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centaurus
15th October 2011, 22:52
Hi guys,

I have a very strange problem with my '99 Gsxr750. The bike starts fine and runs smoothly, but once it gets over 80 degrees, the engine "sputters" and cuts off. If riding, it feels like when you've just ran out of fuel. If I try to restart it, it turns over as fast as when cold, but nothing happens. I even tried to crash-start it downhill and all I got was rubber marks on the road when I dropped the clutch. It's worth mentioning I still have lights and everything electrical when this happens.

If I let the engine cool down below 60 degrees, it starts fine.

This bike is new to me so I don't know if this problems has been before (the previous owner says - no). However, I have just cleaned and gapped the spark plugs, adjusted valve clearances, replaced the cam chain tensioner (it was getting a bit slack) and replaced the oil.

Does anybody know what can be the cause?

DEATH_INC.
16th October 2011, 07:28
I'd be wildly guessing, but I'd start with the engine temp sensor, make sure it's not still trying to run on the cold mixtures from the ecu. (tho the fact the gauge comes up may eliminate this....)
Next time it cuts out check whether or not it still has spark (you may need to pull 'er to bits first and run it 'till it cuts out) when it's hot (electrics can die with heat) and do a quick fuel pressure check (pull the fuel hose and see if it still pumps heaps), be carful, hot stuff and fuel isn't a great combo 248612
Also, ask here http://www.gixxer.com/forums/forumdisplay.php?f=17

actungbaby
16th October 2011, 15:33
Hi also check your coolent system rad etc thinking water pump maybe


Hi guys,

I have a very strange problem with my '99 Gsxr750. The bike starts fine and runs smoothly, but once it gets over 80 degrees, the engine "sputters" and cuts off. If riding, it feels like when you've just ran out of fuel. If I try to restart it, it turns over as fast as when cold, but nothing happens. I even tried to crash-start it downhill and all I got was rubber marks on the road when I dropped the clutch. It's worth mentioning I still have lights and everything electrical when this happens.

If I let the engine cool down below 60 degrees, it starts fine.

This bike is new to me so I don't know if this problems has been before (the previous owner says - no). However, I have just cleaned and gapped the spark plugs, adjusted valve clearances, replaced the cam chain tensioner (it was getting a bit slack) and replaced the oil.

Does anybody know what can be the cause?

centaurus
16th October 2011, 18:22
Thanks for the suggestions, DEATH_INC. I tried as you said and I can still see fuel flowing from the tank, however there was no spark - not at all. After allowing it to cool down, I checked again and there it was - a nice healthy looking and strong spark.

I also discovered it is not a certain temperature. With the tank up, there was more fresh air flowing inside the bike and the engine died just after 100 degrees.

Given that this bike is electronic injection (and the ECU is under the seat - far away from heat), it must be wires, right? What else could it be that would kill the spark when hot.


I'd be wildly guessing, but I'd start with the engine temp sensor, make sure it's not still trying to run on the cold mixtures from the ecu. (tho the fact the gauge comes up may eliminate this....)
Next time it cuts out check whether or not it still has spark (you may need to pull 'er to bits first and run it 'till it cuts out) when it's hot (electrics can die with heat) and do a quick fuel pressure check (pull the fuel hose and see if it still pumps heaps), be carful, hot stuff and fuel isn't a great combo

NinjaNanna
17th October 2011, 20:53
It IS temp related, the general area doesn't get as hot with the tank up of off. That equates to a hotter engine temp to get the ambient temp hot enough to cause the failure.

imdying
18th October 2011, 13:55
Jump the test connector and see if it's throwing a code.

centaurus
18th October 2011, 14:09
Jump the test connector and see if it's throwing a code.

???

I suddenly feel inadequate - have no ideea what you've just said :)

Can you please repeat in simple English so people like me can understand too?

imdying
18th October 2011, 15:35
Typically an EFI Suzuki has a service port (which is a plug on the loom that goes nowhere) which you can jump the pins on with a paper clip). That makes the EFI light flash (on some models you get a code replacing the temperature gauge) in a preset sequence.

The workshop manual will provide a breakdown on what each sequence of flashes means, and detail how to jump the connector. I've never worked on anything that early, so YMMV.

Somebody on gixxer.com et all will be able to provide a link to download a workshop manual.

