502 Merc cuts out over waves

[nova_gts]

A friend of mine has a Baja 27 with a fuel injected 502, he is having an issue where when he will hit a wave the engine will cut out completely and come back on a split second later. It also is bogging down and will not run full throttle. Any suggestions?
He had the motor pulled and replaced last year as well as replaced the distributor cap, it was doing the same thing before and after.
Any suggestions as to where to start would be appreciated.

 

[Bondo]

Re: 502 Merc cuts out over waves

Ayuh,... A Shake, Wiggle, Pull Test....

Shake, Wiggle,+ Pull each, 'n every wiring connection in the igntion,+ fuel circuits...

 

[commander315]

Re: 502 Merc cuts out over waves

Sounds like an electronic fuel injection problem

 

[nova_gts]

Re: 502 Merc cuts out over waves

One other person who listened to it said maybe try the fuel pump?
Would this be the symptoms? Not sure how easy that would be to get to either?

 

[nova_gts]

Re: 502 Merc cuts out over waves

oh yea incase it matters:
boat is a 96
motor is 502 magnum mpi

 

[nova_gts]

Re: 502 Merc cuts out over waves

Would electronic fuel injection be the "brain" going bad? or is there another module?

 

[Bondo]

Re: 502 Merc cuts out over waves

he is having an issue where when he will hit a wave the engine will cut out completely and come back on a split second later.

Ayuh,... That, I believe is an Electrical issue...

It also is bogging down and will not run full throttle.

And That is probably a fuel delivery issue....

Being a 'puter driven motor,... Your Bud needs some Diagnostics done.... There's No Easy Fix Button....

 

[keithH]

Re: 502 Merc cuts out over waves

A little more info (I'm the friend mentioned)...

Had a similar problem with the cutting out last season after the (sea) water pump fried, caused overheating, replaced pump. To try and get rid of the engine cutting out problem, I replaced the distributor cap/rotor which had some wear and corrosion. Overheating (likely) caused the heads to slowly warp, which later (likely) caused two blown head gaskets. I did not get the plug wires right at first, which likely contributed with the overheated/warping heads, accelerated the blowing of the head gaskets. Then piston hydrolock stopped engine from turning over, which caused flywheel gears to strip when running starter to troubleshoot -- the inability to turn engine over and drive out water resulted in rust inside engine. So, I had the engine pulled, machine shop did minor rebuild on the short block (new rings/bearings/hone) and put engine back in boat. Altogether no fun whatsoever, finished very late fall, considered driving the rig off a cliff somewhere.

ANYWAY, this season starts. Drop the boat in, starts fine, idles fine. I try to get on plane and the engine boggs down, slow to get out of the hole. I pull back to 2/3 throttle to get on plane, the engine smooths out and has more power, and makes a distinct hissing sound (the hiss I recall as typical) while slowly getting on plane and thereafter. Pushing to higher throttle and/or attempt to pass 4000 RPMs, I lose the hissing sound, and do not get more power, possibly even a power reduction (bogging down). When there is chop, the engine will cut out very briefly (like 1 sec or less). RPM drops from 3500 to 2000, then goes right back up.

Since the engine cutting out seemed kinda like the kill switch, I bypassed it. The immediacy of the drop and return seems to me to point to electrical vs. fuel, but I?m open for opinions on that one. Just seems like if the fuel pump was shutting down, it would happen more gradually. I did ensure the fuel filter/separator did not have any water in it. I tried banging on any electronic components I can locate in the engine compartment to see if anything can cause the problem to occur at idle, nothing.

Loose connection seems likely, but since the motor was mostly taken apart, the likelyhood of the same thing to be reconnected loosely seems less likely. I suppose a wire could be mostly severed in a not-noticeable place, but which wire(s) would be likely candidates for this? I am also thinking I have more than one problem. Possible timing issue? Sorry, lots of info, but not sure what little piece of info is significant.

 

[smarks]

Re: 502 Merc cuts out over waves

Have you looked at the Ignition switch and fuse for loose wires?
Steve

 

[keithH]

Re: 502 Merc cuts out over waves

Have you looked at the Ignition switch and fuse for loose wires?
Steve

Will check for that, possibly even bypassing the ignition switch to test. Since the kill switch is not the problem, I suppose I can hook that back up and temporarily use that to turn ignition on/off.
I actually got my mechanic to come over for a housecall to try and troubleshoot the problem. When he arrived, I thought my batteries were dead (would not start). A few tests later it looked like my starter was bad, removal of starter confirmed it is full of rust and inoperable. Glad it started the last time I brought it back in! Got new starter, needs install (upside down pain in the rear and elsewhere).
Starter was a year new - getting water from somewhere. I know others (not with a Mercruiser) who have had water in the flywheel housing, which spins water up into the starter each start. I think that if you get water in the housing, there is no way for the water to get out? Something to try and determine when putting in new starter - i.e., is there water in there? If there is water in the flywheel housing, I may have to drill a hole in the bottom of the flywheel housing to let it out (and I am sure it will be challenging to get to). Thoughts on that?

 

[wire2]

Re: 502 Merc cuts out over waves

To definitely determine whether it is or isn't the ignition cutting out on a wave, I suggest the following;

Temporarily connect a typical automotive relay with the coil to ground, other side to ignition coil+. Supply the relay common with +12 from the purple harness wire or battery. Connect the normally closed terminal to a piezo buzzer (or other 12v sounding device). Ground the 2nd terminal of the piezo.

