I have been chasing a intermittent lose of power problem with our 98 series 60 DDEC III for about 8 weeks now and think it is finally fixed. I will try to recall and explain the events, as most of you know explaining things is not my strong suite but I'll try, this may help someone down the line.

About 4k miles into a trip in August we had a sudden lose of power. The turbo boost fell to about 2 psi with the throttle on the floor, then the engine came back to life and spooled up about 28 psi of boost shifted the transmission down and took off like normal, this went back and forth for about 5 minutes, it felt like it was running in and out of fuel. I pumped the throttle a couple of times and the check engine and the retarder lights came on with the throttle a about 50%. All if the instrument panel gauges had normal readings thru the entire event. It was raining cats and dogs. I did'nt have the presents to check the Pro Driver during this event.

Next day. I did a visual inspection of everything I could think of, found nothing out if the ordinary. Changed the fuel filters out of desperation. After about 4 hours of normal running I got a check engine and a stop engine light at the same time for about 5 seconds, no lose of power all instruments normal. Clear warm day.

Next day normal running all day. By now we had arrived at a town that had a Detroit dealer, Fairbanks AK. took the bus in to have the ECM read for codes and some advise. Recorded codes were low coolant level, high coolant temp, throttle position sensor fault low, no active codes. Advise, we don't know, it's not doing anything now and what ever we do will be a guess, honest enough. Cleared the codes.The parts department had a throttle position sensor that looked like the one in the bus so I purchased it just in case.

Next day installed the new throttle position sensor to make sure the bus would run with it, it did, so I left it in. The part was a Bendix not the OEM Williams Controls unit so it was a crap shoot.

Over the next couple of weeks it acted up a few times, sometimes lose of power, sometimes lights and sometimes both with the Pro Driver display reading throttle position sensor fault low sometimes, always with the drivers instruments normal. At this point weather did not seem related to the events.

By now we had arrived at another town with a Detroit dealer, Spokane WA. took the bus in to have them read the ECM. The recorded codes were high coolant temp 17 times and throttle position 5 or 6 times. I told the Tech that I had replaced the TPS and he ask if I had replaced the harness with it, I said no, he said it should have come with the switch, of course the one I got did'nt have a harness. The Tech suggested replacing the coolant temp sending unit for the ECM because we had so many over temp codes and the drivers gauge had never been over 210 degrees, the one for the instrument panel gauge uses a different sending unit. They had a ECM temp sending unit so we purchased it and installed it later that day when things cooled down.

A couple of days with no problems and then the engine went to idle and would do no more, this is usually an indication of a TPS failure of some sort. Stopped the engine and installed the old TPS, the engine started and ran bad for a few seconds and then back to normal. This is getting old, we were on a hill with no shoulder.

Got home and ordered a new TPS from Prevost, which comes with the harness and installed both. At this point I don't believe the problem has been fixed. A good friend that has a bunch of experience with 60's said "you have a short some place", we hooked up his reader and got over temp and TPS codes like every time before.

I decided to start the search with the ECM, took it off the engine for a good inspection. Mine is the older type with machine screws holding the large connectors in place and bail clips on the smaller connectors (the newer type have a cam lock I'm told). What I found was two dirt stains on one side of the connector housing, these looked like a wire draw (read path) into the connector and two of the pins in the ECM on the engine control side had dirt and a stain connecting them together! I cleaned the mess up and resealed the connectors and the engine has performed normally for 1500 miles now. Still have my fingers crossed but believe the real problem was a poor seal at the connectors on the ECM letting dirt and moisture in.

What a PITA !!!