Toyota Tercel 1986 spark knock


Old 07-26-05, 10:07 AM
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Toyota Tercel 1986 spark knock

I have a spark knock in my 1986 tercel. New plugs, cap rotor, plug wires. There was a lot of rust dust inside the distributor cap. I posted a message here and was advised to clean and lube the area in the bottom of the distributor which I did. The problem seemed to be intermittent, but returned and is worse despite advancing and retarding the timing, etc.

I removed the distributor again, cleaned it better and was able to see that the spring mechanisims and mechanical parts in the bottom of the distributor move freely.

Time for a new distributor? This is the one with three vacuum hoses coming out of it. Are there any valves or things outside the distributor that could be suspect??

Thanks for your time.
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Old 07-26-05, 11:11 AM
Join Date: Aug 2003
Location: Cape Cod
Posts: 4,320
Have you tried increasing the octane in the fuel you're using?
Higher mileage engines can get what's called "octane creep"
As carbon builds up on the pistons and chambers, the compression increases
This can create a need for higher octane gas to get it to stop the knock or ping from pre-detonation

I would at least try and rule this out as a cause before replacing any parts
A tank of the good stuff and some octane boost should give you an idea before your through with the tankfull
Old 07-26-05, 12:52 PM
carguyinva's Avatar
Join Date: Nov 2003
Location: Shenandoah Valley
Posts: 1,147
carbon buildup over time... real and can cause mild spark knock.

the biggest causes of spark knock are timing incorrectly set (set it per the manufacturer's procedure and then don't mess with it)...EGR system not funtioning properly...there is a back pressure transducer that sense exhaust back pressure (a modified exhaust system can alter this) and modulates the EGR valve. there's quite a bit of checking to rule out ALL possibilities with the EGR system...some detailed service info is necessary. the last thing is temperature...a cooling system that's not up to par can cause spark knock.

if your engine uses some oil...then carbon buildup may be the culprit...there are several products on the market to get rid of it (keep in mind that after you burn some more oil, the spark knock will return) my favorite carbon treatment is GM top engine cleaner (sorry, you gotta buy it at a dealer...or an AC Delco parts distributor)

if the spark knock is heavy or loud...i'd count on something in the egr system...a bad valve, plugged up passages or a bad transducer. if it's mild...then possibly the carbon treatment will correct it.
Old 07-26-05, 07:25 PM
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Toyota Tercel 1986 spark knock

Thanks for the advice. I tried the octane boost with no help. The car has 80,00 original miles and doesn't burn oil, so I will leave this problem to the professionals. Will be taking it in on Monday.

Thanks again.

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