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Spark Knock or Exhuast Leak?; Could a flange gasket leak be mistaken for engine rattle?
Topic Started: Mar 29 2011, 03:25 PM (2,308 Views)
macboy91si
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Slapped and often called Susan...
[ *  *  * ]
One of the things about having a new exhaust on a car is that you hear everything else. When my car was having the super-rich running condition, I noticed that some of the fuel smoke from the engine came from where the exhaust manifold and the pipe meet. I would assume that this is a source for sound leakage as well. When you have your foot into the gas a bit, sometimes the car sounds like it's spark rattling, sometimes not. I was curious if maybe it could be the flange gasket making that sound under load. Is this hard to change? On a side note, if it's NOT the gasket, I'm not sure what would cause the spark rattle, timing is on 8* BTDC and seems to have normal power response.

Thanks, and sorry for the amount of questions, now that I'm regularly driving the car, there's a lot of bugs to get worked out.

-Tim
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Coche Blanco
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Move it down to 5* and see if it goes away. It's probably exhaust though, that's what mine was.
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Bad Bent
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Facetious Educated Donkey

If you want to find an exhaust leak then get some Seafoam and slowly pour it into the Throttle Body while someone looks for leaks in your exhaust. Clean the carbon and find a leak. :thumb Any smoke in the engine bay is suspect, granted you are not down wind. :smackface You can pour 2-3 ounces down the TB and 2-3 ounces into the brake booster vacuum hose, disconnected at the booster.

A video would be nice... but the "donut gasket" at the exhaust manifold was a snug fit, the last time I changed one. One of the bolts/springs was cross threaded into the manifold. :banghead

Did you solve the super rich condition?
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macboy91si
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Slapped and often called Susan...
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I actually did use some Seafoam to ID the leak source. I set the the timing back at 6 deg and seafoamed the car. The car still has that sound, but the tone is different, maybe from the timing change. It's amazing the extra little oomph you get from the 2 degrees. I did get the super-rich condition solved, it turned out to be a bad CTS.

I'll get a new flange gasket and see what it does.

Thanks!

-Tim
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Bad Bent
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Facetious Educated Donkey

While you are at it you might head over to Harbor Freight on Winchester and get a mechanic's stethoscope?

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macboy91si
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Slapped and often called Susan...
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Harbor Freight can be a dangerous place for me... They have so much cool stuff there. There is one a mile from here, I haven't been in a while. I need to get a slide-hammer soon, I think I am going to convert my brakes to vented rotors and rear drums from a 97 with the larger studs. That however is the topic of a different post. I really missed having a Metro.

-Tim
Edited by macboy91si, Mar 29 2011, 10:05 PM.
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macboy91si
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Slapped and often called Susan...
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I'm thinking that the sound was pinging. I set the timing back to 6* and the sound pretty much vanished. I also Seafoamed the car, but no sound. The only thing I notice is a "less than inspiring" response from the engine. Is this normal. I'm starting to question my timing belt installation, 8* is not that much advance, it shouldn't cause pinging should it?

-Tim
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Coche Blanco
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Miles on engine? Compression test results?
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mcmancuso
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could be carbon build up in the cylinders causing the ping...
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CityConnection
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Sir, yes sir!

Totally unrelated Harbor Freight post: I just went there tonight for some odds and ends, that I found, and also a 50A battery load tester. I've wanted a battery load tester for years but even at HF they were expensive (for what they really are, a voltmeter and length of carbon). Now? Closeout for $9.99 :D
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macboy91si
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Slapped and often called Susan...
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I've got 175 +/- 5psi across the board dry compression, I think it was 180, 170, 175. I've Seafoamed the car several times by feeding into the throttle body and choking the engine with it. I let it sit for a few minutes and then try to drive it kinda hard. Lots of smoke usually, which is how I ultimately found the flange gasket leak. So I'm assuming that the ping at 8* is not normal? This car also has no EGR valve for what that's worth. Seems like the EGR would allow more advance possibly? I too am leaning towards carbon buildup. My last Chevette rattled all the time, regardless of timing. I never could get it to stop, and after spending quite a bit of money on it, I sold it for $400. The new owner yanked the head and the engine was caked. Still runs to this day. If it is carbon buildup, what can I do to clean it up without tearing the engine apart?

-Tim
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Coche Blanco
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MMO in the cylinders. Let it soak overnight. Then crank it over with rags in the holes...spark plugs back in and run it.

Get a mister/spray bottle and spray seafoam in the throttle body as you run it.

Run Techron or something through the fuel for the next thousand miles.

(all these will do something, which one will do the most? I don't know)
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macboy91si
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I soaked the cylinders in MMO (quite messy in the evacuation process BTW :smackface ). While I had everything apart, I replaced the oil pan sealant with a cork Felpro gasket and pulled the distributor and found a suitable o-ring for it. I also bought some brake cleaner and started degreasing some more of the engine.

The results (which are starting to frustrate me greatly :die ) were as follows:

Oil Leak: still there, same spot. should I make a new post for this?
Pinging: Still there at 8+* but goes away at 6 or is too faint to hear.

Is there a possibility that I have the timing belt a tooth off here? I plug both of the hoses (the car is a 91) going to the distributor when doing so. Right now, the car's base is 6* with the hoses unhooked, and I think 10 or 12 with them reconnected at idle. I am not jumpering the connector on the left shock tower since it has a vacuum advance. The car runs smooth, just not very gutsy (even for a Metro), the extra +2 advance however seems to make a noticaeble difference, but under a good load the higher gears it can really rattle. I have singled out the pinging as not being exhaust noise.

On a side note, I've never seen so much smoke from a car in my life, the fire department was called... :fon

Thanks for the help

-Tim
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macboy91si
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Slapped and often called Susan...
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So a further development, the "rattle" as I call it is coming back, but now at 6*. Under load and sometimes lighter load at higher RPM (winding out a gear or something). Also something that I've noticed is an intermittent ticking from what sounds like the top of the engine. The engine is pretty noisy (always has been) when cold, and that sound is no longer going away completely when warm, just gets a little quieter. Is it possible that the "rattle" is actually just a something weak in the valve-train that manifests itself under higher load conditions? Would gunked or worn lifters cause any of this? Should I just get another head and rebuild it and put it on?

In the meantime, would there be any significant damage to running the timing back up to 8* as I miss the little extra uphill zoom that it gave me.

-Tim
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Coche Blanco
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Could you get a quality video (with audio...lol) of the noise? Have you tried running mid grade fuel? 89+?

The fuel should stop the pinging, if it is indeed pinging.
Edited by Coche Blanco, Apr 8 2011, 10:03 AM.
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