Inconsistent rpm at idle, stalling + jerky acceleration GT250 EFI 2010
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Dear Hyosung riders,
As written in the topic title, the bike struggles to hold consistent RPM and keeps stalling when on idle. Additionally, sometimes accelerating is very jerky and unpleasant although last time I gave it a ride it had no problems with acceleration. Note: that bike was mostly stored outside affected by the weather elements.
<h4>Little history about the bike:</h4>
New Varta battery
New NGK CR8E spark plugs x2
New Fuel line (from pump to fuel line splitter)
That’s for the new parts ^
<h4>Additionally:</h4>
Fuel pump changed 3 years ago
ISC changed 3 years ago (idle speed control sensor)
Fuel filter cleaned
Cleaned gas tank that was covered in rust ( cleaned with vinegar and screws method)
Fuel injectors (cleaned in ultrasonic cleaning machine)
Three phase voltage regulator tested ✅ (with the help of this video)<hr />
Since this model of Hyosung’s idle RPM is regulated with the ISC (idle speed control sensor) correct me if I’m wrong. I think the ISC is the main culprit in my case.
When I changed the ISC with a new one, there is a way to test if it functions properly which I read somewhere but can’t remember where, maybe from the service manual.
When you turn the ignition key to the on position, ISC preforms a self test where the silver colored cone moves to a certain position and then back if I remember correctly.![Genuine Idle Speed Control Sensor [EFI] Hyosung GT250 GT250R GV250](https://i0.wp.com/www.koreanbikeparts.com/media/catalog/product/cache/ae09f82b1adefc120d6a7c6fa60a3b97/p/b/pb214085.gif?resize=225%2C225&ssl=1)
But what happened with mine is it got shot out of place since it has a little spring in the housing and I had to chase the parts on the ground, which makes me think that the ISC is getting wrong values that make it not function properly. Then I got my bike to a local mechanic that has some experience with the Hyosung’s and he told me the only method to make the bike work is by making the ISC mechanical instead of electrical. So he went ahead and drilled the ISC through the middle and created a cone that you can screw in and out to make the RPM adjustments (if done properly it could maybe work?).
Note: my old spare ISC is connected to the bike so it does not show the red FI error on the dashboard.
Bellow you will find the videos, don’t mind the chickens 🐔1. Video with the ISC and the hose to the throttle body connected (https://www.youtube.com/watch?v=wgaLlT5zICo)
When the hoses are connected and if the video was long enough the bike would eventually stall on idle like it did on 0:352. Video with the ISC and the hose to the throttle body disconnected (https://www.youtube.com/watch?v=JTJFEs4OlUw)
When hoses disconnected and the air coming to the cylinders freely the bike is not stalling.Bellow you can find the service manual for Hyosung Aquila 250 FI and the Comet 250 / R FI
GT/Aquila 250 FI Service manualHere are pictures of spark plug caps, they are the same on both cylinders.
Here is a picture of the ECU unit
Picture of voltage regulator which I think is not the factory one, probably one of the past owners changed it. Contacts have some corrosion that will be cleaned.
I am looking forward to get a reply from you and hopefully we can solve this problem together. If you have any additional questions or request please ask!
Thank you!
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Okay,
I have to ask though, how is the engine compression ? Get the bike warmed up hot …. remove both spark plugs , check compression at full throttle and tell us the result.I might have a small suspicion that one of the cylinders may be a little lower than spec but we shall see after your report , because it seems like you changed everything to all new parts?
Also , why not change the fuel pump as new again incase the old one of 3 years is no longer performing well, you said it was okay in the early days but now the bike is misbehaving a little bit, so it could be the pump needs changing again , usually sometimes rough running or rough idle is the pump.
Try that too, and also check the TPS using service manual again to check its in spec, the idle can be affected , then reconnect the ISCV
Though if you said “i removed the pipes from ISCV” and the engine idled normally, = normally on any motorcycle more in the engine to make it idle usually means the air filter is stuffed (intake system chocking) or the ignition parts are producing weaker spark causing a rich condition that includes quickly fouled up plugs
// Meditation doesn't mean you have to sit still....
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Okay, I have to ask though, how is the engine compression ? Get the bike warmed up hot …. remove both spark plugs , check compression at full throttle and tell us the result. I might have a small suspicion that one of the cylinders may be a little lower than spec but we shall see after your report , because it seems like you changed everything to all new parts? Also , why not change the fuel pump as new again incase the old one of 3 years is no longer performing well, you said it was okay in the early days but now the bike is misbehaving a little bit, so it could be the pump needs changing again , usually sometimes rough running or rough idle is the pump. Try that too, and also check the TPS using service manual again to check its in spec, the idle can be affected , then reconnect the ISCV Though if you said “i removed the pipes from ISCV” and the engine idled normally, = normally on any motorcycle more in the engine to make it idle usually means the air filter is stuffed (intake system chocking) or the ignition parts are producing weaker spark causing a rich condition that includes quickly fouled up plugs
Hey Marcel, thanks for the reply!
