Aprilia RSV4

Aprilia RSV4s are seriously nice bikes and are possibly the closest to a race bike that we can currently get our hands on. That being said, they are not without problems. Aprilia’s oil-pressurized tensioners are lacking, and the bike has quite a serious fuelling issue at 7200 rpm.

JP contacted me via our page and told me about the issues he was having with his RSV4. He also wanted to be sure that bike was properly set up after fitting an Arrow slip on.

After lengthy discussions and a dyno assessment, JP decided to leave the bike with me for tuning.

The first pull I did was with the dB killer fitted and there did not seem to be an issue. Only once the dB killer was removed, could you feel the problem at 7200 rpm. The dyno graph confirmed what I was feeling.

At first I thought this was an injector phasing issue; I was sure Aprilia was switching the primary injectors off and switching the secondary injectors on a couple of milliseconds later. I was wrong! But we will get back to that later.

I searched the web for someone experiencing the same issue and found a forum where an RSV guru claimed that the only way the issue could be sorted was with an aftermarket ECU like Magneti Marelli or Motec. This was obviously out of the question because of the expense. I advised JP that we should try flashing the ECU with a Rexxer map from Germany through a Cape Town supplier. This obviously adds quite a bit to the total invoice but we were determined to get a good result.

I had previously installed a Power Commander 5 and Secondary Fuel Module to another customer's RSV4. He was not entirely happy with the result and eventually the kit was removed from the bike.

So I was hesitant to fit the PC5 and SFM because of this previous experience, but I figured a Rexxer map would definitely resolve the injector issue, and I could take control of the fuelling via the Dynojet kit.

There is just something about the way Italians build bikes, man it is so tight, it’s like the manufacturer doesn’t want you to work on it.

After fitting the PCV and SFM, it’s quite a battle getting the tank to fit properly.

Stock graph.

The torque curve reveals the hesitation at 7200 rpm.

I contacted Redewaan for the Rexxer map and he was there in a ‘flash’, pardon the pun.

First Rexxer map versus stock.

Because the change was hardly noticeable, we moved onto the next map.

Second Rexxer map versus stock

The power was increasing but the problem remained.

Third Rexxer map versus stock.

By this time both Redewaan and I were pretty frustrated and reverted back to the first map.

I made the decision to go ahead and custom map the bike and see how the bike responded.

After mapping 2% to 10% Throttle Position (TP) with Tuning link, I decided to stop and just run the PC5 software.

I was curious to see what the injector duty cycle was doing. To my surprise the primary injectors fire for the total RPM and TP range. Then spotting the secondary injectors, regardless of TP, at 7200 rpm the two rear secondary injectors come on at a whopping fifty percent duty cycle and 400 rpm later the two front secondary injectors come on with 40% duty cycle.

With my tuning experience, this seemed like an easy fix; just pull out the fuel at these points.  I was wrong again. Instead I found myself adding heaps of fuel to both primary and secondary injectors at these points. This did not make any sense but I carried on mapping as I was keen to get the bike back to JP. Worryingly, my other work was piling up with one staff member lost to another shop.

Eventually I got the tuning done on each cylinder and could do a final run.

Final Run

As you can see there is still an issue at 7200 Rpm, but that is because the power has been optimized before and after the problem area.

I then softened the power quite a bit before this area and slightly less after.
Below is a graph showing stock with the dB killer fitted, stock without the dB killer, and tuned with the midrange softened.

The bike is now silky smooth and the rider cannot find the problem even if he spends all day looking for it.

Now!!! That’s all fine and dandy but what is causing the lean fuelling in this area? Again getting into the very bright brain of Eddie Henry, he suggested “fuel pressure”. How obvious is that?!

So I plumbed into the fuel line with a pressure gauge and guess what? The fuel pressure drops from +/- 3 bar to sometimes as low as 1.3 bar for just a split second. This means that when the two rear, secondary injectors come on at this huge duty cycle the fuel pressure drops to ALL the injectors.

Our next exercise is to prevent the fuel pressure drop without causing negative effects elsewhere.
I just need to find the time to do all of this.

JP’s feedback has been very positive and he now seems to be enjoying his RSV4. 

Julian, Superbike Solutions