Evil Merc MAG MPI 5.7L kills coils!

[Luna Sea]

Trying to sell my boat. I took 3 guys out for 3 separate sea trials this past week, and all 3 ended the same-blown coils! Needless to say, the boat is still mine....

First sea trial, 3800 rpms no problem, slowed town to 1800 and the engine started skipping and hesitating. Shut it down and couldn?t restart it. When I took the coil out I could see the crack on the tube diameter the coil wire goes on.

Second sea trial, the guys serious, already been on board, brought beer and was making ?plans?, 40 minutes out to sea at 3500 rpms, motor dies completely, pull the coil out, another cracked coil!

Third sea trial this morning, cruised fine for about a half hour, another coil ?incident?.

A little history on the 2000 MerCruiser Mag MPI with 400 hours. First year I had it it wouldn?t run for long over 3500 rpms without starting to break down. Did a complete tune up and plumbed in a separate fuel system, as the symptoms sound like fuel problem. Finally changed the coil, and it ran great, for about a half hour, broke down, towed in to marina and they told me I bought a bad coil, so they replaced it and showed me the cracked coil. Boat ran ok for the last 2 years but since I?m usually towing my inflatable, I don?t push it. Although I did get a couple speedy runs in earlier this year.

In the past week I?ve done the wires, plugs, cap, rotor, ignition switch, (and fuel fillter). Old plugs looked fine, it is firing on all 8 cylinders. On the second sea trial, when I opened the hatch I could see a lot of spray down there, so I figured the coil was getting wet. My Grady has a tunnel pocket so the water pools around the shaft log and sprays around down there. Confidence was high this morning as I mopped the bilge dry and added the di-electric grease around the outer coil tube before installing the wire. Today?s coil, although I haven?t looked yet, probably didn?t crack, but it definately crapped out like my original coil did.

Anyways, with a shoebox full of cracked coils, plus the two that only work at low rpms, I figured I?m overdue for this post......

Any and all advice welcome.
Thanks.
Mike

PS I do plan to check the voltage tomorrow at the coil.
PSS I also made an appointment at the boat yard, but I?m seeing another $500 coil job there. I need a permanent fix, in case I get another offer, sigh.

 

[Don S]

Re: Evil Merc MAG MPI 5.7L kills coils!

Do an ohms check on all the plug wires. A non firing plug wire, or spark plug, bad cap or rotor could all cause high voltage to look for a place to go when it can't reach the spark plug. It will crack the coil tower.

 

[Luna Sea]

Re: Evil Merc MAG MPI 5.7L kills coils!

Do an ohms check on all the plug wires. A non firing plug wire, or spark plug, bad cap or rotor could all cause high voltage to look for a place to go when it can't reach the spark plug. It will crack the coil tower.

Thanks Don,

An electrical engineer at work explained that to me after first coil blew last week. So I put in brand new wires, plugs (gapped to .035), cap and rotor, and ignition switch. Need to dig deeper into the subject.

Any websites with a good "how to do an ohms check on spark plug wires" ?

 

[Luna Sea]

Re: Evil Merc MAG MPI 5.7L kills coils!

Update, I have a still interested buyer who wants this problem fixed. Neither of the local boatyard service departments wants to take on this job. Guys I have 10 grand at stake here, need some ideas. Bringing in a box of old coils to work tomorrow for one of the electrical engineers to test, this guy builds transformers so maybe he can help. Also, gonna change the ignition sensor assembly next, along with another coil...............


9/19- 3800 rpm's up the North River, sounds good. Engine running rough/skipping on ride back (1800 rpm's).

9/22- Engine wouldn't start, coil tower had crack in it. Replaced with "questionable" returned coil from Portside. (customer returned as faulty, but Rob said it bench tested ok)
Engine ran for 5 minutes, coil began to make shorting/arcing sound, engine died. Another cracked coil tower.

9/25- Changed wires, plugs (gapped to .035 and all 8 old plugs looked ok/same), cap and rotor plus new coil.

