No spark 2003 Mercruiser 5.7 with thunderbolt style ignition

[Karen S]

Our boat would not start last fall, we replaced the distributor pick up sensor. When trouble shooting old sensor, we used a test light on each lead, one had power and the other did not even when we were rolling over the engine. Then we replaced with a new pick up sensor and checked output lead on sensor when rolling over engine and it went on and off as it tripped the sensor, after that engine fired up. We only ran boat long enough to take out of the water. Now this spring, we started up engine to drain antifreeze and motor ran for 5 minutes and then stalled. Now we have no fire and checked distributor pick up sensor and it has power on one side but does not blink on output side when rolling over. It appears that the sensor is defective again. The one we replaced last fall was a sierra brand not OEM. Is it possible we have a bad sensor or is there something else causing the sensor to go bad? Any help would be appreciated.

 

[Fun Times]

Hi there, welcome to iboats!

Is your engine MPI or carbureted? Posting your engine serial number helps us help you better.

If it's MPI (fuel injected) Two main things seem to kill the ignition modules quicker than usual...One is heat and the other is a power spike.

If it's a carbureted, then power spike and a bent rotor wheel will kill them the quickest.

If it's the sensor I'm thinking it is, then Merc OEM would be best. Please post a link or part number to the sensor you bought as well to make sure.

 

[Karen S]

We think the engine serial number is 10243880. It is MPI. He doesn't know what the part number is. He bought it online last year. We are going to get a Merc OEM this time. We just bought our boat last year and are new to boating. Thank you so much!

 

[Fun Times]

We think the engine serial number is 10243880. It is MPI. He doesn't know what the part number is. He bought it online last year. We are going to get a Merc OEM this time. We just bought our boat last year and are new to boating. Thank you so much!

Thanks Karen but that number is a GM engine ID code and won't help find the correct parts needed for your engine model.

The Mercruiser serial number should start with 0M much like something in-between this serial number range only as an example 0M300000 THRU 0M599999

To find the Mercruiser serial number look either on top of the engine stickers or just above the engine starter like these,

 

[Karen S]

I think I found it, OM094034. Can you tell what year it is? We bought the boat last year and the guy told us that two years before, the guy that winterized it did not do it right and ruined the motor so a new one was put in so I don't know what year the motor is. Thank you!

 

[Karen S]

He also had the coil hooked up but not setting in the bracket when he started it last year with the new sensor, would that ruin the new sensor? I am hoping that if we replace the sensor with a new OEM sensor, it won't quit on us again. Thank you!

 

[Fun Times]

Sorry I can't give you an exact date your engine was built but jugging by the serial number, it looks to be in the 2001 era. Typically when it comes to finding the correct parts for your engine model, Merc doesn't really go by year but rather engine serial number breaks/ranges such as you'll find in the following parts catalog for your engine serial number provided above...http://www.mercruiserparts.com/selectSerailRange.asp?doc_nbr=5.7L+EFI++GM+350+V-8++1999-2001

Did you find the number on top of the engine or down by the starter like in the photo above? And do the numbers match as sometimes they'll change the engine block and reuse all the bolt on accessories to make the engine function.

If you really want to know the exact date of the engine you can either call a Mercruiser dealer with the serial number or call/send an email to Mercruiser directly in the following link, https://www.mercurymarine.com/en/us/contact/mercruiser-customer-assistance ...Just hope the engine wasn't reported stolen.:gossip::mod::bolt:

Unfortunately that sensor under the distributor can be sensitive to many things and typically there really isn't an indentation of a failure about to happen as most times, It just goes....Some have reported that the engine may first run rough though. Also there's a chance that the sensor was just lacking quality and went out on it's own as yours wouldn't be the first to read on the boating forums that this sensor went out in a short time frame and they installed a new OEM one and has been fine since. That mentioned, it's advisable to carry an extra one onboard along with the tools to change it if ever needed...As you found out/mentioned above, one of the quickest ways to know if it's working is to use your test light connected to 12v power and touch the negative side of the coil and see if it's blinking or not at engine crank speed. Here's an old example for you but keeping in mind that it's just out of your serial number range. Sensor Failures in MEFI-3 Mercury Distributors Used on V6 and V8 305/350 cid Engines

It's possible the coil not installed properly could have played a role in shorting out the sensor had it touched something or got/gets excessively hot.

Be sure to check that all power and ground cables/wires going to, from and on the engine are clean and tight.

Ensure the distributor housing assembly is clean and seated all the way down to the intake manifold and tight. Ensure the distributor shaft isn't excessively loose, bent, wobbly, etc..

