DT 300 - fail to start - TPS voltage value at 0 position ?

[Henry]

@Henry, I still think it's somehow "by-air" related.

-intake manifold,
-vacuum tubes,
-manifold o-ring or gasket,
-false air caused by an worn out throttle axle,
-injector o-ring,
-hose-clamps pinch not tight,

- intake manifold test: out, spray inside with a little fuel, dust outside with baby powder or chalk dust, if there is a hair gap, it shows on powder.

Three more thoughts:
A) if you separete those 3-pronged plug between generator and regulator, did you see burn-signs on its plastic body?
If yes, could mean your regulator was overcharged and caused erratic in your ECU.
Q: did you change your regulator for a new one?

B) both battery cables OFF battery, hold them together for a minute or so, to discharge your ECUs diodes.

C) take a cable of appr. 10mm2 and connect your
battery MINUS with your motor GROUND close to its starter motor to have a 100% circuit.

Interesting tip with the baby powder ! I have no baby but baby powder 
I don't get the how to  I spray with fuel the inside of the manifold (through the hole left by the throttle body removed ?) or the outside close to the gasket ?

A : plugs in perfect condition, charging is OK, 14,4V at 4kRPM
B : I'll give it a try
C : I'll do so, I need to find a piece of 10mm2

I already sprayed around the manifold gasket with brake cleaner, if there was a leak, the brakes should be aspired and the idle should be rough but no, it passed. I could also spray around the throttle body and the sensors, I'll try tomorrow.

[Henry]

Your fuel filter is over half blocked by that black stuff! The filter is a white nylon-plastic-screen thingy. That black stuff is some kind of Martian snot that should not be there!

I don't think so, it looks like, but the black dots are actually fuel blocked into the plastic pattern, it reacts with the light probably, when you touch it, the fuel goes out of the square and it becomes white. Strange but true !

[Henry]

@CROSSBOLT, this looks to me like a pattern on a fabric.. those black thingys....reminds me of a babys stocking..

@Henry, maybe this link unravels something..
At chapter 13. is a ECU testing diagram....
-check the tilt switch too

https://www.google.com/url?sa=t&source=web&rct=j&url=http://kymco.at/pub/media/Download/Kymco/Downtown300iFehlercode.pdf&ved=2ahUKEwjT_PG6jeT0AhWTg_0HHaRTAJMQFnoECDQQAQ&usg=AOvVaw1NYgIIcBUDGUBOzA8Ouyh7

If the tilt switch was involved, it would be after start no ? I'll test it anyway !

[Henry]

He can try swap ECU only if DT350 is Euro 3, because Euro 4 have EVAP system, he mention DT350 is 4 years old, It should be Euro 4

It is more complicated then "dtc will pop out". In 15 years ECU diagnostic I have encountered many illogical problems and I can tell you ECU self-diagnosis is unreliable...very much!

@Henry

You must have O2 voltage cycling on idle when engine is warm, also when you hit throttle you should have spike to 0.9, and zero when you leave throttle (fuel cut off).. pls play with that little bit and write results here! Maybe it is clue for something...

Ruffus write very good check list, you should follow that!
My DT also stay all the time outside and I have habit once in year spray non water proof connectors with contact cleaner just for prevention!

My DT350 is from 2016 and is euro3 !

The O2 sensor in not cycling at idle, stays at 0.07, it does cycle to 0.90V when I hit throttle, I will check when I leave throttle if it goes to 0. The fact that the O2 sensor does not cycle at idle could reveal something ? That would be a good news !

[dr.jazz]

Oh here is so much troubleshooting lol

About any air leak ...etc.. you can test that with Fi tool, just watch MAP pressure value, it should be steady on idle like 35-45 (also observing rpm so you will now why pressure rise or drop)  if you have steady rpm and your pressure change, that is indication for something!

You dont need to test ECU with multimetar like Ruffus write, you do all that with FI tool, dont waste time

Also tilt swtich is good according the FI tool!

About that black stuff on fuel filter, I dont think that make any issue because you have good pressure!

Conclude; ECU read all good value, so could be wrong handling through the software or my theory (read bellow) 
O2 sensor cycling on idle is way how ECU preform injection timing however it need some time to start cycling you should put some rpm-s. Not cyclinging on idle can indicate air leak (you can test that observing MAP pressure or baby powder method), O2 sensor problem or ECU software problem, in my experience I encountered all three problems 
I write you before... try play with throttle and observe O2 behaviour and report here...


