MCM 3.0 keeps frying ign modules

[Delmagtech]

Installing old distributor for that AC test now. Really don't want to smoke another module. It's been sitting now for over an hour. Hopefully it'll start. If not, I'll call it a day and try again tomorrow. Just so happens there's an alt shop right up the street...

 

[Delmagtech]

Well, it's back to original, and I can't get it to hit a lick. I hooked up a battery charger and turned it over longer than I probably should have. I had my meter set to AC and hooked to the battery at the same time, and I was seeing about .12vac, but at one point while cranking it spiled to 20vac. Not sure how much that info means with a 20vdc charge coming in at the same time. I'm tempted to pull the alternator now and just have it tested tomorrow, but I might just come back tomorrow when I know it'll start.

 

[Delmagtech]

I noticed the other day, that with a battery charger connected, the boat would run 3 times as long before quitting. I wonder if that's because with a charger, the alternater wasn't really being called on. About 30 seconds after unplugging the charger, it quit.

 

[glenn property of pam]

It is interesting. Might be worth a few bucks and the effort to have it tested. I wouldn't have expected to see a large ac reading while cranking then again ive never tried to test one while cranking.

 

[Delmagtech]

Well, shoot. Alt shop just called to say there's nothing wrong with it. I think I'll still check it again myself this evening, once i get it back on. He didn't seem too motivated...

 

[Delmagtech]

I spoke with him directly. He said when the alternator was under a full load, it was making .48 vac. He's of the opinion that's acceptable. You guys concur? I thought I read a mercruiser bulletin yesterday that said .25vac was max, but I can't find it again to save my life. Maybe it said 2.5vac.

 

[Delmagtech]

Well, I found the service bulletin. It says below .25vac is good, above .25 is bad. That's while testing in the boat at above 1000 rpms with a fully charged battery.

http://www.marinemechanic.com/merc/distributors/mercurymarine/sterndrive/testingalternators.PDF

The alternator shop up the street said he saw .48vac, but that was with the alternator charging at full load. Point being, I wouldnt see .48vac if I go bolt it back up and do the test.

I should be excited that this is the root of my problem, but my gut still says otherwise.

 

[Delmagtech]

I hope you guys don't mind me babbling on here...

As noted above, I don't have a warm fuzzy. There's another alternator shop 10 miles up the road. So I called the guy and shared this info with him. He was interested in discussing and he'll get my future business. Here were his thoughts...

He said he's never tested an alternator that didn't make close to .5vac whilst charging at 100% capacity. He agrees that the mercruiser bulletin test wouldn't show this much current because it won't be charging anywhere near that hard. Basically, he also, feels there's nothing wrong with what my alternator is doing.

He had another take that I thought was interesting. He suggested that poor plug wires or a cracked spark plug could be putting some of that high volt spark back into the block, and hence, into the module, overheating and popping it. I've never heard of that, but it makes some sense.


All this makes me feel good that I have parts to basically replace everything from the spark plugs back. Its clear that I'm not ever going to find a specific AHA moment that will prove just exactly what was going on.


With two guys telling me that these alternator results are very normal, I'm inclined to leave it. If you guys have a differing opinion, I'd love to hear it. The battery is fully charged - I'm going to reinstall the alternator, run it at 1100 rpms, and test it with my own meter, just for piece of mind. Thanks for reading.

 

[alldodge]

Have you check the resistance of your coil, if not get an ohm meter and measure the primary and secondary resistance. Most coils will have a resistance reading of about .7 - 1.7 ohms for the primary winding and 7,500 - 10,500 ohms for the secondary winding.

Primary across the + and - connections
Secondary across the + or = connection and the center coil contact

 

[glenn property of pam]

.5vac sounds ok at full load. If the diode had failed it would be way higher.

 

[glenn property of pam]

this site has coil and module test procedure I know that you have changed out the parts but how about doing the pick-up test from the link below on the old parts.

http://www.boatfix.com/merc/Bullet/90/90_15.pdf

 

[Delmagtech]

AllDodge - It looks like I have .4ohms on the primary, and 8,400 on the secondary. This is true of the old coil which is still on the engine, and the new coil in the box. Of course, I just took those measurements, and everything is cold. I haven't had it running since yesterday.

Glenn - I actually had that printed and was following the procedure on page 6, because I was unsure with 4 wires and a post, which was the primary and which was the secondary measurements per AllDodge's suggestion.

I did find something interesting. Per the Mercruiser sheet, the .4 is correct, as is the 8,400. HOWEVER, per that same sheet, measuring resistance from connection B (12v connection to the coil) and the metal body of the coil is supposed to be 'infinite'.

On the old coil, with that test, I'm measuring 8.5 ohms there. On the new coil, no connection at all.

