mercruiser ignition control module?

[sgwill122]

I have a 2003 5.0L Mercruiser with alpha gen2. Two years ago I replaced the ignition sensor module in the distributor when we could not get the boat to start, which fixed that problem. My boat started misfiring/backfiring/stuttering when under load around 2-3K RPM last year. Replaced the cap and rotor which immediately solved the problem. It has been a year now and the engine has started misfiring again after running 20 minutes, sometimes I just get no power after 2000rpm's no matter how far forward the throttle is pushed. Problem alway occur under heavier load. I replaced the cap and rotor again with no change, also tried a new Coil which did not make any difference. I am thinking it could be the ignition control module but wanted to get opinions before spending $500 on a guess.

 

[Bondo]

Re: mercruiser ignition control module?

I have a 2003 5.0L Mercruiser with alpha gen2. Two years ago I replaced the ignition sensor module in the distributor when we could not get the boat to start, which fixed that problem. My boat started misfiring/backfiring/stuttering when under load around 2-3K RPM last year. Replaced the cap and rotor which immediately solved the problem. It has been a year now and the engine has started misfiring again after running 20 minutes, sometimes I just get no power after 2000rpm's no matter how far forward the throttle is pushed. Problem alway occur under heavier load. I replaced the cap and rotor again with no change, also tried a new Coil which did not make any difference. I am thinking it could be the ignition control module but wanted to get opinions before spending $500 on a guess.

Ayuh,.... Change the fuel Filters, 'n inspect the contents of the old 1...

 

[PuddleJumper]

Re: mercruiser ignition control module?

Consider spark plugs and wires as well.

 

[sgwill122]

Re: mercruiser ignition control module?

I should have added that I also changed the plugs and plug wires last year.

 

[81 Checkmate]

Re: mercruiser ignition control module?

I would rule out the fuel system first........before droping $ 500.00 bucks.

Do as Bondo said.....

 

[sgwill122]

Re: mercruiser ignition control module?

I replaced the fuel filter at the beginning of this year and checked the inline filter for blockage today but saw nothing. I don't suspect fuel supply issues as I can go WOT when the engine is cool or if the boat is lightly loaded. When boat has been running 20 minutes and under load(climbing a wave or heavy boat) I lose power at around 2000rpm or start missing.

 

[Bondo]

Re: mercruiser ignition control module?

I replaced the fuel filter at the beginning of this year and checked the inline filter for blockage today but saw nothing. I don't suspect fuel supply issues as I can go WOT when the engine is cool or if the boat is lightly loaded. When boat has been running 20 minutes and under load(climbing a wave or heavy boat) I lose power at around 2000rpm or start missing.

Ayuh,.... Yer symptoms say you have a Fuel issue, not the module...

Fuel filter don't have an expiration date, Time is irrelevant...
If it picked up some Water, the day you installed it, it needs Changin', Again...

But more importantly,... Check it's Contents...
It's cheap, 'n easy, 'n Important to rule out the fuel delivery...

If it's full of clean gasoline,...
Maybe We can get Don to post up the T-Bolt V diagnostic chart...

 

[sgwill122]

Re: mercruiser ignition control module?

Just replaced the filter and dumped the gas into a clear glass. No water in the gas, there was a light peppering of dark specs on the bottom of the glas.

One other tid bit I can add is the tachometer started intermittantly working and completely stopped working a month ago. I assumed it was unrelated but thought I would share in case it was related. I assume it is the tach as I used to have to tap on the gauge to get it to work.

Will low fuel delivery cause misfiring?

 

[SC_Regal]

Re: mercruiser ignition control module?

I have a 2000 5.0 EFI. I am almost certain that there is an ignition relay in the Tach. If your tach is going bad you can get intermittent ignition issues until complete failure or replacement. (I went through this several years ago so confirm before you act)

 

[sgwill122]

Re: mercruiser ignition control module?

Just spent some quality time reading the merc manual and ran across an ignition troubleshooting section that said a faulty tach can cause misfiring and/or failing to advance/poor performance. I will disconnect the tach and see if christmas comes early.

 

[sgwill122]

Re: mercruiser ignition control module?

