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So, you bought yourself a fuelie?

by Chilly (rev. 6/06)

Motor vehicle manufacturers are mandated by the EPA to produce vehicles that meet specific smog standards. To meet these standards with the current TC88 and exhaust technology, the MoCo tunes their engines relatively lean. As a result, bikes produce less smog, mileage is better, but lean tuning denies you max performance, and causes excessive engine heat which, in turn, negatively affects engine life. Tuning your bike to provide optimum fuel/air mixture provides better performance and engine life at some loss of mileage. For carbureted engines it's relatively simple to fix by tweaking your carb. But, fuel injected systems have matrices stored in the Electronic Control Module (ECM) called maps which control fuel/air and ignition timing for different RPMs and throttle positions. To optimize your fuel/air mixture or ignition timing you need to either remap the Electronic Control Module or provide a downstream correction. This is especially important if you make changes to your breather, pipes, cams or heads.

The MoCo's Solution

Harley provides two solutions for those making modifications to their bikes- The Stage I/II/III ECM Calibrations (aka chip burn, re-flash, etc.) which are simple solutions for re-mapping the bike's ECM for typical configurations, while increasing idle mixture, and increasing the rev limiter to 6200 RPM; and the Screaming Eagle ECM Race Tuner which allows much finer control of your bike's fuel/air and ignition maps.

For most folks, a stage one upgrade (aka "The Harley Tax") means changing to free-flowing breather and pipes. But the stage one re-flash is not designed for a free-flowing exhaust system. Changing both the breather and pipes provides increased air flow, and with the right fuel mixture, provides greater performance. Doing such an upgrade with only a stage one re-flash could create an excessively lean condition. If you perform only the MoCo recommended Stage One mods, leaving stock pipes in place, a stage one reflash might be acceptable.

For those performing more extensive modifications, the ECM calibration re-flashes do not allow tweaking for specific choices of breather, pipes, cams and heads. Since every combination is going to have different affects on your torque and HP curves, a simple re-flash is not likely to allow a bike modified beyond stage one to achieve its full potential. For that, you need fine control of your fuel/air mixture maps.

It does increase the rev limiter, so if your Wide-Glide with hot cams, SE breather kit and White Bro's 2 into 1 pipes makes its peak hp at 5600 rpm's, (higher than the stock rev limiter), the chip burn will allow you to reach it's peak. For those into getting the last bit of performance out of their bikes, this might be important. For cruisers, that higher rev limit may be of little or no practical value.

To provide the racer with finer control, Harley sells the Screaming Eagle ECM Tuner. This is a software package you load on a computer, with a cable and a dongle that plugs into your ECM. It allows you to re-flash your ECM with either standard calibrations, or with your own custom maps. The calibrations that come with the system are the same as those your dealer offers, and as of this writing, there are no custom maps available from Harley or any third party. However, you can precisely adjust fuel/air mixture at different rpms and throttle positions, as well as to advance/retard ignition. It comes with directions as to how to adjust settings based on feel, dyno runs or track runs. You can take a track run, download performance curves from the ECM, make adjustments and upload the new maps.

However, this amount of control comes with a price - $460, and use of it voids any warranty. It requires a great deal of technical knowledge and commitment. Further, the dongle is a security device that does not allow you to use the system on more than one bike. The first time you use it on your bike, it handshakes with the ECM and will forever only work with that ECM. Own two fuelies? Get two systems.

Power Commander

The Dynojet Power Commander (commonly referred to as a PCIII) is a fuel injection and ignition timing adjustment unit that plugs inline with the bikes' stock ECM. Changes are made to the bikes fuel and ignition curves without making any permanent changes to the bike's ECM. The PC uses original equipment style connectors allowing you to plug it in without splicing or cutting of the wiring harness. Removing the PC returns the bike to its previous stock condition.

The unit comes with computer software and a USB cable that allows you to select a specific map, upload it, or fine tune maps. The PC is pre-loaded with a base map which generally provides an improvement for stock bikes. Alternate maps are available for most typical configurations (i.e. TC-88 w/ stage 1 calibration, SE Air Filter and V&H Staggered Dual pipes). Each PC is supplied with a CD-ROM with common alternate maps. More maps are available for download on their website.

The software provides a spreadsheet interface allowing one to make fuel/air adjustments at specific RPM and throttle positions. The resulting custom map can be uploaded via the USB cable.

