A Simple Test To Isolate Fuel and Ignition Problems

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  A Simple Test To Isolate Fuel and Ignition Problems

search | FAQ | profile | register | author help

Author Topic:   A Simple Test To Isolate Fuel and Ignition Problems

wldrns1 posted 05-05-2009 06:56 AM ET (US)
You must isolate fuel problems from ignition problems. Then you can look at the failure in better detail. If both fuel and ignition are not the problem, the last possibility is mechanical. You can check ignition and fuel yourself without too much difficulty.
If you or someone you know is comfortable under the hood, buy yourself a simple in-line ignition tester. It connects between the spark plug boot and any good ground. You may need to chip away some paint on the block to get a good ground. One person operates the key, the other looks at the tester. Work safely due to moving parts. Experiment at the dock with the tester with the safety lanyard connected and disconnected and observe the tester at both conditions (with ignition and without). Then go somewhere calm and duplicate the problem. When the failure occurs, immediately check your ignition. Since the engine shuts down completely, checking for ignition at one plug should be enough. Either you have it or you don't.
Is there fuel in your engine mounted fuel filter (if equipped)? At the dock make sure the engine runs then shut it off and check your engine fuel filter to observe how much fuel it contains when you know the engine will run normally. You may need to unscrew the cup or disconnect the hose, depending on your equipment. See your engine owner's manual for details. When the failure occurs, immediatley check for no fuel at the filter to eliminate no fuel delivery for some reason.
Don't assume a self venting fuel cap is not defective. Unscrew it a bit and see if the problem goes away. Watch for spillage.
You also need to know what water looks like in the fuel supply. At home, put some gas in a glass jar and add a small amount of water and observe. Look at it in bright sun to learn what you're looking for. Water problems must also be eliminated. Any real plumbing supply house will sell you a paste that turns bright pink when exposed to water. They use it on the end of a probe to test tanks. Experiment with the gas and water mix glass jar to see.
Some other information that would be helpful include: Does the problem only occur at WOT? What does your tachometer read? Is it always the same RPM? How long before you can restart? Are you bouncing in the waves or on flat water?
If the failure is immediate and your engine has a self protection system (Guardian or Smartcraft) the system may be activating for some reason. A dealer would likely be needed to resolve this. Look for a Mercury Premier Dealer as the Premier designation requires the dealer to be trained and have computer hookup capability to service modern engine electronics.
Good Luck!
jimh posted 05-05-2009 07:43 AM ET (US)
I have been recommending use of an in-line spark tester, too. However the in-line spark tester is inserted in-line with the spark plug. If the spark voltage is strong it will fire across the gap in the in-line tester and the gap in the plug.
20610 LISLE In-line Ignition Spark Tester
http://continuouswave.com/whaler/reference/images/ lisleSparkTester300x191.jpg
adlert posted 05-05-2009 09:27 AM ET (US)
Very nice write-up wldrns1.
I hope you don't mind my adding another few cents worth that I've preached before on this topic. For stationary tests in line testers are good, adjustable air-gap testers are better however because they can be properly set to "load" the ignition system depending on ignition system design specifications. These types of testers are more expensive however and are usually purchased through specialty marine tool outfits. These are the types of testers dealers use (or should be using).
For on the water testing, i.e. being able to conduct an ignition test immediately when the engine starts acting up, an inductive timing light is an excellent way to go. By far the best way in my opinion. You can hook it up and leave it hooked up even with the engine cowling properly fastened down in most cases for increased safety and comfort. When the engine starts acting up, depress the timing light trigger and aim the light at yourself. If the light is going off and steady, you've got a steadily firing plug too.
Leaning around the back of an engine running at high speed while simultaneously tring to shield the sun so you can properly view a spark tester is VERY hazardous. Particularly if not on glass calm water.
wldrns1 posted 05-05-2009 11:20 AM ET (US)
adlert:
Great points however my suggestion for ignition testing away from the dock is to determine either you have ignition or you don't once the engine has stopped. I don't recommend any testing while under way except for those experienced technicians or owners equipped to do it.
Also in my last original paragraph I wrote 'if the failure is immediate'. That should have read 'if the failure is ignition'. Sorry...too early in the morning.
The defective fuel cap venting problem can vary depending on how much fuel the tank contains. Nearly full will cause fuel starvation much faster than a nearly empty tank.

