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Discussion Starter · #1 ·
Got a 04 400ex that has no spark. Been trying to figure out what is wrong with it for about 6 months now. I have replaced the stator, cdi, rectifier, the stator pickup, and coil. I have stripped my wiring harness to check if there were any broken wires. Nothing wrong with main harness or the start/kill/light switch that I can see. Tried a few things I've seen on forums. I don't know what else it could be. I'm stumped and I have worked on multiple 400exs and never have had this problem before. If anyone could help me out, that would be great.
Thanks, Cody
 

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I'll try to help you as best I can

First of all, the 400EX does not need a battery or rectifier to make spark - the battery is there to turn the engine via the starter motor and the rectifier is there to turn AC into DC to charge the battery

Therefore the ignition system consists of the stator, pulse generator, the CDI box and the coil

Coils seldom go bad, but the plug cap does go bad more often than the coil - stators have the highest failure rate followed by CDI boxes and then pulse generators

To begin with, you have to eliminate the "kill" wire - it's the black wire with the white stripe - connect that wire to ground and the spark goes away

If that does not fix it, then check all the connections - a bad ground at the coil or at the motor mount points (common on powder coated or freshly painted frames) will kill the spark also

The alternator is a 3 phase unit - 2 phases are used for charging the battery and one phase is used to excite the CDI - if the engine does not have a good ground, the stator does not have a complete circuit and the CDI box needs a good ground on the green wire with a white stripe

Hope this helps a bit
 

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Discussion Starter · #3 ·
Is there supposed to be 12 volts going to the CDI box? If so, I am not getting anything even when the motor is turning over. The Black/Red Wire is the one I am testing which is on the two wire plug.
 

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No - there is not 12 volts to the CDI box

You need a peak voltage tester to check the stator output voltage between the black/red wire and the green/white wire - with the engine cranking (spark plug out) you should get 100 peak volts
 

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Got a 04 400ex that has no spark. Been trying to figure out what is wrong with it for about 6 months now. I have replaced the stator, cdi, rectifier, the stator pickup, and coil. I have stripped my wiring harness to check if there were any broken wires. Nothing wrong with main harness or the start/kill/light switch that I can see. Tried a few things I've seen on forums. I don't know what else it could be. I'm stumped and I have worked on multiple 400exs and never have had this problem before. If anyone could help me out, that would be great.
Thanks, Cody
I think i ended up with your quad.
4069
 

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I'll try to help you as best I can

First of all, the 400EX does not need a battery or rectifier to make spark - the battery is there to turn the engine via the starter motor and the rectifier is there to turn AC into DC to charge the battery

Therefore the ignition system consists of the stator, pulse generator, the CDI box and the coil

Coils seldom go bad, but the plug cap does go bad more often than the coil - stators have the highest failure rate followed by CDI boxes and then pulse generators

To begin with, you have to eliminate the "kill" wire - it's the black wire with the white stripe - connect that wire to ground and the spark goes away

If that does not fix it, then check all the connections - a bad ground at the coil or at the motor mount points (common on powder coated or freshly painted frames) will kill the spark also

The alternator is a 3 phase unit - 2 phases are used for charging the battery and one phase is used to excite the CDI - if the engine does not have a good ground, the stator does not have a complete circuit and the CDI box needs a good ground on the green wire with a white stripe

Hope this helps a bit
Hello I’m having the same problem with my Trx400ex I bought everything brand new wire harness,new Cdi,New ignition switch,New pickup coil,new solenoid,new spark plug,new stator,relay rectifier and I’m still not getting any spark where was the black and white wire that you was talking about that if it’s grounded it doesn’t let the spark plug spark ? Or what should I do ??
 

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Hello I’m having the same problem with my Trx400ex I bought everything brand new wire harness,new Cdi,New ignition switch,New pickup coil,new solenoid,new spark plug,new stator,relay rectifier and I’m still not getting any spark where was the black and white wire that you was talking about that if it’s grounded it doesn’t let the spark plug spark ? Or what should I do ??
Pictured below is the ignition system for up to 04 models - in 05 reverse was added and the ignition is a bit more complicated as a reverse speed limiter was added.
4799


Starting at the beginning - when did you lose spark? While riding? After powder coating or painting the frame?

What happened between the last time it ran and losing spark?
 

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Pictured below is the ignition system for up to 04 models - in 05 reverse was added and the ignition is a bit more complicated as a reverse speed limiter was added.
View attachment 4799

Starting at the beginning - when did you lose spark? While riding? After powder coating or painting the frame?

