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ZAMM Fanatic
2,730 Posts
Discussion Starter #1 (Edited)
The ECM receives information from the throttle and several engine sensors and, based on its map, commands (energizes) the fuel injectors as to when to start and how long to spray (pulse width) fuel into the intake tract, while the throttle body butterfly regulates the air supply.

>H-D's Electronic Control Module (ECM) is located either under the seat or behind the chassis side panel. Look-up tables, also known as [fuel and ignition] maps, are stored in the ECM for a specific engine and are used to provide the correct amount of fuel [to be injected] under various engine settings, [operating conditions, such as idle, wide-open throttle, and cruise conditions] temperature, and weather conditions. If the engine is upgraded with [less restrictive] exhaust, [wilder, greater valve overlap] cam, head porting, [increased] displacement, or other modifications, the map must be updated for the new parts combination.

>Electronic fuel injection [EFI] reduces [vehicles] emissions because it meters fuel more accurately than a carburetor. It also offers riders the benefits of improved cold or hot starting, crisper acceleration under varied operating conditions and smoother running at high altitudes.

A real WEALTH of information on tuning on THAT site...

>ThunderMax is a... performance engine management system for EFI equipped Harley Davidson models. The ThunderMax ECM replaces the stock module and helps “unlock” various performance advantages not possible by “Flash” systems and other post-[ECM]“piggy-back” tuning devices.

ThunderMax’s key performance advantage relies upon its proprietary AutoTune technology which utilizes 18mm Bosch wide-band oxygen sensor feedback to provide continuous AFR tuning corrections based upon [actual] riding conditions like temperature and altitude.

And the book I'm currently reading:


ZAMM Fanatic
2,730 Posts
Discussion Starter #3 (Edited)
Given A) The popularity of HD as a brand, and B) the number of riders who modify stock exhaust systems, add K&N filters, etc, and C) Believe they must then re-map the fuel and ignition curves (which may or may NOT be true) to achieve good tune.......

It would seem a thread on HD fuel injection and tuning would be worthwhile here on MCforum, if only to provide an overview of the basics, vendors and choices available, and links to MORE ADVANCED discussions like those above.

My goal MIGHT be to one day write some sort of UNBIASED 1000 word "overview" that could be handed to any HD purchaser/owner to give them some VALID guidance on tuners and tuning, vendors, etc.

Take the Dynojet operator's course if you get the chance. :)
I'd love to take that course. Tell me more. (or should I just Google it?)

The question I'm currently trying to answer is, "The Screaming Eagle Tuner" supplied by H.D., is that something an owner/USER can adjust/tune/remap, or is one strictly locked into paying a HD dealership to (re)tune the bike (because of proprietary software they ONLY sell to dealers to interface with the Screaming Eagle.)

I've read one answer, and gotten another from Covington Cycles and a couple of other non-HD dealerships. (They say HD locks anyone but HD out of adjusting fuel and timing maps USING A SCREAMING EAGLE TUNER)

Apparently there are SEVERAL version of "Screaming Eagle" tuners available from Harley, (Pro, Street, ...) and AT LEAST one firm offers laptop software for users to adjust SCREAMING EAGLE fuel and ignition maps, like ""

>...If you use a Screamin’ Eagle Pro Super Tuner (SEPST), Screaming’ Eagle Street Tuner, TTS, Power Vision, or Screamin’ Eagle Race Tuner (SERT), MyTune is the Harley Davidson tuning software you need. MyTune is an easy to use Windows program that takes data logged from your bike and generates a tune tailored specifically for your bike. It was developed by a home tuner for home tuners. You don’t need to have a deep understanding of the Harley Davidson EFI system to use MyTune. It takes care of all the hard work for you.

What I REALLY need is 10 minutes on the phone with a REAL expert on HD fuel injection technologies who doesn't have an axe to grind for or against the factory tuner. This is clearly an area where A) I don't know what I don't know, and B) I know just enough to be dangerous and could easily spread misinformation!

I do know that the Screaming Eagle is KEYED to the bike's ECM, cannot be moved to another bike, and must be either REPLACED or re-keyed (at enormous expense) if a bike's ECM must be replaced.