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: A Simple Test To Isolate Fuel and Ignition Problems
wldrns1	posted 05-05-2009 06:56 AM ET (US) You must isolate fuel problems from ignition problems. Then you can look at the failure in better detail. If both fuel and ignition are not the problem, the last possibility is mechanical. You can check ignition and fuel yourself without too much difficulty. If you or someone you know is comfortable under the hood, buy yourself a simple in-line ignition tester. It connects between the spark plug boot and any good ground. You may need to chip away some paint on the block to get a good ground. One person operates the key, the other looks at the tester. Work safely due to moving parts. Experiment at the dock with the tester with the safety lanyard connected and disconnected and observe the tester at both conditions (with ignition and without). Then go somewhere calm and duplicate the problem. When the failure occurs, immediately check your ignition. Since the engine shuts down completely, checking for ignition at one plug should be enough. Either you have it or you don't. Is there fuel in your engine mounted fuel filter (if equipped)? At the dock make sure the engine runs then shut it off and check your engine fuel filter to observe how much fuel it contains when you know the engine will run normally. You may need to unscrew the cup or disconnect the hose, depending on your equipment. See your engine owner's manual for details. When the failure occurs, immediatley check for no fuel at the filter to eliminate no fuel delivery for some reason. Don't assume a self venting fuel cap is not defective. Unscrew it a bit and see if the problem goes away. Watch for spillage. You also need to know what water looks like in the fuel supply. At home, put some gas in a glass jar and add a small amount of water and observe. Look at it in bright sun to learn what you're looking for. Water problems must also be eliminated. Any real plumbing supply house will sell you a paste that turns bright pink when exposed to water. They use it on the end of a probe to test tanks. Experiment with the gas and water mix glass jar to see. Some other information that would be helpful include: Does the problem only occur at WOT? What does your tachometer read? Is it always the same RPM? How long before you can restart? Are you bouncing in the waves or on flat water? If the failure is immediate and your engine has a self protection system (Guardian or Smartcraft) the system may be activating for some reason. A dealer would likely be needed to resolve this. Look for a Mercury Premier Dealer as the Premier designation requires the dealer to be trained and have computer hookup capability to service modern engine electronics. Good Luck!
jimh	posted 05-05-2009 07:43 AM ET (US) I have been recommending use of an in-line spark tester, too. However the in-line spark tester is inserted in-line with the spark plug. If the spark voltage is strong it will fire across the gap in the in-line tester and the gap in the plug. 20610 LISLE In-line Ignition Spark Tester http://continuouswave.com/whaler/reference/images/ lisleSparkTester300x191.jpg
adlert	posted 05-05-2009 09:27 AM ET (US) Very nice write-up wldrns1. I hope you don't mind my adding another few cents worth that I've preached before on this topic. For stationary tests in line testers are good, adjustable air-gap testers are better however because they can be properly set to "load" the ignition system depending on ignition system design specifications. These types of testers are more expensive however and are usually purchased through specialty marine tool outfits. These are the types of testers dealers use (or should be using). For on the water testing, i.e. being able to conduct an ignition test immediately when the engine starts acting up, an inductive timing light is an excellent way to go. By far the best way in my opinion. You can hook it up and leave it hooked up even with the engine cowling properly fastened down in most cases for increased safety and comfort. When the engine starts acting up, depress the timing light trigger and aim the light at yourself. If the light is going off and steady, you've got a steadily firing plug too. Leaning around the back of an engine running at high speed while simultaneously tring to shield the sun so you can properly view a spark tester is VERY hazardous. Particularly if not on glass calm water.
wldrns1	posted 05-05-2009 11:20 AM ET (US) adlert: Great points however my suggestion for ignition testing away from the dock is to determine either you have ignition or you don't once the engine has stopped. I don't recommend any testing while under way except for those experienced technicians or owners equipped to do it. Also in my last original paragraph I wrote 'if the failure is immediate'. That should have read 'if the failure is ignition'. Sorry...too early in the morning. The defective fuel cap venting problem can vary depending on how much fuel the tank contains. Nearly full will cause fuel starvation much faster than a nearly empty tank.