What happened between the last time it ran and losing spark?
Thanks for responding. Okay my quad is a 2002 Trx400ex I lost spark while riding the quad just turned off on me so I went home and check for spark and nothing at all so I got everything new wire harness,cdi,stator,rectifier,pickup coil,solenoid, and ignition switch and spark plug and I tested for spark again with everything new and still nothing so now I have no idea but the thing you said about my grounding is what might be my problem well I don’t know yet that’s why I’m asking you for help?.
 

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The spark plug grounds to the engine and the coil grounds to the frame - if the connection between the engine and frame is lost, so is the spark - of course new parts can have their own faults. I have restored spark by making my own wiring harness eliminating everything except the connections necessary to produce spark.

In the above diagram is the bare bones connections to produce and kill spark - first eliminate the kill function by disconnecting the blk/wht wire. Now use an ohm meter to verify all wiring connections especially grounds - actually start with grounds, when you have verified all the components have good grounds, verify continuity of the wiring from each component to connected component. Verify continuity of each testable component. Finally, get a peak voltage tester and verify the voltage output of each component.

Now although all the parts you say you installed new are available from Honda, I seriously doubt you spent $835 for parts in your quest to fix the issue. I suspect you bought parts from Amazon or Ebay, so you have a collection of Chinese counterfeit parts on your vehicle, so this complicates matters because instead of troubleshooting the parts that were working prior to the failure, you decided to throw parts at it to see if it would stick.

Now the one part of the ignition system you did not replace was the flywheel. I have seen flywheels come loose and the woodruff key that positions it on the crank shears throwing it out of time. Before you started throwing parts at it, did you verify the position of the flywheel with the engine at TDC? You are going to feel really silly if you find out the key sheared and the timing is off.

Compression, fuel and air in the right ratio going in and coming out, spark and spark at the right time and the engine will run, but if the flywheel is out of sync with the CDI unit, there will be no spark, weak spark or spark at the wrong time and the engine will not run. It's actually rather common for a running engine to lose spark suddenly due to the flywheel being out of time.

Let me know if this gets you any closer to getting spark back. I might have to guide you through the peak voltage tests to restore spark.
 

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The spark plug grounds to the engine and the coil grounds to the frame - if the connection between the engine and frame is lost, so is the spark - of course new parts can have their own faults. I have restored spark by making my own wiring harness eliminating everything except the connections necessary to produce spark.

In the above diagram is the bare bones connections to produce and kill spark - first eliminate the kill function by disconnecting the blk/wht wire. Now use an ohm meter to verify all wiring connections especially grounds - actually start with grounds, when you have verified all the components have good grounds, verify continuity of the wiring from each component to connected component. Verify continuity of each testable component. Finally, get a peak voltage tester and verify the voltage output of each component.

Now although all the parts you say you installed new are available from Honda, I seriously doubt you spent $835 for parts in your quest to fix the issue. I suspect you bought parts from Amazon or Ebay, so you have a collection of Chinese counterfeit parts on your vehicle, so this complicates matters because instead of troubleshooting the parts that were working prior to the failure, you decided to throw parts at it to see if it would stick.

Now the one part of the ignition system you did not replace was the flywheel. I have seen flywheels come loose and the woodruff key that positions it on the crank shears throwing it out of time. Before you started throwing parts at it, did you verify the position of the flywheel with the engine at TDC? You are going to feel really silly if you find out the key sheared and the timing is off.

Compression, fuel and air in the right ratio going in and coming out, spark and spark at the right time and the engine will run, but if the flywheel is out of sync with the CDI unit, there will be no spark, weak spark or spark at the wrong time and the engine will not run. It's actually rather common for a running engine to lose spark suddenly due to the flywheel being out of time.

Let me know if this gets you any closer to getting spark back. I might have to guide you through the peak voltage tests to restore spark.
yeah I threw some Chinese parts in there to see if I got it running but I don’t know how to check the wires with the voltage meter I will need help and yes the timing is good but when I put the new parts in I didn’t check if my flywheel was at TDC I just put the parts in and cranked it the plug gave me spark at first but then after no more spark and engine made a weird noise but can you help you on how to do the voltage test and how to check if my flywheel is in good condition and TDC? Thanks!!
 