Now I will write what I think what is the problem (my fameous theory), after read all post my conclusion is FUEL! I know first you gonna think it is premimu fuel must be good etc... However you have trouble with two identical scooter, identical hot start problem....and you said you feed them with 98 fuel, that could be a trick!

Well, we should look wider picture, EFI in DT300/50 is basic I would say primitive if we compare some other systems...
System lacks of auto-adjusting feature for fuel octane, so it can make trouble advancing ignition timing during start because of ignition map limitiation  if you pour higher octain fuel. When engine is cold ECU advance igntion more then hot, that is why you dont have a problem, however that changes when engine is warm, there is no need for too much advanced igntion and ECU retard it and makes trouble beacause of fuel resistance (bigger preigntion time). What I wanna said, iginition map is fixed and adjusting for higher octain fuel is not possbile so you should remove all the fuel and put 95 octain fuel, start engine leave it work some time to clean all remain fuel, get some rpm-s (I assume you cant drive because it is not in one piece) and test hot start. Maybe is "shot in the dark BUT" like Crossbolt write, but for sure you would not be the first with such a problem related with fuel octane. There are not many "cases" related with octain value but they exist and main problem is engine starting not performance so give it a shoot you gone loose few Eur on fuel 

[Henry]

Oh here is so much troubleshooting lol

About any air leak ...etc.. you can test that with Fi tool, just watch MAP pressure value, it should be steady on idle like 35-45 (also observing rpm so you will now why pressure rise or drop)  if you have steady rpm and your pressure change, that is indication for something!

You dont need to test ECU with multimetar like Ruffus write, you do all that with FI tool, dont waste time

Also tilt swtich is good according the FI tool!

About that black stuff on fuel filter, I dont think that make any issue because you have good pressure!

Conclude; ECU read all good value, so could be wrong handling through the software or my theory (read bellow) 
O2 sensor cycling on idle is way how ECU preform injection timing however it need some time to start cycling you should put some rpm-s. Not cyclinging on idle can indicate air leak (you can test that observing MAP pressure or baby powder method), O2 sensor problem or ECU software problem, in my experience I encountered all three problems 
I write you before... try play with throttle and observe O2 behaviour and report here...


Now I will write what I think what is the problem (my fameous theory), after read all post my conclusion is FUEL! I know first you gonna think it is premimu fuel must be good etc... However you have trouble with two identical scooter, identical hot start problem....and you said you feed them with 98 fuel, that could be a trick!

Well, we should look wider picture, EFI in DT300/50 is basic I would say primitive if we compare some other systems...
System lacks of auto-adjusting feature for fuel octane, so it can make trouble advancing ignition timing during start because of ignition map limitiation  if you pour higher octain fuel. When engine is cold ECU advance igntion more then hot, that is why you dont have a problem, however that changes when engine is warm, there is no need for too much advanced igntion and ECU retard it and makes trouble beacause of fuel resistance (bigger preigntion time). What I wanna said, iginition map is fixed and adjusting for higher octain fuel is not possbile so you should remove all the fuel and put 95 octain fuel, start engine leave it work some time to clean all remain fuel, get some rpm-s (I assume you cant drive because it is not in one piece) and test hot start. Maybe is "shot in the dark BUT" like Crossbolt write, but for sure you would not be the first with such a problem related with fuel octane. There are not many "cases" related with octain value but they exist and main problem is engine starting not performance so give it a shoot you gone loose few Eur on fuel 

I have no problem trying to feed the engine with 95 ! I just filled it full yesterday with 98 
The MAP reads the value at the trottle body, I wonder what it could read if I had a vacuum leak at the injector ? I'm going to check into my o-ring box if I have one that could fit there, just to test.

I still dont get the baby powder trick, I do for an oil leak test, but for a vacuum ?

[mousejunks]

I have no problem trying to feed the engine with 95 ! I just filled it full yesterday with 98 
The MAP reads the value at the trottle body, I wonder what it could read if I had a vacuum leak at the injector ? I'm going to check into my o-ring box if I have one that could fit there, just to test.

I still dont get the baby powder trick, I do for an oil leak test, but for a vacuum ?