It may be that a sensor has failed and the code will tell you which one. Maybe not, but as it is free to try it's worth a look.

MSTRS
18th October 2011, 17:09
Under the pillion seat is a little white block with 2 wires going into it (mine is on the left side). It has a black rubber cap covering the other side. Remove the cap and push the ends of a paper clip into the appropriate holes (the ones the wires go into the other side of). You may need to file down the paper clip to allow it to fit.
What will happen now, when you turn on the ignition is the digital readout for the temp on the tacho will have 3 or 4 dashes only. Run the engine until your problem shows up. The digital readout will probably now read 'C.... (the dots will be a number). Look up google for Suzuki fault codes to see what the number refers to.
That is what your computer is reacting to, but the problem is probably only a faulty sensor.

GXSR.com has this to say on the entire process (http://www.gsxr.com/showthread.php?t=1234)

centaurus
18th October 2011, 20:45
I found the test connector, jumped it and ran the bike until it died. It showed C00 all the way (even after the engine died). I'm assuming this would mean the ECU and all the sensors are ok?

What is strange is that when the engine dies, it doesn't stumble, fluctuate on revs, bog down or miss a beat. It runs perfectly and stops suddenly, just like i have hit the kill switch, and even though the spark dies, no other electric component seems affected (dashboard, lights, signals, horn, etc...)

MSTRS
19th October 2011, 06:51
No fault code suggests it is not a system monitored by the ECU that is breaking down.
Sign up to GXSR.com and ask on there. Someone will have had the problem and sorted it...

imdying
19th October 2011, 08:27
The tip over switch is mounted correctly? Not half hanging off its mount?

centaurus
20th October 2011, 21:35
The tip over switch is mounted correctly? Not half hanging off its mount?

Checked it and it it mounted correctly. I even opened it up to make sure the internals are good and I have the right way up.

onearmedbandit
20th October 2011, 23:32
Question. How long did you have it before it started playing up? Only just got it that afternoon? Or you'd had it for a few days? Weeks?

centaurus
21st October 2011, 07:13
Question. How long did you have it before it started playing up? Only just got it that afternoon? Or you'd had it for a few days? Weeks?

I've had it for a few months now but I bought it crashed so until the other day it hasn't been ridden - just started it briefly when brought it home to confirm it was running. Since then I did all the normal maintenance jobs (replace all fluids, adjust valve clearance, clean spark plugs, air filter, etc...)

imdying
21st October 2011, 08:11
Any chance you've overtightened a valve?

centaurus
21st October 2011, 08:42
Any chance you've overtightened a valve?

It's not impossible, but then it would not die instantly (it would run unevenly or at least complain before dying) and it wouldn't be a spark problem, would it?

Plus, when starting, it starts incredibly fast, which means the compression is there and is good. With an overtighten valve, I would have compression leak and it would either idle rough or take its time to start. Correct?

SS90
21st October 2011, 08:50
I am surprised thatvno one has mentioned this, but I from the symptoms you described, I would suspect that your ignition pick up (reluctor) is the culprit.

It is a small pickup, located on the end of the crankshaft.

If memory serves me correct, it is under the right hand side front engine cover on a 99 GSXR, behind the starter gear.

This little pick up is responsible for signaling the ECU when each cylinder is due to spark, in relation to crankshaft position.

Over the years, most every manufacturer has had trouble with these wee sensors, and the common faults seem to manafest when the engines are hot.

Normally, the windings in the magnetic coil, responsible for the signal develop an internal short when they get hot, making the signal essentially "out of range" for the system, basically having the same effect as if it was not even there.

I seem to remember that the GSXR's (what is the collective term for GSXR's by the way) have a single wire pick up, meaning that measuring the resistance can't easily be achieved.o

With a two wire system you can measure this when the engine is cold (sparking), and Hot (not sparking)

manufactures specify an Ohme range.

For the single wire systems, some times the process is a little different.

There are several manufactures BMW, Piaggio, and so on, that have a plug in ignition pick up sensor testing box, basically you plug the sensor lead into the box with the unit on the bike, and crank it over, if the LED on the box lights up, the sensor is working..... These test boxes are not manufacturer specific generally speaking, and you only need to connect the wire, and turn it over to test.

You may need to take the bike to a workshop, if money is an issue (NZ bike shops do have a high labour rate these days), you can save a few bucks by removing all the bodywork.

