1988 mercruiser 3.0 stalls and starts hard when warm

[Bad86ta]

1988 mercruiser 3.0 (C394105) after about an hour the motor begins to run rough and stalls. After the motor stalls it starts hard or does not restart unless it sits for 15 or so minutes.


I do do not believe it is fuel related.
I have done the following:
fresh fuel (non-ethanol)
new fuel lines
checked fuel vent
checked for plugged pickup
new fuel pump ( mercruiser/quicksilver)
Carb is still getting fuel after it stalling
Note: electric choke was replaced with manual by previous owner.

Previous owner had installed a Mallory 61001m E-spark conversion kit.
I took it to a marina for this issue and they stated The module was overheating and replaced with a Mallory 6100m module. (They also replaced fuel pump at this time)
I have done the following:
Replaced factory coil with new
Replaced new coil with Mallory 29219 coil per their help line recommendation. (Internally resisted coil)
I have ran the coil with the resistor wire and with it bypassed.
I have ran the Mallory module on the coil and on its own 12v source.

Through all all of these steps this problem persist. The boat starts great cold and runs great for about 30-40 minutes. It then begins to stumble, misses and will eventually stall. The boat either starts hard or does not start at all after this. After letting it sit for a while it will restart and runs good until it gets hot again.

Temp gage shows 130-140 degrees when warm. IR temp gun shows about 150 degrees on motor, distributor and coil.

Sorry for for the long winded post but I wanted to provide lots of details.

Mallory also says I need to add a circuit guard which I understand the purpose of but not sure it will help?

I'm running out of ideas and any help would be greatly appreciated!

Thank you for any suggestions!

 

[fishrdan]

Sounds to me like the E-spark module is overheating. Did they use heatsink compound while installing the module, underneath the module? Pop the distributor cap and rotor, then look at the edges of the module, there should be some white grease oozing out from underneath the module, slight bit. I would want heat sink compound under the mounting plate, and the module.

I used to own a hot rod with a Mallory Unilite distributor (looks similar to the Espark module) and the module went out 2-3 times. Running fine one day, then dead the next, no warning it was going out. Just for that, I wouldn't own a Mallory again. I didn't have a circuit guard" installed back then, not sure they were even available 15 years ago, but I would run one with a Mallory module....

If the engine dies again, hook up a timing light to the coil wire, and see if the ignition has spark.

 

[Bad86ta]

Sounds to me like the E-spark module is overheating. Did they use heatsink compound while installing the module, underneath the module? Pop the distributor cap and rotor, then look at the edges of the module, there should be some white grease oozing out from underneath the module, slight bit. I would want heat sink compound under the mounting plate, and the module.

I used to own a hot rod with a Mallory Unilite distributor (looks similar to the Espark module) and the module went out 2-3 times. Running fine one day, then dead the next, no warning it was going out. Just for that, I wouldn't own a Mallory again. I didn't have a circuit guard" installed back then, not sure they were even available 15 years ago, but I would run one with a Mallory module....

If the engine dies again, hook up a timing light to the coil wire, and see if the ignition has spark.

Thank you for the suggestion.
I forgot to mention, yes the module did have heat sink paste under it.
I also reapplied new paste after I checked it.

I plan to check timing this weekend and I will hook up a timing light to check for spark when it stalls.

I've read many post about the mallory stuff being a pain.. Thinking about just converting it back to points...

 

[starcentral]

I read a tonne of posts on mysterious stalling that occurs on Mercruiser 3.0L only once boat has run for a while because I had this issue on a recent outing and was looking for answers. But for me it was only when reducing speed down to no wake zone and struggling to run between 1500-2000 rpm. I'm still trying to figure it out.

But for your problem, from other posts I've read it seems to point to being heat related, vapour lock, fuel vent. etc.

Have you tried opening gas gap? Have you replaced or checked your spark plug cables? If they are bad they can overheat and ruin your new coil, so can bypassing the resister. What's your voltage on the coil when starting, and after it's started, any voltage drop?

 

[havoc_squad]

If carb is dripping gas from venturies around 700 rpm or when engine is turned off, do a fuel pressure test.

Several people have bought/used the wrong thickness gasket on the mechanical fuel pump and experience fuel overpressure on 3.0L engine, causing flooding condition.

I think normal psi should be 4 to 7. Any more psi than that the needle & seat can't handle it in the carb.

As for the ignition, I can't comment on that part. I had Delco EST on mine.

 

[Bad86ta]

Did some work on the boat this past weekend...
Timing was off 2 degrees, i corrected but this was not causing my issue.
I can now say for sure this issue is related to spark.
The boat began to miss and stalled after about an hour.
Coil was checked for spark. No spark or at very best intermittent and erratic spark.
I took an extra coil I have and hooked it up with the same outcome.
In my mind this eliminates the coil so it has to be the module.
After everything cools the motor will fire up and runs good until i believe the mallory module overheats...

I have a mallory 1.4 ohm resisted coil.
I have by passed the resistance wire and used the resistance wire (12v and resisted 9.7v to coil)
I have done the same for the module power and the module has a power filter.
Any ideas on why the module is overheating?
Mallory tech line states that the negative side of the coil should read 6-9V. I have tried several different methods of hooking the coil and the module up and the best voltage I have seen from the negative side of the coil is 4.9V.

I'm stuck with this one...
May be going back to points..
Thanks for any help!

 

[achris]

You have had 2 modules doing EXACTLY the same thing? I'd suspect something else.

Chris...

 

[Bad86ta]

You have had 2 modules doing EXACTLY the same thing? I'd suspect something else.

Chris...

I'm not suggesting that 2 separate modules are bad, however I am fairly confident that something is causing them to overheat and cut out.

When the motor begins to miss I can soak a rag in the water, put it on the distributor under where the module is located and the motor begins to quit missing within 20-30 seconds.. Take the rag off and the motor will start to miss within a minute or two.

 

[achris]

Have you pointed an IR gun at the distributor? What temperature is it getting to?

 

[Bad86ta]

Have you pointed an IR gun at the distributor? What temperature is it getting to?

Yes, about 150 degrees.

 

[achris]

Yeah, that's too high. You might have a distributor shaft problem. Might be worth pulling the distributor and checking the bushings.

 

[Bad86ta]

Yeah, that's too high. You might have a distributor shaft problem. Might be worth pulling the distributor and checking the bushings.

What should the temperature be?
The tempature of the distributor is very close to engine temp when I hit them with an IR gun

 

[achris]

I'd expect it to be a lot lower, as it's in 'open air'. If the body is 150, the core is far higher. Remember that the outside temperature is as low as the module can get... Pull the dizzy and make sure it's free to turn without any binding. Sounds like temperature is being generated, not just convected. (not a real word, but you know what I mean)

Chris.....

 

[Bad86ta]

I'd expect it to be a lot lower, as it's in 'open air'. If the body is 150, the core is far higher. Remember that the outside temperature is as low as the module can get... Pull the dizzy and make sure it's free to turn without any binding. Sounds like temperature is being generated, not just convected. (not a real word, but you know what I mean)

Chris.....

I pulled the distributor yesterday.
The shaft had a slight amount of play vertically but was tight side to side and spun easily.

I didn’t have time to start and test anything. I won’t be back to my cottage for a few weeks and I had to drain the water and fill with Antifreeze to prepare for a few cold nights. Maybe I’ll get another chance in a couple weeks.