Jump to content
Sign in to follow this  
ChappyMike

MerCruiser 5.0 Stalling / Not Starting

Recommended Posts

Here's a little backstory...

2003 Mercruiser 5.0 EFI with Bravo 3...approximately 480 hours. Boat is new-to-us as of April, freshwater only, and we've only had it out three times. Boat ran fine during 30-40 minute sea trail. Brought it home and launched on our home river. Posted on here a few months ago after our first outing about the port motor on my 280 Signature running fine but then not starting. IAC had gone out on the starboard motor and was replaced before I bought it. Posted on here and on the Facebook page and the general consensus was to replace the port IAC as well (when one goes, the other isn't long behind, right?) Replaced with an aftermarket one (not OEM). Boat ran fine on the next trip.

Fourth of July weekend, we did a little cruise on the boat and I noticed the RPMs on the port engine were dropping about 500-800 RPM while cruising. It would be a quick hiccup, then back normal for 10 seconds, then hiccup again for 1 second, then back. Didn't really feel it while cruising along (it was a short 5-10 minute cruise) and figured maybe it's a funky gauge issue. Dropped anchor, enjoyed the fireworks for a few hours, then low and behold, port engine wouldn't start again. Starboard fired right up, so we motored in on one and about a 1/4 mile from the marine, the port one finally lit up and ran. Idled back to the dock, shut down. Next day, engine fired up as normal at the dock, RPMs were fine, like nothing was wrong. Didn't take it out to test, but let it run for about 10 minutes at the dock. No issues.

TODAY'S TRIP. Starboard fired right up. Port didn't want to stay lit. Would crank and crank and finally catch, rev once or twice, then die out. Did this a few times and after about 6 or 7 tries, I was able to keep it on for about 5 minutes before RPMs fluttered and it died. Tried starting again and no luck. Decided not to waste the day at the dock so we motored right out of the marina on one engine and dropped anchor in a cove around the corner from our inlet (at least we were floating, right?). On the way out I was able to get the port one started again but the RPMs were fluttering again and this time I could feel it. Cruising at about 1500 RPM (both engines on), I could physically feel the boat slow when the RPM would flutter. Shut it off, dropped anchor, and enjoyed the day. Went to leave after a few hours and both fired up just fine. Idled back in and after 5 minutes (about half way back) it started fluttering again. I just kept is at idle, and as we pulled in, the port one fluttered and died again.

Any ideas what this could be? Could it be the aftermarket IAC is no good? I've already got a OEM MerCruiser one on the way to try out next. Anything else to look for? Boat was serviced right before purchasing and ran fine during my sea trial. Compression tested and all ok. Starboard engine purring great. When the starboard was running problem free during sea trial and our first outing, it sounded great too. Now I'm too nervous to go farther than a few miles just in case we have to get back on one engine. 

Any thoughts or help would be great! Thanks in advance!

Share this post


Link to post
Share on other sites

The IAC won't cause the flutter and shut-down while underway. It's an idle air control valve that adjusts the amount of by-pass air around the throttle plate during low engine RPM, to compensate for different engine loads. It's a guess at this point but I would take a close look at the distributor cap and rotor. Moisture can leach out of a cracked cap upon warm-up and bad things happen. Then after it sits a while, the thing works fine. Pull the cap and turn it over looking for carbon tracing and free moisture. Next suspect would be the ignition module itself which were problematic in that era. Spark coils too can break down with heat. Lastly, fuel pressure gauge at the fuel rail, and a test ride. I still think it's an ignition issue so I would start there.  W

Share this post


Link to post
Share on other sites
5 hours ago, Wingnut said:

The IAC won't cause the flutter and shut-down while underway. It's an idle air control valve that adjusts the amount of by-pass air around the throttle plate during low engine RPM, to compensate for different engine loads. It's a guess at this point but I would take a close look at the distributor cap and rotor. Moisture can leach out of a cracked cap upon warm-up and bad things happen. Then after it sits a while, the thing works fine. Pull the cap and turn it over looking for carbon tracing and free moisture. Next suspect would be the ignition module itself which were problematic in that era. Spark coils too can break down with heat. Lastly, fuel pressure gauge at the fuel rail, and a test ride. I still think it's an ignition issue so I would start there.  W

Great thanks for the heads up. I'll start by looking at the distributor cap/rotor and seeing whats going on there. Are these pretty generic parts? For a 2003 5.0 MPI, any idea what the part number would be or are they universal?

Same goes with ignition module - are these somewhat uniform? What would symptoms of a bad module be? 

Should I rule out the fuel filter or could this be suspect too? 

Thanks for your help!

Share this post


Link to post
Share on other sites
3 hours ago, ChappyMike said:

Great thanks for the heads up. I'll start by looking at the distributor cap/rotor and seeing whats going on there. Are these pretty generic parts? For a 2003 5.0 MPI, any idea what the part number would be or are they universal?

Same goes with ignition module - are these somewhat uniform? What would symptoms of a bad module be? 

Should I rule out the fuel filter or could this be suspect too? 

Thanks for your help!