You can also change the fuel curve with the faceplate buttons. This adjustment moves the fuel curve richer or leaner in each area of the map. For instance, if you're riding heavily loaded or its particularly hot weather the PC can be temporarily adjusted at the faceplate to eliminate the "pinging" that is so common during these conditions. If you are about to make a long highway run, you can temporarily make the mixture more lean for better mileage.

For some bikes, Power Commanders can also adjust the ignition curve for increased throttle response, increased peak power, or to eliminate detonation. On most models the ignition curve is close to optimum for "pump" fuel.

For greater optimization or to develop a custom map for a special application, there is a network of "Dynojet Approved Power Commander Tuning Centers" throughout the country that can dyno-tune your bike.

One poster (MRBHD) had a PC installed in his 98 bagger. His Comments: "The bike had the HD stage II and Sampson slip-ons already. On the dyno prior to the power commander, the bike made 58 HP with about 60 ft/lbs of torque as verified by the dyno. After the power commander the bike now makes 76 HP with about 72 ft/lbs of torque! All of these are at about 3800 rpm due to the stage II cam. The bike now runs FANTASTIC, and it doesn't ping!!!"

Power Commander Web Site


A less expensive (~$240) and a simpler solution is the device designed by Mark Dobeck and sold by Dobeck Performance as the Techlusion Fuel Injection (TFI), and by RevTech as the Digital Fuel Optimizer (DFO).

Like the Power Commander, they plug inline with the ECM. Adjustments to fuel/air mixture utilizes four adjustment pots which work similar in concept to carburetor jet and mixture screw adjustments - An idle and low speed circuit (pilot jet\mixture screw), mid range and throttle response circuit for acceleration (needle and slide), a main circuit for wide open throttle and power (main jet), and a circuit which provides an adjustable accelerator pump function that senses when you grab a handful of throttle.

They are inexpensive, easy to install and easy to tweak, They do not require (or allow) a computer interface, downloads, extensive mapping, etc. They only add fuel, they do not allow you to reduce it as other solutions do, and they do not provide for changes to ignition timing.

Dobeck Performance
Revtech's Web Site


Yup, lots of others, more coming, and they change all the time. S&S, Daytona Twin Tech, Daytona Sensors ... Wide band systems, oxygen sensors ... This is only an overview of the issues, and the most common solutions. See "Other Forums" below for places where you can get deeper into it, and keep up with it all.

Will any of these void my warranty?

Maybe, probably. Especially if it can be proved your use of such a device caused damage. (i.e. you burned up your valves by running excessively lean). If you are concerned, check with your dealer. And if you don't like the answer, check with other dealers in the area. OTOH, If you're not ready to accept full responsibility for modifications you make, maybe you should stick with what the MoCo offers or leave your bike stock.

Jeeesh, are there any other downsides . . .

Sure, if you enrich your system, fuel economy is going to suffer. When your bike runs lean, you burn less fuel. If you make your fuel/air mixture richer, you can expect a drop in MPG. One poster experienced a 10 MPG drop using a standard map for his bike. Dyno tuning can provide a more optimum map and fuel rate.

Then there's the ever-evolving issues with legality of futzing with your systems, environmental issues, noise issues. Consult federal law, state code, lawyers, and spiritual advisors for advice in these areas.

What to do, what to do?

If you can afford it, if you have a better than average understanding of how to tweak maps, and if you want the finest control over your ECM, the Screaming Eagle ECM Tuner is certainly a clean, first rate solution.

Many in this group like the PCIII and enthusiastically recommend installing them. The TFI/DFO solution is certainly a viable alternative for folk looking for a simpler solution.

The ongoing, raging controversy is whether to do the MoCo's ECM calibration first or to save the ~$150 re-flash cost. The stage one setup will enrich your idle (which neither the PC nor the TFI/DFO do) and will increase your rev limiter to 6100 RPM (which neither device does). If your PC/TFI/DFO craps out, and you have a stage 1 kit, you can simply unplug the PC, reverting to the OEM system in a matter of minutes and you're back on the road with a less than optimal, but probably not dangerously lean condition to worry about. If you have a bike modified beyond a simple stage one, the extra $150 might be cheap insurance. Some feel (and others don't) that the MoCo's ECM calibration should be done regardless.

There are hundreds of messages on this topic in RMH. A Google search of the archives will give you a wealth of experience with these issues.

Other Forums

This is bar talk, if you want a more technical discussion there are other online forums which go into much more technical detail:

Harley Email Digest
Harley TC88 Email List