'90 240 now runs better than ever... Could this be why?

[Randy G.]

I have been driving this car for three years, and have put about
30,000 miles on it in that time. it was a bit carboned up when I got
it, and I think the previous owner drive it gently- too gently. It
uses very little oil and is a dream to drive.

I recently did two jobs on my 1990 245 with just over 200,000 miles.
First I replaced the timing belt and cam seal. The leak was barely a
dribble, but it was nice to get it done. The idler pulley was also
replaced.

The other job was to stop the annoying exhaust header pipe rattle. At
about 2,000 RPM the inner and outer layers of the exhaust header pipes
would rattle annoyingly, very much noticeable inside the car. I
drilled two holes in each pipe, about 25-30% from each end, and
inserted short sheet metal, self-tapping screws. Once the holes were
tapped, I removed them and cut them off so that they would protrude as
little as possible into the exhaust flow. Rattle completely gone.

Since that time the car is running noticeably better- smoother, with
more power, and better low-end torque. This is not just a matter of
some psychosomatic reaction to the work I did

Here's my theory: I do not believe that it was the timing belt. The
rattling of the pipes, even at times when inaudible, created some
frequencies that were picked up by the anti-knock sensor which was
retarding the timing a bit. Is that possible?

 

[Michael Baldwin]

Randy writes ;

Here's my theory: I do not believe that it was
the timing belt. The rattling of the pipes, even at
times when inaudible, created some frequencies that were picked up
by the anti-knock sensor which was retarding the timing a
bit. Is that possible?

My ol'mind and memory is beginning to fade. I can't recall the proper
wording however I know a similar phenomenon did occur on mid-eighty's
Oldsmobiles with 5.0 L (307) V-8's. The KS's were picking up ambient
_signal_ noise (not sound in itself) and retarding the timing. Product
Engineering's fix was to increase the "buffer period" (wrong term)
between the KS's "hearing & reaction" time.
Regardless Randy, I like your willingness to explore the not so
obvious alternatives.

Best Regards - Mike Baldwin