Help needed :( Cylinder 1 & 2 not firing CB400SF

[Pepper9187]

Hi there, 

Yesterday i started the bike, all fine, then while it was IDLE 2 cylinders went off (15sec after the start), so the bike is shaking like an old tracor, no power, can't run it.

Checked and pipes for cylinder 1 & 2 are dead cold, i checked / replaced the spark plugs, 1 and 2 were soak, i emptyied all the carbs and they all had gazoline....

 

I first thought that one ignition coil was dead, but after checking the service manual it turns out that tere's 2 ignition coils, 1 for cylinder 1 and 3, the other one for 2 and 4 so it can't be that.

 

What else could it be ? I'm starting to be really worried now, and i'm not a mechanical expert :(((

 

The model is CB400SF vtec 3 (NC39)

Thanks .....

 

[no deal]

i think about piston ring, how many miles you have on the bike,you live by the ocean?

[no deal]

best thing to do is a compression test,if you have news spark plug,gas in the cylinder,and good compression,is your ingnition...

 

[Pepper9187]

I live in BKK, the bike has about 40K km, i had the carbs cleaned / sync and valve clearance checked about 3-4 months ago, could they have <deleted> something ? (well i already know the answer).

Would it have taken 4 months before smt went bad if they did something wrong !?

 

Edit : He checked the compression 4 months ago and said it was all good (dont have the numbers, but he was very "happy" about it).

Edit 2 : When you seat on the bike, from left to right, cylinders 1 and 2 are not working, and they're both controlled by a different ignition coil so ????

 

Edit 3 : Thanks for your messages BTW

[stubuzz]

Swap the ignition coils from side to side. See if that moves the problem to 3and 4.

[OneMoreFarang]

You obviously have gasoline. Do you have a spark? Check it with spare spark plugs.

Did the cylinders die exactly at the same time or one after the other? Different symptoms = different problems.

[Pepper9187]

Just now, OneMoreFarang said:

You obviously have gasoline. Do you have a spark? Check it with spare spark plugs.

Did the cylinders die exactly at the same time or one after the other? Different symptoms = different problems.

Exact same time, 15sec after start, while it was IDLE, that's why i thought (and really REALLY hope) it's only a small electrical problem.

 

I'll swap the coils tomorrow and check the sparks, too much rain right now & too dark & too sad :(((

[Anythingleft?]

Start with the simple stuff
Spark first before you start tearing anything to bits
Change over components from one circuit to another

Two cyls failing together would indicate a common issue leading to the pair so doubtful it's the cyls or rings

Have you got a multimeter at home......

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[Pepper9187]

Thanks.

Yah i got a multimeter, what's your plan ?

PS : i rank 1/10 on the McGiver tech scale so i might not be able to do crazy things.

[Fruit Trader]

I have 1 4 - 2 3 for the Honda coil pairs but might be wrong in the notes.

[Pepper9187]

It's like that :
So 1&4 / 2&3, that's why i doubt it's a coil issue, it doesn't match with my 1&2 not working ????

 

[stubuzz]

So it runs ok for 15 seconds and then fails? If so it points to the ecu/cdi.

[Pepper9187]

12 minutes ago, stubuzz said:

So it runs ok for 15 seconds and then fails? If so it points to the ecu/cdi.

Yap, just like you said. ???? I'll check all the electronic more in detail tomorrow, i'll post the results here.

For tonight I'm just gona drown my sorrows until i don't ever remember my bike's broken.

 

Thanks everyone *opening the first Leo*

[Pepper9187]

Update :Da-fack, tried to start the bike it's even worst, almost not starting anymore it's really stuck in there.

 

Update 2 : Bad hangover i'll continue tomorrow

[Crossy]

When you surface ????

 

Is your fuel good? Empty the tank and drain the carbs. Put 1/2 a gallon of fresh fuel in the tank.

