Is there any common denomnator

Are the engines that run fast are a particular manufacturer?  Are they 6 six wheel truck units?  Is there any thing common.  You have indicated the decoders are Lenz & Digitrax decoders, are the models a factor? Is there any others electronic differences?  Were some DCC ready & others not.  

Digitrax system?

If so, maybe those few decoders happen to have a 14 or 28 speed-step status setting. If so, you'd see that the first "click" of the throttle, or moment the loco moves, is more than "1" on the readout such as going straight to "3" or "7". Unless you're using a UTxx throttle in which case you might not know.

Otherwise, maybe those few are set by chance to use speed tables with a weird curve, and the rest are set use basic CV2, 5 and 6? 

These might be way off base but it's all I could think of after the stress of the Jays game. 

All but one 6 axle

Larry

All of them but one are 6 axle locos and I believe they are all Atlas 60M.  The other one is a 4 axle and a 40-2 model from Atlas.  So not sure what the issue is.

Pete

No I already fixed that issue.  That is why I said speed step 1.  Everything is running 128 speed steps.  I might ask digitrax if they know

Check

The minimum and maximum voltage on your decoders.  The units your describing all should start at 1.5 volts DC.  The initial sustained velocity should be 2-3 SMPH.  With the pulse wave, the unit will start at a lower V, but the V will climb very rapidly.  Just a few tenths of voltage will cause the velocity to be 20-30 SMPH.  

The problem may be in the minimum voltage settings.   I would verify the cv settings on the "good" engines are the same. As the "not so good".  If they are, then the relevant voltage that the motor is seeing from the decoder is different between these good and not so good units.  The motors also do respond differently, but only a few SMPH for Atlas China units.  I have seen the variation between decoders of the same model to be larger.  You need to work the min voltage and speed table to get closer to what you want.  

For grins, I would swap a "good" unit decoder with a "not so good" decoder and see if the problem goes w it's the decoder.  Obviously, that is easier to do with DCC ready plug and play units.  That would verify that the issue is with the decoder or f it follow s the decoder, the. What I said above is w hat you need to do.  If the does not, then the motors are involved.  The remedy may still be voltage and speed table, but it may lay else where.

FYI for others

Well sent a support ticket to Digitrax and they replied back in a few minutes telling me to reset all the decoders.  Well what do you know that worked.  The simpliest things LOL.  I didn't even think of that.  Oh well I am a happy camper now.  I did find an awesome site that showed what each of the common decoders CV values are to reset everything.  That came in real handy.  Cause I found that some of the decoders that I thought were digitrax were actually NCE and Lenz.

Decoder data

To keep track of what is in what, I write the decoder mfr (TCS, NCE etc) and the model number (T1, LL8 etc) on the bottom of the fuel tank, along with the road number. It saves a lot of guessing disassembling. On my P2k units, engines with replaced axles (the originals crack) have an "A" marked.  Might be smart to mark the reset CV and the proper value to reset the engine, too.

Great

We're these decodes new in as received condition?  I did not think about this.  I have had enough issues with new decodes that I always reset twice before I do any running.  Why twice? Because once does not always clear a problem.  I may just not be patient enough.  I've always felt it was electronic garbage from the shipment.  

Good work.

common decoders CV values

toysforme     Could you post the site you mentioned in your last post.  This information would be a great help for all of us dealing with these problems.      Thanks,   Jim

Link as requested

Hi Jim sorry I didn't see this sooner.  Here is the link that I found with the different CV to reset decoder back to stock.

https://tonystrains.com/how-to-rescue-a-faulty-decoder/

The Instructions Again

This is not meant to be a "read the instructions" answer.  But, from my conversations with a lot of guys, few seem to know that the little instruction sheet that comes with most decoders is a very abbreviated version of the detailed instructions.  

Most of the decoder manufacturers that I have dealt with have a detailed instruction manual available for download.  These are packed with an incredible amount of useful information.

This page at digitrax, for example - You'll notice there up to 4 documents for some decoders. The "decoder manual" appears in many of them. It's about 90 pages long.

This page at soundtraxx is similar. Notice separate manuals for diesel and steam.  Each has a "user's guide" and a "technical reference". Both are in the 100 page vicinity.  These were incredibly useful in making the Tsunami's do what I wanted them to do. 

Now these aren't easy reads. There is a lot of tightly packed information, and a lot of it needs experimentation to really understand. But if you really want to make your decoders and engines perform to your liking, this is where you'll find the info.  The tiny little data sheet that comes packed in the bag is just a start.

Don't be afraid to ask questions. I'm thinking that anyone that reads these docs will have a whole new set of questions to ask.

gs