Engine knock/detonation

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Regular Member
Posts: 10
Joined: Sat Oct 16, 2021 5:56 pm
Location: 59034
Isuzu vehicle(s): 1991 pickup

Engine knock/detonation

Post by Nick91 »

Hi everyone,

I tried searching the forum for my problem but couldn't find anything specific for my question. If it's been beaten to death already I apologize and please steer me to the thread that talks about it.

I have a 1991 pickup with a 2.3 in it. I got it running pretty decent and drove it a few thousand miles. It has always had a bit of a knock which I presume is detonation. If I set timing at 6 degrees it is significantly worse than at 0 degrees. If I pull the vacuum advance line it almost goes away at 0degrees. I have been running non ethanol 91 octane, changed spark plugs, set valves, put in a new coil and swapped on a Weber carb. I plugged all the vaccum ports and removed everything but choke wire and vacuum advance hose With all of this, it still detonates some under load at lower rpms (it seems to go away at higher rpm, though it may just be covered by engine wind noise?). Then today, I was running down the highway and it lost power, it didn't die, but ran really crappy off and on all the way to work (about 15 miles of interstate). I haven't been able to detect any vacuum leaks so I'm not sure what to look at next? Is there a knock sensor on these motors? If so, could that be my issue? Any other ideas of what else I can check? Thanks!
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