TPIVette8

Hey, everyone. I'm trying to get rid of this spark knock/detonation issue. 5k miles on the new engine and have yet to eliminate it. It typically happens when feathering the throttle at higher speeds around 2k rpms and then at higher rpms at lower speeds and WOT.
I've tried everything from running race gas to retarding the timing(with est wire unplugged) to the point where the headers glow, and it didn't seem to make a difference. When I do unplug the est wire, though, the pinging is gone completely.
Am I missing something here? Any help would be appreciated because I'm about to pull my hair out here.

leesvet

ok, you say build,, whats IN the build?

cause....
if there was much done to enhance then the tune needs to be different..Timing/fuel curves need to be changed.
The est wire offers a clue. That takes the curve out of the ecm and the "tune" is reduced to a base timing program...flat with little advance.
So, if you have eliminated things like bad wires, fuel, dist off 1 tooth, plug gapped too wide, the wrong type of plugs cause this too, then you need to look at the tune and get a tune thats appropiate for this build. If you have more compression thats harder for the ign to generate a good spark.
Also, can you ID the noise as ping? sounds like it might be ping...thats different than knock...
ping comes from things in the combustion chamber getting overheated and staying so hot that it ignites the fuel charge before its time...so it clatters. Pre-Ignition. Ping.

Knock is incomplete combustion..similar rattle but usually under a load or sudden WOT at low rpm, low speeds. Knock will send some smoke out the pipes from the unburned fuel.

Ping is more a high rpm issue or heat related, where knock is associated with the loads on the engine.
Knowing which is everything when it comes to solving the problem..

if you feel like its PING, take the gimick plugs out and put good Delco plugs in. Too many of the plat + 8 or whatever splt tail 4 plugs WILL cause ping because their extra electrodes often glow red hot and cause early ignition...

Knock...can come from plugs not gapped right for the compression,. too cold a plug. The art of getting the correct spark plug for what the engine is and does, has all but been lost...
It does matter. A new build with some goodies inside may need a hotter plug to get a good burn. Another engine may do better with a colder plug to prevent PING...

JackDidley

Send a datalog to PCM forless. They can tweak the tune.

TPIVette8

Thanks for the replies. My build is in the sig. The only thing I haven't checked that was mentioned was the distributor jumping off a tooth. I actually just changed the spark plugs a week ago since I originally thought that was the problem. I had the original spark plugs in with the vortec heads, so I changed them to the Delco R44LTS plugs. Still no change.
The noise sounds like more of a ping. It only occurs when feathering the throttle around 2k rpms and under WOT in the upper rpms, not WOT at lower rpms.

TPIVette8

I also forgot to mention I gapped the plugs at 0.45 and I had a mail order done by pcm4less.

Cliff Harris

Sounds like your timing isn't what you think it is. The ECM adds 20° at idle, which you are removing by disconnecting the EST connector.

I suggest checking the harmonic balancer to see if the outer ring has slipped. Happened to me on both my '78 and '86 Corvettes.

TPIVette8

I'll check it out. But, even if that is the case, wouldn't the the glowing headers be a sign I'm retarding too much, even though it's still pinging? That's what I'm confused about. It's either glowing headers with ping, or no glowing headers and ping.

TPIVette8

Here's a link of a video I took this morning. It's hard to get the pinging to stay constant when sitting still. It's best heard at 0:25-the end.


I unplugged the EST wire today and actually took it out on the road, and honestly, it seems to run better, No ping, and pulls just as hard IMO. Yet, with the wire unplugged, the highest I get when throttle is given is 15* advanced. With the EST plugged, I get about 20* advanced.

WW7

I turned my volume way up and all I could hear was a little bit of rocker noice/clatter, I heard no pinging or spark knock...Do you have aluminum roller rockers??..But,most pinging /spark knock, happens when the motor is in gear and under load.....WW

TPIVette8

No roller rockers, just the GM stamped rockers. It sounded like valve clatter to me too, at first. Until I unplugged the EST wire and the rattle went away. That would eliminate the valvetrain issue, wouldn't it?

Red 91

On my 91 the knock sensor lost sensitivity, I checked it and another KS with a meter set to MV tap on block end of sensors and compare results. Hope this helps good luck!

Cliff Harris

Are you datalogging? That will show you the knock counts.

Also I think you will see an error code 43 if you've got excessive knock counts. I'm not sure about that one. I do know that you will get an error code 43 if the knock circuit is NOT working. The ECM tests it at startup by adding an extra 20° of advance and looking for knock counts. If it doesn't see at least 2 knock counts it will set error code 43.

Have you pulled error codes?

rad928music

Sounds like maybe a rocker arm adjustment issue.