Mercruise 5.0 non start

Tailsme

I have a 2003 Rinker 312 with 2 Mercruiser 5.0 MPI engines. I have had an ongoing problem with the port engine for some time now, on occasions I will go to start the engine and it just cranks over but will not fire up, the engine will turn and expels air/fuel mixture from the air filer when I stop cranking, there is fuel to the engine, I have a spark and the fuel regulator pressure is correct. There seems to be a timing problem and I have tried changing the coil, crankshaft sensor and fuel regulator with the other engine to no positive results. The strangest thing about this is that I will try to start the engine again after some time (from 1 day to several weeks) and it will then fire up like there was never a problem. This has happened to me on at least 4 or 5 occasions since the summer and although it corrects itself over time there is a problem that I would like to resolve, I never know when this will happen and it does not seem to be consistent with hot, cold or damp weather. I am leaning towards the issue being electrical with a breakdown in a sensor or module that seems to correct itself at times. I have not been able to get a computer plugged into the engine while this problem exists and when the engine fires up again no faults are showing. I also wondered if this could be a distributor issue? It is a mystery to me and if anyone has any ideas on what this could be I would appreciate the input.  

Thanks in advance for any help

Darren

frenchship

This one is for 212 rowboat pretty sure he will come up with good ideas, he is probably the most knowledgable member for this type of problems on this forum.
good luck

rowboat212

You say you've spark, but where have you measured that? 

Case in point: I too lost spark at the end of last season.. I pulled the boot off the coil and measured, and thought "well, that's good".. It still wouldn't start/run.. after a few minutes I checked spark again, but this time by pulling the boot off the dizzy tower.. one look explained it- it was straight up broken filliment.. swapped cables and it fired right up and didn't miss a beat. 

The coil firing is one thing... The fire getting to the tower and then distributed out to cylinders is another.. even if you had one or two wires bad (from the dizzy) the other cylinders would fire, making a rough running engine, but coughing as in running all the same.. this kinda indicates a central problem... 

A new dizzy cap and wireset is never a bad idea, anyway, for a winter project... I rec you swap em out, and pay close attention to the rotor button making sure it's seated properly.. word to wise: the last cap I bought was purchased with screws already in the cap, which weren't the right ones.. I pulled the screws out of the old cap and used them and went about my business... That is where your story points, my friend. 

rowboat212

Thanks for the vote of confidence, frenchship!  

Tailsme

Hey 212rowboat, thanks for the input, I will definitely try your suggestion. Do you think this would explain the intermittent problem of non start and then starting? I think it is worth changing out anyway as you suggest but I never know if my issue has been corrected because the engine seems to correct itself until the next time it wont start. Thanks for your advise and I will definitely change the cap, rotor and cables out, it cannot hurt.

rowboat212

The intermittent starting/running is why I suggest what I did.. especially since you changed camshaft and crank position sensors already.  It points to a central spark issue (north of dizzy) due to no coughing but plain no start.. 

If there are good connections to the pcm and good grounds on that engine, it should at least cough of spark is even partially present.  Check your grounds, and before investing money in wire sets, pull #7 wire and use it as your coil wire, leaving #7 vacant.. I bet it fires and runs rough.. 

luckydog

My 312 did exact same thing today, I couldn't get the starboard engine to start

rowboat212

Revisiting this: I bet your distributor cap is cracked.. I've seen and felt the despair of that precise thing before.. had a heckuva time tracking it down because when it ran it was flawless... 

A crack small enough to not be seen will allow moisture to collect on the points when a hot engine is turned off and slowly cools... A wet distributor flat out won't distribute spark... Until it's dry, or at least partially dry- when just a bit of spark is capable of flash frying a point dry, and then another, and another- and the seconds the engine catches life it's dry, and left a phantom to hunt, and never find... I can't tell you how lucky I was to figure that out, and the crack wasn't visible.. It took using it as a cup to see a drip on the outside.. The evidence? Strange deposits on the points... 

Good luck, sir. 

Tailsme

Hi Rowboat 212, I have only just got round to checking this out and I switched over the main lead from the coil to the distributor with the other engine and sure enough it fired up, but the other engine also fires up with the other lead. I think you have hit on the right problem and I think I will just change the lead and cap and see what happens. Thanks so much for your help, I hope this will resolve my issue.

rowboat212

Sweet... Hope it's that easy!!! Check your block grounding straps too, though... Grounding issues can cause the same thing

MarkB

Drew is da man!

raybo3

Who's Drew???

Tailsme

Hey 212 Rowboat, just wanted to give you an update, today I removed the distributor cap, when I looked inside, there was powder like material around all of the contacts, I cleaned this off with a wire brush and put back on the engine and it fired up straight away. I believe you may be right that there is a very fine crack because this build up would not be there otherwise, it must be moisture getting into the cap to cause this. I cannot see any cracks visually but have ordered a new cap to replace. Thank you so much for your help,

MarkB

Is the crack anything that can be repaired easily like with rubber paint/sealant?

rowboat212

Nope... Anything you do is a bandaide... Replacing is only fix...

The plastic distributes heat fairly evenly unless there is a crack, or something touching it... With a crack, heat will focus there and make deteriorate even quicker... A decent cap is $15 or so... Don't cheap out!!!

rowboat212

That white appearing dust is actually tiny shards of burnt metal... As in electrified... Most times the make a build up on the points or rotor, which are tiny welds... If its wet, even slightly, it won't weld or burn, or run. That dust is evidence of wet... Good job noticing it!!!

Cableguy Greg

212rowboat said:

A decent cap is $15 or so... Don't cheap out!!!

100% agree!!! Somethings are worth the money!!!

MarkB

That's pretty cheap.

ohana

Hello Tailsme. I’m having this exact situation. Did you ever figure out the exact solution?

J3ff

Looks like he got a new cap. 

GMSLITHO

Some caps are cheap my son graduated today the cap he had cost a bundle 

aero3113

GMSLITHO said:

Some caps are cheap my son graduated today the cap he had cost a bundle 

LoL!

Dream_Inn

GMSLITHO said:

Some caps are cheap my son graduated today the cap he had cost a bundle 

My daughter has her last day of high school in 3 days.  I'm not looking forward to paying for that next cap either!   Congrats!!

reneechris14

Paying for the cap isn't so bad as long as they move the tassel over at the end. 

Willhound

Our tassel only cost us 100 G"s. So far. Now she's going post Grad. Another 100 large. She owes me a 342 someday!

GMSLITHO

Yesterday graduation ant today a job interview he seems to think he did good .phys ed teacher .hes been volunteering at the high school helping coach the hockey team got good references from 2 of the teachers just hoping he gets it 

Michael T

Put 250K into account for grand daughter - probably only way she will afford it. Told her to get working. She's in grade 4 LOL!