bavarian banshee

so just last night i think i heard my car detonate. im torn because i'd never heard it before, and i've been told that when i hear it, i'll know because its a nasty noise, and sounds as bad as it is for your engine. but thats not what this sounded like. on full boost, 15lbs, i heard a ticking, but it was tiney, and hollow, like someone throwing small pepples pretty rapidly, at my exhaust manifold. so its not what i imagined detonation to sound like, but i cant think of anything else that it might be. im still paranoid about the heat and the turbo.

take care,
brian

nine-44

Detonation sounds like a diesel. If nothing is newly done or obviously wrong, you may have some bad/cheap gas. I would think that the DME would have corrected the knock before you had heard it though, you may have a problem. I can't recommend anything. Guys, a little help here?!?

bavarian banshee

yeah, you'd think the knock sensor would have picked up on that... im really curious. it might be cheap gas, we get some pretty weird crap here in the summer. but i never put anything other than premium in, not even on my old n/a. the day i cant afford it is the day i sell the car. anyways, it didnt sound like a diesel at all, and thats similar to past descriptions of detonation
-like a sledge hammer on the side of the block...
all just lay off of it until i can figure this out.

thanks guys,
brian

badass951

That is exactly what my car sounded like. Exactly. Now I am replacing the head gasket and hoping nothing else has gone wrong. Wish I could get the damn bolts out of the camshaft cover though.

nine-44

Were you in a corner? Hopefully not a rod knock! The 944/951 cars have a problem with the #2 rod bearing due to air in the oiling system under hard cornering. An oil pan baffle kit seems to cure the problem. Look into the noise!

Bri Bro

Brian, check that the knock sensor is working. Your description on the knock sound is exactly what detention sounds like.

Chris White

A couple of thoughts come to mind –
If you are running 15 lbs of boost how have you modified it from stock? The primary way the stock system protects itself is to lower the boost via the cycling valve when knock is detected. If you have added a restriction to the boost line then it cannot do that.
Second – ‘mild’ knocking under boost can be a fairly tiny sound – especially if you have a cat bypass – the engine & exhaust noise will hide a lot of the ‘pinging’.

Chris White

Chris White

A couple of thoughts come to mind –
If you are running 15 lbs of boost how have you modified it from stock? The primary way the stock system protects itself is to lower the boost via the cycling valve when knock is detected. If you have added a restriction to the boost line then it cannot do that.
Second – ‘mild’ knocking under boost can be a fairly tiny sound – especially if you have a cat bypass – the engine & exhaust noise will hide a lot of the ‘pinging’.

Chris White

special tool

That is a perfect description for the sound of detonation - what was the temperature in Phoenix, last night?

<img border="0" alt="[bigbye]" title="" src="graemlins/xyxwave.gif" /> <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />

bavarian banshee

yeah, i asked around at work and they all agree that im definatly pinging. so the problem lies in the fact that the welmeister chips shim the wastegate, no banjo bolt. that makes frequent changes from summer to the other half of the year kind of a pain. it also makes the possibility of just getting a boost controller and turning it down out of the question. the temp when i heard it was about 95ish. it really shot up this past week, from about eighty to a high of eighty five the last couple of weeks, and i never heard it then. i was playing with it tonight on my ride home, and i could hold seven pounds or so with NP. i didnt have the ***** to go above that. im going to try the adjustment on the computer and see if that helps a bit, but thats a band aid i think. as it stands we have between ten and twenty more degrees to go before its "summer". thanks for all of your help guys! oh, also,what year did porsche start adding the knock sensor? one of the guys said he thought they didnt add it until 88. anyway i can do a visual?

take care,
brian

Bri Bro

It is on the 86 951. It is a black flat device about the size of your thumb. It is bolted to the block by one bolt and is located under the idle controller, between spark plugs two and three..closer to three.

Jeremy Himsel

Brian,

You may want to look into this further. Turning down the boost is just hiding the problem. I'm running 15 lbs (Autometer Gauge) with crappy chips and am not detonating at all. Are you positive that your only running 15 lbs? If so, I think you should check your fuel system, fuel grade (and brand), plugs, or check for vacuum leaks. I hit full boost several times on the way home from work today and it was fine.

Give me a call if you want to chat about this. In AZ, Unical 76 and Texaco are the only grade A fuels. Mobil is a B, Cheveron and Exxon, and Diamond Shamrock is a C, Arco and others are D's. Fuel quality is just as important as octane.

jason952

I agree, sounds like pinging, I get it occasionally. keep it floored when you are in the boost. consider diff chips (guru) and higher FPR.

Danno

Hmm, the Weltmeister chips and their wastegate shims are a matched set that's programmed for each other. This ugprade alone should not be causing any detonation at all.

The Welmeister kit should only go up to 13-14psi or so. Do you see 15psi even at 5000rpm+? This may indicate some sort of a wastegate upgrade that can hold max-boost to redline. Perhaps the wastegate shim was installed improperly and it's causing the wastegate valve to bind and not operate correctly?

Perhaps you have a leak in your vacuum lines or a crack in the cycling-valve that's letting out pressure going to the wastegate prematurely? This would cause higher-than-expected boost levels. In fact, you might be getting much more than 15psi because the stock gauge only goes up that high. Others have seen 20-25psi after hooking up an aftermarket gauge while the stock one maxes out at 15psi.

Be careful! A headgasket replacment may be around the corner!! <img border="0" title="" alt="[Frown]" src="frown.gif" />

Lorenfb

Try and isolate the problem by focusing on
one area at a time:

1. try replacing the chips in both the
DME and the spark box with the OEM
2. make sure that the vacuum line to
the spark box is OK,
3. determine if you may have more boost
than indicated and,
4. try a different gas.

The key point is to not let detonation occur.
In the short term, pinging is ok if brief until
you find the problem.

Good luck
Lorenfb@aol.com