Engine will not switch off.

[river_bouy]

Hi,
I have a 1984 Suzuki DT50. When I switch the key off on the remote control box, it does not turn the engine off. Just started happening recently. Any ideas? Currently I am disconnecting the fuel and waiting for it to run out of gas which is a real hassle.

Thanks in advance.

 

[James R]

Re: Engine will not switch off.

The key switch in the off position must connect the ignition to ground to shut the motor off. You either have a bad switch or a bad connection. Try disconnecting the main harness plug in the motor, shoot it with WD40 and reconnect and disconnect a few times to clean the contacts.

 

[river_bouy]

Re: Engine will not switch off.

Thanks James R.

I have the manual for this engine but the wiring diagrams in PDF format are unreadable.

What does connecting to ground actually do? Just stop the spark in the cylinders?

 

[DJ]

Re: Engine will not switch off.

This is not an uncommon problem with many outboards.

Disconnect the battery-FIRST, then, disconnect all the major connectors and clean them, re-connect.

"Grounding out" disables the ignition.

 

[James R]

Re: Engine will not switch off.

Grounding out does stop the spark to the cylinders but it does this through an input connection at the cdu. A good used manual can usually be found for little money on Ebay. Granted I have to use a magnifying glass to read the printing and wire colors on the schematics. However, Suzuki generally use the same color codes for most motors. Black is always ground.

 

[Silvertip]

Re: Engine will not switch off.

Before you tear your hair out trying to diagnose this problem, if the engine has a kill switch, start the engine and pull the lanyard. If it still fails to stop, the ignition switch is not the problem and neither is the kill switch. The problem lies in the ignition lead between the engine and control box. you might just disconnect the large engine harness connector at the engine and check it for corrosion. Sometimes just disconnecting and reconnecting it a few times is sufficient to burnish the terminals and everything makes contact again.

 

[river_bouy]

Re: Engine will not switch off.

Great info guys, thanks for the help.

I made sure the main engine wiring harness is cleaned and in good condition. However, engine still won't stop. I will have to dig a bit deeper and make sure all connections in that circuit are good.

I don't have a kill switch on this engine, so the ignition switch itself could still be the problem.

So, when the wire from the magneto is 'grounded' by switching the key 'off', basically the charge from the magneto is running to ground instead of running to the spark plugs, hence no ignition, right?

Thanks again.

 

[James R]

Re: Engine will not switch off.

This is not a Magneto system. This is a CDI system. You have a computer chip with a capacitive discharge ignition. The grounding at the key switch tells the computer to shut the motor down. You can see all this from the schematic in the manual. Best advice is to get a manual.

 

[river_bouy]

Re: Engine will not switch off.

Thanks James R.

Yeah, I have a PDF form of the manual and the wiring diagram is to blurred to read.

I didn't realise the CDI was actually a computer chip, thanks for the tip.

 

[Silvertip]

Re: Engine will not switch off.

The CDI is not a computer chip and the engine is not controlled by a computer (at least not in 1984). While the CDI has some solid state devices in it, that does not make it a computer. And yes, by definition this is still a magneto system since by definition it is self powered. The battery is not required for the engine to run. Power for the ignition is created by magnets in the flywheel spinning past the stator windings. The battery is used only to spin the starter. The engine stops when the "M" terminal is shorted because that shorts the CDI input to ground which stops it from functioning which stops spark to the plugs, which stops the engine.

 

[river_bouy]

Re: Engine will not switch off.

Thanks for the great explanation silvertip.

I always like to understand 'how' things work rather than just following troubleshooting steps in the manual.

 

[James R]

Re: Engine will not switch off.

Silvertip.
In a sense you are correct but to the layman the burnt in chip could be considered a computer chip. It figures out a various variety of conditions and performs accordingly. Needless to say the "Magneto" is not shorted to ground to stop the motor.
Perhaps we are getting a little bit too technical. In any event if the input is not shorted to ground the motor will continue to run.

 

[HVSTRINE]

Re: Engine will not switch off.

I used to have an old chrysler 45hp that would sometimes stick wide open throttle. The only way i could shut it off was by pulling the choke. I know this isn't a solution to your prob but maybe in a pinch til you figure it out you can choke it.

 

[Silvertip]

Re: Engine will not switch off.

Disagree -- a CDI is made up of a collection of solid state devices including diodes, transistor, and chips which more accurately are defined as integrated circuits (not computer chips). They can contain many hundred of these individual components. The CDI is a collection of diodes and transistors and IC's that accomplishes a switching function that breaker points and condensers used to perform. A computer chip by definition has processing power and requires software or firmware and performs a set of instructions based on one or more varying inputs which creates one or more varying outputs. These are two very different characteristics and we should try to use correct terminology.

 

[river_bouy]

Re: Engine will not switch off.

Thanks HVSTRINE, I figured out that the choke cuts the engine pretty quick so I will do that as a temporary measure.

I have a digital voltmeter, is there some way I can use it to test the cut-off circuit?

I am trying to think of some way to do this, but seems hard as I assume the current for this circuit is coming from the magneto (not battery) and when it is grounded it cuts the engine which means the magneto stops and no more power in this circuit?

I suppose I can just check for continuity whilst the engine is off.

 

[James R]

Re: Engine will not switch off.

Riverbouy. The answer to your question is yes. Pull the main plug in the motor and measure using an ohms range on the meter. You are checking the remote control end to see if the switch is functioning. Go between the ground pin, connected to the black wire and the pin connected to the green wire. This should show continuity when in the off position. If it does not then you either have a bad switch or a broken wire. If you show continuity the the problem is at the other end.On the engine side connector go between black and the motor casing. If no continuity the you have a bad connection to ground or the wire is disconnected. If you have continuity then check that the bullet connector found in the Black/red wire feeding into the CD unit is connected properly. Dont use the test meter connected to the Black/red wire.

One last remark for Silvertip. I am pleased that you are so familiar with the make up of CD units however the Suzuki units have adjustment and sensor monitoring capabilities that the basic CD does not. Early computers,those that I had designed, used transistors etc untill our friends,Motorola,TI and Fairchild gave us the and/or and the nand/nor to work with and on from there.
Anything that has an analyctical programming can be considered a computer.
After all, the poor systems used in automobiles are refered to as "Computers".
It's all in the way we understand things I suppose.
This is what these Forums are all about, exchange of ideas.

 

[Silvertip]

Re: Engine will not switch off.

So auto ECMs are not sophisticated in your view? That would be a surprise to those engineers and software folks. I would agree that if one would compare the technology today unsophisticated would be a fair comparison with 1984. Note the term is engine management module (not computer) in the auto industry, even if it has many CPUs as part of the entire system. Without software or firmware, you have a switching system, not a computer sytem.