Install a new rotor and turn the engine over checking to ensure the rotor wheel isn't hitting the sensor as it passes through.

Mercruiser recommends putting a small dab of blue Loctite on the shafts keyway and or locating key of the rotor wheel to help keep it from lifting at high RPM. Page 4B-6, http://www.boatfix.com/merc/Servmanl/16/16B4R2.PDF

The latest sensor and rotor OEM part numbers are 13524T1 & 87-892150Q02 or item numbers 5 & 6, http://www.mercruiserparts.com/Show...=80&bdesc=Distributor+And+Ignition+Components

Be sure to tightly connect the black sensor ground wire to the rear of the engine ground stud where the battery cable normally connects to... Doing this should give you the best results plus it will give you the chance to inspect the battery ground cable condition.

Hope this helps, good luck.

 

[Karen S]

Thank you! I found it down by the starter. You have helped us a lot! Thank you! We should have it running soon!

 

[Karen S]

We put the new pick up sensor in, it tried to start and then didn't. Checked the fire and we are not getting any. Is there something else we need to do? Thank you again!

 

[Karen S]

Can I test my distributor pick up sensor by checking the output side with my test light and should the light go on and off as I turn over the engine? I know the input side lights up my test light steady while rolling over the engine.

 

[Karen S]

Just saw this again, "As you found out/mentioned above, one of the quickest ways to know if it's working is to use your test light connected to 12v power and touch the negative side of the coil and see if it's blinking or not at engine crank speed." We will try that tomorrow. Thank you!

 

[JaCrispy]

Disconnect the shift interrupter switch, then diagnose if it still doesnt start.

 

[Karen S]

We will try that. Thank you!

 

[Fun Times]

Disconnect the shift interrupter switch, then diagnose if it still doesnt start.

Thanks JaCrispy and yes that's a good idea of one test to try doing on an alpha stern drive package.

In this case though, Karen S has a Bravo stern drive which doesn't utilize the shift interrupter switch. (MERCRUISER MEFI3 3" RISERS 5.7L EFI BRAVO)

Karen S, How are you testing for no spark?

If you also have a timing light, connect it to the coil wire running to the distributor cap. While the engine's cranking over, check to see if the timing light flashes. If the test light blinks at the coil but no spark/flash from the timing light = bad coil.

 

[Karen S]

A spark plug grounded to the engine is how we tested it. We do have a timing light and will do that tomorrow. Thank you!.

 

[Karen S]

Update: From further trouble shooting with info given here, checked negative wire on distributor by hooking test light to 12 volts, the test light goes on and off as it should and motor tries to start and also at same time, timing light hooked to coil wire light flashes normal. When I remove the test light from negative side of coil, it fires a couple times and then quits firing. Also, something odd, when we touch the test light to the negative terminal, fuel pump comes on for a brief time just like we are turning on ignition switch. We checked the ground wires and they seem to be grounded good. We also tried another coil and coil wire and get the same thing. If we hook our test light that is connected to 12 volts source back to the negative on the coil, it fires again and tries to run. Any thoughts would be appreciated.

 

[Karen S]

It sounds like a ground problem, would it be feasible to run a ground wire from the battery to the back of the engine where the sensor is grounded?

 

[Karen S]

Update: tried the new ground wire and it didn't work. Checked the fuses for ECM and they are good. Checked the throttle position bypass loop and that was good. Does have power to the input side of the pick up sensor and positive side of the distributor. We did call a marina and talked to Mercury and tried the things they said which are these things posted.

 

[Fun Times]

From further trouble shooting with info given here, checked negative wire on distributor by hooking test light to 12 volts, the test light goes on and off as it should and motor tries to start and also at same time, timing light hooked to coil wire light flashes normal.

As long as you have a continuous (very fast) spark from the timing light then you have spark... if it goes away then something is wrong. If it's continuous then move the timing light connector to all 8 spark plug wires and check for a timed flash as the engine turns over a few times. If the light don't flash properly then you have a cap, rotor or wire problem.

If the light stays flashing then you may have a fuel problem.

When cranking engine over, can you see the tachometer (RPM gauge) moving up to around 400 RPM?

Have you tried disconnecting the gray wire off of the back of the tachometer (RPM gauge)? An intermittently failing tach gauge would cause no spark too.

When I remove the test light from negative side of coil, it fires a couple times and then quits firing.

What stops firing, the engine from starting or the timing light?

 

[Karen S]

We do not have a tachometer. The only time we have fire is if we have the test light connected to 12 volts and touching it on the negative coil terminal. Everything quits firing when we remove it.