IF something cuts the 12v to the ign coil, the relay will drop out, sounding the buzzer.

Or, a simpler method;
connect a small 12 v lamp to ign coil+ and engine ground. The lamp will be on when the engine is running.
If the lamp goes out when the engine dies, it's ignition related.

 

[smarks]

Re: 502 Merc cuts out over waves

Please let us know what you find out, very curious.
Steve

 

[keithH]

Re: 502 Merc cuts out over waves

To definitely determine whether it is or isn't the ignition ...
connect a small 12 v lamp to ign coil+ and engine ground. The lamp will be on when the engine is running.
If the lamp goes out when the engine dies, it's ignition related.

Thanks Wire2- this is a great idea. Unfortunately, after installing my new starter (and getting sent out of town for two weeks for work, UGH!), when I tried this (connected to the 12 input to the ignition coil) the problem occurred and the light remained on and bright. So, it appears the ignition coil is getting consistent power.

I managed to borrow an engine interface cable and software, so I have a lot more information (although it remains to be seen if any of it is useful).

I ran the Diacom Marine software for GM-Delco MEFI 1 ? in mode 1, and got the following data:

Code 43- Electronic Spark Control Malfunction
Code 42- Electronic Spark Timing Malfunction

So, these need to be addressed, perhaps this is the problem, or perhaps this is in addition to the problem.
Not sure how universal the code numbers are, but I found this description of the error codes: Buick Regal
Under 42 it says: An open or ground in the EST circuit will stall the engine and set a Code 42. The engine can be re-started but it will run on ignition module timing.
Under 43 it says: Loss of the ESC signal to the ECM will cause the ECM to constantly retard the timing to its maximum. This results in sluggish performance and a Code 43.

The sluggish performance fits pretty well, but again, I don't know how universal the GM codes are.

I was able to get the attached graph (I hope it attached?) that shows two examples of the moment the motor cuts out momentarily.

These before/after data values changed, and may mean something to someone:

Engine Speed drops from 3568 913 RPM
Manifold Absolute Pressure increases 26.2 29.4 inHG
MAP Sensor Voltage increases 4.14 4.8 VDC
Injector Pulse Width decreases 8.6 7.1 ms
Spark Advance drops 28.48 14.77 Deg
Fuel Flow Rate drops 13.33 12.33 GPH

 

[keithH]

Re: 502 Merc cuts out over waves

Please let us know what you find out, very curious.
Steve

OK, it seems I have found the problem - short answer is when demonstrated at sea for my mechanic, he immediately said the engine was leaning out because of a fuel problem.
Even though it was less than a year old, I replaced the fuel filter/water separator (checked the contents in an old pickle jar and there was no water, fuel seemed clean).
Mechanic stated the first place he would look is the Vapor Separator Tank, since it can "get gunked up" and clogged. Seemed like an easy thing to check for, so before taking it in to the shop, I decided to go ahead and clean it out. I unscrewed the 6 phillips bolts, and found what I thought to be moderate debris clogging the fuel screen inside the VST chamber. A little brake cleaner to clear the screen, reassemble, and the engine runs like a champ again! Can't say for sure if it was the debris in the VST fuel screen or the fuel filter (or both?), but the problem appears to be correctly identified as lack of fuel and is now fixed.

 

[Don S]

Re: 502 Merc cuts out over waves

Glad you got it fixed, I would like to ask one question/comment though.
Did anyone ever remove the engines water separating fuel filter, pour it's contents out, then reinstall the filter back on the engine? If so, that is how the debris got past the filter.
When the filter is emptied, the last contents of the filter may not get washed out of the filter, but they can get washed to the clean side of the filter.
That is why a filter, once removed and emptied should never be reused.

 

[keithH]

Re: 502 Merc cuts out over waves

Did anyone ever remove the engines water separating fuel filter, pour it's contents out, then reinstall the filter back on the engine? If so, that is how the debris got past the filter.
.. a filter, once removed and emptied should never be reused.

OK, now I feel quite chastised, since my answer is yes, I did indeed dump the contents and reinstall the fuel filter/water separator on more than one occasion. I had an incident a while back where the filter performed its water separating job properly, so much so it filled with water, after which the engine quit and would not start. When I dumped the contents into the above-mentioned pickle jar, it was immediately evident there was significant water in the filter. I reinstalled and all was well at the time, and have checked on occasion to see if water was accumulating again.
It seems the checking for water is a good idea, but I needed to follow through with "and install a new filter"
Thank you for the insight as to my root cause, so I know to never reuse a fuel filter again. Good news I already have a spare (bought two), so I am ready should I need to remove the filter for some reason, or have one for the next routine change.
How often should that be? annually?

 

[Don S]

Re: 502 Merc cuts out over waves

Annually at least. Since you have been having water problems, maybe more often. When you get to changing clean filters, move up to longer periods of time between. But never more than a year.

 

[HT32BSX115]

Re: 502 Merc cuts out over waves

You might also consider having a look in the fuel tank during winter lay-up etc.

There might be enough water in the tank that it's starting to get picked up and sent to the filter. Good thing the filter is preventing the contamination from getting into the fuel injection system!!