Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

[moos0004]

I have a 1997 Bayliner with a mercruiser 5.7L V8 with thunderbolt V ignition that misfire after about 30 minutes of use. I can continue to use the boat but i have to keep it unter about 2800RPM. It starts and idle fine all the time. It seam if i run the blower i can go longer. I have replace the coil, dist cap and rotor, new wires (wire orders are correct), spark plugs are good, New water separator, check anit-siphon, and tube in gas tank...all good. I think i rule the fuel out but not sure about the ignition. Any ideas on what the problem could be? Engine temp is constant 173-175. I believe this model has a 160F thermostat. I would like to check the ignition module but i am not sure if the flow chart in the manual will dectect the problem if it only does it when the motor is warm. Any adeas on how to check the module or what you think the problem could be. Its not surging. It more like the someone is turning the key off and on really fast. Any suggestion will be appreciated
Thanks

 

[John_S]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

I would agree, the T5 diagnostic flowchart is for non-working systems. Many people report heat related problems with coils, but you have already replaced it. On the ignition side, you basicly just have the ICM and ign sensor left.

Being a heat issue, you might be able to isolate by cooling the module after it acts up. You want to cool the plate it is attached to vs the module. I have a "freeze it" spray from electronics supply house. Also can just check to see if there is thermo transfer compound between the metal plate of the ICM and mounting plate.

Also, would like to verify you have a 2brl model which wouldn't have a knock module.

Cutting out could be shift interupt switch bounce, or grounding out ignition sensor wire, etc.

 

[moos0004]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

I do have a 2 bbl carb. There is no knock module. I removed the module and add thermal grease. Is there a way to check the module other than the flow chart in the manual. I check it that way and its functioning. Also I did spray cold water on the back (shiny side) of the module and place a cool damp cloth to cool it down. It did not help. I can replicate this problem on the muffs by running the boat for 10 minutes and then let it sit for 10 minutes and the problem is there. Any suggestion what i should be looking at. I notice if i run the blower the boat will work long before it starts to act up. I was thinking about replacing the 160F thermostat with a 140F but i know this is not the root cause of the problem. Any advise will be welcome
thanks,
moos0004

 

[John_S]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

Don't lower the thermostat. Your engine temp is fine.

While I wouldn't have used water (ICM is not sealed), would have expected a change with cooling. You can clean contacts and observe timing in base and normal mode. I would not jump on changing the expensive ICM yet.

Try cooling the coil case after recreating it. If it is in the wiring/connections, they can be "fun" to find. You can go through all the ignition wiring and make sure all connections (grounds, bullet connectors, etc) are good, clean, and tight.

PS: I sent an IM if you would like to try a different, used ICM, for diag purposes, and return.

 

[moos0004]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

Update i replace the two piece ignition sensor in the dist with a new one (one piece) but it did not help. I then proceeded to try an cool the module again. This time i used really cold water and cold damp cloth. I spray the water on shiny surface of the module and wrap the cloth around the riser. I would run the boat for about 5 minuets then let it sit for 10 minuntes then start up to verify problem is present (present every time) then proceed to cool module and riser with the water and cloth for about 3-5 minutes restart engine to see if problem is present. The first 3 times i did this problem went away after the cooling. On the 4 try, it did not but it was late at night and i did the last cooling really quick (not as good as the first three...i was feeling confident). What are your thoughts? Ps. I was careful not to get water in the module...just squirting it on the shiny back surface.
Thanks

 

[John_S]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

OK, good news on getting it isolated. Coat that shiny metal on the ICM with heat sink compound and get good contact to the metal mounting plate. If that doesn't work, either fab a better heatsink or bite the bullet on the module replacement. The new style does not have a metal plate for heat transfer, but is significantly larger than the old one.

 

[moos0004]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

Hi imported_John_S or anyone, is there a way to check the shift interupter to verify if funtioning correctly? Can it be done on land or on muffs?...for eg. checking the ohms. I was looking but could not find much in the manual or online.
Thanks
moos0004

 

[moos0004]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

Forget to ask. Would the shift interruter cause this missfire, even when the gear is non engage?
Thanks
moos0004

 

[John_S]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

The shift interupter grounds/kills your ignition momentarily in normal operation as you shift out of gear. I think there is a good explaination in the stickys. If it happens to be bouncing/vibrating at that particular rpm, maybe. Seems like a streach. Since you can readily recreate problem, easy to eliminate. Pull the bullet connector that comes from the switch that goes to ICM. With it seperated, and you can still cause problem, it is not the interupter.

 

[moos0004]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

Thanks, i will try it this afternoon and keep you posted. Thanks again for the advise.

 

[84Monaco]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

I was having a very, very similar problem on a boat with similar components. Looks like mine is the coil since cooling it seemed to do the trick, but cooling the amplifier did nothing. I found that on the lake if I ran the boat with the doghouse off the problem never really came, I guess since the breeze/extra ventilation kept the engine compartment cooler.

Hope you're able to track it down!

 

[rocklodger]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

I'm having a similar problem with my 1997 5.7l as well. I also have a mettalic popping noise when it firsts acts up. I work at a Ford dealership and my service director (fromerly of a GM franchise) said it is almost surely the ignition module. GM used to have a lot of problems with the module for this design.

 

[John_S]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

GM used to have a lot of problems with the module for this design.

While the problem may be related somehow, the Mercruiser T5 module is not GM Delco.

 

[moos0004]

Re: Mercuiser 5.7L with Thunderbolt V misfire after warmup will not go over 2800 rpm

Fixed: Replaced ignition module on friday and the boat is working perfectly. I used the boat alot the past 3 days with no problems. Thanks to everyone for thier help.
moos0004