750 SRAD Wont Rev - HELP! - Suzuki GSX-R Motorcycle Forums Gixxer.com
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post #1 of 31 (permalink) Old 11-28-2016, 05:26 AM Thread Starter
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Unhappy 750 SRAD Wont Rev - HELP!

Hi guys,

Not long picked up my first bike, 1999 SRAD 750.

Cannot wait to pass my MOD2 and get on the road, but i have encountered some issues with the bike and was wondering if you can help me

Bike starts and idles ok, but when you try and rev it... cold or warm it seems to stuggle though the rev range from around 4k rpm, if i keep going past this it will get to around 9k rpm but then will start backfiring and popping.

Best way to show you is for you to watch the video i uploaded on youtube.

So far i have cleaned fuel tank (inc pump filter), cleaned injectors, new fuel, new air filter.

Any ideas will be greatly appreciated.

Thanks

Andy
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post #2 of 31 (permalink) Old 11-28-2016, 05:27 AM Thread Starter
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Re: 750 SRAD Wont Rev - HELP!

- See video
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post #3 of 31 (permalink) Old 11-28-2016, 07:37 AM
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Re: 750 SRAD Wont Rev - HELP!

Hmm, I'd start with the easy things:

Change the plugs.
Check the fuel pressure.
Is it throwing any FI codes?

Probably a silly question: there's no chance it's been restricted at any point, is there?
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post #4 of 31 (permalink) Old 11-28-2016, 08:28 AM Thread Starter
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Re: 750 SRAD Wont Rev - HELP!

I have changed the plugs, the originals were black,

I put it into "dealer mode" - no fault codes,

How would i go about checking the pressure?, im assuming you mean blockages in the fuel system?

Andy
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post #5 of 31 (permalink) Old 11-28-2016, 12:23 PM
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Re: 750 SRAD Wont Rev - HELP!

Have you checked the down pipes to see if it running on all 4 cylinders ?
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post #6 of 31 (permalink) Old 11-28-2016, 02:48 PM
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Re: 750 SRAD Wont Rev - HELP!

Engine idle should NOT be that high after letting go of throttle. were all the plugs black?
I think u may have a potential air leak between throttle body (TB) and intake. possible vacuum line/s removed or leaking going to TBs.
With no codes being indicated the ECM assumes all input components are functioning and you should as well.
It also sounds like a rev limit may be being imposed WAY TOO EARLY.
check electrical connections for corrosion. Continuity is one thing, while the ability to 'flow' current and voltage is another.
'Black' plugs indicate a rich condition which can be the result of;1) too much fuel, or 2) restricted air flow, or 3) combination of both.
There are several sensors that aid in compensating the fuel injection time. A service manual will tell u what each one does to either enrich or lean the mixture.
As always, the battery condition must be good and strong. Low voltage signals from battery will cause ECM to increase fuel injection time which will cause a rich condition.
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post #7 of 31 (permalink) Old 11-29-2016, 09:00 AM
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Re: 750 SRAD Wont Rev - HELP!

Quote:
Originally Posted by Andrew Moule View Post
How would i go about checking the pressure?, im assuming you mean blockages in the fuel system?
There's a little meter you can buy which you place inline between the fuel pump and the throttle bodies while you run the bike. It's essentially checking the fuel pump operation by checking the fuel pressure it puts out.

Also, as someone else mentioned, are you sure you're running on four cylinders? Just check that all four of the exhaust downpipes are hot.

Might be worth checking all the hoses and clamps in and around the airbox & TBs too. If you've black plugs your mixture isn't right.
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post #8 of 31 (permalink) Old 11-30-2016, 01:40 PM Thread Starter
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Re: 750 SRAD Wont Rev - HELP!

I have checked and bike runs on all 4 cylinders,

I hooked up a make shift pressure gauge and got around 3 bar of fuel pressure. Is this normal?

Ran the bike with no air box and had same issue,

Adjusted the throttle position sensor and it seemed to idle a lot better but still have the issue.

Found that even with the throttle pinned open it wouldn't go past 9k RPM and still has the juddery revs..

Still stuck where to go :/
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post #9 of 31 (permalink) Old 11-30-2016, 01:49 PM Thread Starter
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Re: 750 SRAD Wont Rev - HELP!

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post #10 of 31 (permalink) Old 12-01-2016, 06:45 AM
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Re: 750 SRAD Wont Rev - HELP!

Pressure seems to be about right (although check the manual to be sure). Have you measured flow?
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post #11 of 31 (permalink) Old 12-02-2016, 03:56 PM Thread Starter
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Re: 750 SRAD Wont Rev - HELP!

