Rough Idle - Page 2
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HT4100 4.1, 4.5, 4.9 Discussion, Rough Idle in Cadillac Engine Technical Discussion; I believe if the alternator and voltage regulator are working fine you should have more like 14.0 -14.5 volts when ...
  1. #16
    leftoverture is offline Cadillac Owners Fanatic
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    Re: Rough Idle

    I believe if the alternator and voltage regulator are working fine you should have more like 14.0 -14.5 volts when you check with the engine running. That is the case with every engine/vehicle I have ever owned (save the Beetle with the 6 volt system). I'd take your alternator to a shop and have it tested.

  2. #17
    Stoneage_Caddy's Avatar
    Stoneage_Caddy is offline Cadillac Owners 10000+ Posts
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    Re: Rough Idle

    perhaps the fuel pump is getting weak and the draw from the headlamps was bogging it down ? but now it is so weak that perhaps when at idle the pump has a chance to bring the system to full pressure as it doesnt need the pressure it needs at drive idle and the alternator is produceing more volts in park idle than drive idle ?

    basicly in drive you need more pressure and amperage than your needing at park idle

    I wonder if we can find the spec of how many amps the fuel pump pulls new vs how many your pump is pulling now , then we could measure yours thru the fuel pump fuse ?

    then again if it draws too many amps it will blow the fuse ......

    edit :tell ya what , measure how many amps your pulling thru your pump fuse and ill measure mine !

  3. #18
    caddy john is offline Cadillac Owners Member
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    Re: Rough Idle

    I just checked the amps on my fuel pump it is between 17.9-18.1. I also checked the out put of the alternator and it is only 13.4 volts. I checked my other cars and they were between 14.4 on one and the other was 14.6 volts. Do you thtink that 1 volt could be droping a little more at time and causing a problem. If you think so I will get another alternator, I believe it is 140 amp. output, where can I get a good one that will be reliable. Please let me know, and I really thank everyone for alll the help. Thanks from Florida

  4. #19
    100
    100 is offline Cadillac Owners Enthusiast
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    Re: Rough Idle

    I don't have any numbers to be referenced... But 13.4 volts doesn't seem to be too low... Well, I may be wrong.

    But, based on your description of troubles, a bad alternator kind of seems to make sense to me. I would hate to recommend something and you buy that part and it wound't fix the problem... I believe you can bring the old alternator to Autozone or whatever parts store to test it, you may want to try that and see...

    Good luck.

  5. #20
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: Rough Idle

    Check the grounds like the "Horific idle" thread. Sounds like it may be related problem.

    just a thought, easy and cheap to troubleshoot.

    Tom

  6. #21
    caddy john is offline Cadillac Owners Member
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    Re: Rough Idle

    I went and got a Haynes manual, I had the alternator checked and they said it was with specs. I then checked everything out, the timing was set at 8 degrees, so I changed it to 10 degrees advanced. I readjusted the ISC, it was off quite a bit, set up the idle stop to 525 rpms, as the book said. I applied voltage to the ISC and retracted it fully, adjusted the set screw to .035 clearence. hooked everything back up and reset the codes. I have been driving it for the last hour, it seems to be OK. Hope it stays, will keep you informed it it gets rough again, and again thanks to everyone who helped out. caddy john

  7. #22
    ronneal is offline Cadillac Owners Member
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    Smile Re: Rough Idle

    theres a ground strap under the car near the catalyitic convertor make sure this is connected too this will cause the same problem and and you need to change the fuel filter more often and use BP or Amoco 93 octane fuel and change air filter too these engines like alot of clean air Also check your gas cap and make sure its screwed on all the way.

    Ron

  8. #23
    DFBonnett is offline Cadillac Owners Fanatic
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    Re: Rough Idle

    You might have an intermittent dead short somewhere that is pulling all the current the alternator can produce. Look for some burned looking, bluish wiring somewhere. Many years ago a friend had a VW Beetle that refused to start. I noticed the wiring to the electric choke was really fried. After pulling the wire off the choke, it started immediately. Putting the wire back on while running caused a near stall bad idle. In that instance a new choke solved the problem. I'd be looking for any wiring touching metal where it may have worn through due to abrasion, or just wiring that looks fried.
    FWIW
    YMMV
    DFB

  9. #24
    CadiJeff's Avatar
    CadiJeff is offline Cadillac Owners Connoisseur
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    Re: Rough Idle

    If you are still having problems try changing the coil/cap/rotor that could cause rough idle as well.

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