Well I removed the wire to the tachometer, removed the fuel flow meter I installed a couple years ago, replaced the fuel filter. Took the boat out today and the problem has become very consistent now and that is no power after 2-3000rpm(guessing on rpm as my tach is not working). It is no longer misfiring, just no power. Just to summarize the history of events:

2 years ago boat would not start, ended up replacing ignition sensor, problem was fixed.
1 year ago boat was misfiring/backfiring/stuttering and no power, replaced the cap/rotor/spark plugs and plug wires, problem was fixed immediately.
This year the boat started occassionally misfiring, so I replaced the cap and rotor again with no real change. Misfiring turned to loss of power which is very consistent now.

Any ideas what to try next?

 

[Pete104]

Re: mercruiser ignition control module?

I quess it's OK to quess you have Thunder 5 ignition?
Who's to say the sensor didn't fail again? Typically, an ICM will create a "no start" situation. The sensor, was it OEM or aftermarket? Are you sure you have a V-8 rotor & wheel assy? V-6 will fit a v-8 & raise hell as your describing. Check these things out.

Think you hot wire that engine @ the engine? Disconnect the main harness & fire it up. Won't have any gauges but that's fine. Doing this will isolate the dash from the engine.

 

[Scott Danforth]

Re: mercruiser ignition control module?

Mallory ICM's are fairly inexpensive. factory TB IV units manufactured by Cherry were not conformal coated from the factory and tended to corrode.

 

[sgwill122]

Re: mercruiser ignition control module?

Cap and rotor are definitely a mercruiser V8 replacement kit.

Would a sensor cause a lack of power issue?

 

[Scott Danforth]

Re: mercruiser ignition control module?

quick question - is your fuel system EFI or Carb?

if its EFI and its the MAP sensor or temp sensor, yes, it could cause lack of power due to improper fueling.

 

[sgwill122]

Re: mercruiser ignition control module?

It is carb and thunderbolt V ignition.

 

[Scott Danforth]

Re: mercruiser ignition control module?

with a carb, the ECM controls ignition advance, knock control, rev limiter, and shift interupt with an alfa drive.

if the ICM goes bad, it simply stops working and the engine quits running.

the black flakes in the fuel would be my guess as the cause of your problems. and yes, if your running lean, you can get a "lean sneeze" which is a backfire.

 

[sgwill122]

Re: mercruiser ignition control module?

Took the boat out today with my brother who is a auto mechanic. He adusted the timing and hooked up a pressure gauge on the fuel line. Pressure looked good while running. We still had the same problem, would not advance past 3000rpm and no power on WOT under load. He tried dumping fuel directly into the carb and the engine just bogged down each time so fuel starvation is not our problem. He tried adjusting the timing while under power and seemed to get a bit of improvement. He hooked up a spark checker and did not see any misses. Looks like problem is either sensor or ICM at this point. I am thinking of converting to a electronic distributor, anybody have any opinions on doing so?

 

[Bondo]

Re: mercruiser ignition control module?

Took the boat out today with my brother who is a auto mechanic. He adusted the timing and hooked up a pressure gauge on the fuel line. Pressure looked good while running. We still had the same problem, would not advance past 3000rpm and no power on WOT under load. He tried dumping fuel directly into the carb and the engine just bogged down each time so fuel starvation is not our problem. He tried adjusting the timing while under power and seemed to get a bit of improvement. He hooked up a spark checker and did not see any misses. Looks like problem is either sensor or ICM at this point. I am thinking of converting to a electronic distributor, anybody have any opinions on doing so?

Ayuh,.... You said you found the duagnostic tree for the T-Bolt V in the service manual,..?? The Merc manual,..??

If so, follow it, step by step, 'n it'll tell ya Which piece of the ignition is Bad...

 

[sgwill122]

Re: mercruiser ignition control module?

Replaced the ignition sensor and coil with no change. I now have spares of each. I made sure the shift switch is not getting activated during throttle advance. The only thing left is the ICM. Does anybody know if a merc dealer can run a diagnostic on the ICM to determine if it is bad or does it just get replaced when you run out of cheaper options?