9/26-Ran 2/3 of the way out to Misery at 3200 rpm's and back at 3500 rpm's. Seems ok.

9/28- Sea trial, 3500 rpm's, a couple miles outside the islands engine shuts down. Open hatch, back of engine wet and some steam, cracked another coil tower. Put in defective (but not cracked) coil to get home.

9/29-New coil, pumped bilge dry, added di-electric grease to outside of coil tower. Sea Trial, 3500 rpm's, right between Misery and Bakers engine starts acting up, slow engine down and things are ok, but throttle up and engine starts missing/losing power/ dropping rpm's. Exactly what my "defective" coil sounds like.

9/30-New coil, ran up and down the North River, 4400 rpm's, all seems fine, until about 40 minutes/11th or 12th run, sounds like the defective coil again.

Last 2 coils have not been bench tested, and may not be the problem, BUT, with the cracking of the other coils, and the fact that the boat operates EXACTLY as it did back in 05 with a defective coil, I'm assuming it's the same problem-engine killing coils!

Additional info- Back in 05 the boat wouldn't run over 3200 rpm's for more than a half hour or so. Did complete tune up, and hooked up separate fuel supply. Still ran rough, finally changed coil, boat ran great, for about a half hour, then died, towed in to Port Marine, mechanic determined I bought defective coil (showed me the crack and I returned it) I don't run the boat hard, so problem either never went away, totally, or is just back to haunt me. Either way, sea trials blowing coils is not allowing me to sell this boat!

Voltage at coil is 12 ? volts, verified it is a 12 volt coil.

 

[bomar76]

Re: Evil Merc MAG MPI 5.7L kills coils!

Thanks Don,


Any websites with a good "how to do an ohms check on spark plug wires" ?

1. Buy DVM (multi meter)at Harbor Freight ($2.99 on sale)
2. Remove plug wires one at a time.
3. Set dial on DVM to one of the middle of the Ohms settings
4. Touch one end of probe (it doesn't matter which one) to distributor cap terminal on spark plug wire, other probe to spark plug terminal.
5. Observe reading on display.
6. Write it down.
7. Repeat for all 8 and the coil wire.
7. Post results...and what scale you had it set to.

BTW, normal wires have in the area of 10,000 -15,000 Ohms resistance per foot.

 

[cooter2506]

Re: Evil Merc MAG MPI 5.7L kills coils!

[




.
QUOTE:

9/28- Sea trial, 3500 rpm's, a couple miles outside the islands engine shuts down. Open hatch, back of engine wet and some steam, cracked another coil tower. Put in defective (but not cracked) coil to get home.

9/29-New coil, pumped bilge dry, added di-electric grease to outside of coil tower. Sea Trial, 3500 rpm's, right between Misery and Bakers engine starts acting up, slow engine down and things are ok, but throttle up and engine starts missing/losing power/ dropping rpm's. Exactly what my "defective" coil sounds like.

According to this I think he has a water problem. Looks like for what ever reason he is getting water on the coil and shorting it out causing it to crack. Oh and as you can tell I never used the quote feature before!

 

[MikDee]

Re: Evil Merc MAG MPI 5.7L kills coils!

If you have Non resistor spark plugs in there, That could be it! they build up an electrical field around them with the wrong type plug wires, especially copper wires, it would look like a light show under the hood at night. Make sure you have the proper heat range (plug number), AND resistor plugs.

 

[Luna Sea]

Re: Evil Merc MAG MPI 5.7L kills coils!

Thanks guys,
and this really is a ten thousand dollar question, sigh.

bomar, I'm bringing in old coils tomorrow for electrical guy to test, I'll grab some wires and have him show me what ohms range to use.

cooter, I was hoping it was water/spray creating this, but with the dry bilge I still had a problem. Although coil didn't crack, it seems to be breaking down at the same speed/time interval. (May be coincidence, haven't eliminated fuel problems, but the telltale cracked towers have me focusing on voltage right now)

MikDee, good point, plugs looked like old ones, but they are a cross referenced AC Delco part number in there now (dealer supplied....)

