spark knock problem
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From: nova scotia
spark knock problem
took my truck and had the timing checked because of a spark knock. it was right on 10 btdc. found out that my vacuum advance was not working and fixed that i think. does the vacuum line that goes to the distributor go directly to carb or is it joined to another vacuum line? now my problem is even worse spark knock. could the carb be causing this by running lean? any help would be appreciated. thanks
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From: Virginia
It's hard to say how the vacuum line was hooked up on your truck. You could look at the diagram on the radiator support to see how it was originally hooked in, but the non-emissions way is directly to a ported vacuum source on the carb.
I suspect part of your pinging problem is the egr not working, either because someone disconnected it, or you have a modified exhaust system.
I suspect part of your pinging problem is the egr not working, either because someone disconnected it, or you have a modified exhaust system.
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From: nova scotia
i believe my truck is "emissions". the egr is hooked up and works. my ehxaust has an thrush turbo muffler and no cats.
edit: when i say "emissions" can i assume that you mean the tag on the rad support says "catalyst" ?
edit: when i say "emissions" can i assume that you mean the tag on the rad support says "catalyst" ?
Laughing Gas
Joined: Feb 2010
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From: Sanford, NC
If the carb is stock and you haven't changed anything about it then it is probably not
running lean. That would leave your problem to be a timing/advance problem. You
might also have a carbon buildup in the combustion chambers that could effect the
spark knock issue. The vacuum advance line is hooked up to the carb on the side of
it which is a ported vacuum source which controls the distributor vacuum advance.
running lean. That would leave your problem to be a timing/advance problem. You
might also have a carbon buildup in the combustion chambers that could effect the
spark knock issue. The vacuum advance line is hooked up to the carb on the side of
it which is a ported vacuum source which controls the distributor vacuum advance.
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From: Virginia
How do you know the egr works? And with the free flow exhaust you have on it, if the egr is working, it's not working like it should. I have been down this road before though, and one thing I did that made a big difference in the pinging was to change to a 180 degree thermostat. The original thermostat was a 195, but like I said since the engine emissions has been modified, you will now have to compensate by changing a few other things.
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From: nova scotia
i checked the egr by moving the diaphram in the egr valve with the truck idling and the truck would run rough. i know there is a 195 thermostat in it. the heat riser valve is disconnected,the air pump is not there and the efe valve is not hooked up.this spark knock was there before we fixed the vacuum advance but it is way worse now. what other things would i have to do to fix this problem? thanks again
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From: Virginia
With the truck fully warmed up, pull the vacuum line off the egr valve, and rev the engine and see if you have vacuum coming through the hose. If you do, then that's all you can do about the egr, you already confirmed the passageways are clear under the valve.
You can also take the vacuum advance off the dist and plug it, and see how it does. If it's better, you can buy an adjustable unit and try to tune the ping out, but I would put the 180 degree thermostat in it before I did this. You can also set the timing back a little bit to help it out.
You can also take the vacuum advance off the dist and plug it, and see how it does. If it's better, you can buy an adjustable unit and try to tune the ping out, but I would put the 180 degree thermostat in it before I did this. You can also set the timing back a little bit to help it out.
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