My gut feeling is that the pick up is the culprit.

MSTRS
21st October 2011, 08:51
It's not impossible, but then it would not die instantly (it would run unevenly or at least complain before dying) and it wouldn't be a spark problem, would it?

Plus, when starting, it starts incredibly fast, which means the compression is there and is good. With an overtighten valve, I would have compression leak and it would either idle rough or take its time to start. Correct?


Nope. Would only show up (unless valve stem is under pressure to start with) when temperature causes metals to expand.
And you are right about not being an effect on the spark.

MSTRS
21st October 2011, 08:55
SS90 - you mean the Crank Angle Sensor? Wouldn't this be monitored by the ECU and show as a fault?

SS90
21st October 2011, 09:10
SS90 - you mean the Crank Angle Sensor? Wouldn't this be monitored by the ECU and show as a fault?

In some circles, yes,it is reffered to a Crank angle sensor (one of those parts that known by many names)

I too would have thought that it would be monitored by the ECU, but I have seen more than one self diognosis feature not register faults such as these.

Many modern mechanics have come to rely on fault codes and such like, and some of the old fault finding skills have long been forgotten.

For me, the clue is in the not sparking.

With a fuel injected bike, you generally need a crank angle sensor, as well as a camshaft position sensor, quite often the camshaft position sensor is only needed to start the bike (after the ECU has established the camshaft position in relation to the crankshaft, it becomes redundant), so in this scenario, I would not suspect the camshaft position sensor as faulty (if it where, it would only create a fault after shutting down, not cause a fault where by the bike actually shuts down, as the crankshaft sensor would)

The fact that the fault is 100% repeatable, and, totally dependent on temperature, as well as manifests itself by causing the coils not to fire eliminates things like fuel pump, injectors an so on.

The fault is something related to signalling the coils to fire, the ECU is unlikely to be at fault...... The symptom is too dependent on mechanical temperature, I suggest that something physically bolted to the engine, that is assosiated to the ignition system is at fault.

MSTRS
21st October 2011, 09:10
Something to be aware of...
Often it is the simplest things that are overlooked.
A while back, I was having a problem too. Not one that stopped the engine, but had no other symptom apart from triggering the F1 light. At least until the speedo/tacho needles would drop to zero, and then the F1 light would come on. Fault code/s showed the problem to be 'loss of power to the injectors'. All four of them. Yet the engine never missed a beat. Hmmmm...
Remembering an intermittent problem I had with my Commodore, I cleaned the battery terminals on the GSXR. Problem fixed.
ECUs are very sensitive to changes in voltage, and heat increases resistance in wiring, right?

MSTRS
21st October 2011, 09:15
The fact that the fault is 100% repeatable, and, totally dependent on temperature, as well as manifests itself by causing the coils not to fire eliminates things like fuel pump, injectors an so on.

The fault is something related to signalling the coils to fire, the ECU is unlikely to be at fault...... The symptom is too dependent on mechanical temperature, I suggest that something physically bolted to the engine, that is assosiated to the ignition system is at fault.

You could be onto something here.
Or one of us is...

centaurus
25th October 2011, 08:35
In the end I have acknoledged my limits and taken it to the shop. Now I'm waiting to see what they find.

centaurus
7th November 2011, 18:12
I took it to the shop and it turned out to be the camshaft position sensor. After they replaced that it worked fine...

So I took it for a test ride on the south island this weekend. It ran ok for close to a thousand k's then it decided it can't calculate properly how much fuel it needs anymore so it will use twice the amount it needs. I barely made it back from chc.

First I thought it was running on only 3 cylinders but a spark plug inspection showed all four were sparking but all of them were covered in that dry black dust/powder that indicates an overly rich mixture. Plus, the smell of unburnt fuel that I left behind me all Sunday was speaking for itself

I suspect this last issue is not related to the initial one but rather a failure in one of the sensors that dictate the fuel mix (oxygen sensor or vacuum sensors). So the bike it back in the garage and I'll have to check all wires and vacuum hoses before I make any decision as to what needs to be done and whether I need to take it to the shop and fork out big bucks again :(

Thanks guys for your suggestions. Looks like some of you were quite on the money, and the ones who weren't made very valid and valuable suggestions. It's good to know the art of motorcycle maintenance hasn't died yet in NZ (I posted on some US forums and got no reply at all).