to start anymore.

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  3. #2
    caddydaddy's Avatar
    caddydaddy is offline Cadillac Owners Connoisseur
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    Re: Weird 4.9l issues

    How is electrical system? I'd check the battery, alternator and all the cables and wiring.

  4. #3
    I~LUV~Caddys8792's Avatar
    I~LUV~Caddys8792 is offline Moderator
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    Re: Weird 4.9l issues

    Yeah, sounds more electrical than anything else.
    "They call Alabama the Crimson Tide, call me Deacon Blues."

  5. #4
    MitchMeister- is offline Cadillac Owners Member
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    Re: Weird 4.9l issues

    Battery is a 6month old delco 950 CCA. Alternator is 3 week old delco also. I'm gonna double check that a wire isn't burned through and the ground cable.

  6. #5
    caddydaddy's Avatar
    caddydaddy is offline Cadillac Owners Connoisseur
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    Re: Weird 4.9l issues

    Just because the parts are fairly new, doesn't mean they are good! I'd double check the battery and alternator output as well as the wiring.

  7. #6
    MitchMeister- is offline Cadillac Owners Member
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    Re: Weird 4.9l issues

    Well i seemed to have figured it out. I went back and checked the ICM after reading things on here and low and behold it had stopped working, and not only that the unit was cracked in the middle. I removed it, adjusted the idle screw and it's running like it used to... makes me so happy .. lol. I still need a ICM but i'll order that on monday, funny thing is i'm no longer getting the 47 error code and before i was getting the 'no battery charge' notice also, and that's gone. Weird thing is i'm not getting any codes with it removed. Oh well...

    And BTW... anyone know where i can get a blower motor for this car? the last two i've ordered are for the 4.6L even tho i specifically asked for the 4.9L. Thanks.

  8. #7
    Cadillacon22s's Avatar
    Cadillacon22s is offline Cadillac Owners Fanatic
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    Re: Weird 4.9l issues

    When was the last time you changes the fuel filter? If it has been a long time or maybe never and you run your your fuel level low you might have a blockage in the filter from build up. This is a good inexpensive place to start. Try it! Sounds simple but effective.

  9. #8
    MitchMeister- is offline Cadillac Owners Member
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    Re: Weird 4.9l issues

    Actually i just did the filter recently. Well.. the car runs a bunch better, but i still get the dimming lights under acceleration and now i'm getting a 'no battery charge' notice. Kinda angry cause this is the 5th alternator i've gotten from nappa in the last year.. the first 4 the pulley came off... they changed the design... and now it stopped charging after a month. And yes, i checked all the connections. Will have to swap out this weekend.

  10. #9
    MitchMeister- is offline Cadillac Owners Member
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    Re: Weird 4.9l issues

    Ok.. so my alternator was bad... replaced it, working fine. Ordered a new ISC and replaced that, and now the rough idle is back and the weirdest thing is that when you give gas quick in park, it stays at high rpms and eventually comes down. So im really lost here, and really sick of putting more and more cash into a car that gets 12mpg that know one wants to buy because they're afraid cause of exact issues ive been having.. lol. Anyone have any ideas... This all started after i replaced the fuel pressure regulator last winter. Since then i've replaced the EGR, MAF, TPS, O2, ICM, and i'm still running like crap. No check engines anymore either to give me a clue. Any ideas would be great. I'm gonna pull a plug and see if any are fouled out.. but they are only about a year old... same as the wires/cap/rotor.

  11. #10
    kdcing is offline Cadillac Owners Fanatic
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    Re: Weird 4.9l issues

    For the hi idle speed:

    1. Inside the ISC, there is a switch that is made when the gas pedal is not pressed. Test the switch via the onboard diagnostics to determine if it is working correctly. I don't care if the ISC is new, test it to be sure. If the switch is working ok, go to 2.
    2. Disconnect the battery for 5 minutes. Reconnect battery. Idle in park for 3 minutes. If the idle does not drop to 650rpm, go to 3.
    3. Get under the hood, open the throttle to 2k rpm, press the ISC plunger back.....when the ISC plunger fully retracts, disconnect the ISC at the connector that will be just behind the alternator. Determine if the idle drops to 400-600. If the idle does not drop, then there may be a vacuum leak (could simply be that the idle speed screw too far out also.)

  12. #11
    kdcing is offline Cadillac Owners Fanatic
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    Re: Weird 4.9l issues

    For the rough idle:

    At night or in a dark garage, start engine, open hood, look for lightning strikes.

  13. #12
    MitchMeister- is offline Cadillac Owners Member
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    Re: Weird 4.9l issues

    ok i'll try that asap. the other thing that i'm noticing now that i replaced the ISC is that when i'm doing about 40-50 mph and pretty much coasting along... at 1200rpm's the engine shakes like mad... like it's missing or something.. but i'm not loosing any power. It's making me angry.

  14. #13
    MitchMeister- is offline Cadillac Owners Member
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    Re: Weird 4.9l issues

    Ok well im thinking that the New ISC is bad now... cause on the way to work i was idleing at aroun 900-1200 rpms and i got a Code 30... .ISC out of range. Waste of $90 i guess. Anyone want to buy a 94 caddy? lol

  15. #14
    Jesda's Avatar
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    Re: Weird 4.9l issues

    Make sure the ISC you buy is an OEM AC Delco part.

  16. #15
    MitchMeister- is offline Cadillac Owners Member
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    Re: Weird 4.9l issues

    well checked the ISC, seems to be working... but where do i check it in the onboard diag? which #?

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