4.9 Reluctant to Start, Sometimes Dies at Idle
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9 Reluctant to Start, Sometimes Dies at Idle in Cadillac Engine Technical Discussion; Folks: Any suggestions on this would be appreciated: in the past two or three months, my 4.9 began to take ...
  1. #1
    EldoRedo91 is offline Cadillac Owners Member
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    4.9 Reluctant to Start, Sometimes Dies at Idle

    Folks:

    Any suggestions on this would be appreciated: in the past two or three months, my 4.9 began to take a little longer to start than "normal:" cranked just fine but would not turn over right away. I wrote it off to winter temps (it's parked outside) and lived with it.

    But during the past two weeks, it has refused to start once (it did start the next day), and on several other occasions, has taken much longer to start (like 20 to 30 secs of cranking; which, again, it does just fine). In addition, (and most annoyingly) the engine will sometimes just die from normal idle when I'm stopped at a light. But if I shift into park, it immediately restarts (no hesitation at all). (By the way, I cannot restart it in neutral -- is that normal?)

    If the following is of any help, I have been able to prevent the "sudden death" problem by shifting into neutral and pushing up the RPMs a bit until the light changes; and the tach shows normal in-drive idle varying between about 625 and 575. When I have been able to observe this "idle death," the tach suddenly drops to about 300 then the engine immediately dies. But there's no roughness or other indication this is about to happen; and the car runs fine otherwise.

    Of course, it won't exhibit either problem for my mechanic, who believes this is either a fuel or a spark problem. He checked the fuel filter and it's fine. No codes have been set.

    If anyone has any experience with this I'd appreciate hearing from you.

    Thanks!

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    Jesda's Avatar
    Jesda is offline Super Moderator
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    Just a shot in the dark: It could be your idle control valve/plunger. Push on it with your finger a few times (with the car off) then try driving. If it makes a difference at all, it needs to be replaced.

  4. #3
    creeker is offline Cadillac Owners Connoisseur
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    Did your mechanic do fuel pump pressure reading,this is a common problem.

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    EldoRedo91 is offline Cadillac Owners Member
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    Yes, he did a fuel pressure reading and it seemed to be OK at the rail. Only possible clue is that he found a little air at the end of the rail at first by pressing in on the Schraeder valve at the end -- but then as I say, the pressure tested normal from there on....

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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    When I have been able to observe this "idle death," the tach suddenly drops to about 300 then the engine immediately dies.
    Put a fuel pressure gauge on the fuel rail and tape the gauge to the windshield. Watch the fuel pressure when this happens. I'd suspect the pump is weak and intermittently failing.

  7. #6
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    Your ISC is malfunctioning or out of adjustment. There are hundreds or posts in this section describing how to adjust it so the searching should be easy. Good luck.

  8. #7
    EldoRedo91 is offline Cadillac Owners Member
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    Thanks for the responses -- I'm taking it back in tomorrow to get a leaky radiator replaced (good news - still under warranty!) and will run these suggestions by him. I'll let you know what I find out.

  9. #8
    HUF's Avatar
    HUF
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    Check out also your throttle body/bores/blades for carbon deposits. While there clean the two EGR tubes inside the throttle body with a piece of coat hanger. I do not see how RPM could drop to 300 because of bad ISC motor (it could be bad). If nobody touched minimum air screw, the RPM should not drop below some 450-500 RPM. Check also the FPR - fuel pressure regulator. It is a mushroom-shaped device behind the throttle body with a vacuum tube attached. Turn the ignition ON and pull the vacuum tube off. There should be no fuel on the nipple.

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    creeker is offline Cadillac Owners Connoisseur
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    Quote Originally Posted by EldoRedo91 View Post
    Yes, he did a fuel pressure reading and it seemed to be OK at the rail. Only possible clue is that he found a little air at the end of the rail at first by pressing in on the Schraeder valve at the end -- but then as I say, the pressure tested normal from there on....

    Do you remember what the reading was? if I remember correctly it should be around 40 psi.

  11. #10
    drewsdeville is offline Cadillac Owners Master
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    I agree with HUF. Check the FPR. If you can keep the engine running by opening the throttle blades, chances are you are dealing with a rich air/fuel ratio. If the fuel pressure was too low, cracking the throttle open at idle probably wouldn't do much of anything for you.

    The FPR leaking fuel into the intake manifold can be causing your hard start problems.

    Pull off the vacuum line from your fuel pressure regulator and take a sniff. Smell like gas?

  12. #11
    EldoRedo91 is offline Cadillac Owners Member
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    Update:

    Apparently the starting problem was a bad ignition coil. I didn't mention that about seven years ago I added an MSD ignition. When my mechanic disconnected it today, the coil was so weak it wouldn't start the car. He put in a new standard coil and it starts right up like a champ! I'm actually a little relieved to be rid of the MSD -- it was inducing faint static into my XM Radio and I hadn't gotten around to resolving that yet anyway. I'm not convinced the MSD was really doing me that much good, regardless.

    I'm going back tomorrow to wrap up the idle issue -- mechanic says it's still hunting around a little bit.

    Huf: I may have accidentally misled you on the 300 RPM part -- what I was trying to say is that I saw it drop to 300 for about half-a-second before it just shut down entirely...

    I'll report back again tomorrow, thanks for all the input.

  13. #12
    steelybill is offline Cadillac Owners Enthusiast
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    The radio noise with after market race-type ignition systems is common. If the stock distributor components are good, it will work fine. The MSD is over-kill on a stock engine.

  14. #13
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    HUF
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    Quote Originally Posted by EldoRedo91 View Post
    Update:

    Huf: I may have accidentally misled you on the 300 RPM part -- what I was trying to say is that I saw it drop to 300 for about half-a-second before it just shut down entirely...

    I'll report back again tomorrow, thanks for all the input.
    I see.

  15. #14
    EldoRedo91 is offline Cadillac Owners Member
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    Update:

    Well, for better or wor$e, I am now getting a new distributor! It's apparently the original distributor and I do have 200K+ miles on it. I did examine it at the shop today today and the wire windings are pretty fried. Confidence is high this will clear things up -- it damn well better as I'm running out of moola...!

  16. #15
    steelybill is offline Cadillac Owners Enthusiast
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    Re: 4.9 Reluctant to Start, Sometimes Dies at Idle

    I sort of wonder if fuel volume is OK even if the pressure is within limits. Dying during idle etc and hard starting seems like (to me) it's not getting fuel when it needs it.(?)


    The new distributor results should be interesting.......

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