[Justgrazing]

Simple test as alluded to by another member above .. Remove the leads from the two dead cyls and put a spare plug in them .. Ensure body of the plug is touching engine then spin her over .. if there's a cracking spark at the plug electrode then its not likely to be ign .. Make sure there's no spilled petrol or vapour around and hold the lead with a rag if you do this test .. Let us know how you get on .. 

[no deal]

22 hours ago, stubuzz said:

Swap the ignition coils from side to side. See if that moves the problem to 3and 4.

good idea

[no deal]

i think your ecu go bad

[VocalNeal]

I think those Hondas run a wasted spark system so each set sparks at the same time. So as you say 1 and 4 and 2 and 3. So with 1 and 2 not firing it involves each coil failing but that is not the case as it running on the other two cylinders also involves both coils. Trace the HT leads back to the coils see if anything looks amiss. If it will start run it at night and have a good look around in the dark for any sighs of an errant spark.

 

Is there any fuel in the tank?

[Pepper9187]

Sorry for no update :

 

Updates : it's been a shitty rainy busy and sad week, havent done sh*** on the bike, i ordered a kit to check the engines compression but well it's ebay China so god only knows when it'll arrive here.

 

If no rain i'll check the sparks tomorrow

[Pepper9187]

Ok sorry for the delay,

 

I checked and .. no sparks in cylinder 1 &2, so it's electrical or ECU ....

 

 

[Pepper9187]

PS : i checked the wire, putted some contact cleaner where it was necessary but still the same shit at the end.

[Isaanbiker]

28 minutes ago, Pepper9187 said:

PS : i checked the wire, putted some contact cleaner where it was necessary but still the same shit at the end.

I hope you're still alive and not too hungover? Here's what you should do:

 

   Please check if the non functioning cylinders are on the same coil?

 

  The firing order is 1-3-4-2, do not check your compression now, the chances that two potts suddenly fail because of mechanical problems are slim.

 

  I guess you've got to take the tank off to see the coils? Each coil should have plus when ignition is on, you can even build your own tester with a bulb....

 

  Check the voltage at your coils, but please check all the cable connectors, many are inside the lamp. 

 

  But first check if you've got spark without the caps of the plugs? Once the spark plugs got very wet, they do not fire anymore, that's why you should check it at the ignition cable.

 

   If both cylinders fail, it can be a loose connector, follow the cable from your ignition lock to the coils, then to the pick up. If that's all okay, it could be your electronic unit.

 

  Please check the coils, plugs, caps first and report back. Trying to walk you through. 

 

Charge your battery, some electronic doesn't produce a spark if the battery is under 12 volts. 

  

 

   

[Pepper9187]

8 minutes ago, Isaanbiker said:

I hope you're still alive and not too hungover? Here's what you should do:

 

   Please check if the non functioning cylinders are on the same coil?

 

  The firing order is 1-3-42, do not check your compression now, the chances that two potts suddenly fail because of mechanical problems are slim.

 

  I guess you've got to take the tank off to see the coils? Each coil should have plus when ignition is on, you can even build your own tester with a bulb....

 

  Check the voltage at your coils, but please check all the cable connectors, many are inside the lamp. 

 

  But first check if you've got spark without the caps of the plugs? Once the spark plugs got very wet, they do not fire anymore, that's why you should check it at the ignition cable.

 

   If both cylinders fail, it can be a loose connector, follow the cable from your ignition lock to the coils, then to the pick up. If that's all okay, it could be your electronic unit.

 

  Please check the coils, plugs, caps first and report back. Trying to walk you through. 

  

 

   

Aha no it was a busy week + my battery was pretty much dead i had to order a new one and lazada f*** up the delivery, it never came, had to cancel and blabla basically it took forever.

 

Yap i have to remove the tank but it's super easy on that bike, 3 screws.

That morning the cylinder 1&2 seems to have started for like 2 seconds, exhaust pipe were hot, then nothing again after ????, that was at my first attempt with the new battery.

