Aside from running a 19 year old bike at redline and having it start to crap out….. how does it run otherwise?

 

Idling and up to 11/12k it runs great. As for history, I've owned it for 12 years and have had zero issues during that time. I've only had to do normal maintenance items. I'm not looking to bounce it off the rev limiter, I'm concerned about it leaning out and hurting the health of the motor.

 

how many miles on it?

Did you clean up the stick coils and test them while you were changing the plugs?

When has the last tune up service been completed? ie....... adjusting the valves, compression and leakage test, synchronizing the throttle bodies etc...

Test fuel pressure drop while riding, or maybe just pull the pump and see how dirty the filter sock is........ they can easily flow more than the minimum in the book at idle/prime even when they don't work for shit in use

 

Thanks for the suggestions Riverszzr, i forgot about the stick coils. I just tested them, all primary windings came back at 1.6 ohms. Three of the four secondary windings came back at 9.5k with the fourth jumping between 15-20k ohms. I didn't check voltage but I just ordered a new set and I will replace the bad one. I couldn't find anything in the manual about cutting the injector to that cylinder if the secondary winding has issues, only when the primary winding has failures. Is anyone familiar with what the ECU would do in that situation? Sorry I'm a bit of a novice...

As for your other questions, the bike has 40k miles, valves were checked at 28k. Throttle bodies were synced somewhere around 25k, not exactly sure though.

 

Just did some research... If my understanding is correct, the bike is having a harder time driving the spark to that cylinder and it can't keep up at high RPMs so the ECU cuts fuel? The manual mentions shutting down one injector but maybe it's cutting fuel to the whole motor?

New set of coils are on the way, I'll follow up once i get a chance to put them in and test.

 

Only if the ecu recognizes a code............ So do you have a code and an FI light?
if not you are simply losing spark and the raw fuel is still flowing in that cylinder

 

Pressure tester came today. With the engine off but primed it rose to 44 psi and then slowly dropped. I think i maybe had a tiny leak because it kept dropping past the 41 psi that it is supposed to stay at. With the bike idling it flickered between 43 and 44 psi. Unfortunately it snowed today so i couldn't ride it but i gave it a few light revs and it stayed at 43/44 psi. I'll do another test under load on Saturday when the new stick coil is supposed to arrive.

If the stick coil doesn't fix it and the pump is fine, would the next thing be a bad ECU?

 

Pressure tester came today. With the engine off but primed it rose to 44 psi and then slowly dropped. I think i maybe had a tiny leak because it kept dropping past the 41 psi that it is supposed to stay at. With the bike idling it flickered between 43 and 44 psi. Unfortunately it snowed today so i couldn't ride it but i gave it a few light revs and it stayed at 43/44 psi. I'll do another test under load on Saturday when the new stick coil is supposed to arrive.

If the stick coil doesn't fix it and the pump is fine, would the next thing be a bad ECU?

Does not sound like a bad ECU. If it was you would have problems at all rpms. Sounds to me like fuel or spark related. Replacing the ignition coils is good, hopefully you purchased OEM or OEM spec coils for the replacements so they are plug n’ play. Replace and properly gap the spark plugs as well. For fueling- replace the fuel pump or clean the filter if it is not integrated into the pump. Last thing would be to clean the injectors. Motion Pro sells a tool and the cleaner to do it yourself or you can send off the injectors to get them cleaned.

 

I'm thinking you should sync throttle bodies...needs to perfect at idle ..AND at high RPM. if you have sync gauges ...at idle it might look like good sync...but if you bring up rpms to 3-4k it MUST still be in sync.

I had similar issue and was having a hard time syncing my 03 636. Eventually I figured out the air inlets behind the sync screws were partially gunked up.

and I also had a similar issue until I cleaned the injector fuel screens...(only one needed it)

if one of the screens on incoming fuel side of on an injector are a little cruddy or throttle body sync is just slightly off on 1 cylinder it could show up like this aka only at high RPMs.

 

The coil came in today so i went for a ride and there was no change.

I also tested the fuel pressure... In 6th gear at 8k rpm opening the throttle up the PSI stayed at 42/43. I did a few more pulls and regardless of gear, it seemed to stay in the low 40s. I pulled over to test the pressure at the 13-15k RPM range. I didn't want to do this while riding since my guage was at me knees. Right when I get to the problem area it starts to drop a bit towards 40 or high 30s and then really starts dancing between 30 and 50 PSI. It is very unstable while the engine is breaking up and then rebounds as soon as I let off the throttle followed by a big cloud of white smoke out the exhaust. You can see the pressure gauge in the video Here (slowed down 1/4 speed).

So i guess i need a new pump? The way it spikes to 50-60 PSI almost seems like the pump is trying to fight an obstruction or something...

I do have a buddy that has a spare set of injectors/fuel rail that he's going to loan me. It's been sitting on a shelf for at least 5 years though so the injectors might be gunked up anyways. What do you guys use to clean the fuel system if i dissemble everything? Some threads have talked about people letting stuff sit for a day in something like seafoam. What would you recommend?

 

I routinely see them climb into the 50's and even mid and upper 50's for fuel pressure above 10k......... if yours ever falls under 40 then flow is falling too and spray pattern is getting droplets instead of atomization to burn as the injectors only make a good spray pattern above x pressure (usually 40/41 is the bottom on plenty of sportbikes)

So yes, sounds like you need a new pump or new regulator or both (as long as all wiring is good)

 

New fuel pump came today (OEM) and it is still doing the exact same thing. I believe on these models the regulator is inside the pump? I still haven't tried my buddy's injectors and fuel rail, I guess that will be my next step once I try to clean them.

Anyone have any other ideas what could be going on? When you say wiring, do you mean voltage at the pump?

 

I have this same bike..and to my knowledge there is NO REV limiter...There is a Shift light.

HAVE YOU LOOKED AT YOUR FUEL INJECTORS? They have little screens that can have have buildup on them.I looked at mine 4-5 years ago and 2 of 4 had buildup.

 

The bike does have several 'Fail safe' or limp modes...but you would DEF know if you were in those modes. I have had to replaCE AN AIR INLET TEMP SENSOR. that can also get clogged...

you never answer about whether the Throttle bodies are synced... it might be a good thing if they are not synced..because it can/has kept you from blowing up the motor redlineing it.

 

Any updates on the situation. I had rust in my tank cut the tank open fully cleaned it by blasting it and put all together cleaned up fuel pump pulled it all apart. Starts right up runs perfect revs up to 13-15 k just fine no problem but will start braking up. Bike is a stunt bike. Havnt done plugs yet since I got it that’s next but I saw that it didn’t help u. So any updates would be awesome 🤘🏼