4Rt No Spark - Help!

[thall1]

yes checked the fuel pump.....all ok.....

[jrsunt]

This is a long shot, but, how long was it in bits for? If the stator and throttle body have been disconnected for some time, maybe a week, then the throttle body will need re programming as it can loose its memory.

If you know anyone with another 4rt, try your throttle body on theirs.

Edited August 17, 2015 by jrsunt

[aussiechris]

Sounds like you've done a pretty thorough job checking every thing including the eliminating the back angle sensor and ignition coil.

Using a test lamp to check voltage going to the coil may not prove anything (you'd have to try your lamp on a working bike). The attached image shows how short those pulses are (that's measuring the coil terminals on my 4RT idling).

Assuming no wiring faults I think it's starting to point to a crook ECU/throttle body or faulty condenser. Any chance you could borrow such items to substitute?

Chris.

[thall1]

the stator was disconnected for the oil filter change, just had the casing tie-wrapped onto the casing to prevent pulling the cables. There is a chance of borrowing bits but i'm a bit reluctant as its a new bike!...will have to see....

[thall1]

I have been led to believe that a faulty condenser should not stop the bike running? can anyone confirm this?

[aussiechris]

According to my 2015 owners manual, if the engine does not start you should check the “engine does not start” items below (using the special PGM-FI checker box)...

Cause - Symptom
Faulty ECU - Engine does not start
Open or short or faulty Manifold Absolute Pressure sensor – Poor idle
Open or short or faulty Engine Coolant Temperature sensor – Hard starting when cold, fan does not stop
Open or short or faulty Throttle Position Sensor – Poor engine response
Open or short Inlet Air Temperature sensor – Engine operates normally
Open or short or faulty fuel injector – Engine does not start (would still have spark)
Open or short or faulty bank angle sensor – Engine starts but stops after a few seconds.

It goes on to say that if the above checks out ok, then replace the condenser with a new one. If the engine now starts then the old condenser was faulty.

Just for testing purposes, you could go to an electronics store and buy a 10,000 microfarad capacitor (at least 35 volt rating) and connect that in place of the original one. Ensure you connect the negative terminal to the earth side (green wire) and the positive to the power side (red wire).

I don’t believe having the alternator disconnected will cause the ECU to lose memory (the maps and program are all in Flash memory).

Since you say the plug is getting wet with fuel, this would suggest the ECU and fuel injector is working. Looking at the other “no start/no spark” items, I think you’re left with the ignition coil (and associated wiring) or the condenser. You’ve tested the coil on another bike so it’s either the coil wiring (did you try the other guys coil on your bike?) or the condenser.

 

I hope you find it soon.

Chris.

[littleo]

I had exactly the same experience on a 2008 4RT, it appeared I had disturbed a short in the wiring which could not be detected with tests.........ended up replacing the loom at a cost of £65. Bike starts & runs fine now.

 

Hope this helps

Alan

[honda_freak]

Hi there.

 

Here is my story of a Honda Montesa 4RT from 2005 with ignition problems there maybe can help you !!!.

 

I had a call from the local Honda Montesa dealer here in Denmark which told me that he had got 2005 Honda Montesa 4RT with some strange ignition problems that the owner of the bike had given up on.The owner had done a lot of things to get the missing spark back on his Honda Montesa 4RT by swapping part from a doner bike and still with a negative result - no spark.

 

The first thing I did were to confirm whether or not there were spark at the spark plug and there was no spark at all. Then I made a resistance-test from the ECU to the individual components with a good result - which was perfectly fine and normal readings.

 

A dirty test of the condenser can be done with a multimeter with the settings on ohm scala and the measurement done across the two terminals on the condenser - a good condenser should show infinite resistance or (OL) on the multimeter.

 

The next thing I did to verify that the bike wasnt producing any electrical current was to connect a 12 volt automotive battery to the wiring harness of the Honda Montesa 4RT. 

The first thing you must do to make this test is to disconnect the electrical connector coming from the flywheel alternator and then disconnect condenser plug and connect a 12 volt battery to the condenser male plug.

 

When I first made this test, I got a strong spark at the spark plug and then I knew it was the bike that did not produce an electrical current or perhaps the electrical current wasn't being at the rectified at the rectifier/controller.

 

I already knew that the condenser was good, so the only thing left on my diagnostic game plan, was the rectifier itself. The strange thing about this test is, there isn't any diagnostic test shown in the workshop manual of the Honda Montesa 4RT.

 

The next test was to test the rectifier/controller with a multimeter setting in diode setup and a diagram showing the electrical connection inside the rectifier. My test showed a bad diode inside the rectifier, but here is the tricky part of my diagnostic test, it only shows poor connection when i push a little on the terminal pins, so sometimes there is connection and other times not !!!!!!!!!.

 

I got a new rectifier/controller and the bike started first time I hit the kickstarter.

 

Here at the end I want to say, be very careful when you connect the 12 volt battery to the wiring harness of the Honda Montesa 4RT - that you didn't make any short circuits if you decide to follow my diagnostic game plan.

 

I hope you will find the root cause to this problem as I did.

 

Best regards

Honda Freak

Edited August 18, 2015 by honda_freak

[thall1]

I have been led to believe that a faulty condenser should not stop the bike running? can anyone confirm this?

[thall1]

its running!...I had a chat with 'Feet up trials sport' and one suggestion was that the idle was too low?! couldn't understand how this would prevent a spark but anyway, it turns out that the day before we did the oil change , my son, who's bike it is, ran the bike up in the garden. As we have been using Gas Gas bikes up to know, he thought that it was running to fast and turned the idle down! it continued to run fine, then he turned it off and that was the last time it was tried to be started until after the service!

 

I try to encourage him to look after his own bikes so cant say too much! - at least I'm now very familiar with 4rt's!!

 

Anyway, many thanks too all those that posted and to 'Feet up' who pointed me to the solution.  

[fred_savage]

had the coil and lead put onto another bike - it works fine.......

 

I'm new to 4rt -so who is this 'well know' specialist?

 

Google Montesa 4RT specialist

 

That will answer your question.............................

 

 

[aussiechris]

That is strange that it showed as no spark.  Perhaps the ECU decided the Throttle Position Sensor was out of range.  Even so, it is supposed to still run just with poor throttle response.  Handy to have one more check (idle speed adjustment) in the fault finding arsenal along with the rectifier possibility from honda_freak.

 

Glad you got it running again.

[sportsawyer]

That is strange that it showed as no spark.  Perhaps the ECU decided the Throttle Position Sensor was out of range.  ....

 

Seemed strange to me too. Also, the idle adjust screw doesn't change the TPS because it doesn't move the butterfly valve. The idle adjust screw changes the opening through an air port that bypasses the butterfly valve.

 

But... it's working, so enjoy the bike.

 

Edited August 23, 2015 by sportsawyer

[honda_freak]

To be quite honest I don't think the trick with idle adjuster screw is the main cause to the missing spark although it seem to work this time.
After have read your first post again, have I come to another conclusion or a theory regarding the missing spark you had experienced.

It has something to do with low engine rotation speed which could be caused by clutch drag. According to the patent document from Keihin Corp. battery-less system
is there a claim regarding "low engine speed " that says if the rotation speed falls below 600 RPM it should abort the startup sequence.

It's just a thought I wanted to share with you.

Best regards
Honda Freak

[thall1]

Dragging clutch is a thought but it was in neutral so I would presume that would rule it out. It did start on the 3rd kick once the idle was turned up - I can't really understand why it works but it does! I may try turning it back down to see what happens......