Posted to HD/Fleet Forum on 3/29/2013
93 T600 Kenworth 3406B PEEC CAT hiccup
We are working on a 93 KW that has 415K original miles on
it. 3406B PEEC Caterpillar 4CK20959. The story is the truck
was bought by an owner operator, then he went under, so a
farmer bought it and let it sit in his barn for years. Then
the farmer passed away and the current owner bought it.
While sitting, it rusted through the liners and had to have
an inframe overhaul. After that ran great.
Now, the current owner took it to the local truck wash last
weekend, and afterwards the engine had no power and ran
poorly. So he dropped the trailer at the truckstop and
bobtailed to our shop. At some point before he arrived, he
changed the fuel filters, which seemed to help some, but not
much. When we checked things over, we found we could not
communicate to the ECM. Check engine light flashes a 55,
signifying all is well, so we didn't worry about
communicating that way. Found a few loose connections at
circuit breakers, cleaned and tightened, all look good now.
Continued testing, found that when the engine runs, it has
what sounds like a random, single miss, and other times
sounds like a single knock or ping, as would a mechanical if
you opened the rack suddenly. But it's just one miss, or one
knock, at random times, with no apparent stimulus. May be 30
seconds after starting, then three seconds later a miss,
then 20 seconds later a miss, then a minute later a knock...
there is no pattern to it that I have found. This is just an
example of the randomness, not necessarily what it has done
We checked the rack motor, found it to be sticky, so it was
replaced with a new one. This made no difference in our
issue. We verified that the timing motor operates, observed
it and tested the motor, all is well. From time to time, the
rack motor will flick, but there is no change heard in the
engine running, as you would expect from a timing change. It
flicks towards the rear of the engine, and flicks back to
original position very quickly, seemingly at random, the
whole time the engine is running. Does not seem to
correspond with the engine miss or knock.
I checked the rack sensor on my graphing scanner, found that
SOMETIMES when the knock occurs, it shows a slight voltage
spike and back to normal very quickly, and sometimes when
the miss occurs, it shows a slight drop then returns to
normal voltage. I would guess this to be .5V change in
either direction when this happens. Sometimes when we hear
the knock or the miss, the graph reflects, other times we
see the graph spike or drop but hear no change in engine
idle. Other times the knock or miss will be heard but the
rack sensor shows a steady signal.
This miss or knock occurs randomly at any RPM range, and
doesn't necessarily happen more often at higher RPMs.
Sometimes the square wave going to the rack motor would look
funny, or not quite the same as it had awhile before, but
had no correlation with the miss or knock. Rack motor seems
to run between 1.6v to about 3v wide open, and increases off
time of pulse width to increase RPMs.
We did find the J1587 datalink wires have 1.1V drop on them
with a 4 amp load. That's why our scanner won't communicate,
but should have nothing to do with the engine running fine
on a PEEC ECM, right? Should only be for scanner
communication I believe.
I cannot find anything definitive here that will scream "I'm
the problem!" and I'm not completely sure that it's in the
electrical system, but with a base mechanical fuel system,
could the plungers in the fuel pump have taken on rust with
the truck sitting so long? Seems to run very well if that
were the case, but not right. We think it sounds like a
timing issue, but the timing sensor reading stays put when
the miss or knock occurs, and the timing motor does not get
told to change the timing from what my graphing scanner
shows. By the way, this engine does not smoke when the knock
or miss occurs, just makes the noise. And the driver said
when he pulls a hill, it'll sometimes start knocking until
he lets out of the accelerator, and getting back into it
then will resume normal engine behavior. Makes us think
timing, but all seems to test ok!
Any input would be appreciated, we are going nuts here,
running out of things to test! Sorry for the long post, just
want to make sure I include all the details I can think of!
Rosencrans Truck Repair
Columbia City, Indiana, USA