Why is my Walthers GP8 is running weird?

[Omaha53]

I have a Walthers GP8 with a factory installed QSI decoder. It has run perfectly for five years. Now it is having problems:

1. when I apply DCC power (or DC) to the track the sound will start and then stop, with no movement of the locomotive. If I slide it on the track slightly the sound will start and stop as before.
2. sometimes when I do get it to run it seems to be real jerky at slow speeds but then that goes away as it speeds up.

I have tried the following remedies:

1. I have cleaned the track and wheels with alcohol several times and it does not seem to make a difference (all may other DCC sound locos run without problems).
2. I reset the decoder several times and that seems to help for awhile, but eventually it will stop on the track and the whole process begins again. After resetting it ran fine for at least a half hour and then it stopped and started with the problem described in point 1.
3. I checked the continuity of the power pick up from all the wheels to the decoder and so far everything seems to be making good contact. The problems are not specific to any section of track. They occur all over.
4. I also experimented with acceleration rate settings and using Regulated vs. Standard throttle control, but that did not seem to make a difference.

Does anyone have any bright ideas?

[Jacktal]

It may be connections to the motor that came loosened with time.I've had a similar problem with a Tsunami,a loose motor connection made it stop and flash a trouble code every now and then.

[cacole]

If the wires to the QSI decoder are connected with those black plastic slip-on wire holders, solder all the connections to insure good contact.

[ricktrains4824]

Normally I advise: clean the wheels.

Now, however, I will ask: Did you also clean the axle bearings/contact wipers? You can have no continuity issues, but when trying to move however...... Intermittent contact like the type stated, I start by looking at wheels/rails, than contact wipers, than wiring.

[GGOOLER]

i had a simular problem with two of my kato ho scale sd90. i ran them so much that i started having problems. i found that if i would squeeze them near the motor brushes that they would run fine, soon as i would let go they would either stop running or just run bad. found out the brushes wore so much the spring could not help make the brush keep in contact with the commutator. new brushes are in order. so check your brushes in the motor. hope that helps

later

g

[PennCentral99]

You haven't mentioned which DCC/Command Station you are running. I had a loco that, after sitting in a box for a few months, was sporatic and jerky. Seems that my command station (Digitrax Zephyr Xtra) needed to be reset/purged. Also, any other throttles on the layout with that loco dialed up?

[MisterBeasley]

Is just this engine stopping, or are you getting a short that shuts down the whole system?  Put another engine on the tracks with its lights on, and see if they shut down or stay on while you try to run this engine.

You may have done something as simple as picking up a bit of wire in the wheels, causing a short.  I'm going to agree with the other posters who said you might have a loose wire as the most likely explanation, but while you've got it apart, debris in the wheels or even the gear train could cause similar problems.

[Omaha53]

Thank you everyone for you suggestions. I will be systematically doing some more testing.