VFR FI Woes - Diagnosis / Opinions welcome!

I know that I have read on the forum before something that is similar to the problem that I am having, but since I do not know the name of the parent thread I'm afraid I'm going to have to start a new topic on this - Sorry everyone if I'm duplicating!

Symptoms - In order of appearance, all of which are occurring now:

1. Lumpy idle: I know that this is a V-4, but the idle is lumpy. It oscillates back and forth at idle about 200 rpms in both directions, and it didn't do this when I bought it, so don't tell me it's supposed to do that please, I've already been told that before.

2. Random bog/surge: Usually lower in the power band, I'm getting an EXTREMELY random bog and surge, where the engine will drop to idle for a few seconds, stay there while I'm twisting the throttle like a moron trying to figure out what is going on, and then surge after approx. 2 to 3 seconds. This only happens once, almost every other or third time I take the bike out, usually happens in 1st or 2nd gear.

3. Non-linear/rough throttle: In neutral or with the clutch pulled in, the throttle bounces back and forth about 250rpms in both directions getting a little more extreme as I give it more revs. Also, with the throttle held in a constant position, after a second or two of having the revs be a little stable the bike revs down a few hundred rpms, still oscillating but basically like I have rolled off the throttle.

4. Airbox backfire: Usually just after starting the bike, already warm, a stab of the throttle will illicit a popping sound from the front of the bike, which I'm assuming is a backfire through the airbox. It has only done this a few times. Also, when testing for bullet point number three, I found that at about 3k-3.5k revs, I'm getting a popping sound, very sight but noticeable from the front of the bike and audible over the sound of the engine. Didn't rev the engine any higher than that so not sure if it gets any worse with more gas.

Any thoughts? I've left out my opinions on the matter because I know that I am not qualified to make any kind of intelligent assumption on what this could be, but I'd love to get some opinions on anything that you might think it is. Thanks for the help!!!

 

Sounds like a bad/dirty 02 sensor or a loose 02 connector to me. I had a Buick that would do exactly what you describe with the throttle bogging down randomly, because the engine would lose 02 signal, freak out because it now thought the mixture was too rich, and basically cut the fuel down to bare minimum for a few seconds. Turned out the cable had fallen out of it's little plastic clip (thanks GM!), allowing the connector to hit the exhaust and begin melting.

I would expect wonky fuel delivery such as you describe is most likely caused by the ECU not receiving an accurate signal from the 02 sensors. Try some 02 sensor eliminators if you have not already, or pull your sensors and clean them and inspect the connections.

 

Is the FI light on or flashing at any point?

 

No, I've never gotten any kind of FI light, solid or blinking, from this problem.

 

That in itself is a clue, the failure is not a system that is being monitored by the ECM. As described it sounds like it could be as simple as a large air leak in the intake system. Inspecting the throttle body connections and just aboot everything in the related area sounds like a good step. I am in Sacramento as well so I you need a hand let me know and we can look at this together over a beer or two.

 

I'd love to bring it by for a look, but I'm out of town at college, and the bike won't be back in NorCal til the summer. I am coming up on being due for a service soon, I may just have to wait and have them take a look at it and see what they can find...

 

Offer shall remain open.

 

Sounds good, and we still need to get that NorCal Sacramento-Tahoe trip going, never could get it together this year but I'll make sure to send out the info earlier next year when I'm back.

 

I too experienced a lot of the symptoms that you have described upon getting my VFR. I found that there were three things that completely got rid of the problems. The first was slightly increasing my idle speed to about 1350 RPM. The manual states that it should be 1200 +- 100RPM but 1300 wasn't quite enough. The second thing that I did that helped the most was to do a starter valve sync. Things ran smoother, sounded better, etc after this. The third was replacing my exhaust system, thus eliminating the O2 sensors and PAIR valves. This cured other things higher in the power band than was you describe but also helped quite a bit with the very abrupt off/on throttle response.

I will insist that you can perform both of these yourself if you are able to turn a screwdriver. I was a more than a bit nervous doing the starter valve sync myself but it turned out to be super simple once you get into things. The ony odd tool that you will need for this is a 4-bar manometer. After hooking it up to the vacuum lines, it really is as simple as turning the screwdriver a tiny bit to get them all synced up. After that is done, a quick idle adjustment and you should be good to go.

If you are skeptical, I highly suggest taking Toe up on his offer. He is well equipped to handle the situation so long as you make sure that he keeps his hands away from moving parts such as belts and pulleys.

 

I have had the exact same problems on my bike. Mine is/was a 2002 model with a similar problem which had been getting worse over the years. Eventually I tried replacing the ECU with an American 2006 model (including wiring harness) and the problems got worse to become exactly as you describe - hunting idle, hunting revs when holding the throttle open in neutral and also the sudden drop in rpm.

At that point - after years of throwing stupid ideas at the problem I bought a 2006 wreck and put the motor and ECU (Aussie 2006 ECU) into my frame. That was August this year.

I now seem to have replaced one problem with another one. The bike is now extremely rich when cold and I've had to put in startup fuel in my Powercommander of -17% until the motor hits 70 degrees C. I have replaced the ECT, the IAT, and the MAP sensor, all to no effect. I have disconnected and reconnected the PAIR system (and disconnected it again), also to no effect.

Personally, I'm stumped!

I will say this though: the lack of ECU error codes means very little. For one, if you have a power commander faulty injectors don't bring up an FI code. Also, things like sensors mildly out of range won't bring up an FI error code either - the part has to literally fail or get disconnected for an error code to pop up. These ECUs are useless compared to an average OBD-II compliant ECU in a car because you literally can't get any data out of them.