4.3 Mercruiser won't start getting spark

[BugsyK]

I have a 2003 4.3 Mercruiser carbureted motor with the Thunderbolt V ignition. Just had it out 2 weeks ago and it ran fine. Tried to start it this morning but it runs for about 2 seconds and shuts off. I put a timing light on the plug wires to check for spark and it seems to be producing spark. I shot some quick start in the caburetor and got nothing. Any help is appreciated.

 

[Haut Medoc]

Re: 4.3 Mercruiser won't start getting spark

Welcome to iboats Sounds like a fuel issue.....Did you try pouring a little gas into the carb.? Will it start then? Sounds like a bad fuel pump to me.....JK

 

[Don S]

Re: 4.3 Mercruiser won't start getting spark

If you can crank it over and it will start and run for a few seconds then stop, you may have a bad oil pressure switch that controls the electric fuel pumps on Mercruiser engines.<br />They are designed for the pump to run while the engine is cranking and once oil pressure builds up, the fuel pump gets power through the oil switch. This way if the engine dies the fuel pump doesn't keep pumping gas if the switch is still on.<br />#5 is the switch I am refering to.<br /><br />

 

[BugsyK]

Re: 4.3 Mercruiser won't start getting spark

Thanks for the help guys. I tried pouring gas into the carb but still the same result. Where is the oil pressure switch located and can it be tested? Or should I just replace it and give it a try?

 

[Haut Medoc]

Re: 4.3 Mercruiser won't start getting spark

Follow the purple wire......Check your connections & switch......Don is probably right on.....Time for the DVM & some testing ....JK

 

[Don S]

Re: 4.3 Mercruiser won't start getting spark

It's real easy to test the pump. The purple wire is hot (12V) any time the ignition switch is on. Just disconnect the 2 wires from the oil pressure switch and hook them together with the ign. switch on. You should be able to hear the pump run with the wires together. If you can, see if it will start and keep running.<br />You may have it flooded from dumping all the gas in the carb.<br />If you are getting spark, open the throttle to WOT and crank the engine (Don't pump the throttle as that just adds more gas)<br />The switch is located over the block oil filter housing. Port side a few inchs above the pan on the back of the engine.

 

[BugsyK]

Re: 4.3 Mercruiser won't start getting spark

Well, I replaced the oil pressure switch and put a new fuel filter on. Still won't start. I even tried having my wife turn the engine over while I sprayed quick start in the carb, still no go. By the way thanks for your help so far.

 

[Don S]

Re: 4.3 Mercruiser won't start getting spark

How sure are you that you are getting spark? And stop using that starting fluid on the engine before you destroy it. If you are getting spark and gas and the engine has compression, it will start. No need for starting spray.<br />Pull the coil wire out of the distributor cap and hold it about 1/2" from a good ground while you crank it and see if you have spark.

 

[BugsyK]

Re: 4.3 Mercruiser won't start getting spark

Don,<br /><br />I'll try coil wire but several different locations on plug wires and coil wire were firing a timing light. Thanks again for your help.

 

[Don S]

Re: 4.3 Mercruiser won't start getting spark

When you operate the throttle, does gas squirt from the 2 accelerator pump jets in the carb?<br />Do you have the TKS system on your engine?<br />Better yet, what is the Merc Serial number of your engine.<br />Even though the spark may be firing a timing light it may not be firing the plugs. Have you done a tuneup lately (New Sparkplugs????)

 

[newport dave]

Re: 4.3 Mercruiser won't start getting spark

Sometimes after sitting for a few weeks the needle will stick to the seat in the carb and not allow fuel to enter the float bowl. You can tap on the carb a few times with a small hammer or something, sometimes that will free it up.<br /><br />Dave

 

[THE BEEF]

Re: 4.3 Mercruiser won't start getting spark

BUGS:<br />It doesn't take much voltage to fire a timing light.<br />The clamp you put on the spark plug wire checks for a magnetic pulse when the plug fires.This pulse triggers the light to fire from high voltage in the guns circuit. A weak spark will fire the gun.I believe this unit fires at a much higher voltage then the old units. What is the plug gap on this engine? The larger the gap the higher the voltage needed.<br />Hope you find it. Let us know. <br />The Beef

 

[BugsyK]

Re: 4.3 Mercruiser won't start getting spark

Don, What is the TKS System?<br /><br />Dave, I'll try the hammer. Softly right (just kidding).<br /><br />Beef, you are right. I'm used to working on old cars that don't use such high voltage.<br /><br />The serial # is OMG628618, plu gap is 0.045 and it has a Thunderbolt V Ignition.

 

[Don S]

Re: 4.3 Mercruiser won't start getting spark

It's called Turn Key Starting (TKS) and your SN doesn't have it, so it's not a concern.<br />Do check the spark, also pull the plug wires off the spark plugs and check to see if the spark will jump a 1/2" gap there also (just stick a well insulated handled phillips screwdrive into a plug wire and hold the shank next to a ground)<br />The problem I see here is by using the starting fluid spary, it should have fired and tried to run and probably diesel backwards some, gas or no gas. But you apparently have nothing at all, or you just failed to mention it.

 

[Fishermark]

Re: 4.3 Mercruiser won't start getting spark

Hi BugsyK,<br />Here is a link showing a chart for troubleshooting the Thunderbolt V ignition. It is on page 1C-9 of the document. Troubleshooting<br /><br />Hope it helps!

 

[BugsyK]

Re: 4.3 Mercruiser won't start getting spark

Right Don, I got nothing at all no dieseling, nothing. I just put the screwdriver in the coil plug wire and it jumped over to the exhaust manifold. I'm beginning to get concerned that its something major but last time I took the boat out it would go 45 mph or better. I'll try the plug wires next.

 

[Don S]

Re: 4.3 Mercruiser won't start getting spark

I doubt it's major at this point, especially since you said it started for a couple of seconds. <br />The first step in troubleshootin now is to isolate the problem to fuel, ignition, or compression. And I assume (Stupid thing for me to do) that it sounds normal while cranking so you probably have compression.<br />Pull the spark plugs and have a look at them also. Are they wet with fuel (or water) dry, black, tan, look like new, what ????????

 

[BugsyK]

Re: 4.3 Mercruiser won't start getting spark

OK, I checked 2 of the plugs, they are getting spark. The plugs are black like it's been running too rich. Here's the weird thing; when I removed the plug at the back of the head it released alot of air. Never had that happen on my car motor before. Is this air that went into the chamber and did not fire because it didn't get spark?

 

[Don S]

Re: 4.3 Mercruiser won't start getting spark

OK, we will say for the moment you have spark to all eight.<br />How about an answer to the question I asked earlier, "When you operate the throttle, does gas squirt from the 2 accelerator pump jets in the carb?"<br />Have you tried pouring a couple of ounces of gas down the throat of the carb (then put the flame arrestor back on) and try to start it. NO Starting Fluid.

 

[BugsyK]

Re: 4.3 Mercruiser won't start getting spark

I'll have to check the carb jets tomorrow. It's dark here now. Thanks for all your help today Don. I can't express how much I appreciate your time.