I will do the compression test on both the cylinders at full throttle, I have never done one of those before but I found some resources online.
I thought the fuel pump was ok? I can change it again but it’s pricey 130 eur.
TPS will be checked and I will report back. As for the airbox I never changed it and don’t have a picture of it but by the looks of it looks like new.
Is there a way to test the Ignition parts? Ignition parts are: Front and back ignition coils as well as the spark plug caps?
What do you think about the mechanical ISCV solution or should I be getting a new one?Thank you!
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Knowing that particular model very well your issues sound electrical to me, there are a sets of connectors under the tank on the left hand side fixed to the frame unplug & clean them they are particularly bad for grime, the idle circuit runs through one of them, also check those plug caps very prone to failure
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Knowing that particular model very well your issues sound electrical to me, there are a sets of connectors under the tank on the left hand side fixed to the frame unplug & clean them they are particularly bad for grime, the idle circuit runs through one of them, also check those plug caps very prone to failure
Hey Simon, thank you very much for the reply!
Have you had an issue with the ISCV as well? I will most definitely check the wiring loom on the frame and find the adequate wiring for the ISCV, and also clean the contacts with contact spray. Is there a way to test the plug caps?Thanks!
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Yes you can check the resistance of the coil & the plug caps with a multimeter, it did think at one time the ics was faulty but it was not the case, also check the pipes from the ics for leaks, can’t remember of the top of my head what the readings of the coils & plug caps should be but Marcel will probably know
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Yes you can check the resistance of the coil & the plug caps with a multimeter, it did think at one time the ics was faulty but it was not the case, also check the pipes from the ics for leaks, can’t remember of the top of my head what the readings of the coils & plug caps should be but Marcel will probably know
Found the reference values for ignition coil resistance in the manual, here is the picture if anyone needs it in the future.
You can find it on the following link. https://ibb.co/QMgXn3W -
Hello everyone!
Just to remind you the bike is still running with the makeshift mechanical ISCV not the original part.
So a few updates, as Marcel requested:1. I have checked the compression on both cylinders and they seem to be even, I don’t know the recommended values so if you can please let me know.
Front Cylinder showed a compression of 175 psi / 12 bar / 12.2366 kg/cm²
Rear Cylinder showed a compression of 175 psi / 12 bar / 12.2366 kg/cm²2. Throttle position sensor (TPS) on my bike is a 1 bolt type and it has been checked, it showed a reading of 1.09V on closed throttle and 4.45V on full throttle I believe that is in spec though I would appreciate if you could confirm this value.
3. The pipes leading from the Idle speed control valve (ISCV) to the throttle bodies have been checked and they don’t have leaks.
Unluckily I haven’t checked the resistance of the ignition coils & the plug caps, so I will do that next time.
Thank you everyone!
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Engine Compression is very good! TPS = It looks OK , the manual says replace it if it causes problems because we can’t manually make adjustments to it.
Glad to hear that the compression is very good 🙂
Next step will be to order a new ISCV, and before attaching it check all of the wiring from the ISCV to ECU I guess.
I will keep you updated. Thank you! -
Hey Everyone, Happy New year and holidays!
I just wanted to update you on the issue. The new ISCV valve has finally arrived and the thing I was afraid will happen, happened again.
Upon swapping the ISCV with the new part and turning the ignition key to the on position valve again please check the video bellow.https://www.youtube.com/watch?v=Ish1Kvtzwsg
Notice how after the fuel pump noise I switched the key to the ON position and the valve springed out off place.
I would appreciate if someone could measure the values on their ISCV using the multimiter when the ignition is switched to the off and on position, without the engine running so I can compare it to mine. I am afraid there is something wrong with the ECU and it’s providing the ISCV valve with bad current/values.
Thanks!
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Can you confirm that if the ISCV actually sits inside the airbox or it has its own clamshel ?
I believe you have a clamshell that hangs on the frame to feed air on the 3 pipes sticking out of it.
I have an idea = Put the ISCV back in place and fit it inside the metal shell or airbox = Does it still “hit” the end of the airbox/clamshell?
If you pull it out again, it should have been keept in place instead of springing forth too far out.
Next tip = It will sound foolish but bare with me….
1. If you have a metal shell , put the ISCV inside it and screw it in so the O-Ring doesn’t leak air.
2. BIG pipe going to airbox ==> clean that area (hygiene!)
3. 2 pipes sticking out at the bottom ==> your other hand expose its palm to them.4. blow air with your own mouth (unless you have a very LOW volume air compressor machine , attach pipe to it)
Can you feel air coming out on both bottom 2 metal holes ?(these holes feed the intake pipes anyway)
Turn the KEY ON
Keep blowing
Do you feel the air getting more restricted ?
