MTH Railking GS-4

OK, but what is the track voltage at "full throttle"?

19 volts on dcs

Have you done all the usual things like checking the motor and gear train for any binding or friction?  How about making sure the wiring is all secure so that full voltage is getting to the DCS boards?

All of the other engines run fine on my dcs system and i have checked the motor and gearing for any binding

You've probably already checked, but is the max speed set lower that the 120 mph through the  DCS remote?

Menu/Advanced/ reset engine/ Feature rest.. This one fixes a lot of stuff.

I did a feature reset and a factory reset and it still wont run properly and the max speed is set to 120 mph

I figured so, but sometimes the simplest things......

Turn the cruise off, same problem?  One problem though  .. I forget how to do it in command mode.

I know if the  gap between the timing tape and reader is too large the engine runs  fast and may even take off.Maybe the opposite is true.

what is cruse

Spelling mistake sorry .. cruise control.  MTH engine have cruise control, which keeps the engine going at a set speed (you decide with the remote) up or down hill. Great feature.

If it's too close to read, you get the same runaway issue as being too far away.

how close should the reader be from the tape

Thickness of a dime.

the spacing is correct and still runs very slow

Obviously, something else is amiss.  Does this have the 5V PS/2 board?  Look at the charging jack on the tender, is it round or square?  How "slow" is slow?  If you put another PS/2 locomotive on the track in front of it and use the "all engines" control to command both of them to move, does the other engine rapidly move away from the GS-4?

Yes it is a 5v board and it runs about 1/4 the speed as the other locomotive

I suspect a useful thing might be to test the board independently and see if it's the boards or something on the locomotive.  If I had this issue, I'd probably put a 'scope on the encoder output to see if it's got some noise that could be fooling the engine to thinking the motor's running faster.

There has to be a reason for the problem.

How do i test the board?

Well, you'll need to take it to a tech that has the board tester.  I'd recommend swapping with another locomotive, but I am loath to suggest that as sometimes that ends up creating two bad boards.

Visually inspect the motor internal armature.  Is the wiring dark or bright.  If dark the motor may be going bad.

Do you have test set (voltmeter) and a general understanding of testing?  If so I can give you some things to check, but if your not comfortable, best to give this to a tech.

You have to start eliminating issues such as mechanical, circuit board, motor, tach reader, etc....  G

How about running the motor on DC to see how it acts without the control system?

i put the original sound file back on and solved the problem

That would have been nice information to know originally.  The sound file has the speed programming.  Depending on what file you added the program would not send sufficient voltage to the motor for the given speed.  Hence the jerky motion until higher speed ordered and the motor had enough voltage to run smoothly.  I assume it also ran slower than scale speed.  G

Amazing how one little piece of information changes the whole picture!

sorry is that because of drive wheel size

Yes, drive wheel size, gear ratio, and programing can do that.  Normally Premier to Premier and RK to RK file swaps especially for steam.  If you tried to use a switcher sound file in a big steam even if both premier it wouldn't run right.  G