How Dyno tuning (strapping the bike to, and using an actual dynamometer) compares to "adaptive, self-learn" algorithms for HD tuners is another big unknown to me.

I do know that tuning by feel, that is, go ride it, come back tweek it, rinse, repeat was good enough for the first 80 least for those who knew how to adjust /rejet carburetors.

I'm also aware HD has had two "flavors" of fuel injection, an early system that worked poorly (and often lead to overheating), and a newer system by Delphi, but that EVEN the newer Delphi uses narrow-range 02 sensors where (imho more advanced) systems like the ThunderMax replace these with wideband 02 sensors and at least theoretically SHOULD be capable of better self-tuning.

(I'm also aware PLACEMENT of 02 sensors in exhaust manifolds is critical to getting good readings - depth, angle of the bung, proximity to the exhaust valve, etc)

What I learned with the 2-Brothers Juice Box (aftermarket tuner) the PO "slapped" on my Concours is that a non-expert can VERY RAPIDLY screw up the tune on an otherwise well engineered and well running bike, or AT LEAST have the ECM and tuner locked in a never-ending struggle with each other

In CLOSED LOOP operation, where the 02 sensors are being continuously monitored by the ECM, that the tuner will be ignored/overridden by the ECM which will enrich/enlean the mixture to where it sees proper 02 switching, regardless of what the tuner TRIES to do downstream, like widening/narrowing fuel injection pulses.

That's why my Concours FALSELY REPORTED over 70mpg at high cruise with the 2-brothers tuner on; it was leaning out the fuel pulses that were being excessively widened by the "Juice Box"

Back to DynoJet, at first glance it looks to me like ONE MORE aftermarket HD tuner/software/vendor. I don't know how they stack up against ThunderMAX or the other aftermarket HD tuner competitors, other than they strongly emphasize dyno usage.

Can you provide some perspective?

My experience with Dynos and Dyno tuning can be summarized as "There are guys who know how to use dynos to good effect and those who don't. Nobody wants a bike that only runs well at the same ambient temperature / conditions it saw WHILE ON THE DYNO."

Having said that, my favorite treatises on dyno turning can be found HERE:

Alright? Time for everyone with some REAL WORLD HD EFI tuning experience/knowledge to chime in!

17,857 Posts
A document such as you are thinking about writing would be very useful information, especially for new owners. I'm not sure how many people are going to come here looking for information on how to tune their hogs, but a solid, unbiased explanation of their options might have very wide appeal. Good luck to you if you decide to take that on! (And even more luck to you if you decide to update it every 6 months or so to keep it current. Things change pretty rapidly. )

You wanted some opinions from people that have real world experience tuning EFI bikes, so here's some of mine.

There's several paths to tune a Harley EFI bike:

1) You can re-program the ECM using proprietary software and a proprietary computer. This is called a DTII, or, Digital Technician II, and is only available to dealerships. ( It's actually a pretty amazing piece of equipment and takes vehicle trouble shooting to a whole new level.) As far as I know there is no aftermarket substitute yet for the DTII. Even if you were to get your hands on one it would shut itself down as soon as it connects to Milwaukee from a network Harley didn't recognize. Obviously, if you go that route you're dependent on the dealer for any future modifications.

2) You can completely replace the factory ECM with an aftermarket one that's more Indy-friendly. That would be units such as the Zippers/Thundermax and S&S units, and any such unit will have its own tuning software. I assume they will also self-mate to the TSSM, but I have never installed one so I do not know exactly how that is handled.

3) You can use a flash tuning interface such as the SERT, SEST, SEPST, and so on. These will allow you to rewrite the lookup tables on the factory ECM, and the various models have various features and options. Some are from Harley, and some are aftermarket, and I'd guess there's probably 8 to 10 different products out there easily available. Which one is best? Everyone has an opinion and when you figure out the ultimate answer please let me know.