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One step at a time: Remove the spark plug, remove the timing inspection cap and crankshaft nut cover from the LH engine cover (alternator cover) - using a plastic or paper drinking straw position the piston at TDC - the straw is used to insert through the spark plug hole and feel the position of the piston - turn the crankshaft in a counter clockwise direction with a socket on a t-handle or breaker bar - when the piston it at TDC, the straw will begin to move downward whether the crankshaft is turned either way from TDC - you should see the T mark in the inspection hole when the piston is at TDC - if not, turn the crankshaft clockwise until you see the T mark - if the mark shows up within 90 degrees of rotation it is an indication that the flywheel key has sheared throwing the timing off far enough to lose spark. If the T mark is in the inspection hole at TDC, then we will move on to testing the ignition system.
 

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One step at a time: Remove the spark plug, remove the timing inspection cap and crankshaft nut cover from the LH engine cover (alternator cover) - using a plastic or paper drinking straw position the piston at TDC - the straw is used to insert through the spark plug hole and feel the position of the piston - turn the crankshaft in a counter clockwise direction with a socket on a t-handle or breaker bar - when the piston it at TDC, the straw will begin to move downward whether the crankshaft is turned either way from TDC - you should see the T mark in the inspection hole when the piston is at TDC - if not, turn the crankshaft clockwise until you see the T mark - if the mark shows up within 90 degrees of rotation it is an indication that the flywheel key has sheared throwing the timing off far enough to lose spark. If the T mark is in the inspection hole at TDC, then we will move on to testing the ignition system.
Okay so I checked it and it was good at TDC so next step is to test the ignition system how do I do that?? thanks for the help too
 

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You will need to buy or borrow a multimeter with a peak voltage function - first test the pulse coil for continuity and if good, check for peak voltage output - typical is .7volts (7/10 - seven tenths of a volt) with the engine cranking normally.

The pulse coil just tells the CDI unit when to fire the plug

The exciter coil has to charge the CDI unit - the exciter coil should generate about 100 volts peak and the voltage to the coil should be about 100 volts also. If the exciter coil has the proper output and the voltage to the coil is low, the CDI unit is the culprit - if the voltage to the coil is OK, then the coil or the spark plug cap or the spark plug are the problem
 

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You will need to buy or borrow a multimeter with a peak voltage function - first test the pulse coil for continuity and if good, check for peak voltage output - typical is .7volts (7/10 - seven tenths of a volt) with the engine cranking normally.

The pulse coil just tells the CDI unit when to fire the plug

The exciter coil has to charge the CDI unit - the exciter coil should generate about 100 volts peak and the voltage to the coil should be about 100 volts also. If the exciter coil has the proper output and the voltage to the coil is low, the CDI unit is the culprit - if the voltage to the coil is OK, then the coil or the spark plug cap or the spark plug are the problem
Okay so those are the only things I will be testing with the multimeter? I also have an extra coil incase this one won’t give me the voltage it supposed to and one question is it okay for me to keep the Chinese Wire harness with the rest of the parts would the bike start even tho they Chinese?
 

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Yes - whether or not the wiring harness is OK depends on the results of the tests - if all test good, you will have spark and all will be well.
Okay that’s fine I’m pretty sure everything is fine but I will double check by testing it but I’m pretty sure I have a bad ground wire or no ground. I also have 91 psi because my cylinder stud nut is stripped so it’s not torque so compression leaking from the head gasket I don’t know if that could be it too it was running like that before tho.
 

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A leaking head gasket will not cause a loss of spark, but it will keep the engine from running. It needs a minimum of about 110 to 120 psi to start - under 100 it would have to be pull or push started
 

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A leaking head gasket will not cause a loss of spark, but it will keep the engine from running. It needs a minimum of about 110 to 120 psi to start - under 100 it would have to be pull or push started
Ohh okay I will try to fix that leaking head gasket problem as well to i will keep you updated if the bike does start I will text you for help if i need. thanks for helping.
 

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A leaking head gasket will not cause a loss of spark, but it will keep the engine from running. It needs a minimum of about 110 to 120 psi to start - under 100 it would have to be pull or push started
HelloI finally got spark on my bike but I have a question I put a longer stud nut in my cylinder to replace the stripped one but now I don’t have space to torque the spark plug im getting spark but would the bike start with the spark plug loose just tight a little bit or would I have to tight it to it’s torque?? Because I left it loose tight it wit my fingers and the bike wanted to start and was shooting blue smoke from the exhaust ???
 
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