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busa cold idle issue
GreigM - 5/4/13 at 09:56 PM

So one of my final issues with the megabusa is a cold idle problem. It starts ok, but runs really rough if cold, and under light throttle will misfire until about 4000rpm when it seems to "clear its throat" and run fine. Once warm in any way it will start no problem, and generally for the rest of that day and even into the next day.

I've changed out: plugs, coils, injectors, ECU and some of the ropey-looking vacuum hoses and nothing seems to make a difference.

It doesn't seem to be a single cylinder which is affected as while running rough I can disconnect each of the coils in turn and hear the distinctive noise change.

So any ideas what to try next? I'm kind of assuming its a fuelling issue while cold, but I don't think there's a cold start sensor on the hayabusa (2000 engine) so not sure what controls the cold-start.

On a slightly related issue I have a power commander 3 USB but can't get it to run - even with a "zero" map if the PC3 is plugged in the engine will immediately stall - same behaviour with two separate PC3s - wonder if its all related.

dave_424 - 5/4/13 at 10:11 PM

Cold start should be from the temperature your ECU sees from your coolant temp sensor.

You said 'some' of the vacuum hoses, how many do you have that are in use? can you simplify them to 100% determine that they are not the issue?

Are you trying to plug in a power commander to an engine that is running?

GreigM - 6/4/13 at 07:20 AM

quote:
Originally posted by dave_424
Cold start should be from the temperature your ECU sees from your coolant temp sensor.

You said 'some' of the vacuum hoses, how many do you have that are in use? can you simplify them to 100% determine that they are not the issue?

Are you trying to plug in a power commander to an engine that is running?


I'm not sure how the coolant temp sensor would be wired - is the sensor built into the engine? I have 2 coolant temp sensors that I know of - one which goes to my dash gauge (standard westfield issued VDO gauge) and one which feeds the electric water pump controller, is there a hidden other one for the standard bike/ECU setup.

The vacuum hoses - I have one from the fuel pressure regulator, one from the original bike sensor and they both T into a single hose which runs to another T which collects up the 4 small hoses from the throttle bodies. I've replaced all but the ones directly connected to the throttle bodies (which seem a bit welded on so was reluctant to change) - and I've done the "carb cleaner trick" to see if I can find a leak but no joy.

With the Power Commanders - no installing them properly when engine is off. I can basically start with no PC3, and the engine will idle without assistance. If I then switch off the engine, install the PC3 and start up again the engine will splutter and die pretty much immediately.

dave_424 - 6/4/13 at 09:17 AM

Looks like you may have found your problem, that your ECU isn't getting an engine coolant signal, unless it is tied into one of the sensors you have but you are unaware of it.

In the wiring diagram below for a 2000 hayabusa, the coolant temp sensor is marked as ECTS and is on the back cylinders below the throttle bodies, this would be the sensor that the ECU know's the certain resistance values for it's range of temperatures.

Looks to be a B/BL wire which

GreigM - 6/4/13 at 10:00 AM

that would explain a lot (and possibly even the PC3 issue) - will check the wiring later today (I just checked and its a 1999 engine but believe its the same colour wires).......great stuff, thanks dave.....will report back on success (or not!)

SJL - 7/4/13 at 10:50 AM

Greig , the air temperature sensor has the same connector as the coolant sensor I think they are even the same colour plug from memeory. You wouldn't be the first to get them mixed up

GreigM - 7/4/13 at 05:13 PM

Fortunately I have previously marked the airbox connector, so sure they aren't mixed up (and the plug for the coolant sensor has the B/BL wire and the airbox the Green so I'm sure they aren't mixed up).

So went out today and the car struggled to start and was really rough - let it warm for a few minutes and cleared. I then plugged in the bike clocks and got a temp reading on the clocks, so starting to think the coolant sensor and wiring is fine, as I understand the clocks are fed by the ECU and if it wasn't gettting a reading either would the bike clocks.....will try firing it up from cold again tomorrow with the clocks attached, but think I'm looking for another solution.

Could it be an imbalance in the carbs/TBs? Or low compression? - would these only affect it when idling cold?

GreigM - 8/4/13 at 12:49 PM

..in fact, forget that - it IS the coolant temp sensor at fault.

I just went out and tried it from stone cold with the bike clocks attached - even before I had turned the starter the gauge was showing nearly over-temp, then once I do start the car and let it idle up to temperature it all of a sudden picks up the correct temperature and the gauge returns to where it should be - so a new sensor is on order...

dave_424 - 8/4/13 at 01:50 PM

Do you have a multimeter? might be worth checking the resistance values of the temperature sender to see if that's what is at fault.

If it is returning the right value after it is started then it is working, might be something wrong in the clocks or wiring that is giving it an incorrect reading when the engine is not started.

Just a thought before you buy a new temp sensor.

GreigM - 8/4/13 at 01:57 PM

I'm sure the wiring is ok as I can see the needle jump to the default 80C value if I disconnect the sensor plug (and also get a C15 code). Have ordered the new sensor now, wasn't very expensive as its a common part used on many cars and was under £10 (even though some places will try to charge £60+ for it!)

HPDxxx - 12/7/13 at 02:46 PM

hello,
with new water temp sensor have you solve the problem of cold idle?
thanks

GreigM - 12/7/13 at 02:57 PM

Yes, completely. It also solved my powercommander problem where the engine would stall when cold and the powercommander connected.

HPDxxx - 12/7/13 at 03:13 PM

quote:
Originally posted by GreigM
Yes, completely. It also solved my powercommander problem where the engine would stall when cold and the powercommander connected.

very good! thanks for your input. have you bouught original suzuky sensor or generic?
with new sensor have you notice better fuel economy?
thanks
Davide

noc231073 - 12/7/13 at 06:50 PM

What about hot idle.
My busa cuts out on idle when hot.??