Thursday, April 21, 2005

Until we arrived here at the Grand Canyon Caverns, we'd been in fairly balmy weather for the last few months. Now that we are at nearly 5,000' elevation and a bit north, the temperatures have been dropping into the thirties at night.

One of the many problems that remain on our to-do list is the issue of air pressure bleeding off in cold weather. I'm not certain if this is coming off the ride-height valves, or simply leaking around various fittings in the air system due to differential contraction of the metals (or hardening of the seals). In any case, it is a known problem, and we will have the air system gone over completely in July, when Odyssey returns to Infinity Coach, who now have a lift.

Often, when we experience this amount of leakage, it overwhelms our tiny little electric air compressor, which tries valiantly to replace the lost air until it overheats and it's internal thermal circuit breaker trips it off. We reset the compressor, if needed, every night before we turn in, but, invariably, it trips off in the night, and we wake up with the coach tilted because the suspension has dropped.

The last few mornings, upon awaking in this condition, we have started the main engine to air the coach up. Two out of three of those mornings, the engine sounded rough, like it was surging a bit, but nothing too serious. We attributed it to the cold, and possibly some fuel gelling or similar problems, and have been running the pre-heater to minimize it.

Then came this morning. I started the engine, and within four or five seconds, it raced immediately to redline. I shut down and restarted several times with the same result -- various surging, eventually going to redline, with me hitting the kill switch as fast as I can. Given this new behavior, I decided to look at the Accelerator Position variable in the engine computer. It took a few tries to dial that up before the engine redlined, but I finally managed to get it on the display. Sure enough, the Position was all over the map, from 0 to 100%. The throttle, of course, was untouched.

It is actually a small comfort to know that the surging is not a mechanical problem with the enigne, but rather something electrical. Curiously, turning the ignition on without starting the engine shows the Accelerator Position to be rock-steady at 0%, or wherever I position it with my foot. It is only after actually starting the engine that the variable seems to go haywire. Also, the problem seems to go away completely when the engine warms up.

We had experienced this problem once in the past, when still at Infinity, after the coach became soaking wet in a storm. The Detroit guy gave me an extra position sensor (unfortunately, not the right model for my treadle) and basically told me that the problem can't be diagnosed unless it is actally happening real-time. Of course, we could not get it to repeat no matter what we did. But, in that instance, we attributed the problem to some part of the harness getting wet and causing a resistance-value change.

It's dry as a bone here, of course. Nevertheless, it's been cold enough at night that there might be a dew issue, so this could still be moisture-related. That would explain why it goes away after the engine warms up, but it would still not explain why the position shows steady with the engine not running.

Harumph. This is gonna be a bear to track down.

1 comment:

  1. Unplug the plug to the TPS and put some dielect grease on the plug to stop the short across the pins, you may have to remove the ECU plugs on the engine and do the same
    I work on MCI and Prevost and have to do this to them in the spring .


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