Does this mean the oil coil is internally shorted? When the engine gets to temp and dies,(earlier this week) I did try to quickly plug in the new coil. This didn't result in the engine starting. However, through this whole thing, I've been relatively certain that the module is junk and just wanted desperately to find the problem rather than throw new parts at it.

So, is a slight short to ground in the coil possibly causing the module to pop? The new module will make the ignition fire properly, and the new coil will keep the module healthy?

Maybe the module isn't really junk, maybe the short in the coil overheats it til it won't run. It might be interesting to install new coil, with old module while cold and try it out, just to learn. It's getting the whole new system before it leaves for sure.

I better check my brain resistance. I'm all over the place here

 

[glenn property of pam]

if the coil terminal B reads 8.5 ohms to metal part and B to A reads reads 8000 ohms then A (high tension lead) would read 8008 ohms to ground which would be real bad for any thing that's sensitive to spikes. I was always interested in your first post where the module died when the engine went to wot. My thought was the alternator got worse at high rpm but as that was proved wrong I could not see where rpms would matter. Now if the coil was shorted internally then the faster the engine the more spikes etc might make sense. Be interesting to know if the owner has a stereo/radio if it was making a buzzing noise when switched on.

 

[Delmagtech]

I couldn't resist, I went back out there, and checked resistance from the high tension lead to ground, and you're precisely correct. So you agree, we've found the problem, right? I can feel good about buttoning it up and taking it out?

She does have a stereo. I'll ask her if she was getting any noise, but I doubt she was ever out there long enough to turn it on.

Here's an unrelated question for you... I spent about $250 on a digital meter off of the Mac tools truck 9 years ago, and it's really served me pretty well. But tonight, I played heck with it and ended up grabbing a $40 junker out of a coworkers toolbox. It worked fine. (I'm not buying an advance auto digital meter though). Do you think the upwards of $400 for a new Fluke is worth the cash? Measuring resistance accurately for me is really important. I work on equipment that primarily communitcates via CANbus.

 

[glenn property of pam]

all 5 of my meters are flukes including the one at the house so I may be a little biased. Glad to know that you understand canbus so next time my truck messes up and the dash goes out until I use the electric windows I will know who to ask
I think you have found the problem now. A test run and a shake down cruise will be the real test.

 

[Delmagtech]

Of those 5 meters, is there a model # that you're partial to? I do understand Canbus, at least how it's used in my drill rigs. I'd love the opportunity to return the favor, but I'm probably stronger at electric over hydraulic problems! All I have to know is that a 120ohm resistor on each end, in parallel should be about 60ohms measured at any point in the middle. Past that, the problem is always a node (German word for PLC) putting 'static" on the line. Looking forward to bolting everything back up, setting base timing and taking a ride up the St. John's River tomorrow...

 

[glenn property of pam]

t5 is my favorite its as dumb as a rock has a built in amp ring and wont blow up in your hand if you screw up and test 480v in ohms mode the draw back is it only does 1kohm and its not very accurate (that's a advantage when you don't care about 0.1 of anything). Any of the $150+ meters works well once you get use to auto ranging (I manually set range 90% of the time and only use them to test caps or inline amps which the t5 can not do). Removable display is a nice option for safety (waiting for the price to drop before buying one for the house). when it has to be right I use the company 744 because that's calibrated every year but that's a boat load of money. the others are specialty meters for working in ma and stuff like that. I work E&I so I collect meters like mechanics collect hammers.

 

[Delmagtech]

T5 probably isn't for me then, since I just want one. Being able to read .4 on the primary side was important. I really don't like the auto range setup on my current meter. Some times I want 8000 to read 8000. I realize all the good ones probably auto range though. I do read mA often. All of our hydraulic pumps adjust stroke via mA. The removeable screen would be cool, depending on the range. I wouldn't need it for voltage safety, but it would be nice to clamp to a coil, and then hop in the cab to operate the function and see the screen in my hand. Last time I looked I couldn't justify the cost though. I'll have to dig in again and see what's available. Simple and as reasonably accurate as possible, I suppose is the goal.

Anyway, I sure appreciate everyone's suggestions and help in the past days.

 

[Delmagtech]

So, it's been a heck of a day. I thought I'd share the trials and tribulations. Since she was getting a new ingition, I got new spark plugs. MR43LTS is spec'd on the flame arrest or sticker, so that's what I bought. They came gapped at .045" (also on sticker). That was all good, except it had comparable champion plugs in it. 1-3 might have come out w/o a rachet. #4 broke the moment I touched it. (Remember, this is NOT my boat- helping a new friend)

Beyond pissed at what I'm up against...

The carnage...

I was out of patience, and didn't have three days to soak in marvel mystery oil.. A little pb blaster, a little heat, and a good 'extractor', and some really kick butt luck.

 

[MikDee]

OMG! What grease monkey put those in? I'm assuming it's a cast iron head, thank goodness it's not an aluminum head