The 617.952 in Marlene was doing this for a while. It never died comepletely but there were times when you wondered if it was going to take off from the light. She'd leave an almost opaque cloud of black soot in her wake. Almost like a gasser that would 'foul' the plugs if it idled too long at a stop light. On the highway, there didn't appear to be any decrease in power but there was a slight decrease in economy (usually she runs at 25+mpg and that particular tank I didn't get but 23-24mpg)

I wanted to be methodical about solving this problem so that I would know exactly what casued it so I addressed one thing at a time rather than shotgunning it with several probable fixes at once. Here's the tale:

Generally, rapid-onset problems are related to bad, dirty or contaminated fuel. I looked at the primary filter and didn't see any contamination. I did not change them.

Second the second thing I checked was the was the air filter (easy to do and I had a filter in inventory) which was pretty dirty (about 12,000 miles since changed) so I changed it out. There was no improvement in performance.

The problem (which was intermittent before) was gradually getting worse, with smoke and no power occurring after every extended idle (ie long wait at traffic lights).

I had approximately 3/4 tank of fuel when the symptoms began and was now down to about 1/2 tank. I treated the remaining fuel with Power Service (silver bottle) and continued to drive the car. There was no apparent change in the problem (still no pickup and lots of smoke off idle and no appreciable decrease in performance at highway speed)

I drove the car on a highway trip of about 450 miles, filling the tank (from different stations) two more times. Still no change in problem. After returning, I examined the fuel filter again and did not detect any contamination or blockage in the clear filter.

During this time, my shop was occupied by my son's car and I was unable to perform a regular interval oil change. Consequently, with the road trip I had run that particular lube oil about 50% longer than I usually do. Coincidentially, I had also received an e-mail from a friend that discussed 'black-stacking' on one of a pair of Cat-powered gensets that he is responsible for.

To me, the symptoms sounded remarkably similar: lots of smoke coming off idle and with varying power settings but no change in performance under constant load.

Their fix was to change to a different lube oil. Apparently the oil they were using allowed some carbon build-up in or on the turbo bearings causing exaggerated turbo lag in the transition from no-load to load.

I remembered my tardy oil change and made the connection. So I changed oil and, in less than a day's worth of driving, the problem had gone away entirely.

I'm religious about oil changes now.

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Never a dull moment at Berry Hill Farm.