SPARK KNOCKING

I have a 1992 xj laredo 4.0L with 181k.
It spark knocks at high rpm's and during acceleration.
I've changed out the plugs, wires, & distributor.
The only thing that stops the knocking is 93 octane.
Is there anything else I can do?

Thanks, DBHasta

Bump........I am having similar problems.......planning a O2 sensor replacement to see if it helps. My O2 sensor is due to be replaced.

The AMC242 is an agreeably low-compression engine - but the 1991-up versions lack the knock sensor that the RENIX (1987-1990) had. I'd suspect carbon deposits - and here's what I'd do...

1) Crawl under and disconnect the catalytic converter at the four-bolt flange (that should still be under there. Find some way to disconnect it, or you're going to have to replace it outright...) Make sure that the converter inlet is not directly in line with the end of the downpipe - cover it if necessary.

2) Disconnect the air intake hose from the air filter box. Have the open end held up by the neck on the box, so you can look into it.

3) Start your engine, and have a helper hold the throttle at about 1200-1500rpm.

4) Have a spray bottle filled with PLAIN WATER (distilled is best, R/O filtered is acceptable. Do not use tap water! It will leave mineral deposits in your engine...)

5) At intervals of 45-60 seconds, spray one full squeeze only into the open air intake tube.

6) Repeat until you no longer get black clouds out the disconnected tailpipe.

7) Re-attach catalytic converter at flange, using a new gasket or RTV Copper.

What Happens:
The fine mist of water travels down the intake into the combustion chamber, where it is soaked up by the carbon deposits. "Flash" combustion temperature average 1800*F or so, so the water will be "flashed" into steam. You are literally steam-cleaning the inside of your combustion chambers, and that black stuff coming out your tailpipe is the carbon that used to be in your chambers. You will not harm your engine if you keep the water use in moderation (Note the intervals and conditions above - but they're easy.)

Why It Works:
The water gets absorbed by the carbon deposits, and then flashed into steam. The expansion of the water being "flashed" literally blows the carbon right off of the surface where it was deposited, to get blown out the tailpipe.

You can safely do this every couple of years without harming anything - I do.

The best solution is to quit using cheap fuel (the most common cause of carbon deposits,) but that's difficult to do these days. I do this shortly before each smog check - the State of California gives me a reminder of the time to do it every two years... Converter flange gaskets are just something I buy in bulk (along with thermostat gaskets - you never have one around when you really need one...)

Thanks for the input. Looks like I have a weekend project now.
I put a pint of Seafoam in the gas,oil, and a 1/3 pint down the throttle body,
it smoked like a b*tch after doing it, but its helped a LITTLE.
This sounds like it might be a more permanent fix than bottle.

iratefla

A more permanent fix would be changing fuel - what are you using?

This just does a better job of cleaning the cylinders, which sounds like what you need.

He's probably using Citgo (7-eleven) gas. I used to use it but my engine just got too much crud in it. I switched to Conoco and its much better running.

Besides I don't want to buy gas from that crazy Hugo Chavez socialist (he practically owns Citgo because his revolution is nationalizing all industry in Venezuela)