Going to do the ignition sensor assy tonight. I replaced that 2 years ago with the newer style. They added a third wire to that, a ground, used to be internally grounded in distributor, I added a stud on engine but need to verify it's a good ground.

Thanks,
Mike

 

[MikDee]

Re: Evil Merc MAG MPI 5.7L kills coils!

MikDee, good point, plugs looked like old ones, but they are a cross referenced AC Delco part number in there now (dealer supplied....)
Thanks,
Mike

Yes, but are they resistor plugs? is there an "R" in the plug number? That's the most important item.

 

[Luna Sea]

Re: Evil Merc MAG MPI 5.7L kills coils!

Yes, but are they resistor plugs? is there an "R" in the plug number? That's the most important item.

I'll be checking for that "R" in the part no. tonight.

Nice car pictures by the way!

Mike

 

[MikDee]

Re: Evil Merc MAG MPI 5.7L kills coils!

I'll be checking for that "R" in the part no. tonight.

Nice car pictures by the way!

Mike

Good,,, Thanks man, wish I had some of those cars today!

 

[Don S]

Re: Evil Merc MAG MPI 5.7L kills coils!

This may not be a simple problem to find.
We had a new 95 Bayliner 24 Classic come into the shop, had about 10 hours on it. Cracked tower on the coil and no spark. New coil and it ran. All plug wires and spark plugs looked good, engine ran fine.
Off he w3nt. 9 hours later, he blew another coil. This went on every 9 hours for about a year and a half.
We replaced (Mercs dime, it was under warrenty) All battery cables and battery switch, Alternator, distributor, all modules, engine wiring harness (Twice), plug wires, numerous spark plugs, everything including the circuit breaker in the system. Mercruiser sent out reps and everything checked fine. But 9 hours, and the coil goes.
Finally went to court. Bayliner and Mercruiser sent out a brand new engine and drive package (EFI this time) new transom shield, trim pump and all.
Replace the boats wiring harness to the helm and all new instruments.
Cured the problem

Now, we put the engine in another boat, and it is working great and has never lost another coil after many years.

Obviously there was a problem in the boats wiring harness or instruments. It all looked good when it was removed. No screws thru it or anything and all the instruments checked ok (but we never used them for 9 hours with that harness to find out)

So don't expect this to be an easy problem to find the cure for.

 

[MikDee]

Re: Evil Merc MAG MPI 5.7L kills coils!

This may not be a simple problem to find.
We had a new 95 Bayliner 24 Classic come into the shop, had about 10 hours on it. Cracked tower on the coil and no spark. New coil and it ran. All plug wires and spark plugs looked good, engine ran fine.
Off he w3nt. 9 hours later, he blew another coil. This went on every 9 hours for about a year and a half.
We replaced (Mercs dime, it was under warrenty) All battery cables and battery switch, Alternator, distributor, all modules, engine wiring harness (Twice), plug wires, numerous spark plugs, everything including the circuit breaker in the system. Mercruiser sent out reps and everything checked fine. But 9 hours, and the coil goes.
Finally went to court. Bayliner and Mercruiser sent out a brand new engine and drive package (EFI this time) new transom shield, trim pump and all.
Replace the boats wiring harness to the helm and all new instruments.
Cured the problem

Now, we put the engine in another boat, and it is working great and has never lost another coil after many years.

Obviously there was a problem in the boats wiring harness or instruments. It all looked good when it was removed. No screws thru it or anything and all the instruments checked ok (but we never used them for 9 hours with that harness to find out)

So don't expect this to be an easy problem to find the cure for.

Wait, I got it!,,, It was Haunted!

 

[Don S]

Re: Evil Merc MAG MPI 5.7L kills coils!

Wait, I got it!,,, It was Haunted!

Nah, I think Luna Sea was right.............. Evil Merc!!!!!

 

[MikDee]

Re: Evil Merc MAG MPI 5.7L kills coils!

Nah, I think Luna Sea was right.............. Evil Merc!!!!!

