Engine won't rev past 6K

[Tonto1]

Fired up my Busa (’02) for the first time after winter mods and sorting a problem with the starter. Engine has been bored out to 1396 and was running 100% before the winter.

Seems to start ok and idles a little roughly but not too bad, has v.good oil pressure, however when it's warmed up I try to rev it and gets to around 6K and then starts miss firing, stuttering and won't rev any higher.

Winter mods consisted of upgrading fuel system with braided lines, Aeroquip fittings, Aeromotive regulator and Sytec pump. All of this appears to be working well with fuel pressure remaining constant. Have also checked all the filters etc and the seem fine (ie no blockages). Everything seems to be plumped up the right way. Everything else on the engine is as it was before the winter. Only other thing I did to the engine was take the clutch out to inspect it and put it back in again.

• I tried re-fitting the old fuel pump, which made no difference.
• Also added new plugs, and then tried refitting the old ones, again no difference.
• All coils seem to be fine have tried replacing all with a spare that I have.
• Have put a temp gun on all the exhaust headers when running and these are pretty much equal.
• Battery has plenty of charge and voltage when running seems to be good.
• Checked all my fuel lines and no kinks or bends or restrictions.
• Double checked all TB vacuum lines all of these as normal.
• CAT/Exhaust etc all in good nick.
• Tried with full tank of fuel.
• Never really messed with any of the wiring on the engine since the engine was last run, but everything looks as it should be.
• Double checked set up of the new regulator, which seems good (set to 55psi which is what I had before and what was recommended to me by my engine builder/tuner. Tried varying the pressure but again this made no difference.

All made zero difference.

Hooked up my a lambda gauge which sits nicely around 0.95 when idling, then suddenly goes crazy around 6k with the mix appearing to lean right off relatively suddenly.


Struggling to think of anything else apart from the injectors being fouled. Injectors are currently being ultrasonically cleaned by local tuning company, so will see what difference that will make.

Not running with the standard Busa clocks, so trying to get my hands on a set of these so I can check for any error codes.

Also planning on working my way round the various sensors (CKP, CPS etc) and check these as per the Suzuki maintenance manual.

Any thoughts or suggestions on what else to try will be much appreciated.

[Commuta_Busa]

Did the tunner do the install as well or did you do it? If he built you a "turn-key" build then I would talk to him first.

[Tonto1]

Originally Posted by Commuta_Busa

Did the tunner do the install as well or did you do it? If he built you a "turn-key" build then I would talk to him first.

Was running fine for over a year since the tuner saw the motor and was running 100% just before the winter! Only thing thats really changed since in the upgrading of the fuel system, oil change and a clutch inspection.

Did have some starter issues a week or so ago, when the engine wouldn't start, but traced this to a faulty sprag gear and the starting system now works great.

[BlueHaya]

You upgraded the fuel system over the winter? I would get it retuned with the new fuel system.

[GIXERHP]

What do you have the static fuel pressure set at?

Have you re tuned since your upgrade?

[GIXERHP]

Never mind about the pressure i just saw it!

You need to back it down to 43 PSI, to start off with, and while your tuning the bike you can increase it as your re mapping! It's way to high!

[Tonto1]

Fuel pressure wise, i have tried running with less. But 55psi is what I was recommended to run and my Power Commander has been set up for. Also have run this successfully on this engine for the last year or so. So pretty sure this is not the root cause of my problems.

Main problem seems to be a lack of fuel at high rev's.

[Mr Brown]

Fuel lines not kinked when you put the tank down? Start with the simple things.....

[Tonto1]

All fuel lines checked and look good (ie no kinks, constrictions etc).

Another quick update:

Got cleaned injectors back this morning and refitted. (These where only ultra-sonically cleaned and not flow tested so can't be 100% they are working correctly).

Did a quick check of all the main sensors in the loom (CKP, CMP, AP, Temps etc) these all seemed good and appeared to be getting the right voltage from the ECU. However never checked these when powered up so no guarentee they are working well when running.

Any suggestions on what could cause a hot rectifier?? Or indeed anythign else worth trying??

[Tonto1]

Quickly fired the enginer up, no imediate difference but did seem to rev a bit better (managed to get to 9K), not enough time to play around.

One thing I did notice was my rectifier and associated wiring getting quiet hot, quiet quickly, which as far as I can remember has never been an issue before. Quickly fitted my spare rectifier, but this made no difference to the cars running.

[Tonto1]

Still struggling with this one.

Pretty sure I can completely eliminate the fuel system as being the problem. As have tried with a second set of injectors and also tested the flow of fuel from the pump and through the fuel rail. (Shop manual states that fuel system should deliver a min' of 1.2Litres in 30 seconds, I got just over 1.5L)

Continued checking all the sensors and wiring, and haven't found any thing obvious yet.

One thing I did notice, when checking my Power Commander, was that when the engine wasn't running, but the ingition on, the PC software would accurately read the Throttle Position Sensor, however as soon as the engine was started the software would only read as if the throttle was fully closed, even when it wasn't.

I double checked all the voltages and wiring for the TPS with and without the PC fitted, including reading the TPS output voltages at the ECU plug and these all seemed good - vaying from 1.1 to 4.3 volts depending on throttle position.

Seemed strange why the PC software wouldn't pick up the TPS reading accurately when running. If the ECU was having similar problems and thinking the throttle was closed all the time, even when I actually have it wide open this could potentially explain the apparent lack of fuelling??

Can't think what could cause this to happen or what else to check!!

[busaville]

Disconnect the PC and see how it runs. Maybe your problem.

[Tonto1]

Originally Posted by busaville

Disconnect the PC and see how it runs. Maybe your problem.

Tried that one dude, didn't make any difference.