For a vacuum leak use smoke

[dr.jazz]

Injector is placed before intake valve, so it is same volume space as map sensor (manifold absolute pressure) location, and bad oring or manifold gasket or any other damage will have impact on map readings! About powder, goal is make dust so you can see air moving you can use indinan stick too to make smoke. From my experience when injector oring wear and doesent seal, there is characteristic high pitch sound because of flow air thoroug small place!


I hope you get clear picture now 

[Henry]

Injector is placed before intake valve, so it is same volume space as map sensor (manifold absolute pressure) location, and bad oring or manifold gasket or any other damage will have impact on map readings! About powder, goal is make dust so you can see air moving you can use indinan stick too to make smoke. From my experience when injector oring wear and doesent seal, there is characteristic high pitch sound because of flow air thoroug small place!


I hope you get clear picture now 

I do now !
I'm pretty sure 02 voltage doesn't cycle ay idle, you think it could be due to air leak, but I saw from the diag tool that the air pressure is within the range, that's weird !
I'm going to re-check that.

95 is my only option now !

[dr.jazz]

Vacuum is strongest at idle when throttle clamp is closed, so if there is any air leak map value will be higher, out of spec, and also unstable..  you said map readings are good so I doubt there is air leak somewhere.

About O2 cycling missing that can point to some software issue howevere that would not have impact on hot start as I mention before ECU is in open loop, BUT if we discover one ECU weak spot that is pointing there can be more like hot start problem!

But still 98 fuel bothers me 

[Henry]

Vacuum is strongest at idle when throttle clamp is closed, so if there is any air leak map value will be higher, out of spec, and also unstable..  you said map readings are good so I doubt there is air leak somewhere.

About O2 cycling missing that can point to some software issue howevere that would not have impact on hot start as I mention before ECU is in open loop, BUT if we discover one ECU weak spot that is pointing there can be more like hot start problem!

But still 98 fuel bothers me 

I just checked, o2 is cycling at idle if rpm is higher than around 1750, just under it stays around 0.07v.
Map pressure is at 34/35

[Ruffus]

@Henry, there are several ways to check a manifold for leaks.
One mentioned by Mouse with a scentstick, bears the risk of dispersion the smoke by breathing or...
Other, powder:
-manifold is on your desk, close both big openings with tape, 
-powder the whole manifold from outside with whatever fine stuff you have,
-spray through this small vacuum intake, brake cleaner or fuel,
-turn the whole manifold slowely in your hands
-if there is a fine gap you will see the conture of this demage on the powdered surface.

It deems to be oldfashioned, this step by step "on foot" manual checking and analyzing.
I do DTCs, if neccessary, on my car with an OBD tester particularely programmed for VOLVO,  because there is no other way to caliprate brakes or rear door closing, etc.

BUT: Before I sit down and plug in, I do a mental analyzing, WHAT and WHERE could be the culprit.
Then I circle it in, digital and manually.

As an engineer you split a challenge down like in an equation, and start with the smallest possible solution which leads you to your next step.

[Henry]

[quote author=Henry link
I still dont get the baby powder trick, I do for an oil leak test, but for a vacuum ?

@Henry, there are several ways to check a manifold for leaks.
One mentioned by Mouse with a scentstick, bears the risk of dispersion the smoke by breathing or...
Other, powder:
-manifold is on your desk, close both big openings with tape, 
-powder the whole manifold from outside with whatever fine stuff you have,
-spray through this small vacuum intake, brake cleaner or fuel,
-turn the whole manifold slowely in your hands
-if there is a fine gap you will see the conture of this demage on the powdered surface.

Okay ! Now I understand, thanks !

[Henry]

Just thought about something... Might sounds stupid but could that come from a tired starter ?

When the engine is cold compression is lower than hot, means the starter has to give less force to start a cold engine compared to when the engine is hot.

Sounds possible to you ?

[Ruffus]

@Henry, YES give it a try.
Didn't think of that anymore.

-pls check first with jumpstarting and shortcut starting by connecting those two bolts on your starter relais with a screwdriver or pliers (gloves and no open fuel close by)

-then order an inexpensive aftermarket replacement and put it in

-make sure this big ground cable (what I suggested to bypass) from battery to this motor ground point is in pristine shape and not corroded within 2 cm inside this cableshoe.
Had this issue and took me awhile to find out.

..pls see link..
https://www.kymcoforum.com/index.php?topic=31637.0