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1993 Deville 4.9 Detonation

3K views 19 replies 7 participants last post by  dennis93coupe 
#1 ·
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.
 
#6 ·
"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.
 
#7 ·
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 ·
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 ·
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?
 
#12 ·
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 ·
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. :helpless:
 
#17 ·
Oh yeah, no vacuum advance for sure. I can't remember about mechanical advance, maybe it doesn't have one after all. If the computer controls it all, then maybe the computer is the problem. FWIW My 92 would never ping so I only had the dist cap off once, only to replace the original. Maybe you should get a second opinion on your pinging. I'm wondering if it could be a leaking plug wire snapping, or crossed plug wires, or an exhaust leak or belt squeal or something totally unrelated. Good luck.
 
#18 ·
Any engine with a mechanical ignition system (distributor) has to have mechanical advance, weather it's computer controlled or not. It can't be done purely by electronics, something has to physically change the position of the distributor cap contacts in relation to the rotor.
 
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