If you turn the key OFF
Is the air completely blocked (you can’t blow no more)
Turn key on , it should retract backwards ? to the OFF state in the picture while key is on (I can’t confirm yet if the ECU can sense if its gone too far out and must retract it back a little bit but it may engage once the MAF sensor tells the ECU how much air is flowing in the throttle bodies while in stand still to maintain 1800 rpm revs, it’s a little trickier to study Sentec/Daewoo ECU’s than it is DELPHI units)
This is a weird test I am suggesting but you want to confirm , the same behaviour is happening to the NEW and OLD ISCV units ? Always make sure battery is charged though because that fuel pump draws a LOT of power and we don’t want to stress the pump too much also. It’s more expensive than the ISCV unit.
// Meditation doesn't mean you have to sit still....
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Nothing sounds foolish to me at this point if you would ask me to read tarot cards to the bike I would try it 😀
Thank you so much for the detailed information.
I am afraid that once the new ISCV springs out of place like mine did it loses it’s calibration or proper function, I might be mistaken here?
My bikes ISCV goes directly onto the plastic air box it does not have the metal shell. Just like in the white picture from the manual in my previous post.
Here is the metal shell I received with the ISCV that you mention that has pipes that get attached to the air hose, here are the pictures of it.
It will take some time before I can get back to the bike and test it but I will report back here. Thank you very much for your prompt reply!
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Hmmm,
If it helps, here is a few spare parts from our ebay
This one is the last one we got and likely may or may not work but i could not test out of the donor bike as engine was removed
https://www.ebay.co.uk/itm/254811047849
If you need just the plate? (Yellow plate goes to the frame, here it is)
https://www.ebay.co.uk/itm/254811047849
On your airbox = you can fit a dead ISCV to block the airbox hole and its 2 nipples under it.
If your frame does not have the welding spot to attach the metal shell , then keep using the airbox for your ISCV unit when the issue is resolved.
The metal shell will just be for testing ?
Good luck!
// Meditation doesn't mean you have to sit still....
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I have saved the old ISCV unit so I can use it to block the airbox hole as well as the 2 nipples.
I will use the metal shell just for testing yes, I guess there will be no problems because there is no air filter attached to the input pipe on the shell?
Also I didn’t reply to your previous question. I will make sure before the next test that the battery is full, and yes the same behavior is happening to both the NEW and the OLD ISCV units. -
The top feed of the shell is usually connected to the air box nipple (one of them underneath)
Hopefully on your tests , we don’t have to replace the ECU as its near impossible to acquire one!
Good luck
// Meditation doesn't mean you have to sit still....
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The top feed of the shell is usually connected to the air box nipple (one of them underneath)
I will have to see about that again when I get my hands on the bike.
I saw this post, what do you think, is it possible to swap the throttle bodies from my EFI model bike with the appropriate carburetor from the older models, would it even fit? -
The top feed of the shell is usually connected to the air box nipple (one of them underneath)
I will have to see about that again when I get my hands on the bike.
I saw this post, what do you think, is it possible to swap the throttle bodies from my EFI model bike with the appropriate carburetor from the older models, would it even fit?
You will change a lot of things: carbs, intake pipe, harness, stator, airbox, dash, many electrics etc – as nothing “efi” is backwards compatible.
// Meditation doesn't mean you have to sit still....
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Some comments regarding the ISC sensor popping out its piston.
In my bike if you turn on the ignition with the ISC out of place the piston also pops out.
From what I have read and my own conclusions this is normal behaviour because it is the ECU trying to calibrate the ISC before each startup.
What seems to be happening is this: the ISC, which is actually a stepper motor, pushes out the piston until it closes out the vent ( when installed of course). As this point the ECU sends out a fixed number of pulses in the opposite direction to open the vent at starting to a certain amount.
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Hey Joeseb, thanks for you contribution!
Yeah that explanation sounds very logical to me. So when your piston popped out could you screw it back in the ISC unit by hand and it functioned properly when you installed it back to your bike? Or you had to replace the whole unit for it to function?
Thanks!
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Jo. It has been a year since I was playing with the ISC so my recollection may not be accurate. But here goes.
You cannot screw the piston back in the normal sense since I believe the piston moves in a guide along the axis. This guide is what allows the in/out movement when the stepper motor threaded spindle rotates inside piston’s “nut”.
I think what I did was align the piston to mate with the ISC housing and then hold the piston and body between thumb and forefinger with sufficient pressure to stop thye piston rotating along with the stepper motor.
Turn on the ignition key and initially the stepper motor would be trying to push the piston further out. During the second phase the stepper motor will rotate in the opposite direct and provide you are still aligned the piston will be drawn back in.
At that point turn off the ignition, fit the ISC back into the airbox, then turn the ignition back on. At this point the system should initiate the piston calibration procedure again.
I am still using the same ISC as I concluded it is not the source of the problem I have with my bike. Hope this helps.
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