I've done hundreds of tunes with the SERT, which is easy to use and is adaptable enough to handle about anything you'd want to do with it. However, it was taken off the market in about 2008 and replaced with the SEST. (It is still available in modified form from TTS.) If you purchased any of these and installed them yourself, you have the software and can make further changes at any time. If you paid a shop to install it, you likely don't have the software and you're dependent on a shop, Harley or independent, to make future changes. Many of them do "marry" to the ECM when you install them.

4) You can use a piggy-back controller. This doesn't make any changes to the ECM programming itself, but rather interrupts the signal to the injector and changes it. The first ones, such as the Power Commander II and the original V&H Fuel Pak, simply changed the pulse width by a specified percentage, but they've gotten more advanced.

(As a side note, I think the current Fuel Pak is about the easiest way for the average home user to go about modifying his fuel delivery if he opens up his engine. It's useless for any kind of precision tuning, but it's a great tool for the average Joe that wants to feel like he's taking control of his bike, and it gives satisfactory results for most situations.)

5) You can use an auto-tuner, such as the Cobra unit or the new Dynojet unit. I have never installed one and have absolutely no idea how they work. :) These started coming out right about the same time I stopped giving a fu^% about getting paid to tune bikes.

6) There' s a small, but vocal minority that tout the use of simple pulse extenders. They swear by them with almost religious zeal, but I don't know any actual technicians that have ever come out in favor of them. From what I have seen they are a serious step backwards from the PC-II.

As for the actual tuning actions, as you probably already know you've got a few options too:

1) You can download a pre-determined set of values. Cheap, easy, and almost always "good enough" for most situations for the average street rider.

2) You can use data logging software and either write your own values, or use a tuning software to write a set for you. The advantage is the data is gathered while operating the bike in real world conditions. The disadvantage is it takes longer and is often awkward. You ride around with a laptop bungeed to the back seat, and you usually have to do it many times to get things dialed in.

3)You can make the changes real time on a chassis dyno. The advantage is it's accurate: all of your roll-on runs will be done with the same environmental variables. It's also faster than data logging, and a heck of a lot more convenient. (And no, your bike will not then just be tuned to one set of atmospheric conditions.) Disadvantage is that it's expensive, and can't be done by the average Joe.

4) You can seat-of-the-pants make changes to your look up tables. I've known one guy that was pretty damm good at doing this. He was also a very good dyno operator and a professional race tuner. I'm not that skilled, and neither are most other technicians.

Oh, and Harley did start using wide band O2 sensors. I think about 4 years ago, but I'd have to look that up. With the current bikes, if you just change out your pipes to get a little better sound, you're not likely going to need to do any of the above. (That's a very broad general statement. :))

The earlier Alpha-N EFI system was phased out in about 2001.

Whew. I can only type but so much at one sitting.

ZAMM Fanatic
2,730 Posts
Discussion Starter #6 (Edited)
Whew. I can only type but so much at one sitting.
Great Stuff.

Hope you'll maybe add to it later.

Clearly there are a LOT of paths HD owners can go buy, but in the long run, is there still time to change the (fuel & ignition) maps you're (they're) on??? :biggrin:

I suspect most HD buyers end up with whatever tuner their local dealer favors, or what their "good buddy" recommends.

Trying to make an EDUCATED choice on tuners, etc...whew! So many choices! Without hands-on experience I rather doubt I could do much in terms of a "guide."

Maybe a better goal would be penning a piece along the lines of

"10 Questions to ask about the tuner you're about to Install on your HD"

I received some feedback on this thread from Dr. Dyno but not sure that reprinting it here would be appropriate. He sez he intentionally sTAYS OFF mc forums so he can get work done, lol. (And his work happens to be TUNING BIKES)

Bottom line is he's not all that impressed with several of the VENDORS selling HD tuning gear, as the profit motive seems, to him, to dominate how they treat customers.

Would I be wrong in suggesting that tuning is frequently a labor of love for those who are really into it? (And may include endless fiddling for not much detectable improvement in either performance OR mpg's?)

I'd have used the word "measurable" but ....

My guess is the enormously popular "Butte Dyno" can only measure changes in increments of about 7 horsepower, and mpg measurements, changes of 2-5mpgs or more with any REAL accuracy... feel free to argue for higher or lower values, point is, there is SOME threshold...
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