Mercruiser 454 Ignition Coils

[jalayo]

I had a situation last week where I lost power on both engines simultaneously. I was able to restart the port engine and make it home. I troubleshooted the engines and found that the ignition coil was gone on the starboard side. I swapped the coil from the port engine and got it to start. I'm having trouble locating a replacement coil. I went to several places and each one was labeled "use with external resistance". Is there one with an internal one that anyone knows (I have not been able to find it), and is it possible that the coil failed because it did not have one?

Thank you

[Tony Meola]

How old are the engines?

[pschauss]

I struggled with this issue for most of the first three summers I owned my boat. My port engine had a Prestolite distributor and took an unballasted coil. The starboard engine had a Mallory and took a ballasted coil. Both distributors had electronic ignition conversion kits. I believe that I used a Sierra 18-5433 (unballasted coil) on my port engine and Sierra 18-5466 (ballasted coil) on my starboard engine. Ultimately, however, I upgraded both engines to Delco Voyager systems.

[S Ritzert]

is there a part number on the coil, I will cross reference it out of my catalog. Do you have the engine serial, or year?

[jalayo]

Thanks for the response:
1. Engine is a rebuilt in 2020 454.
2.The part has the number 29750 writing with a small 0302 number under it. After a long search I found a match with a Sierra 18-5438 HEI Ignition Coil (found it on the Outboard Paradise website. What's not clear is if it requires an external resistance.
3. I found today the same part at West Marine and went to see it and it did not have the number matching but it did have a mark that said it needed external resistance.

So, I guess, my question now is, is it possible it failed because they had no external resistance?

Still leaves unanswered why they both stalled at exactly the same time. Has this ever happened to anyone?

Thank you in advance

[lobsta1]

Like Tony asked, how old are the engines,? I thought most of the older Mercs had an external resister wire built into the wire harness.
Al

[Tony Meola]

The year of the engines would help. I doubt the shop that redid them changed the ignition set up.

Some of the older MerCruiser's, had what was called a Thunderbolt ignition and the coil was completely different from what most of us are used to. Plus in certain years I think they had some funky things going on.

I needed a cooling hose one year and we could not find it any place. The yard searched every Merc manual they had and could not find a match. We finally called Merc and gave them all the information off the engines. They said no such engine. Go figure.

I know they were original engines to the boat since we purchased the boat new.

We had to jury rig a hose. It was strange since the hose reduced in size. Was something like 11/4 inch to 1 1/2 inch.

[pschauss]

If there is a ballast resistor in your ignition circuit, you should see significantly less than 12 volts at the coil. Check it with the engine running since some ignition systems have a relay which bypasses the ballast resistor to give the coil a full 12 volts for starting.

[S Ritzert]

I don't know if this is going to help at all. Reverse crossing from sierra to quicksilver shows that to be externally resisted. This could be a ballast resister (probably not) or a resisted wire (probably so).

The quicksilver number is crosses over to is.... 0418-5438

Like I said, this is all things being equal, and assuming that the sierra number you posted is accurate.

This system also shows to be T-Bolt ignition system.

serial numbers off the engine would help. I used to be a mercruiser certified technician, not that this statement means much. If anyone has ever participated in mercruiser training, you know what I mean. I am stating that, because I probably have the manual to that engine, if that helps, but you need the serial number to get into the right manual.

[Tony Meola]

If there is a ballast resistor in your ignition circuit, you should see significantly less than 12 volts at the coil. Check it with the engine running since some ignition systems have a relay which bypasses the ballast resistor to give the coil a full 12 volts for starting.

Peter

Not sure how old his engines are, but do you still have the manuals I sent you. Perhaps they show the resistor he needs.

[pschauss]

Tony,

I still have the shop manuals. They have been invaluable to me.

For points-type ignition, the shop manual says that the wire which feeds the positive side of the coil should have a resistance of 1.8 to 2 ohms. The manual does not give a resistance spec for the Thunderbolt Ignition, but the wiring diagram shows wires to the coil coming out of the "control box".

Based on the battles that I had with my ignition systems, I still recommend upgrading to Delco Voyagers to get a fresh start.

[Tony Meola]

Upgrading might be the easier and best way to go. Better than chasing a gremlin.

[jalayo]

Hello everyone: Took a few days to get some more intel on the engines as well as had some time to put into it to do some further troubleshooting. So, the engines are Gen IV's 86/90 and has a Thunderbolt Ignition. With that information, and checking with the shop that did the re-man, the ignition system has a resistance so the Sierra coil works in this application. I also double checked with another mechanic and he confirmed the same. Also he checked compatibility with the OEM coil. I replaced the coil and the engine started no problems. We checked the compression and it all was within range (130-120). Oil pressure checked out as well. So as far as why the engine went down, I can only blame the bad coil. Why they both went down at the same time at this point I can only point to coincidence. Thank you all for your input as I am still getting familiar with my move from outboards.