Mercruiser V8 thunderbolt (305) ignition issue

[smtharrison]

Good morning everyone,

recently bought a 2001 bayliner Ciera 2452 with the mercruiser v8 thunderbolt (305 I believe) carbureted...

When the brother and I took her out on the maiden voyage, everything was fine till just as we pulled up to the marina, when smoke began billowing out of the engine compartment. Long story short, the exhaust system overheated pretty good, and have to replace several of those components. I should have consulted with an in/outboard person before running the thing, but that's in hindsight. The engine temp gauge never went past the middle of the gauge (around 160 I suppose?...) Didn't see any water on the dipstick, engine sounds like it has good compression when I crank it, etc, so pretty sure the engine is ok. I'll check compression later on, but wanted to get this ignition spark thing figured out first.

That being said, since I overheated the exhaust elbows, and the rubber boots melted a bit around them, water was splashing out of the exhaust riser and around a bit in the engine compartment when it was running (think I heard some arc-ing noises at one point. The engine just quite (literally right as we pulled into our boat slip!) I have plenty experience working on auto engines, and have quickly boiled it down to an ignition system issue... no spark. But here's the strange thing, if turn the key quickly from off to start, it will turn over 1-2 cycles (about a second), then no spark again. If I turn the key on for a second or two, then try to start, no spark. I have also seen this initial spark (coil wire to screwdriver next to ground). I have checked all the connections as best I can (don't see any melted wires around the over heated area), etc... most of the general ignition system troubleshooting things. I also found this flow chart on another thread that I followed. I have replaced the ignition coil, and same thing. Also did the ignition sensor test, with no luck.

Leaning toward the ICM after following the flow chart, but after looking around online, they same to be scarce and pricy. ICM is a Denso 131800-7071 with another sticker on it that says [ 861459-1 5.0LG+ Alpha ]

So finally, I guess I have two questions:
1. Any other tips or tricks to troubleshoot the ignition sys? Is there a test procedure for this ICM?
2. Recommendation on where to buy an ICM (I don't see one like this on iboats anywhere)... is there a replacement/generic ICM that will work?

Thanks for any help! First time posting here, but it appears there are a lot of knowledgeable people here. (and no I have not bought the selco manual yet... going to do that in a bit

 

[Don S]

Re: Mercruiser V8 thunderbolt (305) ignition issue

The module is an OEM item only. Aftermarket companies don't have them. And yeah, they are pricy anymore. Many people actually install the Delco EST kit and get rid of the Thunderbolt because of the cost. The EST kits are cheaper than the module alone for the thunderbolt.

You don't want to buy the seloc manual, they are just a waste of money. What is the serial number of your engine (not year) to find the correct manual. And what drive do you have?

Have you learned about raw water pump impellers yet?

 

[smtharrison]

Re: Mercruiser V8 thunderbolt (305) ignition issue

Hello Don S.,

Though this is my first thread, I have been doing much browsing on the iboats forums, and already know you are a bit of a legend 'round these parts! : ) Thank you for the quick reply and help!

Serial is L616301

Yes, I know about raw water impellers (at least I think I do I've been replacing them for years on outboards. Not sure why I didn't think to do this on a boat that's been probably sitting up for a while : / On most outboards, you usually get a nice warning buzzer when the impeller isn't working well or you can check that the tell-tale is spiting water : ) The only thing that is a little new to me is why the engine temp remained normal op temp while the exhaust stuff burned up. Having already removed the riser/elbow, I can also see why there was poor circulation/cooling around the exhaust system (mostly on one side) there was a bit of rust/corrosion that was also clogging the arteries. I see there appears to be a water pump on the front of the engine, but where I am not read up yet is whether it pulls water from the same path the impeller pushes water to, or from the hose that comes out by the gimbal bearing, bellows, etc. I just need to look a little closer and read up a little more on the exhaust/cooling system of the sterndrive setup.

That distributor kit looks like exactly what I need... Going to get that ordered asap!

Any other tips for a newbie on the merc inboard/outboard? I also seem to have a little water coming in from the stern, and am planning to get a bellows kit with the gimbal bearing, replace the impeller, etc. and just go over everything down there. Seems to be a few youtube videos on the whole bellows and gimbal bearing thing, and doesn't look too bad to do.

 

[Don S]

Re: Mercruiser V8 thunderbolt (305) ignition issue

Videos are great to get an idea of how to do things, but not something to follow for repair work. Here are links to the OEM manuals for your engine and drive.

Might also want to check out the stickies for a lot of other info.

 

[smtharrison]

Re: Mercruiser V8 thunderbolt (305) ignition issue

Don S.,

Agreed with the videos. Thanks again for the quick response. The 'stickies' are great! going to be reading through them this afternoon. Have a good one!