Put a 92 B230 in my 91. Got a minor spark knock and have done everything to get rid of it - new vacuum lines, new knock sensor, cooler plugs, new cap and rotor, etc. All seemed to help a little. Red line treatment goes in next.

Just thinking - I put in an 87 degree thermostat. Runs slightly warmer than it did (guage is accurate as I put in a bypass kit long ago). Nowhere near running hot.

Any chance a slightly warmer thermostat could cause minor spark knock?

Thanks guys.

Dave
91 240

Dave:

I had a similar knock in my '92 740 NA, and decided to try running 89 octane gasoline instead. I hardly ever hear the knock now.

It's not necessarily the answer to your question, but the car overall seems to run better with the slightly higher grade of gas, and the difference is about $1 per fillup. Others may have different opinions.

Either way, if you run one tank of 89 octane and listen for the effect, it will help eliminate the possibility of anything more severe like rod knock, as was mentioned in another reply.

Whatever the fix, I hope it goes smoothly.

--
Guid ('92 745 233k, '91 940 SE 257k,)

How many times is it "knocking"? Once, twice, or continuously under acceleration? A couple of knocks when you first crack the throttle hard is normal on a hot day, if it doesn't quit, then the knock sensor or ECU is suspect. Any chance you got the connectors swapped between the knock sensor and one of the temp sensors or IAC... easy to do.

One last thought, rod knock and piston slap due to worn internals can sound a lot like spark knock/detonation.

jorrell
--
92 245 245K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently in pieces

A couple times only under heavy load, only when hot. We have a huge hill in the subdivision - will knock on it the longest, but quits after a couple seconds or if you either accelerate or back off the gas...... Its fine on straightaways, normal hard accel, etc.

Mechanic has checked it - said its "normal".......

Dave
91 240