Low rpm miss
How did this start ? After modification - in that case may be just too lean or too rich ... in that case I would just check the AFR with a WBO and start from there. With a fast computer based AFR meter like LM1 any high or low peaks can also be detected. With an IR temp gauge you may be even able to isolate this to a single cylinder in which case the below applies. Do you have access to fast and accurate AFR ? (Narrow band is not really suitable for the purpose).
If not AFR Low RPM miss could be anything from faulty coil, injector, plug etc... down to need for standar service like throttle body synchronization or TPS settings. Also could be various sensors.
Standard service procedure to start for this could be:
1) Disconnect PC or any extras you have.
2) Check TPS settings
3) Synchronize throttle bodies
4) disconnect each coil if one cylinder drops more than others, that may be faulty
5) disconnect each injector if one cylinder drops more than others, that may be faulty
6) if 4) or 5) indicates higher drop from one cylinder, cross check coils (and possibly injectors) by moving coils and injector to other cylinder. This helps to isolate the problem to either to an injector or a coil.
7) acquire a piece of tube (or a stethoscope) and listen for potential vacuum leaks
... etc ...
Prior to start, of course check -C00.
If not AFR Low RPM miss could be anything from faulty coil, injector, plug etc... down to need for standar service like throttle body synchronization or TPS settings. Also could be various sensors.
Standard service procedure to start for this could be:
1) Disconnect PC or any extras you have.
2) Check TPS settings
3) Synchronize throttle bodies
4) disconnect each coil if one cylinder drops more than others, that may be faulty
5) disconnect each injector if one cylinder drops more than others, that may be faulty
6) if 4) or 5) indicates higher drop from one cylinder, cross check coils (and possibly injectors) by moving coils and injector to other cylinder. This helps to isolate the problem to either to an injector or a coil.
7) acquire a piece of tube (or a stethoscope) and listen for potential vacuum leaks
... etc ...
Prior to start, of course check -C00.
Thanks for the answer and tips,yes it started after the mods,but it was a little before. Disconnect PC or any extras you have...........done
2) Check TPS settings,.........done
3) Synchronize throttle bodies,........done
4) disconnect each coil if one cylinder drops more than others, that may be faulty,.....not done
5) disconnect each injector if one cylinder drops more than others, that may be faulty,..........not done
7) acquire a piece of tube (or a stethoscope) and listen for potential vacuum leaks,.......... done
... etc ...
Prior to start, of course check -C00......... done MC express have try to adjust the fuel more and lean but no difference
Edited By lightwave on 1160658638
2) Check TPS settings,.........done
3) Synchronize throttle bodies,........done
4) disconnect each coil if one cylinder drops more than others, that may be faulty,.....not done
5) disconnect each injector if one cylinder drops more than others, that may be faulty,..........not done
7) acquire a piece of tube (or a stethoscope) and listen for potential vacuum leaks,.......... done
... etc ...
Prior to start, of course check -C00......... done MC express have try to adjust the fuel more and lean but no difference
Edited By lightwave on 1160658638
but wery nice 'avatar' You have lightwave....nice
Consistently hesitating below 2500 or just around 2500 ?
I had a problem of not smoothly running engine aroud 2500rpm few months back. Turned out to be;
1) Quite badly synchronized throttle bodies, those need to be very very precisely set for at least in my K5 engine to run smooth
2) Too lean between 2-3k was also an issue. Spent some time with a WBO and Yoshbox to correct this.
3) Engine voltage was fluctiating, fixed with some additional wiring from coils to the key/swithc.
With WBO that point 2) is reall easy to check. With that low throttle position you should be able to even to measure from the pipe tail without a need to carve a hole for O2 sensor. If you dont have a WBO then just use yoshbox to add fuel to that low rpm.
Edited By PetriK on 1160715008
I had a problem of not smoothly running engine aroud 2500rpm few months back. Turned out to be;
1) Quite badly synchronized throttle bodies, those need to be very very precisely set for at least in my K5 engine to run smooth
2) Too lean between 2-3k was also an issue. Spent some time with a WBO and Yoshbox to correct this.
3) Engine voltage was fluctiating, fixed with some additional wiring from coils to the key/swithc.
With WBO that point 2) is reall easy to check. With that low throttle position you should be able to even to measure from the pipe tail without a need to carve a hole for O2 sensor. If you dont have a WBO then just use yoshbox to add fuel to that low rpm.
Edited By PetriK on 1160715008
Just check the throttle body synch after cleaning with carb cleaner and it may deliver an easy solution... besides that in most engines any mods to open up the intake and exhaust is likely to reduce the low end velocity flow (= speed of which air / exhaust gas travels)
I.e. when you introduce a bigger diameter tube on exhaust side, simulateneously you lower the velocity of flow (gas flows slower on the surface of the pipe due to the increased surface area / diameter ). The same reduction of flow applies to the intake side when its opened up. This is most likely one of the reasons why Suzuki desinged an air box with a flap that opens up from 2000rpm onwards.
Additionally when velocity is lower (even though overall performance gains will be achieved) the timing of intake pulses as well as exhoust pulses may not anymore support complete filling of the cylinder at lower rpm. This reduction of VE (volymetric efficiency) is natural consequency due to reduced pulse effect. Hence particulary with bikes that do not have a lambda the autosetting of low end AFR does not happen and the amount of fuel needs to be adjusted for condition.
This may lead into two low rpm problems;
1) The partial filling of cylinder applies, changing the contents of the air/fuel mixture and particularly burning temperature bringing the cylinder temperatures lower. (More already burned gas stays in the cylinder as its not getting completely pumped out due to reduced low RPM VE).
