My SC detonates, even with low advance.

[Gogar]

Okay, so: here I am.

1. New Fuel filter
2. Clean and lube distributor, ala Gunter. Looking great.
3. Reinstall distributor, timing numbers look great.
4. New set of Magnecors
5. 6 brand new injectors, o-rings.
6. Fuel distributor flow test, looks even.

7. Went to Duggan's and got a half tank of 101, smelled GREAT but didn't change much.
Thanks for the suggestion, Grady.

8. So, knowing it didn't change much, I'm looking elsewhere, and adjusted the valves (it's been about 15K), and put in some brand new BP7ES NGK plugs.

No change.


I wonder if I'm just making myself hear this sound, and I should just not worry about it and drive.

I am just concerned and confused that I can make the sound go away if I significantly reduce the timing advance.

[9dreizig]

Hey Jeremy, crazy idea, but why don't you drive it over to Grady's get a second opinion..

[Gogar]

That's CRAZY talk!!!!

[ClickClickBoom]

Hey,
I had a similar issue, 1975 2.7 S, with a totally stock exhaust system. I removed the left exhaust manifold assy and found the internals were adrift and rattling around and at higher RPMs the internal can would shift and block the exhaust and causing detonation at higher rpms and manifold pressures. On a side note I had a cat converter in another car fail and choke the exhaust enough to cause the car to detonate. Make sure your systems are physically intact and correct.
eric

[fritzgator]

Just throwing this out. did you inspect the weights/springs when you cleaned the dizz? if they were flinging out you would get detonation,correct?

[Gogar]

Thanks, Eric.

That's what I'm doing, I guess. I don't mind all the things i've done, it's money well spent anyway considering the 90K miles on stock injectors and plug wires. And a clean, properly functioning distributor is great, too.

The first thing I've learned to check with 'detonation' is timing and mixture, which I really feel I've been pretty diligent about to this point. And, since running a tank of race gas and still hearing the noise I feel like I should look somewhere else. So far that 'somewhere else' has been a valve adjustment. Not to mention I put in a carrera tensioner kit right at the onset of hearing this 'noise", so I'm pretty confident my timing chain stuff is ok.

[Gogar]

Originally Posted by fritzgator

Just throwing this out. did you inspect the weights/springs when you cleaned the dizz? if they were flinging out you would get detonation,correct?

Thanks Gator. Yes I did the whole whammy on the Distributor and it looks great; weights and springs and bushings, shaft play, advance and retard vacuum are just about perfect. I also subbed out a 'known good' freshly rebuilt distributor from my local shop for a few days, with no change.

[T77911S]

i would still put an LM1 on it, just to make sure you are not going lean for some reason. use an LM2, it records and you can see things you dont see while reading it live.
just a last thought, are all the intake manifold bolts tight and the gaskets on good shape?

how loud is the knock? when you hear it, i take it you back off? will it get louder or worse if you dont?

if you are at the end of your rope, maybe checking the cam timing wont hurt. it is easy to do. mine were advanced. someone read the dial in the CW direction instead of the CCW direction.

you got a heater box rattling perhaps? mayeb some sheetmetal?

[jtfreels]

Another crazy idea, can you record the sound and post it?
I went through similar, but the detonation was only on very hot days, obviously not your problem right now.

Jay

[Gogar]

Originally Posted by T77911S

how loud is the knock? when you hear it, i take it you back off? will it get louder or worse if you dont?

It's not too loud, but it's there. It only happens if I'm at a stop light and really go for it in first, or if I'm in second at a low rpm (1500-2000) and hammer it. Noise goes away by about 4Krpm. Or, I can't hear it anymore.

That's why originally I thought it may be a detonation thing where my distributor was advancing TOO MUCH TOO SOON or something. But not so, apparently.

[T77911S]

a bad curve as you say can do it. an LM2 may show you going lean when/if it detonates, the lean can be due to too much advance.

i remember someone else had a detonation problem similar to yours, in the low 2K region, i dont remember who though.


i have a 3.0 TB on my 2.7. i did some timing (vacuum retard) tests on it a while back. what i found was that the retard was not all out until about 2200 rpm. (you know where i am going).
i know a lot of SC owners dont use retard and aparantly dont have your problems, but it is easy and worth a shot. i was told that the SC only has about 5 degrees retard compared to mine, about 15 degrees, so it is not much if it is only 5 degrees, but give it a try. the retard will lean the mixture a little at idle, but as long as you dont change the overall timing, it will be the same once the retard is out.
this is based on the vac port i am using on my TB. with the 2.7 TB, the retard was all out very quickly, like 12-1500 rpm, maybe less.

[Gogar]

Thank you. Already tried it.

[Horrido]

Did you ever resolve your detonation problem?

[jason2guy]

i was having a similar issue. went through all the normal stuff like you. earlier in the year i purchased a M&W pro10 cdi on ebay. my original 6pin cdi was functioning fine, i thought. i installed the M&W and NO MORE DETONIATION. i couldnt believe it. it actually transformed the way the car drives.

[spuggy]

Originally Posted by Grady Clay

Watching this, I’m going to repeat my admonition in Post #21:

This is THE WAY to confirm or eliminate detonation as a cause.

For the additional cost of a few more $/gal it does no harm.

If you take your cat off, you can use the leaded 114 octane for the test.

Best,
Grady

I was surprised how little difference there was topping off at the track with 110 LL race gas (admittedly over a few gallons of premium street gas).

Slightly less detonation == slightly less timing pulled by the Safeguard. Like a degree or two less. Again, only in the low rev range accelerating hard - like joining traffic already on the track. Long before boost was in the picture.

I've never heard any detonation - yet I've seen tell-tale marks in the piston crown and the combustion chamber - and the Safeguard detects it and retards the timing to control it; I'd be concerned if it were audible; that just cannot be good.