I have no ideas on the direction to go diagnosing what I believe is detonation

JMH82SC · 02:41 PM

I'm at my wits end trying to figure out what is causing the detonation I'm hearing. First I do believe it is detonation it sounds like a big glass test tube shaking a metal ball end to end. Next I advanced the timing and the same sound but worse so I think this is what the noise is. Below is a description of who what when why and what I have done.
Who:1982 US 911 SC stock
What: Detonation
When: Starts fine drives fine. If temp is around 170 all is good and you can use as much throttle as you wish. Once you get to 185+ you can hear the ping w/ WOT or with a load on the engine 2/3 throttle or more. The funny thing is if you go for a ride and it is fully warmed up (pinging) and park it for 20 min you can get back in and go WOT w/ no pinging for a bit even oil temp was still over 185, It just like a timer goes off and its time to ping.
Why: This is the part that is killing me.

What I have done:
Rebuilt CIS with all new rubber injector sleeves all o-rings and do not have any air leaks.
Checked AAR and it is closed after warm.
Plugs are Bosch W3CS (COLD PLUGS)
New cap and rotor
Changed plug wires
Changes fan belt

Things I have checked:
Engine dose have 2 Broken head studs one on #2 and one on #4.
Good compression and leak down numbers and NO sign of any exhaust gasses on any heads.
Warm control pressure is 55 PSI
Warm system pressure is 75 PSI
Timing is 5BTDC w/o vacuum hoses @ 950 RPM
Full advance dos not go past mid 20s
CO was set on the rich side by a shop open loop and I have richened it up to the point idle oscillates rich.
Fuel is 93 but we do have 10% Ethanol
Oil Temp is in the low 200s 212-240

DW SD · 08-18-2008, 02:59 PM

run fuel low and add 5 gallons of race fuel and see if it goes away.

Doug

Steve@Rennsport · 08-18-2008, 04:02 PM

Thats very good advice, for now.

mkossler · 08-18-2008, 04:14 PM

I hope it goes without mentioning (hmm, then why am I.. ah whatever) that it does not take a lot of detonation to result in irreparable damage. You want to solve this fast. I am assuming that you are differentiating between detonation and pinging.

Good luck!

JMH82SC · 08-18-2008, 04:30 PM

What I have is detonation / pinging. I do not have pre ignition or at least this is what I have read form days of searching this sight.

Detonation= pining and you can hear it. It's not good and can do damage to engine but not as bad a pre ignition.

Pre ignition= No ping and major damage fast, like hole in piston.

I have been driving as little as possible and as I have tried things I go for a ride and when I hear the ping I back off and cruise home as easy as possible. I could use this car as a daily driver if I only used 1/3 throttle. I'm just so fed up with no hint of results after all i have done. Yes it all has been needed for the sake of maintains but at some point a cure must be found.

David Borden · David Borden's Garage

Clogged injector(s) causing pinging in only one or two cyl? The car would still run rich, but have one or two cyls running very lean..

David

Formerly Steve Wilkinson · 09-08-2008, 06:05 PM

Steve Weiner, who has already responded to this thread, is your Main Man on this question. He knows more about it than pretty much anybody else you'll find on the Net, and even though he has to work and charge money for an honest living, he'll take the time to lead you through it by the hand if you can't solve the problem easily.