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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 (2,307 Views)
macboy91si
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Slapped and often called Susan...
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I can try, but I'm not sure how I'd grab that sound going down the road. I just don't see how THAT much carbon could be in the cylinders. The plugs are not carboned up at all, nice shade of brown/gray. I've MMO'ed and Seafoamed the car several times. My last fill-up was around 37mpg. Also the condition is not always there, sometimes it is silent. I'll see what I can figure out about recording the noise. The top end is generally loud, with a rythmic tapping sound when cold, I was just curious if I was hearing actual pinging or a weak component in the valve train.

It has mid-grade in it right now also.

-Tim
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Coche Blanco
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Troll Certified

Does it make the noise when you rev it with zero load?
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macboy91si
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Slapped and often called Susan...
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No, it doesn't seem to. But I can make it do it if I wind up the engine in just about any gear now, at some point in the higher RPM's it will chatter regardless. Reminds me of valve float in a worn out Chevette.

-Tim
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macboy91si
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Slapped and often called Susan...
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So a better picture hopefully, and a question.

The engine pings when you don't give it enough gas on take off, a very evident knock. Under light throttle while driving, it's silent, but if you have to open up the throttle when the engine is under a good load in 4th or 5th, you will here occasional sharp pings from the engine and they disappear when you start yo back your foot off the pedal. The spark knock is only under heavier throttle and sometimes at takeoff. It also doesn't always do it, but I have a feeling that has to do with the load the engine is under. At interstate speeds in 5th gear I don't notice it or I can't hear it. As soon as I empty the tank out I will try 89 in it. I didn't have 89 in it as stated before because I was not reading the pump correctly. :smackface

Another question regarding setting the timing: The 91 is a vacuum advance with no EGR. When I set the timing, I plug the 2 hoses to the distributor and then set the timing with a light to 6*. When the hoses are unhooked, then engine speed drops down and I set the 6* there. The second the hoses are connected back, the engine speed goes back up and if I check the timing it's 10. What's the point of base timing here? Am I doing this correct, and is the car timed at 6 or 10 like this. I have an electrical connection, but I never connect it since the car has a mechanical advance. I have been seafoaming the engine and I have MMO in the tank, but still a spark knock. I really don't want to blow up my engine driving it like this.

Thanks!


-Tim
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Woodie
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Sounds more like piston slap to me. No way you should be getting ping at 8° advance, it usually starts around 14°. If you had a carbon build up problem, you'd have more than 180 lbs of compression.

That is exactly how the timing is supposed to work. The vacuum hoses provide advance at the distributor. With them disconnected and plugged, you're at base timing. Plug them back in and the timing will advance a little, the idle will increase a little.
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macboy91si
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Slapped and often called Susan...
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I don't know. I put premium fuel in it and now the sound is gone. I have the timing on 10* now and nothing, even to the the floor in 5th it's silent. Maybe the 87 around here is not 87. I am going to try mid-grade and see if it returns. I have set the timing at 8*. It's definitely spark knock, and I have failing valve guides so the car burns oil so it could be carbon. I have almost 180psi across the board now dry compression. This morning is was a blue spectacle on start-up. :stoner

I'll keep you guys posted on what happens. I think I'm going to save up for a Mullet special.

-Tim

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Bad Bent
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Facetious Educated Donkey

Well, if you have to do the valve guides, I'm really curious as to how much carbon build-up is on the pistons. Which I could see you having, raising your compression or causing pre-ignition, and still having 180 psi compression. :-/
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macboy91si
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Slapped and often called Susan...
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Was supposed to read valve seals, not guides, don't know what I was thinking. I have run 2 tanks of 89 octane in the car and the pinging is still mostly non existent. Timing is on 8* and the car is getting about 43mpg combined city/hwy with 13" tires. I would eventually like to get around to a Mullet Special, I've started saving my money and will figure out what to do when that happens. I really do want the car to be around for a while.

-Tim
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Old Man


been a while since I did this, and NEVER on a 3 cylinder engine.

On the larger engines we always pulled a plug wire and ran the engine to find out what cylinder etc was making the noise..........new to Metros so I dont know if this would work on the small engine or not.........
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