1993 Deville 4.9 Detonation
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 1993 Deville 4.9 Detonation in Past Cadillac Vehicle Discussion; I can't get this to go away. I adjusted the timing and followed all the steps with jumping that wire, ...
  1. #1
    Jonathan11 is offline Cadillac Owners Member
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    1993 Deville 4.9 Detonation

    I can't get this to go away. I adjusted the timing and followed all the steps with jumping that wire, replaced the egr valve and solenoid, did a decarb on the engine, I always use 93 octane, the detonation sound occurs when the engine is hot or cold on very little acceleration. I've never been so stuck on a problem like this. Please help me on this.

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    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 1993 Deville 4.9 Detonation

    exhaust leak? does it do it in neutral too? I don't think an engine can have detonation when it is cold. Maybe if the timing is severely advanced but I don't see how it would even start that way. It's a strange one.

  4. #3
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: 1993 Deville 4.9 Detonation

    He says it pings/knocks on light acceleration - that points straight at EGR problems. Are the 4.9's noted for clogged head passages for the EGR system ?

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 1993 Deville 4.9 Detonation

    Did you rod out the two EGR tubes down in the TB?

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    Jonathan11 is offline Cadillac Owners Member
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    Re: 1993 Deville 4.9 Detonation

    I didn't rod it out anything out, I've never even heard of that. And I'm not sure if the 4.9s are noted for clogged head passages. When I
    replaced the egr valve, those passage looked pretty dirty. And what do you mean "rod out?"

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: 1993 Deville 4.9 Detonation

    "Rod out" is an old, old generic term used in any number of mechanical cleaning applications - it literally means to "jam a rod in the hole/tube/channel and clean it out".

    Back in the Dark Ages, in diesel submarines, we used long M1 rifle cleaning rods and steel bristle brushes to clean the hundreds of tubes in the diesel engine salt water/fresh water heat exchangers - the radiators. The same technique is used today to clean out crossflow automotive radiator tubes - after you remove the end tanks.

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 1993 Deville 4.9 Detonation

    The 4.9 is noted for clogged EGR tubes, not heads. Open the throttle plate (engine off of coarse). Look down the TB bore. You will see two EGR tubes staring back at you. If they are carboned closed, rod them out with a coat hangar, screwdriver or whatever it takes to open them up.

  9. #8
    dennis93coupe's Avatar
    dennis93coupe is offline Cadillac Owners Connoisseur
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    Re: 1993 Deville 4.9 Detonation

    Are you sure your plug wires are connected properly?

  10. #9
    brougham is offline Cadillac Owners Master
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    Re: 1993 Deville 4.9 Detonation

    Definately sounds like some sort of EGR problem. If the passages are clean pull the vaccum hose at the EGR with the engine running. At idle it shouldn't have any vacuum but it should as you rev the engine. With the service manual you can get into diagnostics and enable or disable the EGR valve to test other parts of the system to make sure it's working properly.

  11. #10
    Jonathan11 is offline Cadillac Owners Member
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    Re: 1993 Deville 4.9 Detonation

    Thanks for all yall's input. Lol I plugged everything back together but the line going from the solenoid to the TB was cracked. I replaced it and it helped but I still hear that pinging. I'm going to try to rod it out like yall said. Thanks again everyone.

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    Jonathan11 is offline Cadillac Owners Member
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    Re: 1993 Deville 4.9 Detonation

    Well I rodded the tubes out, one of them was completely blocked. The noise isn't going away. I feel like I'm not able to rod it out as well as it should be because the tubes turn 90 degrees at the bottom and I can't get my coat hanger to turn. Is there a better way to clean
    the tubs? Another place to stick the coat hanger maybe?

  13. #12
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    Re: 1993 Deville 4.9 Detonation

    I do believe you have found the problem. Not exactly sure of the tube routing, but you are going to need something flexible. This is where a little Yankee ingenuity and determination come in. Flexible drill bit, sink drain snake, soak it down with carb cleaner to soften it?

  14. #13
    Jonathan11 is offline Cadillac Owners Member
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    Re: 1993 Deville 4.9 Detonation

    That's not a bad idea. I wish I would have seen this when I replaced my head gaskets, I had all of this stuff out. Would have been way
    easier. Thanks for your help man.

  15. #14
    Jonathan11 is offline Cadillac Owners Member
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    Re: 1993 Deville 4.9 Detonation

    Man this is killing me. I took the TB off to get better access and took my air compressor and shot it through the tubes (with the egr valve off of coarse) and a bunch of crap shot out the egr ports. Thinking I fixed it I put it all back together and bam, same noise. I don't
    know what else to do at this point.

  16. #15
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 1993 Deville 4.9 Detonation

    You should check the advance in the distributor, both mechanical and vacuum. Old HEI's used to get sticky mechanical advance action that would cause pinging. This HEI is probably no different.

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