2) The fuel does not get evenly distributed into the air/fuel mixture filling the cylinder. This leads into partial burning or even sometimes no burning at all.
Because of the above you would need higher burning temperatures but simultaneously you would most likely need increased AFR ratio. Saying that we must appreciate that by introducing PAIR Suzuki enabled engines to run richer as the fuel gets burned in the pipe and catalyzator. I.e. systems with PAIR can by nature run richer at low RPM and still meet the federal and EU emission/pollution limits. So it may as well be a case with later bikes that they run richer, but with 1999 from my opinion its likely to be too lean.
Increasing AFR tends to lower the temperature and hence a correct AFR for low rpm / low velocity situation is very difficult to determine with anything else than with a 3 gas analyzator. AFR can give some indication, but its really the amount of unburned fuel that counts. The injectors may deliver correct amount for the amount of air, but the fuel just may not be evenly enough spread amongst the air for ignition to occur.
The above may or may not apply to your situation, but looking at the AFR or even better with a 3 gas analyzator would most likely give a good hint if the above applies or not.
In theory and out of the head the corrective measures could include the following;
1) change AFR to find a better burning combination
2) change longer (sometimes also shorter) velocity stacks to increase the pulse effect on intake side
3) change cam timing to improve low end VE (but usually with cost of high end VE being reduced and hence less high end power)
4) change diameter of headers or collector place on the exhaust side
5) Change to hotter spark plugs
6) Change to have more ignition advance
7) Increase cam lift (to increase low rpm VE)
Anyway as said these may or may not apply 100% to your condition... but with complex problems its good to understand the background.
EDIT: If it is a fuel spread, i.e. vaporization issue - sometimes increasing the cylinder head temperature helps. More warm cylinder head helps in vaporizing the fuel molecules more evenly with air. Once again this is why most engines have different fuel injector sequency with low rpm and with cold engine - even busas have this if I remember corretly. When you inject the fuel on top of the hot injector valves it atomizes and gets more evenly spread. This reminded me about a key question to pipoint this issue:
Is this happening both with cold and/or warm engine ? If its mainly a warm engine issue, then its quite likely related to AFR and/or vaporization... cold engines tend to be programmed to run richer and with a different injector sequency.
Edited By PetriK on 1160745714
I.e. when you introduce a bigger diameter tube on exhaust side, simulateneously you lower the velocity of flow (gas flows slower on the surface of the pipe due to the increased surface area / diameter ). The same reduction of flow applies to the intake side when its opened up. This is most likely one of the reasons why Suzuki desinged an air box with a flap that opens up from 2000rpm onwards.
Additionally when velocity is lower (even though overall performance gains will be achieved) the timing of intake pulses as well as exhoust pulses may not anymore support complete filling of the cylinder at lower rpm. This reduction of VE (volymetric efficiency) is natural consequency due to reduced pulse effect. Hence particulary with bikes that do not have a lambda the autosetting of low end AFR does not happen and the amount of fuel needs to be adjusted for condition.
This may lead into two low rpm problems;
1) The partial filling of cylinder applies, changing the contents of the air/fuel mixture and particularly burning temperature bringing the cylinder temperatures lower. (More already burned gas stays in the cylinder as its not getting completely pumped out due to reduced low RPM VE).
2) The fuel does not get evenly distributed into the air/fuel mixture filling the cylinder. This leads into partial burning or even sometimes no burning at all.
Because of the above you would need higher burning temperatures but simultaneously you would most likely need increased AFR ratio. Saying that we must appreciate that by introducing PAIR Suzuki enabled engines to run richer as the fuel gets burned in the pipe and catalyzator. I.e. systems with PAIR can by nature run richer at low RPM and still meet the federal and EU emission/pollution limits. So it may as well be a case with later bikes that they run richer, but with 1999 from my opinion its likely to be too lean.
Increasing AFR tends to lower the temperature and hence a correct AFR for low rpm / low velocity situation is very difficult to determine with anything else than with a 3 gas analyzator. AFR can give some indication, but its really the amount of unburned fuel that counts. The injectors may deliver correct amount for the amount of air, but the fuel just may not be evenly enough spread amongst the air for ignition to occur.
The above may or may not apply to your situation, but looking at the AFR or even better with a 3 gas analyzator would most likely give a good hint if the above applies or not.
In theory and out of the head the corrective measures could include the following;
1) change AFR to find a better burning combination
2) change longer (sometimes also shorter) velocity stacks to increase the pulse effect on intake side
3) change cam timing to improve low end VE (but usually with cost of high end VE being reduced and hence less high end power)
4) change diameter of headers or collector place on the exhaust side
5) Change to hotter spark plugs
6) Change to have more ignition advance
7) Increase cam lift (to increase low rpm VE)
Anyway as said these may or may not apply 100% to your condition... but with complex problems its good to understand the background.
EDIT: If it is a fuel spread, i.e. vaporization issue - sometimes increasing the cylinder head temperature helps. More warm cylinder head helps in vaporizing the fuel molecules more evenly with air. Once again this is why most engines have different fuel injector sequency with low rpm and with cold engine - even busas have this if I remember corretly. When you inject the fuel on top of the hot injector valves it atomizes and gets more evenly spread. This reminded me about a key question to pipoint this issue:
Is this happening both with cold and/or warm engine ? If its mainly a warm engine issue, then its quite likely related to AFR and/or vaporization... cold engines tend to be programmed to run richer and with a different injector sequency.
Edited By PetriK on 1160745714