Sounds like a good title for a horror movie Don

 

[Luna Sea]

Re: Evil Merc MAG MPI 5.7L kills coils!

This may not be a simple problem to find.

That's why I'm here Don!

Sounds like I need to call Father Damien to perform an exorcism???

Update:
Installed new ignition sensor assembly last night. When I did that 2 years ago, the part had been redesigned with a 3rd wire, a ground, which I bolted to the bracket on top of the motor that supports the throttle linkage. Since a few people have told me the problem sounds like a ground problem, or a "floating ground, I grounded it to the stud on the block where the big battery grounds go. (2 studs on motor, big grounds are on port, now this ground is on starboard.) My thinking was the "painted" bracket may not have been a good enough ground.

Ran it for about 10 minutes at cruise speed and then the motor started breaking down. And that was with the new coil that appeared to be breaking down after about a half hour Sunday.

Ok now, it is a fact I have 3 cracked coils in my posession. First one was 2 years old (no excuse but it was 2 years old). Second one was "questionable" return (half price coil what do I expect?). Third one did get wet (forgot to pump bilge before running-downside to tunnel pocket, water pools around shaft log and splashes)

Last 2 coils have not been proven faulty, yet, have a transformer guy (electrical engineer) at work looking at them today.

I'm no expert, and I could very well be fighting 2 problems simutaneously here. My plan is to hook up a separate fuel supply this weekend, to eliminate venting and fuel pickup.
Again, I'm only "guessing" coil because of the cracked ones and I have an old/bad coil that sounds very similar to what I'm getting now.

Ok now it's time for some debate, some people are telling me if the coil get's wet it will crack (and fail), others are telling me that shouldn't happen, engines are designed to get wet, and some have mentioned hosing down their engines. Fact or fiction with the water/spray on the coil guys? And for the record, the coil is not getting noticibly hot.

And of course the guy that wants to buy it called and told me to have the fuel pump looked at????

Don, can you give me any mor info on that guy with the cracked coils? Before I crack?

Parts guy/Merc dealer also told me to look for a 20 amp inline fuse somewhere, he had one on his shelf, looks like 1" x 1" square, probably 3/8" thick, with a little white button, that he said sometimes won't pop so the insides heat up or short or something, still looking for this item. Guess I can look in the service manual?..
On the same subject, the screws/wires going to the red pushbutton (50 amp) breaker on top of the motor look pretty rusty, those will be the next maintenance item cleaned???

Cheers,
Mike

 

[thrasher]

Re: Evil Merc MAG MPI 5.7L kills coils!

I might be out in mid field here, but the coils in cars are under the hood and must definately get wet when driving in heavy rain. Water gets thrown everywhere inside an engine bay, so I really doubt a coil should break when it gets wet.. The water could short out the coil output, but it shouldn't do any permenant damage to the coil..

Gary

 

[MikDee]

Re: Evil Merc MAG MPI 5.7L kills coils!

If you have some Dialectric grease on all the terminals, and spark plug connectors, water should not be a problem! Did you check to see if they're "resistor" spark plugs?

 

[Luna Sea]

Re: Evil Merc MAG MPI 5.7L kills coils!

I only put the di-electric grease on the coil tower, per the manual. Others are suggesting "spray everything". Any recomendations on best spray to use?

Plugs are ACDelco MR43LTS, there's the "R" you were looking for.

 

[MikDee]

Re: Evil Merc MAG MPI 5.7L kills coils!

I only put the di-electric grease on the coil tower, per the manual. Others are suggesting "spray everything". Any recomendations on best spray to use?

Plugs are ACDelco MR43LTS, there's the "R" you were looking for.

I would put a little Dia. grease on all the Dist. terminals, & on the spark plug terminals, usually it's there from the factory on Boats, & off road vehicles. To help repel any water getting past the boots, and keep them from corroding, under humid conditions. Don't worry about spraying everything IMO. Yes those are the right spark plugs MR43's as used on most of the Chevy marine engines, the LTS means they're a long thread plug (long reach).