Yes there's 2 cable in each coil (i mean 2 cable IN + the 2 cables that go to the spark plugs).

 

It's very hard to follow the cables because at some point they are all mixed together, they all go to the ECU but i couldn't find the same color cable, but i will continue investigating tomorrow if there's no rain.

 

Thanks a lot ????

 

 

 

[Vacuum]

On 6/28/2019 at 12:18 PM, Pepper9187 said:

I'll swap the coils tomorrow and check the sparks,

Check the sparks before you swap the coils.

[Pepper9187]

5 minutes ago, Vacuum said:

Check the sparks before you swap the coils.

Yap, done, no sparks on 1&2

[Isaanbiker]

21 minutes ago, Pepper9187 said:

Aha no it was a busy week + my battery was pretty much dead i had to order a new one and lazada f*** up the delivery, it never came, had to cancel and blabla basically it took forever.

 

Yap i have to remove the tank but it's super easy on that bike, 3 screws.

That morning the cylinder 1&2 seems to have started for like 2 seconds, exhaust pipe were hot, then nothing again after ????, that was at my first attempt with the new battery.

Yes there's 2 cable in each coil (i mean 2 cable IN + the 2 cables that go to the spark plugs).

 

It's very hard to follow the cables because at some point they are all mixed together, they all go to the ECU but i couldn't find the same color cable, but i will continue investigating tomorrow if there's no rain.

 

Thanks a lot ????

 

 

 

 Do you have fuel injection? 

 

    Please take the wires at the coil off, clean the contacts and put them back on. You can use some electrical spray. Then take the spark plug caps off, cut the main cable a few mm and check if you've got a spark. It should be strong and violetish/blueish.

If you have spark at the cable ( ignition wire), then try it with the caps and stick the spark plugs in, hold them on minus at the chassis and see if you've got spark.

 

    If you do have spark, then this should not be the problem. Please swap the spark plugs and put the ones that fired in the cylinders that didn't. Once you've done that and reported back, let's continue.

 

  Are the non functioning cylinders on the same coil( One coil for two cylinders)????

 

   

[Pepper9187]

2 minutes ago, Isaanbiker said:

 Do you have fuel injection? 

 

    Please take the wires at the coil off, clean the contacts and put them back on. You can use some electrical spray. Then take the spark plug caps off, cut the main cable a few mm and check if you've got a spark. It should be strong and violetish/blueish.

If you have spark at the cable ( ignition wire), then try it with the caps and stick the spark plugs in, hold them on minus at the chassis and see if you've got spark.

 

    If you do have spark, then this should not be the problem. Please swap the spark plugs and put the ones that fired in the cylinders that didn't. Once you've done that and reported back, let's continue.

 

  

Will do sir !

It's a carb, and i have fuel in the carbs / cylinder cause the spark plugs were wet (and i emptied the carbs, they were full)

 

PS : i already changed the 4x spark plugs so i cant be that, it's out of the equation.

[Isaanbiker]

2 minutes ago, Pepper9187 said:

Will do sir !

 

PS : i already changed the 4x spark plugs so i cant be that, it's out of the equation.

 Just in case, if the ECU is faulty it can be re -solded, but that's out of question for now.

 

The ignition should have a fuse, considering two coils, I'd think two fuses. Have you checked them already? It's often something very simple. 

[Isaanbiker]

OP, just had an enlightenment, my thoughts went back to a time where I had the same problem. 

 

   I had something very similar in 1977 when I'd bought a Honda CB 500 F from a guy for almost nothing, with the same problem(s). They'd taken the half bike apart, but didn't check on the easy things. 

 

   It took only 20 minutes to find the culprit. One screen inside the tank was so full of dirt that there's no more fuel flow getting to two cylinders. I'd assume that you've got two outlets as well, haven't you? 

 

   Please do following: Take the tubes that go to the carbs/fuel injectors? off, then open and see. The two cylinders not working could be on one particular tube.

 

   Please report back.