Update:

I have tested all sensors with multimeter and found resistance on the orange wire to the cam sensor..

Once running I unplugged the cam sensor and bike runs like a dream.

to eliminate the cable I bypassed the original wiring and ran another cable from sensor to ECU with the same issue..

I'm thinking ECU is knackered?

Anyone got any thoughts?
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post #12 of 31 (permalink) Old 12-02-2016, 05:48 PM
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Re: 750 SRAD Wont Rev - HELP!

I would try a known good cam position sensor. (ebay maybe)
It seems like the ECU is compensating for the info it receives from CMP. You may also want to check the pin on the intake cam that triggers the CMP.
If the gap has increased then the CMP wont return the correct signal to ECU.
with CMP unplugged u should have noticed a fault code and the ECU would just run the best map it could with a faulty CMP sensor.
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post #13 of 31 (permalink) Old 12-02-2016, 09:02 PM
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Re: 750 SRAD Wont Rev - HELP!

aren't they restricted over there?
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post #14 of 31 (permalink) Old 12-03-2016, 05:44 AM
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Re: 750 SRAD Wont Rev - HELP!

Quote:
Originally Posted by Andrew Moule View Post
I have tested all sensors with multimeter and found resistance on the orange wire to the cam sensor..

Once running I unplugged the cam sensor and bike runs like a dream.

to eliminate the cable I bypassed the original wiring and ran another cable from sensor to ECU with the same issue..

I'm thinking ECU is knackered?
As motomedic implies, have you made sure that the increased resistance is not in the sensor itself? How exactly did you measure the resistance "on the orange wire to the cam sensor"? Have you measured the sensor's resistance itself, as described in pages 11-4-35 of the service manual?
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post #15 of 31 (permalink) Old 12-14-2016, 02:56 AM Thread Starter
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Re: 750 SRAD Wont Rev - HELP!

Update:

I have brought a new ECU - No difference,

New cam sensor - No difference,

Unplugging the cam sensor gives the C11 (Cam sensor fault) code but bike runs ok,

I'm still stumped as to why I don't get any error codes with it plugged in and the bike not revving correctly,

Cleaned the Crank sensor (as it was covered in crap) - no joy,

Cam pin (one that gives signal to cam sensor) appears to be ok (visually),

Only thing left I can think is the timing?

Any more ideas?
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post #16 of 31 (permalink) Old 12-14-2016, 06:47 AM
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Re: 750 SRAD Wont Rev - HELP!

Quote:
Originally Posted by Andrew Moule View Post
Any more ideas?
wiring problem between the cam sensor and the ECU and improper cam sensor mounting or other source of misalignment between cam sensor and cam come to mind.
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post #17 of 31 (permalink) Old 12-15-2016, 02:27 AM Thread Starter
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Re: 750 SRAD Wont Rev - HELP!

Quote:
Originally Posted by dpapavas View Post
wiring problem between the cam sensor and the ECU and improper cam sensor mounting or other source of misalignment between cam sensor and cam come to mind.
How would I go about checking the alignment? or the correct fitment? I just thought it bolted in and that's it ha!
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post #18 of 31 (permalink) Old 12-15-2016, 05:54 AM
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Re: 750 SRAD Wont Rev - HELP!

Quote:
Originally Posted by Andrew Moule View Post
How would I go about checking the alignment? or the correct fitment? I just thought it bolted in and that's it ha!
I'm not familiar with that part of your bike. Check the manual to see if it mentions any special instructions. You might also check if it's clean, but I'd start with checking the wiring resistance, since you've found that to be off. It's both easier to check and more likely to be a source of problem.
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post #19 of 31 (permalink) Old 12-21-2016, 09:37 AM
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Re: 750 SRAD Wont Rev - HELP!

I would check the TPS it looks like the best place to check first. The throttle position sensor is on the side of the injector rack.
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post #20 of 31 (permalink) Old 12-24-2016, 11:34 PM
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Re: 750 SRAD Wont Rev - HELP!

Cam pin may be in too far, on the Busa it is supposed to be aprox .315 of an inch high. Can look at an SRAD cam at shop this week. Have had one of my 750's act similar--as well as a couple of Busas on the dyno' seemed to run into limiter at about 9000 rpm, bypassed cam sensor and it went to 13500 as it should. Put in a switch to be able to run bike at Bonneville where it acted up.Cannot remember if I had to reset pin but did replace sensor-- been several years. Have seen several bikes since with similar problems including a Kawasaki.
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