If it looks like the unit on the attached drawing, then the cap is the same as a 1997 Chevy 5.7 pick up as is the rotor. I like the NAPA gold ones as they have brass contacts. The module is marine specialty item as indicated. I don't believe in throwing parts at the thing and before I replaced the fuel filter I would buy a cheap fuel pressure test gauge and hook it up to the fuel rail to determine if you even have a fuel delivery problem.   Could be a primary fuel pump, secondary pump, fuel pressure regulator, collapsed fuel line, bad anti-siphon valve, or filter. Better yet, it could be none of those things and a simple pressure test will tell you for sure.    W

 

http://www.marinepartsplus.com/catalog/mercruiser/serial/5.0L_MPI_ALPHA-BRAVO/884717003/12840-50

 

Share this post


Link to post
Share on other sites

PROBLEM SOLVED. Checked distributor cap and all dry. Even looked relatively new, along with newer wires. Reassembled and still couldn't get it to start/stay lit. Checked all plugs, fuses, and connections and all good. Decided to switch to fuel system and started with the easiest thing first. New fuel filter. BINGO. Fired right up, stayed lit. We put about 3 hours of run time on it yesterday and it performed like a champ. Fired up each time. RPMs rick solid. Cost me a whopping $12.

My other question is - does anyone know the part number or where to buy the in-line filter? Looks like each engine has one and it's a simple canister maybe 4-5" tall and about 2" across. Hose goes in with a hose clamp and hose comes out with a hose clamp. Couldn't find any info on it and the one West Marine tried to sell me didn't look right. Figured I should replace these as well so I know all fuel filters are new at the same time.

Thanks!

Share this post


Link to post
Share on other sites
1 hour ago, ChappyMike said:

PROBLEM SOLVED. Checked distributor cap and all dry. Even looked relatively new, along with newer wires. Reassembled and still couldn't get it to start/stay lit. Checked all plugs, fuses, and connections and all good. Decided to switch to fuel system and started with the easiest thing first. New fuel filter. BINGO. Fired right up, stayed lit. We put about 3 hours of run time on it yesterday and it performed like a champ. Fired up each time. RPMs rick solid. Cost me a whopping $12.

My other question is - does anyone know the part number or where to buy the in-line filter? Looks like each engine has one and it's a simple canister maybe 4-5" tall and about 2" across. Hose goes in with a hose clamp and hose comes out with a hose clamp. Couldn't find any info on it and the one West Marine tried to sell me didn't look right. Figured I should replace these as well so I know all fuel filters are new at the same time.

Thanks!

The inline filter you see is likely not an OEM item, and was probably added by a previous owner to solve a fuel contamination issue. A picture of it would help us know for sure, but Merc does not hose clamp filters.  Either take it to a place like NAPA and match it up, or think about doing away with it altogether and just rely on the OEM fuel/water filter separator. Carry a spare.  W

Share this post


Link to post
Share on other sites

IMG_4812.JPG.882d0b915bef8c3e3f5ebfda249a9ca6.JPG

 

Here's a photo of the inline filter. 

The one West Marine sold me (after giving them my engine serial #) was different and had screw-on fittings at the end. If these are not OEM and not needed, I may remove as you said. One less thing to go wrong.

Thanks!

Share this post


Link to post
Share on other sites

ANOTHER update...Problem was NOT solved!

Took the boat out again a few weeks ago and had the same issue, got up on plane then the starboard engine kept cutting out. Sounded fine when running, then RPMs would drop to 600 then go back to 3500, then drop again. Eventually, they would keep fluttering and die out. Jumped down in the engine room and looks like there is a timing sensor on the lower part of the motor/crankshaft that runs up the front of the motor and ties into a main engine wiring harness. Well, the wires, which are wrapped in the plastic loom, were rubbing on a pulley. It must have been rubbing for a while because it wore through the plastic loom and was rubbing on the wires directly, going THROUGH the protective coating on the wire and causing them to short. This short, being a sensor wire, was throwing off timing to the engine and causing it to cut out/stall.

Lots of poking around through this whole process but glad that it was a relatively simply fixed. I've got the wires taped up, the loom taped up, and everything zip-tied out of the way. Been running perfectly since.

Thanks for all your help along the way! 

Share this post


Link to post
Share on other sites
12 hours ago, ChappyMike said:

ANOTHER update...Problem was NOT solved!

Took the boat out again a few weeks ago and had the same issue, got up on plane then the starboard engine kept cutting out. Sounded fine when running, then RPMs would drop to 600 then go back to 3500, then drop again. Eventually, they would keep fluttering and die out. Jumped down in the engine room and looks like there is a timing sensor on the lower part of the motor/crankshaft that runs up the front of the motor and ties into a main engine wiring harness. Well, the wires, which are wrapped in the plastic loom, were rubbing on a pulley. It must have been rubbing for a while because it wore through the plastic loom and was rubbing on the wires directly, going THROUGH the protective coating on the wire and causing them to short. This short, being a sensor wire, was throwing off timing to the engine and causing it to cut out/stall.

Lots of poking around through this whole process but glad that it was a relatively simply fixed. I've got the wires taped up, the loom taped up, and everything zip-tied out of the way. Been running perfectly since.

Thanks for all your help along the way! 

CPS, Crankshaft position sensor. Yea, that thing is kinda critical. Sorry it took so long to find but at least it was something you could sink your teeth into. Intermittent electrical issues are the worse.  W

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×