Looking for opinions. Do you think it's possible for a defective battery tender to give off a signal or noise that can affect (confuse) the function of the ECM? We know the ECM monitors battery voltage and obviously is part of the "system".

I always keep my bike on a Harley brand battery tender when I'm not riding. For the past two years I've had issues starting the bike. It kicks back, pops through the carburetor, backfires occasionally, no start until I flip the ignition off and on and sometimes it sounds like the pistons are trying to swap holes. I've run several threads on this issue to no avail. I've had the dealer look at it and they find nothing. I've changed several sensors and no improvement. Well, long story short, the past four months I haven't put the bike on the tender and starting within a few weeks of stopping my starting problems have been progressively improving. Now the bike almost without exception starts perfectly. The only variable is the tender so given that, that leads to my question above.

What say you?

 

Well this doesn't exactly answer your question, but it might suggest something that you might be leaning towards. I did the exact same thing with a brand new 2015 Softail Slim and a battery tender. My battery lasted 2 riding seasons, and then started having cranking issues. It was never allowed to full discharge and was always stored inside for winter. Either way, I was left to believe that that battery tender cooked the battery and caused it to fail. Maybe the factory battery was older than it was supposed to be, IDK. These days I refuse to habitually park the bike with a tender. I will occasionally connect it to give it an occasional bump, but that's it. I tossed the Battery Tender brand and went with a Noco charger/ tender. During winter I will remove a fully charged battery and monitor it throughout the cold months.(while stored inside).

 

I've seen them do that. My tender is around 8 years old, so it may have issues. However, the battery on my bike is strong. After I stopped using the tender, I'd say 98% of the improvement was noticed within a little over a week. The other 2% over time could just be my imagination. In my case the bike was losing its mind on startup. I tried to describe it the best I could above, but it was bad enough I kinda cringed when it came to starting it. Maybe it's just a massive cooencidence, but I doubt it. I'm just looking for what is hopefully some confirmation that a faulty tender can cause such a problem.

 

I would think the problem lies in the tender, rather than the bike's systems....

I have 3 bikes; '01 carb, '03 EFI, '16EFI.... all three are left on smart tenders when not riding for more than a few days. I've never had a starting problem that wasn't eventually found to be related to the battery.... and those bikes represent 3 different ECM types.... none of which have been affected by the tender...

I've used smart tenders since 2003, and I have had to replace two because they "went bad" and didn't charge (one case) or overcharged/cooked (one case) the battery. In both cases the tenders ruined the battery, requiring replacement.

Perhaps your tender is not performing properly and you took it out of the loop prior to it damaging the battery...

 

Thanks, but I've had the same battery in the bike over the timespan of the start trouble and the battery has always been strong. The things it's experiencing aren't battery related, but more like ignition/timing. I just find it odd that my start problems went away when I stopped using the tender. Logic would dictate that the tender was messing with the ECM somehow. I simply don't know. I know it doesn't make sense and I'm at a loss for an explanation on the bike healing itself.

 

To answer your question of 'can a tender confuse the ecm', the answer is no. Battery voltage, however, can. Simply, use your tender and after an overnight set, take the tender off and measure your battery voltage. Should be 12.6v or more. If not, you may need a new battery, or new tender.

When running, the battery voltage should be 14+v, give or take.

You don't mention whether you're stock, tuned, etc. My M8 actually did something similar; I tried to tune it out to no avail. I had installed NGK spark plugs when I installed my 120 kit. All else failed, so I decided to try stock plugs. That fixed my starting problem.

 

It's an 07. Bike is stock, except it has a stage one. Factory tune and nothing has been changed over the years. It's exactly as it was when I bought it in early 08.

Along with changing a few sensors, I did install a set of new stock plugs, none of which cured the problem.

 

Seems to me like there are quite a few battery failures due to leaving them on the tender 24-7
I will only put mine on the tender during the winter, but only to bring it up to a full charge then take it off if I have not ridden after a month or so. Otherwise riding the bike will charge the battery so if you do that every month there will be no real reason to keep in on a tender. This is JMO and my batteries have not given me any trouble so take it or leave it.
If you like to just start the bike during the winter and let it idle the battery will not charge as you must bring the RPMs up to charge.

 

I guess I can write it off as being magic. That is if and until the start problems returns.

I'm going to ride it another month without putting it on the tender and if have no problems I'll put it back on the tender. If the crazy start problem returns, there's little doubt the tender is the issue.

 

I might add, batteries have a shelf life which can vary from one to the next. Battery tenders, maybe so but far less frequently the life cycle on a tender. Also the battery condition is apt to have a much greater effect on the ecm than the tender will. Tender should be on with the ignition switch off is a safe way to treat it if concerns are damage to the ecm. A tender not a battery charger also recommended.